Build your understanding of solar EPC: how electricity behaves, how the plant works, and how a project moves from site assessment to ongoing operation.
20–950 kWpOn-grid systemsBeginner levelEnglish
Start here
Electricity and solar basics
Start from zero: what solar EPC means, the essential units, and how they connect.
Solar EPC brings engineering, equipment and construction together to create a working electricity-generation system. Each part has a defined role in the project.
By the end of this topicUnderstand what EPC includes and how an on-grid solar project supplies electricity to a business.
A working plant, visualised
Follow the energy
↔ Swipe across the model to follow the full energy path.
Solar AC output1200 kWAfter the inverterPanels are inactive
Building demand8060 kWLights, cooling & equipment
Grid exchange4060 kWExported to the grid →← Imported from the grid
Solar supplies the business. The surplus goes to the grid. In this example, the inverter delivers 120 kW of AC power: 80 kW serves the building and 40 kW is exported. If daytime demand exceeds solar output, the grid supplies the difference.
The building keeps working after sunset. Solar output is zero, so the grid supplies all 60 kW of building demand through the grid meter and AC board. The solar path is inactive; there is no battery in this model.
Illustrative readings, with downstream losses omitted for clarity; not a generation forecast. kW is power right now; meters accumulate energy in kWh. *A separate generation meter is shown where provided. Only grid imports and exports pass through the bidirectional grid meter. Export requires an approved arrangement. Moving trails show net energy transfer, not the back-and-forth motion of AC current. Simplified flow model, not a wiring diagram.
How a business uses grid and solar electricity
A workshop, hotel or factory uses electricity for activities such as lighting, cooling and production. It normally buys this electricity from a distribution company, often called a DISCOM. Solar can produce some of the electricity at the business premises.
C&I means commercial and industrial. A commercial customer might operate a hotel or a showroom. An industrial customer might manufacture products. The label alone does not tell us the customer's tariff category, operating hours or suitability for solar; those must be checked.
Solar PV means solar photovoltaic: equipment that converts sunlight into electricity. In this course, an on-grid plant is connected to the customer's electrical system and operates with the electricity grid.
What the three letters mean
Part
Plain-English meaning
Typical project output
E · Engineering
Work out what is suitable and how it should be built.
Site assessment, layout, equipment sizing and an electrical design.
P · Procurement
Obtain the agreed equipment and materials.
Panels, inverter, mounting structure, cables and protection equipment.
C · Construction
Install, test and bring the system into service.
An installed plant, commissioning records and customer handover.
An EPC proposal should state exactly what is included. Roof repairs, approval fees, meter work, ongoing maintenance and other items should not be assumed to be included just because the offer says “turnkey.” The written scope defines which of these items belong to the project.
How an EPC project comes together
Worked example
A daytime workshop
A workshop owner wants to reduce electricity purchases. The electricity bill, operating hours and site conditions form the starting information. Engineers assess feasibility. The proposal brings together the plant design, expected generation, usable energy, price and terms.
If the project proceeds, the agreed equipment is installed and the required tests and approvals are completed. The customer receives operating information and the agreed service arrangements.
The owner is buying an operating asset. A panel price alone does not describe the whole project.
What an on-grid system can and cannot do
Solar output varies with sunlight and site conditions. The grid can supply electricity when solar is insufficient.
Export of surplus electricity and how it is credited depend on the approved arrangement. Export credit is not necessarily equal to the retail purchase rate.
An ordinary grid-following on-grid plant does not provide backup during a grid outage. Special backup arrangements are outside this course.
The benefit depends on the customer's actual usage and the complete project economics.
How it works
An EPC project connects the business load and site conditions to a complete system. Its scope covers the agreed design, equipment, installation and responsibilities, rather than the panels alone.
Keep these ideas
EPC means engineering, procurement and construction.
An EPC project delivers a defined working system.
Site assessment and engineering establish whether the system fits the business.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
Voltage and current describe different things. The distinction helps make sense of equipment labels and operating measurements.
By the end of this topicDistinguish electrical potential difference from the flow of charge, and recognise the units V and A.
Voltage: the difference that can drive a current
Voltage is the electrical potential difference between two points. In everyday language, it is the electrical “push” that can drive current through a suitable connected path. Its unit is the volt, written V.
Voltage is always between points. A number such as 12 V tells you the potential difference; it does not tell you how much electricity has been used or how much current is flowing.
Current: how much charge is flowing
Current is the rate at which electric charge flows. Its unit is the ampere, usually shortened to amp and written A. It is not the speed of an individual electron.
In a simple circuit, voltage can be present even while a switch is open and no current flows through the load. When the circuit is complete, the current depends on the supply and the connected equipment. Voltage alone does not determine the current.
V
Voltage
Potential difference between two points. Question: “What voltage is this equipment designed for?”
A
Current
Charge flowing through a path. Question: “How much current is it drawing?”
A useful analogy—with a limit
Water pressure differenceHelps you picture voltage.
Water flow rateHelps you picture current.
Think of pressure pushing water through a pipe. Pressure and flow rate are related, but they are not the same measurement. A closed valve can leave pressure present while flow stops.
The analogy helps with the difference between “push” and “flow.” It is not a wiring model: electricity transfers energy through an electrical system, and electrical behaviour is not fully explained by a pipe.
What an equipment rating tells us
Worked example
A label says 12 V DC, maximum 2 A
12 V identifies a voltage. 2 A identifies a maximum current rating in this example. These are separate specifications.
The label does not prove that the connected device continuously draws 2 A. A rating and an actual operating measurement are different. No billing-energy figure can be obtained from these labels alone without knowing operation over time.
On a solar project, voltage and current ratings help engineers select compatible equipment and protection. Understanding these ratings helps distinguish equipment limits from actual operating conditions. Live-circuit testing remains a task for qualified personnel.
Keep these ideas
Voltage is measured in V; current is measured in A.
Voltage can be present without current through a load.
Equipment ratings are not automatically actual operating measurements.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
Power tells you how quickly electricity is being used or produced. It is the starting point for understanding both a business load and a solar plant's output.
By the end of this topicConvert watts to kilowatts and describe a load's power without confusing it with energy or nameplate capacity.
Think of a rate
At a given moment, a heater, light or machine is taking electrical power. A generating plant can be supplying electrical power. The unit is the watt (W). For larger quantities we use the kilowatt (kW).
1 kW = 1,000 W W ÷ 1,000 = kW · kW × 1,000 = W
Use the same prefix idea for bigger projects: 1 megawatt (MW) equals 1,000 kW. A 750 kW value is 0.75 MW. Always preserve any DC, AC or peak-rating label attached to the number.
Work with a simple load
Worked example
Lights in a small business
Assume each of 20 lights draws 20 W while on.
20 × 20 W = 400 W = 0.4 kW
At that moment, these lights together draw 0.4 kW. If another measured load draws 3 kW at the same time, the combined real power is 3.4 kW.
This tells you the rate of use. We still need the operating time to calculate the energy.
Power written in watts
Same power in kilowatts
100 W
0.1 kW
2,500 W
2.5 kW
30,000 W
30 kW
Rated power and actual power
Rated power describes a specified capability or operating point under stated conditions. Actual power is what the equipment is using or producing at a particular time. They need not be equal.
A machine may cycle, run partly loaded or be switched off. A solar plant's output changes through the day. Never assume that every connected load is running at its full rating simultaneously.
Also check what a nameplate rates. A motor's stated kW can describe mechanical output at its shaft rather than electrical input. Those figures are not interchangeable because conversion has losses. Ask the technical team before using a motor label as a consumption figure.
How it works
Connected equipment describes what is installed. Actual electricity use depends on which loads run together, their operating power and how long they run.
Keep these ideas
kW describes power, not electricity accumulated over a day.
Divide W by 1,000 to get kW.
Check whether a number is a rating, a measurement, an input or an output.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
Energy is electricity accumulated over time. This is the quantity behind the familiar phrase “units consumed.”
By the end of this topicCalculate energy from average power and time, convert Wh to kWh, and distinguish energy from demand.
Add the time dimension
A watt-hour (Wh) is the energy associated with one watt for one hour. A kilowatt-hour (kWh) equals 1,000 Wh. One kWh is commonly called one unit of electrical energy.
Energy (kWh) = average power (kW) × time (hours)
For a changing load, use its average power over the period or add the energy from separate intervals. Do not multiply the highest observed power by every hour of the day.
Calculate a day's use
Worked example
Two operating periods
A business draws 3 kW for four hours, then 1 kW for two more hours.
3 × 4 = 12 kWh 1 × 2 = 2 kWh Total = 14 kWh
Using the 3 kW peak for all six hours would incorrectly give 18 kWh. The actual load profile matters.
For a smaller example, a 20 W light running for five hours uses 100 Wh: 20 × 5 = 100. Divide by 1,000 to get 0.1 kWh.
Explore power and time
Power × time
Adjust a constant average load and its operating time.
1 kW10 kW
1 hour10 hours
The shaded area is energy for a constant load. A real load or solar-output curve can change with time.
Energy used 3 kW × 4 hours
kWh
Equal energy does not mean equal demand
A 10 kW load operating for two hours and a 5 kW load operating for four hours each use 20 kWh. Their power levels are different. A bill may contain both energy charges and charges linked to demand, so the full bill need not be identical.
Some business bills show apparent energy in kVAh. That is a different label from kWh. Record the actual billing unit instead of treating every quantity called “units” as kWh.
Write kWh, not “kW per hour.” kWh multiplies power by time; it does not divide power by time.
How it works
Monthly energy shows how much electricity was used in total. The timing of that use determines how much solar generation can serve the load directly.
Keep these ideas
1,000 Wh = 1 kWh = one unit of real electrical energy.
Use actual interval values or average power when the load varies.
Keep kWh, kW and kVAh distinct.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
A solar plant's nameplate capacity is a rating. It tells you the sum of its module ratings, not the energy the plant will generate each day.
By the end of this topicCalculate DC module capacity and distinguish kWp from actual kW output, inverter AC capacity and generated kWh.
What the p means
Wp means watt-peak and kWp means kilowatt-peak. These describe a module's rated DC output under standard test conditions, often abbreviated STC. Standardised conditions allow ratings to be compared.
A 600 Wp module is therefore rated at 600 W under those test conditions. Its actual output is not fixed at 600 W throughout daylight hours. Sunlight, cell temperature, shading, installation conditions and equipment behaviour affect actual output.
The rating is a reference value, not an absolute physical ceiling under every possible condition. It describes the DC nameplate capacity under standard test conditions.
Add the module ratings
Worked example
A 30 kWp array
Assume a design contains 50 modules, each rated at 600 Wp.
50 × 600 Wp = 30,000 Wp 30,000 ÷ 1,000 = 30 kWp
This is the array's rated DC capacity. The inverter is specified separately. For example, an engineer might describe an illustrative design as 30 kWp DC with 25 kW AC inverter capacity. Those two values describe different parts of the system.
Whether that combination is suitable depends on the detailed design, equipment specifications and connection requirements.
Add up the module ratings
Illustrative ratings only. This is capacity arithmetic, not a plant-sizing recommendation.
10500
Total DC nameplate capacity 50 × 600 ÷ 1,000
kWp
Three numbers that belong on different lines
Quantity
Example
What it tells you
Module-array rating
30 kWp DC
The sum of the module ratings.
Output at a moment
18 kW AC
The plant's measured AC power at that moment.
Energy over a day
120 kWh
The accumulated electrical energy during that day.
All three figures above are illustrative. The 120 kWh is not a forecast for every 30 kWp plant. The same capacity can produce different energy at different sites or in different months.
Capacity, output and generation are different quantities
The phrase “a 200 kW system” is incomplete without a basis. Module DC capacity, inverter AC output and an approved connection limit describe different aspects of the installation.
Do not calculate daily generation as kWp multiplied by all daylight hours. A later generation estimate will need site data, an appropriate solar-yield model, losses and explicit assumptions.
How it works
A 30 kWp DC array has a module rating of 30 kWp. Inverter AC capacity is a separate rating, while energy generation is measured or estimated in kWh for specified site conditions and a time period.
Keep these ideas
Wp and kWp describe module capacity under test conditions.
Label DC capacity and inverter AC capacity separately.
Capacity is not a daily-energy guarantee.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
A solar project contains both DC and AC equipment. Understanding where the conversion happens makes later component lessons much easier.
By the end of this topicDistinguish direct and alternating current and understand the inverter's role between them.
Direct current
DC stands for direct current. In normal DC operation, current flows in one direction and the source has a defined polarity: positive and negative terminals. Solar modules supply DC.
“Direct” does not mean that the magnitude never changes. Solar DC voltage and current can change with conditions and the operating point.
An illustrative DC voltage stays positive relative to its reference. Illustrative waveforms, not site measurements.
Alternating current
AC stands for alternating current. The current direction changes periodically, and the associated supply voltage alternates in polarity. Grid electricity and many business loads use AC.
A cycle is one complete repetition of the waveform. Frequency is the number of cycles per second and is measured in hertz (Hz). A frequency is not a plant capacity or a consumption figure.
One illustrative AC voltage wave alternates above and below zero. Illustrative waveforms, not site measurements.
The inverter connects the two sides
ModulesDC side
→
InverterPower conversion
→
Business / gridAC side
An inverter converts DC electrical power to AC. A grid-following inverter also operates in step with the grid reference. The equipment and design must match the electrical system.
The inverter does not manufacture extra energy. Conversion has losses. “Converts electricity” is a more accurate phrase than “increases electricity.”
Why ordinary on-grid solar is not backup
Worked example
An office during a grid outage
The ordinary on-grid system in this course does not provide backup. A grid-following installation disconnects from an unavailable grid as part of its protection behaviour. Sunshine by itself does not make that system a backup supply.
Backup requires a separate technical assessment and a suitable system arrangement. A larger ordinary on-grid inverter does not create that capability by itself.
Keep these ideas
Modules supply DC; the grid side is AC.
The inverter converts DC to AC.
An ordinary on-grid system is not automatically a backup system.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
The number of phases describes the AC supply arrangement. It is another piece of site information—not a substitute for knowing the load or electricity consumption.
By the end of this topicUnderstand how single-phase and three-phase AC differ and why supply details matter for equipment compatibility.
What is a phase?
In this context, a phase is one AC waveform in the supply system. A single-phase supply uses one phase waveform. A three-phase supply uses three phase waveforms, spaced evenly through a cycle.
The ideal three-phase waveforms are separated by one-third of a cycle, or 120 degrees. You do not need trigonometry for this lesson: look at how their peaks happen at different times.
Three equal illustrative phase voltages are offset by one third of a cycle, or 120 degrees. Illustrative waveforms, not site measurements.
Phase 1 · solidPhase 2 · dashedPhase 3 · dotted
Why a business might use three phases
Three-phase systems are widely used to supply larger facilities and suitable motors. They can serve three-phase equipment, while appropriately connected single-phase loads can also be distributed across the phases.
Three-phase does not mean the customer automatically consumes three times as much energy. Consumption depends on equipment power and operating time. It also does not mean every machine on the premises is itself three-phase.
Look for
Why it matters
Supply type on the bill or approved service documents
Establishes the recorded connection arrangement.
Equipment and inverter phase specifications
Helps the technical team assess compatibility.
Connection voltage and point
Identifies which part of the electrical system is being discussed.
Distribution of loads across phases
May affect the engineering assessment; total kW alone is incomplete.
Two voltage descriptions can refer to one system
In a three-phase system, line-to-line voltage is measured between two phase conductors. Line-to-neutral voltage is measured between a phase and neutral where a neutral is provided. They are different measurements.
So “What is the voltage?” can be an incomplete question. Record the value, its units and where it applies. Actual conductor arrangements vary; phase labels alone are not instructions for connecting equipment.
Do not infer supply voltage, inverter suitability or an approval requirement solely from the requested solar kWp. Read the customer's service information and involve engineering.
How it works
Service documents identify the existing supply arrangement. The connection design then depends on that arrangement, the equipment specifications and the engineering assessment.
Keep these ideas
Three phases are three AC waveforms offset by 120 degrees.
Phase arrangement is not the same as power, capacity or energy.
Record the supply details; let engineering confirm the connection design.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
A business can have both kW and kVA values. They are connected by power factor, but they are not interchangeable labels.
By the end of this topicUse PF = kW ÷ kVA for a consuming load, calculate simple examples and avoid confusing power factor with efficiency.
Real power and apparent power
Real power, measured in kW, is the rate at which electrical energy is converted into other forms, such as motion, heat and light. It includes energy used usefully and real losses.
Apparent power, measured in kilovolt-amperes (kVA), describes the combined voltage-and-current loading of an AC system. Cables, transformers and other equipment have to accommodate current, so this quantity matters.
AC loads such as motors can also exchange energy with electric or magnetic fields. You may see reactive power, measured in kVAr. Recognise that term for now; detailed reactive-power calculations are outside this introduction.
The relationship you need
Power factor = real power ÷ apparent power PF = kW ÷ kVA kVA = kW ÷ PF · kW = kVA × PF
Power factor has no unit. In these consuming-load examples, write it as a decimal from 0 to 1: 0.80 is 80%. Do not enter 80 into a formula that expects 0.80. Use matched quantities for the same operating condition; do not mix unrelated readings from different times.
Worked example
80 kW at a power factor of 0.80
80 ÷ 0.80 = 100 kVA
If the same real load operates at PF 0.95, apparent power becomes approximately 84.21 kVA. The real load is still 80 kW in this comparison.
Explore the relationship
Keep kW fixed. Change power factor.
A simplified consuming-load example using positive power-factor values.
10 kW200 kW
0.501.00
Real power · kW80
Apparent power · kVA100.00
Both bars use a fixed numeric scale of 0–400. They show different quantities. The difference is not “wasted kW.”
Apparent power 80 ÷ 0.80
kVA
Avoid two common mistakes
Power factor is not equipment efficiency. A power factor of 0.80 does not mean a motor wastes 20% of its incoming energy as heat. Efficiency compares useful output with energy or power input; PF compares real with apparent power.
Do not subtract kW from kVA and call the answer a loss. In the 80 kW / 100 kVA example, the 20-point numerical difference is not 20 kW of waste. These are different quantities with different relationships.
Power-factor improvement and a solar installation are separate engineering questions. Installing solar does not automatically correct power factor or remove a charge. The electrical design, metering and tariff must be checked.
How it works
kVA and power factor describe electrical loading. Solar generation and energy savings describe different aspects of operation and need separate calculations.
Keep these ideas
kW and kVA describe different aspects of AC power.
For these examples, kVA = kW ÷ PF.
Solar does not automatically correct PF, and PF is not efficiency.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
A bill or service document may show several capacity-related numbers. Each describes a different aspect of the electricity supply or load.
By the end of this topicDistinguish connected load, sanctioned load, contract demand, recorded maximum demand and billing demand without treating them as a solar-sizing formula.
First, separate installed, approved and measured
A load is equipment that uses electricity. Connected load is an aggregate rating of the connected equipment under the applicable definition. It is not proof that everything runs at full power together.
Sanctioned load is the load approved for the electricity service. Contract demand is the maximum demand agreed with the distribution company in the supply arrangement. The terminology and units depend on the service; copy them exactly from the approved documents.
These are different views of the site. The amount installed, the amount permitted and the amount actually drawn do not have to be identical.
Maximum demand is a measured peak over an interval
Recorded maximum demand (RMD) is the highest demand recorded over the applicable measurement intervals in the billing period. The interval and measurement basis come from the meter and tariff. It is not necessarily a split-second equipment-starting spike.
Billing demand is the quantity the tariff uses to calculate demand charges. It can differ from RMD because the tariff may apply minimums or other rules. We will read those rules with the actual bill in Section 4.
A demand value may be expressed in kW or kVA. Neither is monthly energy in kWh. A customer's 100 kVA contract does not mean a 100 kWp solar plant is automatically suitable or permitted.
Read a fictional service summary
Illustrative field
Value
Interpretation
Connected load
80 kW
An aggregate equipment-load figure, not continuous consumption.
Contract demand
100 kVA
An agreed supply-demand figure.
Recorded maximum demand
86 kVA
The highest recorded interval demand for this period.
Monthly real energy
14,500 kWh
Accumulated real electrical energy during the month.
These are teaching figures, not an AP tariff or a real customer bill. A sanctioned-load field, billing unit or demand rule may differ on an actual service.
You can read the labels and describe what the figures mean. You cannot calculate the exact solar size, daytime load or bill saving from this summary alone. Ask for operating hours, interval data where available, the tariff and site information.
How demand differs from solar capacity
Solar can reduce grid energy purchases when its generation serves the customer's load. That does not automatically reduce the agreed contract demand or remove demand charges. The recorded peak might occur outside solar hours, and the billing rule may include a minimum.
Bill and service details describe the existing connection, recorded demand and energy use. Preliminary sizing combines consumption and timing with site and connection constraints; no single bill field establishes the whole design.
How it works
Demand describes the level of electrical loading; monthly units describe accumulated energy. The daytime load pattern, site conditions and connection rules determine how those figures relate to a solar project.
Keep these ideas
Connected, approved, recorded and billed are different concepts.
RMD is not monthly energy or necessarily an instantaneous spike.
Demand-charge savings depend on the load profile and applicable tariff.
Sources and further reading · online
The lesson and exercises work offline. These optional reference links need an internet connection. Reviewed 19 September 2026.
Use this page to test your understanding. Work out your answer before opening each explanation. Nothing is scored, saved or monitored.
By the end of this topicConnect the essential terms and identify which conclusions need operating data, site information or engineering assessment.
Your quick reference
Term
Meaning
A useful example
V
Voltage: potential difference
An equipment voltage rating.
A
Current: rate of charge flow
A current rating or measured current.
W / kW
Real power
2,500 W = 2.5 kW.
Wh / kWh
Real electrical energy
3 kW for 4 hours = 12 kWh.
Wp / kWp
PV DC rating at standard test conditions
50 × 600 Wp = 30 kWp.
AC / DC
Forms of electricity
Modules supply DC; the inverter supplies AC.
Single / three phase
AC supply arrangements
Three waveforms offset by 120°.
kVA
Apparent power
80 kW at PF 0.80 = 100 kVA.
PF
Real power ÷ apparent power
0.80 is not 80% efficiency.
Contract demand / RMD
Agreed demand / recorded demand
Both differ from monthly kWh.
Practise the essentials
Use a piece of paper if useful. An accurate explanation matters more than speed. If a term is unclear, return to its subsection and then retry the question.
Topic by topic
Each question tests one topic from this section. If an explanation is unclear, return to that topic and try again.
Topic 1.2 · Voltage and current: V and A
An open switch stops current through a load. Does that prove there is no voltage anywhere in the circuit?
Show explanation
No. A potential difference may still be present across points in the circuit. “Not drawing current” does not mean “safe to touch.” Electrical checks belong to qualified personnel.
Topic 1.3 · Power: W and kW
A load draws 2,500 W. What is that in kW, and is this enough information to calculate a day's energy use?
Show explanation
2,500 ÷ 1,000 = 2.5 kW. It is not enough for a daily energy figure. You need the operating time and the actual or average power during that time.
Topic 1.4 · Energy: Wh, kWh and billing units
A load averages 4 kW for five hours. How much energy does it use? How would the energy change if it ran for only two hours?
Show explanation
4 × 5 = 20 kWh. For two hours: 4 × 2 = 8 kWh. Power remains 4 kW in both examples; energy changes with operating time.
Topic 1.5 · Solar capacity: Wp and kWp
A proposal lists 400 modules of 500 Wp each. What is the DC capacity? Does the result tell you the exact daily generation?
Show explanation
400 × 500 ÷ 1,000 = 200 kWp DC. It does not establish daily kWh. Generation requires a site-specific estimate.
Topic 1.6 · AC and DC
Which device converts the solar modules' DC into AC for an ordinary on-grid installation? Does DC mean the power must stay constant?
Show explanation
The inverter performs the conversion. DC describes direction/polarity; its magnitude and power can vary.
Topic 1.8 · kVA and power factor
A load draws 90 kW of real power at PF 0.90. What is the apparent power? Does 0.90 mean the equipment is 90% efficient?
Show explanation
90 ÷ 0.90 = 100 kVA. No: power factor is not an efficiency figure. The equipment's useful output and real input are needed to assess efficiency.
Topic 1.9 · Load and demand terminology
Does a 100 kVA contract demand establish that a 100 kWp solar plant is suitable or permitted?
Show explanation
No. Contract demand is a supply-agreement quantity; kWp is a DC module rating. Suitability and permission require consumption, operating profile, roof, equipment and connection checks.
Across the section
These questions connect ideas from several topics.
Practice
1. What does EPC stand for, and why is a panel price not a complete EPC price?
Show explanation
Engineering, procurement and construction. The project also needs the agreed design, other equipment, installation and testing, plus any approvals and services specifically included in the contract.
Practice
2. Which unit measures voltage and which measures current? Can voltage exist without current through a load?
Show explanation
Voltage uses V and current uses A. Yes: an open circuit may have voltage present even though no current flows through the load.
Practice
3. Convert 3,500 W to kW. A load then draws this average power for two hours: what energy does it use?
Show explanation
3,500 ÷ 1,000 = 3.5 kW. Energy = 3.5 × 2 = 7 kWh.
Practice
4. A load draws 2 kW for three hours and 5 kW for one hour. Calculate total energy.
Show explanation
(2 × 3) + (5 × 1) = 6 + 5 = 11 kWh. Do not use the highest power for all four hours.
Practice
5. There are 50 modules rated at 600 Wp each. What is the array capacity, and what further figure would express a day's generation?
Show explanation
30 kWp DC. A day's generation is expressed in kWh. Capacity alone does not tell you that energy value.
Practice
6. Which side of an ordinary on-grid inverter receives the modules' electricity? Is backup during an outage automatic?
Show explanation
The modules connect on the DC side; the inverter converts to AC. No, ordinary grid-following on-grid solar is not automatic backup.
Practice
7. Does a three-phase connection tell you the monthly energy use or prove all appliances are three-phase?
Show explanation
No. It describes the supply arrangement. You still need load and operating-time information, and the premises may include single-phase equipment.
Practice
8. A consuming load draws 72 kW at PF 0.90. Calculate kVA. Is the difference between kVA and kW wasted power?
Show explanation
72 ÷ 0.90 = 80 kVA. The numerical difference is not 8 kW of waste. Do not subtract these unlike quantities to calculate a loss.
Practice
9. Which describes a supply agreement: contract demand, recorded maximum demand or monthly kWh?
Show explanation
Contract demand. RMD is recorded from operation over the applicable intervals. Monthly kWh is accumulated energy.
Practice
10. Why does a 200 kWp rating establish neither 200 units each hour, removal of demand charges, nor backup during a power cut?
Show explanation
200 kWp describes DC module capacity under test conditions. Actual kWh depends on the site and operation. Demand-charge savings depend on the load and tariff. An ordinary on-grid plant does not provide backup during a grid outage.
Put the ideas together
Worked example
A workshop's electricity use
The workshop has 20 lights drawing 20 W each and another load measured at 3 kW. Assume they all operate together at these powers for six hours. The customer is considering 50 modules rated at 600 Wp each.
Calculate the workshop's combined power in this simplified example.
Calculate the energy used over the six hours.
Calculate the proposed array's DC nameplate capacity.
Explain why those calculations do not prove that the proposal is correctly sized.
Worked solution
Show the workshop solution
Show explanation
Power: 20 × 20 W = 400 W = 0.4 kW. Add 3 kW: 3.4 kW.
Energy: 3.4 × 6 = 20.4 kWh.
Array rating: 50 × 600 ÷ 1,000 = 30 kWp DC.
Missing evidence: the full business load profile, seasonal operating pattern, solar-yield estimate, usable roof, connection conditions and export arrangement. A small simplified load example is not a complete site assessment.
Connect the quantities
Compare a plant rating, an inverter output reading and a monthly electricity bill. Identify what each quantity measures and why its unit differs. Then consider why a solar installation may reduce energy purchases without making the whole bill zero: load timing, grid imports and the applicable charges all matter.
You are ready to continue when you can use the terms without mixing capacity, power, energy and demand. There is no completion button or stored result.
Keep these ideas
Keep the unit beside the number.
State the conditions and time period behind an estimate.
A conclusion is only as strong as the information and assumptions behind it.
Follow the full journey from rooftop modules to the business and grid. Each box has a purpose, and the distribution board is the meeting point.
By the end of this topicTrace the complete power path and understand what changes when solar output, business demand or grid availability changes.
Explore the whole plant
One plant. Four operating conditions.
Follow the arrows through each component. Choose a condition to see what changes.
DC from panelsAC to the businessGrid exchange
On a small screen, swipe the diagram sideways or focus it and use the arrow keys.
Solar AC output50 kW
Power supplied to loads80 kW
At the grid connection30 kW import
Solar and grid supply the business together
50 kW from solar reaches the distribution board. The grid supplies the remaining 30 kW through the net meter. The business receives 80 kW. All solar output is used on site.
50 kW solar + 30 kW import = 80 kW load
Illustrative 200 kWp commercial plant; shown as one inverter path for clarity. Readings are instantaneous kW, not kWh or promised generation. Downstream losses are omitted. A generation meter, where required, sits in the solar AC path and is explained in Topic 2.10. Actual boxes, transformer connections and metering follow the approved design.
Read the diagram as a power journey
Start at the solar modules. They produce DC electricity. The DCDB provides the DC-side connections and protection shown in this teaching arrangement. The inverter converts DC to AC. The ACDB provides AC-side protection before the solar connection reaches the business distribution board.
At that board, the solar supply meets the business circuits and the grid connection. Electricity used by the business leaves along the load branch. Electricity exchanged with the grid passes through the bidirectional net meter. Locally used solar does not have to pass through that meter first.
The board is a connection point, not a traffic controller
Solar and the grid can supply a load at the same time. There is no person or ordinary net meter deciding which individual unit should go where. At this simplified boundary, the power entering and leaving must balance. The diagram shows total real power; it does not show individual phases, neutral conductors or reactive power.
The animated arrows represent the direction of net real-power transfer. They do not represent the rapid back-and-forth AC waveform taught in Section 1. “AC alternates” and “the site is importing” describe different things.
Try all four conditions
Condition
Watch this path
What happens
Solar below demand
Grid → net meter → board → loads, alongside solar
The grid supplies the shortfall.
Solar above demand
Board → net meter → grid
The surplus exports when the approved arrangement permits it.
Nighttime
Grid → net meter → board → loads
The solar inverter is not in the grid-to-load path.
Grid outage
No AC supply arrows
This ordinary on-grid plant provides no backup. DC voltage may remain.
A useful drawing, with a defined scope
This is an illustrative 200 kWp plant, using the middle course case size. The 50 kW and 120 kW readings are example operating points, not predictions from that nameplate capacity. Multiple inverters can feed a common AC arrangement; larger or different sites may also use transformers and different connection points.
DCDB and ACDB functions may be separate or integrated with other equipment. A generation meter, where required, measures the solar branch; it is distinct from the grid meter. Follow the approved site drawing for the actual equipment and metering arrangement.
Keep these ideas
Follow the physical sequence before learning each component.
The distribution board connects solar, loads and grid.
Operating state and page theme are independent: test any condition in either theme.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
A module produces DC electricity from light. Modules are connected into strings, and groups of strings form an array.
By the end of this topicDistinguish modules, strings and arrays, and work out how series and parallel connections affect voltage and current.
Modules → DCDB → Inverter → ACDB → Distribution board ↔ Net meter ↔ Grid Distribution board also supplies the business loads.
Plant anatomy
The starting point: solar modules
A consistent equipment view, with the main functions labelled.
Illustrated module array. Frames and construction vary by product; the drawing does not specify a mounting or wiring design.
Cell, module, string, array
A cell is the light-converting element. A module, commonly called a panel, packages many cells with protective materials and electrical connections. A string is a set of modules connected in series. The array is the collection of modules serving the plant.
The panel rating in Wp describes test-condition power. It does not mean that output is constant in sunlight. Revisit Topic 1.5: solar capacity if Wp, kWp and actual kW still feel similar.
Plant anatomy
From modules to strings
A small, idealised example of electrical connections.
Values are illustrative operating values for identical modules in equal conditions. This is a relationship diagram, not a complete positive/negative wiring schematic or a string-design instruction.
Two connection ideas are enough for now
In an ideal series example, two identical modules operating at 40 V and 10 A give a string operating at 80 V and 10 A. Voltage adds; the same current passes through both modules. Two such matching strings in parallel operate at 80 V and 20 A: current adds while voltage is common.
These are chosen operating values, not a recommended number of panels for an inverter. Real design checks include voltage in cold conditions, current limits and the inverter’s allowed input range. Learners need to recognise the relationships, not calculate a safe string design here.
Why grouping matters
Modules in a string interact electrically. Unequal light or different module characteristics can prevent all modules from working at their individual best points. Engineers therefore consider shading, orientation and input grouping. One shaded module does not automatically mean the entire plant stops; the effect depends on the layout and equipment.
A DCDB may combine suitable strings or provide protection for separate circuits. Do not assume all strings must be joined together into one pair of wires. Separate inverter tracking inputs can serve different groups.
How it works
The panels generate DC. They are grouped into strings so their electrical output suits the inverter. The electrical design determines the actual grouping.
Keep these ideas
Module → string → array describes the grouping.
Series adds voltage; matching parallel strings add current.
Understand the principle; leave actual string selection to the design.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
The DC distribution box sits on the module side of the inverter in our teaching plant. Its role is connection, isolation and appropriate protection.
By the end of this topicUnderstand the purpose of the DCDB and distinguish a fuse, an isolating device and a surge protective device.
Modules → DCDB → Inverter → ACDB → Distribution board ↔ Net meter ↔ Grid Distribution board also supplies the business loads.
Plant anatomy
Inside the DCDB
A consistent equipment view, with the main functions labelled.
Conceptual open-front cabinet, not a wiring drawing. An SPD is a protective branch, not a box through which all normal solar power flows in series.
What DCDB means
DCDB means DC distribution board or box. It is between the array and inverter in the arrangement we are learning. You may also hear array junction box or string combiner box; the names are sometimes used loosely, so check the actual equipment schedule.
A combiner joins suitable string circuits. Other DC boxes keep circuits separate and mainly provide switching or surge protection. A label alone cannot tell you the number of inputs, protection functions or how the inputs connect to the inverter.
Three different jobs
Part or function
What it does
Do not confuse it with
String fuse, where required
Interrupts excessive current in the circuit it protects.
A general manual on/off control.
DC-rated switch-disconnector
Provides the specified switching and isolation function.
An automatic overload trip unless that function is also provided.
Surge protective device (SPD)
Limits brief voltage surges by diverting surge current through its protective path.
An overload fuse, energy saver or complete lightning-protection system.
Terminals, enclosure and cable entries
Support secure connections and the required environmental protection.
Proof that every box has the same contents.
Follow normal power through the box
During operation, module DC travels through the relevant terminals and series-connected protective or switching devices to the inverter inputs. The SPD is connected as a branch across the appropriate conductors and protective arrangement. It is not a converter. The electricity leaving the DCDB is still DC.
Some inverter products include DC switches or surge protection internally. A separate external box is therefore a design choice based on the actual system and requirements, not a universal proof of quality.
An essential operating limit
Stopping the inverter or opening an AC breaker does not remove sunlight from the panels. DC voltage may remain on the array and upstream wiring. This lesson explains equipment recognition; opening enclosures and operating isolation devices require the authorised electrical procedure.
Keep these ideas
DC enters and DC leaves.
Fusing, isolation and surge protection have different purposes.
Check the actual design rather than assuming the contents from the box name.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
The inverter turns the array’s DC output into usable AC and controls how the solar plant operates with the grid.
By the end of this topicUnderstand DC-to-AC conversion, how maximum power point tracking works and why ordinary on-grid operation stops during an outage.
Modules → DCDB → Inverter → ACDB → Distribution board ↔ Net meter ↔ Grid Distribution board also supplies the business loads.
Plant anatomy
The inverter’s main functions
A consistent equipment view, with the main functions labelled.
Generic commercial string-inverter illustration. Screen, cooling and protection arrangements differ between models.
Convert, control and report
The inverter’s power electronics convert DC into AC. The ordinary grid-following inverter used in this course works with the grid’s electrical reference. It controls its output to operate with that supply; it does not independently establish backup power for the building.
It also measures operating information such as power and energy and can report status or faults through a display or monitoring system. Its DC input capacity and AC output rating are different specifications.
MPPT, without the complicated mathematics
MPPT means maximum power point tracking. Under a given set of conditions, a module group has a combination of operating voltage and current that gives its highest available power. The inverter adjusts its operating point as conditions change.
Worked example
Choosing the better operating point
Imagine two measured DC operating points for a module group: 300 V × 10 A = 3,000 W, and 320 V × 9 A = 2,880 W. The first produces more power despite its lower voltage. This illustrates why tracking power matters; it is not a description of the full tracking algorithm.
An inverter with multiple MPPT channels can track suitably separated module groups independently. MPPT does not create extra sunlight or eliminate shade; it helps the connected array operate effectively within equipment limits.
Output has limits
Conversion is not perfectly efficient. Some input energy becomes heat, so cooling matters. When available solar power exceeds the inverter’s AC capability, output may be limited; this is often called clipping. An export control can also reduce production for a different reason. Neither term means the nameplate capacity is the energy produced every hour.
What happens when the grid fails?
An ordinary on-grid inverter stops supplying AC during a grid outage. Protection prevents it from continuing to energise an unintended isolated section of the network; this is called anti-islanding. Reconnection happens only after the applicable checks and settings are satisfied, so the timing depends on the applicable requirements.
A diesel generator does not automatically make solar operation safe or compatible during an outage. Solar–generator operation requires a specifically engineered control and protection arrangement. We are not teaching that arrangement in this on-grid course.
Keep these ideas
The inverter converts DC to AC and controls its output.
MPPT follows an electrical operating point, not the sun’s physical position.
An ordinary on-grid inverter needs an available grid reference.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
After conversion, solar power passes through the AC distribution box before joining the business electrical system in our example.
By the end of this topicRecognise the ACDB’s protection and switching functions and distinguish it from the DCDB and main distribution board.
Modules → DCDB → Inverter → ACDB → Distribution board ↔ Net meter ↔ Grid Distribution board also supplies the business loads.
Plant anatomy
Inside the ACDB
A consistent equipment view, with the main functions labelled.
Illustrative AC cabinet. Actual pole count, ratings, residual-current protection and SPD arrangement come from the approved design.
The electricity is now AC
ACDB means AC distribution board or box. It handles the AC output from the inverter. In a multi-inverter plant, an AC collection arrangement may combine several protected inverter feeders before connecting to the site. Our diagram shows one simplified path.
The ACDB does not generate electricity, change DC into AC or calculate the bill. Its role is to provide the specified connection, switching and protection functions for the solar AC circuit.
Understand the devices by their job
Function
Beginner explanation
Overcurrent protection
A suitable circuit-breaker trips for the overload and/or short-circuit conditions covered by its design and settings.
Switching and isolation
The specified device allows the solar AC feeder to be disconnected. Not every switching device has every protection function.
Surge protection
An AC-rated SPD limits brief overvoltage transients. It is distinct from normal overcurrent protection.
Terminals, bars and indication
Connections carry the power; indicators or meters, if fitted, help show status. They do not replace electrical testing.
Why DCDB and ACDB are different
The DCDB is before conversion; the ACDB is after conversion. Devices must suit the electrical conditions on their side of the inverter. A similar-looking AC and DC switch is not automatically interchangeable. Equipment selection also depends on voltage, current and the available fault level.
MCB means miniature circuit-breaker; MCCB means moulded-case circuit-breaker. Those names identify device families, not an instruction to choose a particular rating. Residual-current protection, where required, must also suit the inverter and installation.
What disconnecting the solar feeder means
Worked example
Solar feeder unavailable; healthy grid remains connected
Suppose the business requires 80 kW and the solar feeder is disconnected under an authorised procedure. With a healthy, adequately rated grid supply still connected, the grid can supply that load through the main distribution board. The building is not automatically switched off simply because solar is unavailable.
This does not establish a switching procedure. The board can have more than one source, and upstream DC parts may remain energised. Electrical operation and isolation remain the responsibility of the authorised technical team.
Keep these ideas
ACDB sits on the AC side of the inverter.
Protection, switching and metering are different functions.
Solar isolation does not necessarily isolate the whole building.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
The business distribution board is where solar, the grid connection and the load circuits come together in our teaching arrangement.
By the end of this topicUnderstand how solar and grid supply can combine and why local solar use does not pass through the net meter.
Modules → DCDB → Inverter → ACDB → Distribution board ↔ Net meter ↔ Grid Distribution board → business loads
Plant anatomy
One connection point, several circuits
A consistent equipment view, with the main functions labelled.
Conceptual distribution cabinet. Real boards include the appropriate phase, neutral, protective-earth and circuit arrangements; these are not shown as a wiring schematic.
What is inside a distribution board?
A busbar is a conducting bar that provides a common electrical connection. A feeder is a circuit supplying another board, plant item or group of loads. The board contains the appropriate connections and protective devices for these circuits.
In this course drawing, the solar feeder enters from the ACDB. Outgoing load feeders serve the business. Another connection goes through the bidirectional meter to the utility grid. The actual approved connection may be at a different board or voltage level.
Use a simple power balance
Worked example
Both sources contribute
The inverter supplies 50 kW AC and the business consumes 80 kW. Ignoring downstream losses, the grid supplies the remaining 30 kW. Both sources contribute while the grid is healthy.
Worked example
The direction at the meter reverses
Later, solar output is 120 kW while the same business load remains 80 kW. With export permitted and no active export limit, the remaining 40 kW goes from the board through the meter toward the grid.
These balances describe instantaneous total real power at a simplified boundary. Real metering may also involve phase-wise measurements, transformer losses and other details that need the actual site information.
“Solar first” is shorthand
For this arrangement, “solar supplies the business first” is a useful way to describe reduced net import. It does not mean that the net meter selects a supply or that electricity must travel through a queue. Connected sources and loads follow the electrical conditions at the board.
Local consumption branches off before the grid meter. The meter sees the balance exchanged with the grid, not every unit generated or every unit consumed. An import of 30 kW can therefore coexist with 50 kW of solar production and 80 kW of consumption.
Why the existing board needs engineering review
A board originally supplied only from the grid may now receive power from another source. Busbar ratings, cables, protective devices and possible fault currents must be checked for the proposed connection. The presence of an empty breaker space alone does not prove that the board can accept the solar plant.
Keep these ideas
A board distributes power through connected circuits.
Solar + import = load + export, at a consistent boundary with losses accounted for or explicitly omitted.
A net meter is on the grid branch, not the local-load branch.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
The net meter is at the boundary between the business and the grid. Its import and export readings describe two different directions of energy transfer.
By the end of this topicTrace both grid directions and distinguish power flow, accumulated meter energy and billing treatment.
Modules → DCDB → Inverter → ACDB → Distribution board ↔ Net meter ↔ Grid Distribution board also supplies the business loads.
Plant anatomy
One meter, two directions
A consistent equipment view, with the main functions labelled.
Generic bidirectional energy meter. Register names, display codes, current-transformer arrangements and billing configuration vary.
Import and export at the site boundary
01
Import: grid → business
Grid → net meter → distribution board → loads. This supplies the solar shortfall or the nighttime requirement.
02
Export: business → grid
Solar → DCDB → inverter → ACDB → distribution board → net meter → grid. This carries permitted surplus solar.
The arrows show power; the register accumulates energy
An instantaneous reading may show power in kW. The energy registers accumulate kWh over time. A meter can record both import and export during the same day because the balance changes through the day.
Worked example
Read the change, not the lifetime total
The import register begins at 12,400 kWh and ends at 12,650 kWh. Import during that period is 250 kWh. The export register begins at 3,000 kWh and ends at 3,150 kWh, so export is 150 kWh.
Use matching start/end times, the correct registers and any applicable meter multiplier. The simple subtraction above assumes the displayed readings already use the correct energy scale. It does not establish the utility’s billing method.
The net meter does not store or route solar
Exported electricity goes into the connected network; it is not stored inside the meter for the customer to retrieve at night. The meter records exchange. A separate billing arrangement determines how eligible export is credited or settled.
A bidirectional meter does not by itself establish export permission, eligibility or a credit equal to the retail purchase rate. Detailed local rules and bill calculations belong in the later bill-reading and finance sections.
What if export is restricted?
Where the approved system limits export, sensing and control can reduce inverter production when the business cannot use all available solar. The extra sunlight is not automatically converted and stored somewhere. The meter measures; the relevant controller and inverter perform the limiting function.
Our export animation assumes export is allowed at that moment. Our outage animation assumes no other supply: neither a net meter nor an export agreement provides backup power.
Keep these ideas
Import comes in; export goes out.
Use the change in a register to find energy for a period.
Meter readings and billing credits are different things.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
The visible boxes depend on a supporting system. Structures hold the array, cables carry power and protective connections help the installation operate safely.
By the end of this topicUnderstand how mounting structures, cables, protective bonding and earthing support the plant and why their functions differ.
Plant anatomy
The equipment around the power path
A consistent equipment view, with the main functions labelled.
The rack is part of the physical support system. Protective-earth conductors are distinct from the normal power path and are not an electricity-disposal route.
Mounting is part of the engineered plant
The mounting system supports the modules and transfers their weight and environmental forces to the roof or other structure. Rails, clamps, supports and fasteners work as a system. The correct arrangement depends on the roof, wind conditions, corrosion environment and module requirements.
A layout must also allow for access, drainage and equipment constraints. “The panels fit” is only one observation; it does not confirm structural suitability. Detailed roof assessment and feasibility belong in Section 3.
Cables do more than connect two boxes
01
DC cables and connectors
Connect module groups to the inverter through the specified DC equipment. They must suit the electrical and environmental conditions.
02
AC cables and feeders
Carry inverter output to the ACDB and site connection, and connect the appropriate load and grid circuits.
03
Cable management
Supports and routes cables, protects them from avoidable damage and helps maintain the intended installation.
04
Data cables or communications
Carry measurements and status. A monitoring connection is not the same thing as a power cable.
Bonding and earthing: a separate purpose
Protective bonding connects relevant exposed conductive parts, such as frames and enclosures, into the protective system. Earthing connects the relevant installation arrangements to earth as designed. These help manage fault and surge conditions together with other protective measures.
They do not send unused solar power into the ground during normal operation. An SPD uses its protective connections during surge events; normal solar generation follows the electrical power circuit. Earthing, neutral and the positive/negative DC conductors have distinct functions and must not be treated as interchangeable.
Supporting equipment is part of the system
A quote that lists panels and an inverter alone does not describe all of this supporting equipment. The scope also needs to cover the specified structure, cable routes, protective connections and site work. Product selection and quantities must follow the project design, not generic assumptions from the lesson illustration.
Existing drawings and authorised survey observations help establish site conditions. Structural certification, roof access and electrical inspection require the appropriate technical expertise; understanding a diagram does not qualify someone to perform that work.
Keep these ideas
Support, power wiring and protection are part of the EPC scope.
Protective earth is separate from normal power transfer.
Feasibility and installation details require the actual site design.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
The same plant produces different power through the day and different energy from one day to the next. Sunlight, module conditions, losses and operating limits explain the variation.
By the end of this topicIdentify the main causes of output variation and distinguish normal changes, losses and production limits.
Plant anatomy
Same plant, different days
Sunlight changes over the day; the output curve changes with it.
The area below a power curve represents energy. These curves are conceptual, with no numerical forecast or guaranteed daily yield. Solid amber: clear-day illustration. Dashed plum: variable-cloud illustration.
Start with the light reaching the cells
The available solar resource changes with time of day, season and weather. Clouds change how much light reaches the modules. Module direction and tilt also affect the light received. A cloudy day can still produce electricity; “cloudy” is not the same as “off”.
Shading from a parapet, tree, building or another row can reduce output unevenly across the array. Because connected modules interact, its effect is not always equal to the shaded percentage of the roof area.
01
Module temperature
For common crystalline-silicon modules, higher cell temperature generally lowers power under otherwise comparable light conditions. A hotter day is not automatically a better solar day.
02
Dirt and deposits
Dust, soot or other deposits reduce the light reaching cells. The effect depends on what accumulates, where it settles and the cleaning conditions.
03
Electrical losses
Cables, connections, mismatched module behaviour and DC-to-AC conversion can reduce energy delivered at the measurement point.
04
Availability and controls
Equipment downtime, a grid outage, inverter limits or an export limit can restrict delivery even when sunlight is available.
Loss, clipping and curtailment are useful distinctions
Term
Meaning in this lesson
Loss
A reduction between available input and useful delivered output, such as conversion or wiring loss.
Clipping
Output is limited by the inverter’s capability when more solar power could otherwise be available.
Curtailment or controlled reduction
Production is deliberately reduced by a control instruction or operating constraint, such as an export limit.
Downtime
The plant or part of it is unavailable for production.
Do not add unrelated percentages blindly
Worked example
Two successive illustrative losses
Suppose an energy amount is 100 kWh before a stage that loses 5%. That leaves 95 kWh. A later stage loses 2% of what it receives, leaving 93.1 kWh. This example explains successive percentages; 5% and 2% are not assumed project loss rates.
A real estimate needs compatible assumptions and measurement boundaries. Do not count inverter loss twice or subtract a loss already included in the model output. Detailed forecasting is outside this lesson.
Why a low reading does not establish a fault
If production is lower today, first identify the comparison: the same time of day, a complete day or a monthly total? Check weather, grid availability and the monitoring timestamp. A single low reading is not enough to conclude that the inverter or modules have failed.
How it works
The plant’s rating stays the same, but actual output depends on sunlight, module conditions and operating limits. Expected energy depends on site-specific information rather than capacity multiplied by every daylight hour.
Keep these ideas
Power changes through the day; energy accumulates over time.
Heat and sunlight are different influences.
Performance comparisons depend on conditions, time period and measurement boundary.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
Monitoring turns plant operation into information. Read the right measurement for the question, and check that the data covers the same period.
By the end of this topicDistinguish inverter monitoring, a generation meter and the grid meter, then calculate simple on-site solar use and total consumption.
One day · worked example
Three readings, two useful calculations
Use readings for the same day and compatible measurement boundaries.
Solar AC generation600 kWhSolar output meter
Grid export150 kWhExport register increase
Grid import250 kWhImport register increase
Solar used on site = 600 − 150 = 450 kWh. Total business consumption = 450 + 250 = 700 kWh. No battery or other generator; losses between measurement points are ignored.
Three views of the same plant
Source
Typical information
What it cannot prove alone
Inverter display or app
AC output, generated energy, operating state, fault information and data timestamps, depending on the equipment.
Whole-site consumption or grid exchange without the required additional measurements.
Generation meter, where fitted
Solar AC energy passing through its measurement point.
All business consumption or the complete electricity bill.
Bidirectional grid meter
Energy imported from and exported to the grid.
Solar energy consumed locally without crossing that boundary.
Where does the generation meter fit?
It measures the solar AC branch, before that output mixes with the site’s other supply. Its exact location relative to AC switching and other equipment follows the approved metering arrangement. It is separate in purpose from the net meter at the grid connection.
An inverter app may present a production estimate from inverter measurements. Additional site meters or sensors are needed for features such as complete consumption and import/export displays. A dashboard field appearing on one product does not mean every installation measures it.
Work through the day’s readings
For the example above, solar generation is 600 kWh and export is 150 kWh. With no battery or other generator and with losses between points ignored, 450 kWh of solar was used on site. Adding 250 kWh of grid import gives 700 kWh total business consumption.
Check both sides: 600 + 250 = 700 + 150 = 850 kWh. This is an energy balance for the same day. It is different from the instantaneous kW balances in the plant animation, and it is not a savings calculation.
Before comparing two screens
01
Check the unit
kW is power at a moment or an interval average; kWh is energy over time. Compare like quantities.
02
Check the period
Today, this month and lifetime totals cannot be compared directly. Use matching dates and start/end readings.
03
Check the timestamp
A stale dashboard can indicate missing communication. It does not prove the physical plant has stopped.
04
Check the boundary
Different measurement locations, meter scaling and losses can explain a mismatch. Escalate unexplained differences with the readings and timestamps.
What monitoring evidence can establish
The site identity, date, displayed status, units, last-updated time and grid availability give a reading its context. The technical team uses that evidence with the relevant operating information to investigate. An app colour alone cannot establish an electrical fault.
This course’s readings are illustrative and work offline. An actual cloud monitoring app may need communications to refresh its data; that requirement is separate from the solar power path.
Keep these ideas
Generation, consumption, import and export are different quantities.
Compare the same units, period and measurement boundaries.
Monitoring helps investigate; it does not replace verification.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
Connect the component functions, power paths and readings. Use the scenarios below to test how the plant behaves under different conditions.
By the end of this topicApply the component functions to work out power flow, protection roles and the meaning of monitoring readings.
Your compact plant reference
Component
Its main job in this course
Modules and strings
Produce and group DC output.
DCDB
Provide the specified DC connections and protection.
Inverter
Convert DC to AC; track output and operate with the grid.
ACDB
Provide the specified solar AC connections and protection.
Distribution board
Connect solar and grid supply to the business circuits.
Bidirectional net meter
Measure grid import and export.
Mounting, cables and protective connections
Support the equipment, carry power and form part of the protection system.
Work it out before revealing the answer
Work through these questions without looking back first. If an explanation is difficult, return to that component lesson or use the interactive plant diagram. No marks or progress are stored.
Topic by topic
Each question tests one topic from this section. If an explanation is unclear, return to that topic and try again.
Topic 2.1 · The complete plant: follow the power
Solar produces 90 kW while the business uses 65 kW. With export allowed, where does the difference go?
Show explanation
25 kW flows from the distribution board through the net meter to the grid. The 65 kW used on site goes directly from the board to the loads, without first passing through the net meter.
Topic 2.2 · Solar modules and strings
Using the same ideal example, what happens with three 40 V, 10 A modules in series?
Show explanation
The string operates at 120 V and 10 A. This is an arithmetic example under equal conditions, not an instruction to connect those modules to an inverter.
Topic 2.3 · DCDB: connections and protection before the inverter
Does the DCDB convert DC into AC? How does its function differ from the inverter’s?
Show explanation
The DCDB provides the specified DC connections and protection. The inverter performs DC-to-AC conversion. Also, a surge protector and a fuse solve different protection problems.
Topic 2.4 · The inverter: conversion and basic MPPT
Does MPPT mean the inverter can always deliver the panel nameplate power, including during an outage?
Show explanation
No. MPPT seeks an operating point suited to the available sunlight and module conditions. Output is also constrained by the inverter and controls. Ordinary on-grid operation does not supply backup during a grid outage.
Topic 2.5 · ACDB: protection after the inverter
Does opening the solar AC feeder prove the panels and DCDB are de-energised?
Show explanation
No. It interrupts the specified AC path. Sunlit modules and DC wiring can still have voltage. Isolation and verification are technical tasks.
Topic 2.6 · The distribution board: where the paths meet
Solar supplies 70 kW and the business uses 100 kW. Does the net meter need to register 100 kW import?
Show explanation
No. In the simplified example it measures 30 kW net import. The remaining 70 kW is supplied locally by solar and does not cross the grid meter.
Topic 2.7 · The bidirectional net meter and the grid
Can a meter show 250 kWh imported and 150 kWh exported in one day? Does that prove the bill charges only 100 kWh?
Show explanation
Both readings can occur because the direction changes over the day. Their arithmetic difference is 100 kWh, but the bill’s charges and credits require the applicable tariff and settlement rules. Do not assume that subtraction alone determines the bill.
Topic 2.8 · Supporting equipment: structure, cables and earthing
Does protective earthing dispose of surplus solar power during normal operation?
Show explanation
No. In normal operation, power is used by the loads, exported where allowed, or production is limited. Protective earthing is part of the fault and surge protection arrangement, not a destination for surplus generation.
Topic 2.10 · Monitoring: generation, consumption and meter readings
Generation is 500 kWh, export is 100 kWh and import is 300 kWh for the same day. Find on-site solar use and total consumption using the example assumptions.
Show explanation
On-site solar use = 500 − 100 = 400 kWh. Total consumption = 400 + 300 = 700 kWh. Check: 500 + 300 = 700 + 100. Do not attach a tariff or savings claim without the billing assumptions.
Across the section
These questions connect ideas from several topics.
Practice
1. Trace solar power all the way to a business load.
Show explanation
Modules → DCDB → inverter → ACDB → distribution board → load, in our teaching arrangement. The local-use path does not pass through the net meter.
Practice
2. Trace grid supply to the business at night.
Show explanation
Grid → bidirectional net meter → distribution board → loads. It does not need to pass through the solar inverter.
Practice
3. Which box converts DC to AC? What do the boxes on either side do?
Show explanation
The inverter converts DC to AC. The DCDB and ACDB provide their specified connection, switching and protection functions on the respective sides.
Practice
4. What is the difference between a fuse and an SPD?
Show explanation
A fuse interrupts excessive current in its protected circuit. An SPD limits brief voltage surges through a protective branch. They are not substitutes for each other.
Practice
5. Two identical modules each operate at 40 V and 10 A. What does the ideal series example give?
Show explanation
80 V and 10 A. Real string design requires additional equipment and environmental checks.
Practice
6. Explain MPPT in one sentence.
Show explanation
The inverter adjusts the operating point of the connected module group to seek its best available power under the current conditions and equipment limits.
Practice
7. Solar output is 120 kW and demand is 80 kW. What crosses the net meter if export is allowed?
Show explanation
40 kW exports. 80 kW of solar is used locally. This is a power balance, not a daily energy estimate.
Practice
8. The grid fails at noon. Does matching solar capacity to load guarantee that the plant keeps supplying the building?
Show explanation
No. The ordinary grid-following plant stops AC supply during a grid outage. Sunlit DC wiring may still have voltage.
Practice
9. Why can hot, sunny weather still produce less than nameplate power?
Show explanation
Actual output depends on sunlight at the modules, cell temperature, losses and operating limits. Higher cell temperature generally reduces crystalline-silicon module power at comparable light levels.
Practice
10. Does a bidirectional meter alone prove the plant may export or that exported units earn the retail tariff?
Show explanation
No. It measures exchange. Permission, operating limits and billing treatment follow the applicable approved arrangement.
Practice
11. An app last updated yesterday shows 0 kW. What should you do first?
Show explanation
Check the timestamp, communications and available operating information. Do not conclude that the plant has failed from stale data alone.
Put it together: one plant, several measurements
Worked example
The 200 kWp teaching case
A business has a 200 kWp on-grid plant. At one moment its solar AC output is 50 kW while its load is 80 kW. For the full day, generation is 600 kWh, export is 150 kWh and import is 250 kWh. There is no battery or other generator; downstream losses are ignored.
Practice
A. What is the instantaneous import, and which path carries it?
Show explanation
30 kW: grid → net meter → distribution board → loads. Solar supplies the other 50 kW through DCDB, inverter and ACDB.
Practice
B. How much solar energy was used on site, and how much energy did the business consume that day?
Show explanation
450 kWh solar used on site; 700 kWh total consumption. These daily values cannot be calculated from the single 50 kW snapshot without knowing the rest of the day.
Practice
C. Did all 600 generated units pass through the net meter? Would this ordinary on-grid plant supply the factory during a power cut?
Show explanation
Only the exported 150 kWh crossed outward through the grid meter in this example; the other 450 kWh was used locally. Ordinary on-grid solar does not provide outage backup. Its inverter stops AC supply when the grid is unavailable.
Keep these ideas
Each component has a distinct function.
The distribution board separates local use from grid import and export.
Power, energy, billing and backup describe different things.
Sources and further reading · online
Technical references reviewed 20 September 2026. Diagrams and worked examples are original teaching illustrations. Manufacturer references explain functions, not a Ray2Volt brand recommendation or an India-specific approval rule. Lessons work offline; these links require internet access.
Engineering determines equipment and project scope.
Confirm readiness
Track permissions, inputs and conditions.
Procure and receive
Order the agreed items; check deliveries.
Install the plant
Coordinate site work and business access.
Commission
Verify the installation and permitted operation.
Hand over
Transfer records, access and customer guidance.
Maintain and support
Monitor, inspect and resolve service needs.
A teaching sequence, not a fixed calendar. Some tasks overlap; an unresolved dependency can hold the next activity.
What the three letters cover
Engineering turns site information and customer needs into the technical solution. Procurement obtains the equipment and materials specified for it. Construction installs the plant. Commissioning then verifies readiness for the permitted operation, and handover equips the customer to use and support it.
The actual agreement defines what the EPC supplier includes. Civil repairs, approval fees and ongoing maintenance are included only where the agreement specifies them. Each stage therefore has both a technical purpose and a defined project scope.
How one stage becomes ready for the next
What has been completed, and what record supports that statement?
What is still needed before the next activity can proceed?
Who will resolve it, and when is the next agreed update?
For example, “modules delivered” is a delivery milestone. It says nothing by itself about whether the roof is ready, the equipment is accepted or the plant can operate. Delivery, acceptance, installation and operating readiness are separate milestones, each with its own evidence and dependencies.
Keep these ideas
Each stage produces an output needed by later activities.
Readiness depends on evidence, not appearances.
The contract defines the actual scope.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
Initial screening gives the engineering team useful facts. A promising-looking roof is a starting point, not a feasibility approval.
By the end of this topicUnderstand the five site-screening inputs and how they support structural and electrical feasibility decisions.
Practical checklist
Five inputs to site screening
Dated records and authorised observations establish what is known about the site and what still needs verification.
01
Roof condition
Roof type, approximate age if known, reported leaks, visible damage, corrosion and planned repairs. Available roof/structural records support engineering review; an initial observation does not certify strength.
02
Shading
Nearby trees, buildings, tanks and other obstructions. The place and time of an observation matter; one photograph cannot establish year-round shading.
03
Available space
Approximate usable area and existing roof uses: equipment, skylights, access routes and planned expansion. Gross roof area and usable solar area are different quantities.
04
Access and logistics
Authorised survey access, site contact, entry restrictions, delivery approach, unloading/storage options and business working hours. Specialist teams plan roof access and lifting.
05
Electrical supply
Recent electricity bill and available service details: connection, sanctioned load/contract demand, phase/voltage information and existing generators or solar. Authorised records provide initial information; opening boards and taking live measurements are technical tasks.
Observation → question → engineering decision
Record the fact
Flag the question
Who confirms?
Customer reports a leak near the store.
Does the roof need repair before solar work?
Relevant roof specialist and engineering team.
A water tank shades part of the roof in the afternoon.
How does this affect usable space and yield?
Solar design team.
Bill details and the customer’s stated supply capacity differ.
Which connection information is current?
Technical team with customer/utility records as needed.
How site information becomes a feasibility decision
A site note brings together dated observations, customer-provided documents, relevant photographs obtained with permission, access restrictions and open questions. Missing details remain unconfirmed until supporting information is available. Engineers confirm the final structural and electrical feasibility and any necessary changes to the proposed capacity.
A 30 kWp site still needs feasibility review. A 750 kWp enquiry may involve more roof areas or electrical interfaces, but capacity alone does not determine the checks or the approval route.
Keep these ideas
Screening records facts and their sources.
Unknowns and risks remain open until assessed.
Engineers confirm feasibility.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
The equipment/material list connects the technical solution to purchasing and delivery. Learn what each entry tells you and what it leaves unanswered.
By the end of this topicUnderstand how descriptions, specifications, units, quantities and revisions define the procurement reference.
Process at a glance
One list, three uses
The agreed revision is the reference throughout the project.
Engineering defines
What is required and why it suits the site.
Procurement orders
What the supplier must provide.
Delivery compares
Whether the received items match the order.
Names such as bill of materials (BOM), bill of quantities (BOQ) and equipment schedule vary. Check the document’s contents and purpose.
Read an entry in plain English
Field
What to look for
Description
The actual item: module, inverter, mounting member or cable.
Specification/model
The agreed type or model and relevant rating. A similar-looking item is not automatically equivalent.
Unit and quantity
Pieces, sets or metres, with an explicit quantity. “One lot” needs a defined scope.
Revision and status
Which version is current and whether it is authorised for purchasing.
Scope notes
Included accessories, exclusions and any items awaiting technical confirmation.
The list extends beyond panels
Expect entries for inverters, mounting components, DC/AC protection as designed, cables, cable supports, earthing/bonding materials, connectors, labels and monitoring equipment. Metering items depend on the agreed arrangement. Section 2 explains their functions; the material list brings those components together into a defined procurement scope.
Plant kWp alone does not determine cable lengths, protection ratings or inverter quantities. A line such as “cables — one lot” refers to a scope that must be defined in the technical/procurement records; it does not mean an unlimited quantity.
Keep these ideas
Read description, specification, unit, quantity and revision together.
Equal kWp does not make equipment interchangeable.
The list records the design; substitutions require authorised review.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
Approvals connect a proposed project to the conditions under which it may be installed, connected and operated. The applicable requirements depend on the actual site and connection.
By the end of this topicUnderstand why approvals are needed, which inputs support them and how a pending item affects project readiness.
Process at a glance
The stages of an approval
These labels describe different milestones, not interchangeable versions of “done”.
Inputs collected
Requested information is available for checking.
Submitted / in review
The relevant request has been made; a decision may still be pending.
Decision and conditions
Check the actual permission, its scope and remaining conditions.
These are project-status distinctions. The technical/project team identifies the applicable route and permissions; the lesson does not prescribe local forms or eligibility rules.
Why approvals appear in the journey
The project must fit the site’s permitted use and the applicable electricity-connection arrangement. Depending on the site, different parties may need to confirm use of the premises, the proposed connection or readiness for operation. A customer’s purchase order is not utility permission, and a submitted application is not permission to energise.
The project team identifies which approvals apply, which activity each one affects and what evidence confirms its status. Engineering, procurement and approval tasks may overlap under an authorised plan. There is no universal rule here that every permission arrives before any equipment can be ordered.
Information that can support an approval
Input
Why it may be needed
Electricity bill and service-account details
Identify the relevant customer connection.
Customer/entity details and authorised signatory
Identify who can submit or acknowledge the relevant request.
Ownership, occupancy or owner consent information
Clarify the right to use the premises/roof for the project.
Available supply records and requested supporting documents
Allow the project team to confirm details or respond to a query.
These are examples of input categories, not a compulsory document pack for every customer. The actual request list and agreed handling process determine which documents are needed and how they are supplied. Detailed rules, forms, charges and eligibility belong in the later local-rules material.
How it works
Physical installation and approval are separate processes. A project can have completed installation work while a permission still prevents the next activity from starting.
Keep these ideas
Inputs received is not the same as permission granted.
Track the evidence and any conditions.
A pending approval affects the activity that depends on it.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
Procurement turns the agreed equipment list into orders and usable deliveries. A truck arriving is not the same as the correct material being accepted.
By the end of this topicUnderstand how an approved equipment list becomes an order, a delivery and accepted material ready for installation.
Process at a glance
From approved list to usable stock
Each handoff should keep the item description and quantity traceable.
Confirm the reference
Use the authorised list and current revision.
Order and plan delivery
Confirm the supply scope and site receiving arrangements.
Receive and reconcile
Record quantity, identity, condition and discrepancies.
Delivery dates depend on actual supply and site readiness. This sequence describes the process, not a fixed lead time.
Before ordering or dispatch
Confirm that the technical specification and purchasing scope are authorised. Resolve open substitutions or quantity questions.
Check the receiving contact, delivery access, unloading arrangements and suitable storage with the site team.
Track what is ordered, dispatched, received and still outstanding separately. A supplier’s dispatch message is not evidence of receipt.
These checks distinguish purchasing authority, logistics readiness and material availability. Selecting substitutes, releasing purchase orders and accepting technical deviations remain with the authorised roles.
Practical checklist
Check a delivery against its reference
The receiving and technical teams check the order, delivered material and supporting records within their roles.
01
Correct identity
Compare item/model labels and relevant specifications with the approved order. Preserve serial or batch records where applicable.
02
Correct quantity
Compare delivered counts and units with the delivery note and order. Record part deliveries and shortages.
03
Visible condition
Record damaged packaging or visible equipment damage using the authorised receiving process. An intact box does not prove internal condition or technical acceptance.
04
Documents and disposition
Retain receipt/discrepancy records. Keep suspect items identified and out of installation until the responsible team decides the next action.
Keep these ideas
Compare deliveries with the agreed order.
Separate received, accepted and held items.
Escalate discrepancies before installation.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
Installation brings the equipment together on site. Access, deliveries and planned shutdowns connect the installation sequence to the site’s ongoing operations.
By the end of this topicUnderstand the main installation stages and how site access, materials and shutdown windows affect their sequence.
Process at a glance
How installation progresses
A typical high-level sequence; the site execution plan determines the actual order and overlap.
Prepare the work area
Confirm access, work zones, materials and site arrangements.
Install supports and modules
The installation team builds the mounting system and fixes the array.
Install electrical equipment
Place inverters and the specified protection, cables and supporting systems.
Complete and inspect
Finish connections, labelling and installation checks before commissioning.
Qualified teams follow the approved design and site work controls. This visual is a process explanation, not a method for installing or wiring equipment.
What site coordination covers
Coordinate
What needs to be established
Access and work zones
Which areas the crew needs, who authorises entry and any restrictions around staff, vehicles or production.
Deliveries and storage
Where material can arrive and be kept without blocking business routes.
Planned shutdowns
Whether a supply interruption is required, the affected operations and the agreed window confirmed by the technical team and customer.
Communication
Site contacts, the update method and who confirms changes to the work plan.
Why an installation task may be delayed
Weather, incomplete roof repairs, restricted access, missing material or an unavailable shutdown window can affect work. Each affects a particular task or dependency. Completion of one activity does not remove a constraint on another; the work plan changes when that constraint is resolved.
How it works
Mounting can be complete while the electrical connection remains pending. If that connection needs a shutdown, it depends on an agreed window between the site team and the business operations contact.
How a scope change affects the project
A new equipment location or an extra cable route can affect design, materials, cost or schedule. The request therefore needs review and authorisation before it becomes part of the installation plan.
Across the 30, 200 and 750 kWp teaching cases, coordination depends on site constraints. A small site with difficult access can be demanding; plant size alone is not a reliable installation calendar.
Keep these ideas
Installation stages depend on both technical work and site operations.
Agree access and shutdown requirements early.
Use the confirmed execution plan for dates.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
Commissioning checks whether the installed plant is ready for its intended, permitted operation. It brings together technical evidence, operating conditions and records.
By the end of this topicDistinguish installation, commissioning and handover, and understand the evidence required for operating readiness.
Process at a glance
Three different project milestones
Each milestone has its own supporting project records.
Installed
Physical work has reached its installation milestone.
Checked and permitted
Technical checks and applicable permission support operation.
Handed over
The customer has the agreed records, access and guidance.
These milestones may occur at different times. None should be inferred solely from panels being on the roof or an app displaying a number.
Practical checklist
Evidence of operating readiness
Readiness depends on records and confirmation from the responsible technical team.
01
Technical checks completed
The qualified team confirms the required installation inspections, electrical checks and trial operation under the applicable authorised conditions. Learners do not conduct these tests.
02
Required permissions in place
Confirm the permissions and conditions applicable to connection/operation. Do not assume that installation completion permits energisation.
03
Monitoring and initial readings recorded
Confirm current data, the site identity and the relevant readings with their units, date/time and operating conditions. Establish what the dashboard actually measures.
04
Outstanding issues assessed
Record unresolved items, responsible owners and follow-up. The technical team determines which issues block operation; blocking issues must be resolved before the affected operation proceeds.
What an initial reading tells you
During a later authorised trial, suppose the 200 kWp plant shows 50 kW solar AC output. The timestamp and operating conditions give this reading its meaning. It is an instantaneous teaching reading consistent with Section 2, not a test pass threshold or proof of daily generation. Commissioning acceptance uses the project’s actual criteria and test records.
A monitoring display from yesterday is not evidence of live operation today. Current data and communications need verification, while the operating and test records become part of the handover evidence. A trial result does not create an annual generation guarantee.
Keep these ideas
Installed, commissioned and handed over are distinct milestones.
Use records and applicable permissions to establish readiness.
Only the responsible technical team assesses test results and operating safety.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
A supported handover gives the customer the records, access and guidance needed after installation. It also makes outstanding commitments visible.
By the end of this topicUnderstand how records, access, operating guidance and unresolved items determine the completeness of a handover.
Practical checklist
The customer’s handover pack
The agreed deliverables establish what was installed, how its operation is monitored and where support is available.
01
Equipment and warranty records
Installed equipment details, relevant model/serial records, product documents and applicable warranty terms. These identify the equipment and the applicable claim route.
02
Commissioning and project records
Agreed test/commissioning records, applicable permissions and completion documents. Include the final project records specified by the contract; this lesson does not teach drawing interpretation.
03
Monitoring access and demonstration
Authorised access to the correct plant, with generation, timestamps and relevant status information understood. Monitoring access does not itself permit changes to technical settings.
04
Maintenance and service contacts
Agreed responsibilities, the service request route, urgent contacts and the actual support scope and terms.
05
Outstanding items and acknowledgement
List each unfinished item, its responsible owner, the agreed next action and follow-up date. Confirm what was received and demonstrated without silently treating unresolved work as closed.
Why access and understanding are part of handover
A monitoring handover is usable when the authorised account opens the correct plant and its user can identify the latest update, distinguish power from energy and find the service contact. Sending documents alone does not establish these outcomes.
Access belongs to the authorised account; another site’s credentials are not a substitute. Available features also depend on the installed monitoring system and agreed scope, so a demonstration must match the actual plant.
Document the remaining commitment
Item
Illustrative owner
Next action
Closure evidence
Customer monitoring access
Assigned service contact
Resolve invitation and confirm customer login at the agreed follow-up.
Customer can access the correct plant.
Missing equipment warranty record
Assigned project contact
Obtain and supply the correct record.
Record matches installed equipment and is received.
The example owners are roles in a teaching scenario, not Ray2Volt staffing assignments. Customer acknowledgement records what was provided. It does not automatically remove outstanding contractual obligations.
Keep these ideas
Deliver records, access and understanding.
Make every open item actionable.
Confirm closure with evidence.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
Operations and maintenance—often shortened to O&M—helps keep the plant supported after handover. It combines routine care, monitoring and a defined route for resolving service needs.
By the end of this topicUnderstand how cleaning, inspection and monitoring support operation, and distinguish warranties from maintenance services.
Process at a glance
Observe, care, resolve
A repeatable support cycle, with responsibilities defined by the actual agreement.
Observe
Review current monitoring information and record concerns.
Care
Arrange the specified cleaning and inspections.
Resolve
Raise service needs, track action and confirm the outcome.
Cleaning frequency depends on site conditions and equipment guidance. This course sets no universal cleaning interval.
Three parts of routine care
Cleaning addresses deposits that reduce light reaching the modules. The plan should account for local dust, other contamination, water availability, access and manufacturer guidance. Inspection looks for condition changes or defects through the appropriate trained team. Monitoring helps identify trends, alarms and missing data; it does not replace physical inspection.
Agree who arranges each activity and keeps its record. Roof work, electrical checks and repairs belong to the appropriately trained service team. Customers should not open electrical cabinets, attempt repairs or walk onto an unsafe roof to investigate a dashboard reading.
Warranty coverage and maintenance have different scopes
Term
Question to clarify
Equipment product warranty
Which defects are covered, for what period, by whom and under what conditions?
Module performance warranty
What module output commitment and claim conditions apply? This is not the same as guaranteed annual plant energy or bill savings.
Installation/workmanship coverage
What installation-related obligations are included in the actual agreement?
Maintenance/service agreement
Which cleaning, inspections, visits, monitoring, parts or labour are included or excluded, and what response terms apply?
Warranty coverage depends on the product and project terms. It does not automatically include every visit, cleaning task, replacement cost or loss of production. A maintenance checklist describes activities, while the service agreement defines which are included.
Make a service request actionable
Identify the site and contact person.
Record when the concern began, the relevant readings/units and the last update time.
Include available screenshots or observations obtained safely.
Use the agreed service route; record the next update and confirmation of resolution.
Report persistent unexplained underperformance, recurring alarms, visible damage or water ingress to the service team. If smoke, fire or an immediate electrical danger is observed, keep people away and use the site’s emergency response route. Do not wait for a routine monitoring review or attempt a repair.
Keep these ideas
Agree responsibility, scope and service contacts.
Use site-specific maintenance arrangements.
Record concerns and confirm their resolution.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
Use the project stages to work out what is complete, what is pending and which dependencies affect progress. Try each situation before revealing the explanation.
By the end of this topicAssess project status from the evidence and identify what still prevents operation or completion.
A compact project reference
Stage
Useful evidence or output
Site assessment
Dated site information, open questions and engineering feasibility decision.
Equipment and readiness
Current material list, agreed scope and applicable approval status.
Procurement
Order, receipt and discrepancy records.
Installation
Completed work and confirmed remaining dependencies.
Commissioning
Technical records and applicable permission for operation.
Handover
Records, customer access, demonstration and open-item list.
Maintenance
Agreed responsibilities and service records.
Check your judgement
These are learning checks, not a certification or authorisation to carry out technical work. No scores or progress are stored. Return to the relevant topic whenever an explanation is unclear.
Topic by topic
Each question tests one topic from this section. If an explanation is unclear, return to that topic and try again.
Topic 3.1 · The EPC journey
Panels are on the roof. Why does this not establish that the project is complete?
Show explanation
Panel installation is one stage. Remaining installation work, technical checks, applicable permissions, monitoring and handover obligations determine whether the wider project is complete.
Topic 3.3 · The equipment and material list
A supplier proposes 500 modules rated 400 Wp instead of 400 rated 500 Wp. The total is still 200 kWp. Is that enough to approve the change?
Show explanation
No. The module count and product characteristics change, with possible effects on space, structure, electrical design, warranty and cost. The responsible team reviews these effects before the substitution can be approved.
Topic 3.5 · Procurement and delivery checks
The supplier offers a different inverter model to avoid a delay. What is the next step?
Show explanation
Submit the proposed change for technical and commercial review, including compatibility, scope and warranty implications. Obtain the required approvals and update the controlled records before treating it as an accepted replacement.
Topic 3.5 · Procurement and delivery checks
Does the signed delivery note prove all 400 modules are ready to install in the case?
Show explanation
No. Receipt and acceptance differ. The two damaged modules remain held for the responsible team’s decision, and the other items still follow the normal acceptance process.
Topic 3.7 · Commissioning: ready to operate
The monitoring screen is green, but an unresolved technical issue is listed as blocking operation. Can the screen override the issue?
Show explanation
No. Follow the qualified team’s documented assessment and the project’s operating permissions. The blocking issue must be resolved; a dashboard colour cannot replace the required technical evidence.
Topic 3.7 · Commissioning: ready to operate
Must a 200 kWp plant show 200 kW during commissioning to pass?
Show explanation
No universal threshold follows from the DC nameplate rating. Output depends on the conditions and system design. The qualified team applies the project-specific commissioning criteria and records the results.
Across the section
These questions connect ideas from several topics.
Practice
1. A roof looks large and clear. What remains before confirming feasibility?
Show explanation
Collect the roof, shade, space, access and supply information. Engineers still need to confirm structural and electrical feasibility; appearance alone is not approval.
Practice
2. The module line is 400 pieces at 500 Wp each. What capacity does it describe?
Show explanation
400 × 500 = 200,000 Wp = 200 kWp DC. It does not establish inverter AC capacity, string design or daily generation.
Practice
3. All customer documents have been submitted. Is permission granted?
Show explanation
Submission and permission are different statuses. Check the actual decision and conditions, and identify any activity that must wait.
Practice
4. Two of 400 delivered modules have visible damage. What should be reported?
Show explanation
Record 400 received with two held for review, preserve the discrepancy evidence and coordinate the technical/procurement response. Do not treat damaged items as ready for installation.
Practice
5. The proposed shutdown window conflicts with production. What is the next step?
Show explanation
Coordinate an alternative with the technical team and customer. The revised plan must respect the technical work requirements; a production constraint does not justify live work as a shortcut.
Practice
6. Installation is complete, but permission for operation is pending. Can the plant start?
Show explanation
Not on the strength of installation completion. Keep the affected operation on hold until the applicable permission and technical readiness are confirmed.
Practice
7. A customer signs the handover note with monitoring access still pending. What remains?
Show explanation
Keep the access item open with a responsible contact, agreed action and follow-up. Confirm successful customer access before recording closure.
Practice
8. Does an equipment warranty automatically include regular cleaning?
Show explanation
No. Check the actual warranty and service agreement. Cleaning scope, responsibility and frequency need their own confirmation.
Practice
Which milestones are complete, and why is the whole project not yet complete?
Show explanation
Installation and the recorded technical checks are complete. Operation still depends on the required permission, and handover still includes unresolved monitoring access. The project team follows the permission, and the service contact resolves the invitation. Neither open item is closed simply because physical installation has finished.
The same dependencies apply across project sizes
Completed → pending → owner → next update. This is useful for a 30, 200 or 750 kWp project. The supporting record, dependent activity and responsible contact explain the project status. Capacity alone does not establish the approval route or duration.
How it works
Project progress depends on completed work, unresolved conditions and the action needed to satisfy each dependency. That relationship is the same even when the plant size changes.
Keep these ideas
Check readiness at each stage.
An unresolved dependency can hold the next activity.
Carry support commitments through to closure.
Sources and teaching notes · online references
References reviewed 21 September 2026 for general technical principles. US guidance is not an Indian approval rule. Checklists, process explanations and case events are original teaching examples, not Ray2Volt policies, approved designs or contract terms. The lesson works offline; external reading needs internet access.
A bill is a record of one electricity connection over a stated period. Read its quantities before interpreting its rupee total.
By the end of this topicIdentify the connection, period, units and meter calculation, and separate consumption from the amount payable.
FICTIONAL AP-STYLE TEACHING BILL
LT bill A · a daytime workshop
Original simplified training layout. All rates, charge amounts, demand inputs and adjustments are invented for arithmetic practice.
Connection and account
LT business · TRAIN-LT-01A fictional low-tension supply account; LT describes the electricity connection, not the solar capacity.
Billing period
1–30 April · 30 daysConsumption belongs to these 30 days; the payment due date is a different date.
Energy register
12,500 → 15,500 kWhCurrent minus previous reading; multiplier = 1.
Sanctioned load
25 kWAn authorised connection quantity; it is not the month’s consumption.
Bill line
Working / meaning
Amount
Energy
3,000 kWh × ₹8/kWh
₹24,000
Fixed charge
25 kW × fictional ₹40/kW/month
₹1,000
Illustrative duty
3,000 kWh × fictional ₹0.06/kWh
₹180
Period adjustment
3,000 kWh × fictional ₹0.05/kWh
₹150
Current-period charges
24,000 + 1,000 + 180 + 150
₹25,330
Previous balance
Unpaid amount brought forward
+ ₹1,200
Credit already recorded
A credit in this account; not solar export
− ₹200
Amount payable₹26,330
The four current-period charge lines total ₹25,330. The amount payable also contains an earlier balance and a recorded credit. This teaching bill is reused in Topics 4.3 and 4.4.
Start with identity and supply
LT means low tension; HT means high tension. These describe the supply-voltage class. A business bill identifies its account/service number and tariff category, which tell you which connection and billing schedule you are studying. Read the actual voltage and category from the records. A 30, 200 or 750 kWp solar proposal does not by itself assign an LT or HT category.
Match the account, premises and meter number across the bills. A business with two service connections needs two separate consumption histories. Also check whether existing solar, a meter replacement or a change of category affects the period. The date a bill was issued and its payment due date do not tell you how many days of electricity it covers.
Billed meter energy = (current reading − previous reading) × multiplierFor LT bill A: (15,500 − 12,500) × 1 = 3,000 kWh. For a different metering arrangement, the bill may state a multiplication factor (MF). Apply it once, only to the raw readings that require it.
Know what the energy register measures
Quantity
Meaning
What to do with it
kWh
Active electrical energy over time. One electricity “unit” commonly refers to one kWh.
Use the register label and bill’s energy basis; do not assume every displayed “unit” is kWh.
kVAh
Apparent energy accumulated over time.
Keep it distinct from kWh when the tariff uses kVAh for energy billing.
kW or kVA
Power/demand quantities, rather than accumulated energy.
Find whether they describe sanctioned load, contract demand or recorded/billing demand.
In a CT/PT metering arrangement, current transformers (CTs) and potential, or voltage, transformers (PTs) scale down what the meter senses. The stated multiplier translates those readings into the actual quantity. The bill or metering records must establish the factor; employees should not guess it from the meter photograph. If readings are already multiplied, multiplying again overstates consumption.
A reading may need an explanation
An estimated/provisional bill, meter change, correction or unusual reading date can interrupt a simple subtraction. Record the status and obtain the supporting history. A total of 3,000 kWh is useful only when you know the period, register, meter basis and whether it is an actual or adjusted quantity.
Keep these ideas
Identify the exact connection and period.
Keep energy and demand units separate.
Account balances are not electricity consumption.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
Energy describes how much electricity accumulated. Demand describes the rate at which it was required. A business can use fewer units and still have a substantial demand charge.
By the end of this topicDistinguish authorised, recorded and billed demand, and interpret power factor without assuming solar removes every charge.
Follow the quantities
Three demand figures, three purposes
01
Contract demand
The contracted supply quantity. Our HT teaching case states 300 kVA.
02
Recorded maximum demand
The highest demand registered under the meter’s interval method. The case shows 240 kVA.
03
Billing demand
The quantity used to calculate the charge. The teaching bill supplies 270 kVA.
All three numbers can differ. The applicable tariff and agreement determine the billing-demand calculation; the example does not prescribe a minimum-demand rule.
Why the distinction matters
Sanctioned load and contract demand describe authorised connection quantities as defined in the relevant records. Recorded maximum demand (RMD, introduced in Section 1) is the highest demand recorded over the applicable measurement intervals, rather than a sum of all equipment nameplates or an instantaneous startup spike. Billing demand is calculated under the applicable terms; it may include contractual minima or other provisions.
In the HT example, use the stated 270 kVA billing demand × ₹400 = ₹1,08,000. Using 240 kVA would calculate ₹96,000, which does not reproduce this bill. We deliberately supply 270 kVA rather than teach a fictional rule for deriving it. On a real account, the reason for any difference must be checked.
Power factor links useful power and apparent power
For the simple power example in Section 1, power factor = kW ÷ kVA. At 100 kW and a power factor of 0.80, apparent power is 125 kVA. At the same 100 kW and 0.95, it is approximately 105.3 kVA. The kW requirement is unchanged, while the apparent power differs.
On a period bill, use the meter’s power-factor definition. When matching cumulative kWh and kVAh registers are provided, their ratio can help interpret the period’s active versus apparent energy: 30,000 ÷ 32,000 = 0.9375 in our HT sample. Do not substitute this ratio for an instant power-factor measurement or combine it with unrelated peak-demand readings.
Figure you notice
Interpretation to investigate
Low power factor or high kVAh
Understand the active/apparent energy relationship and the actual tariff treatment; do not automatically add a separate penalty.
Solar generation reduces imported kWh
That does not establish the new kVAh or peak kVA. The timing and electrical quantities need assessment.
Maximum demand occurs after sunset
Daytime solar does not directly supply that night-time event.
Lower daytime import demand
A contracted billing minimum may still matter, depending on actual terms.
Power-factor correction and changes to the electrical system need technical assessment. This lesson explains the bill; it does not prescribe capacitor sizes, inverter settings or repair work.
Keep these ideas
Use the billed quantity to reproduce a demand charge.
kWh reduction is not proof of the same kVAh or demand reduction.
A monthly bill cannot locate the exact time of the maximum demand unless it supplies that information.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
The payment figure combines different kinds of charges and account movements. Reconstructing it reveals which parts are linked to energy and which require separate treatment.
By the end of this topicReconcile current charges and amount payable, including time-of-day lines and adjustments without double counting.
Follow the quantities
Build the amount payable
01
Current-period charges
Energy + fixed/demand + applicable period-specific charges.
02
Account movements
Add unpaid balances or applicable late charges; subtract recorded credits/payments as shown.
03
Amount payable
Reconcile the final figure, including any stated rounding or due-date treatment.
Use the bill’s own signs and labels. A payment already included in its closing balance must not be subtracted again.
Read a charge by its basis
Line
Why it appears
Check
Energy charge
Payment for billed energy.
Is the basis kWh, kVAh, a slab or time band? Which rate and quantity apply?
Fixed or demand charge
A capacity-related or fixed supply charge.
Which sanctioned/contract/billing quantity, unit and period are used?
Time-of-day (ToD)
Energy can have different treatment at different times.
Whether rates are band-specific or a separate adjustment; do not apply both twice.
Duty / levy / surcharge / adjustment
A defined additional component where applicable.
Its legal/tariff basis, effective period and applicable quantity. Names and calculations vary.
Arrears, credit, late charge
The account’s history or payment timing.
Do not treat these as the current month’s energy use.
Reconcile LT bill A
₹25,330 current charges + ₹1,200 arrears − ₹200 credit = ₹26,330 payableCurrent charges = ₹24,000 energy + ₹1,000 fixed + ₹180 illustrative duty + ₹150 period adjustment.
Dividing ₹26,330 by 3,000 kWh gives about ₹8.78 per kWh. That is this bill’s blended amount payable per unit, including balances. It is not the energy tariff of ₹8/kWh, nor the amount automatically avoided for each solar kWh. Even ₹25,330 ÷ 3,000 includes the fixed charge.
A small time-of-day exercise
Imagine a separate, simplified energy line: 400 kWh in a ₹10 band and 600 kWh in a ₹7 band. Energy charge = 400 × 10 + 600 × 7 = ₹8,200. The 1,000 kWh total alone cannot reproduce that charge without the time split. These bands and prices are invented and are not an AP schedule.
On some bills, a base charge and a separate ToD adjustment express the result instead. Read which method is being used. A night-heavy business may have a different charge from a daytime business even when their monthly energy is equal; direction and size of the difference depend on the actual schedule.
Keep these ideas
Reconcile the current period before adding account history.
A blended ₹/unit is a diagnostic ratio, not an avoided-energy tariff.
Apply only the charge components that belong to the actual connection and period.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
Two months from the same fictional workshop show how meter readings, closed days and account balances affect the bill.
By the end of this topicWork through LT readings and charge totals, then explain a change without confusing lower consumption with a tariff change.
FICTIONAL AP-STYLE TEACHING BILL
LT bill A · regular operation
Original simplified training layout. All rates, charge amounts, demand inputs and adjustments are invented for arithmetic practice.
Connection and account
LT business · TRAIN-LT-01A fictional low-tension supply account; LT describes the electricity connection, not the solar capacity.
Billing period
1–30 April · 30 daysConsumption belongs to these 30 days; the payment due date is a different date.
Energy register
12,500 → 15,500 kWhCurrent minus previous reading; multiplier = 1.
Sanctioned load
25 kWAn authorised connection quantity; it is not the month’s consumption.
Bill line
Working / meaning
Amount
Energy
3,000 kWh × ₹8/kWh
₹24,000
Fixed charge
25 kW × fictional ₹40/kW/month
₹1,000
Illustrative duty
3,000 kWh × fictional ₹0.06/kWh
₹180
Period adjustment
3,000 kWh × fictional ₹0.05/kWh
₹150
Current-period charges
24,000 + 1,000 + 180 + 150
₹25,330
Previous balance
Unpaid amount brought forward
+ ₹1,200
Credit already recorded
A credit in this account; not solar export
− ₹200
Amount payable₹26,330
Daytime workshop; 26 operating days in a 30-day billing period. Operating days are supplied site information, not inferred from the bill. No solar is installed in this example.
FICTIONAL AP-STYLE TEACHING BILL
LT bill B · a holiday month
Original simplified training layout. All rates, charge amounts, demand inputs and adjustments are invented for arithmetic practice.
Connection and period
Same LT account · 30 daysSame tariff assumptions; compare like-for-like period lengths.
Energy register
15,500 → 17,900 kWh · MF 12,400 kWh for the full billing period.
Sanctioned load
25 kWUnchanged from bill A.
Operations supplied by site
20 operating daysClosed days still have some standby use; this is additional business information.
Bill line
Working / meaning
Amount
Energy
2,400 × ₹8
₹19,200
Fixed charge
25 × ₹40
₹1,000
Illustrative duty
2,400 × ₹0.06
₹144
Period adjustment
2,400 × ₹0.05
₹120
Current charges
19,200 + 1,000 + 144 + 120
₹20,464
Prior balance / credit
Assume earlier amounts cleared; neither added here
₹0
Amount payable₹20,464
All prices and charges remain fictional. This month has no prior balance or credit, so current charges equal amount payable.
Explain the difference in layers
Bill B uses 600 kWh less, or 20% less energy than bill A. Current charges fall by ₹25,330 − ₹20,464 = ₹4,866. That is 600 × (₹8 + ₹0.06 + ₹0.05); the ₹1,000 fixed charge remains in this example. The payable amounts differ by ₹5,866 because bill A also carried a net ₹1,000 account balance.
Average calendar-day use falls from 3,000 ÷ 30 = 100 kWh/day to 2,400 ÷ 30 = 80 kWh/day. Dividing total monthly energy by operating days gives 115.4 and 120 kWh per operating day respectively, but those are allocation ratios: both totals also include closed-day energy. They do not measure the operating-day load profile.
Connect the bills to a 30 kWp candidate
30 kWp × assumed 4 kWh/kWp/day × 30 days = 3,600 kWhThis is generated solar energy under a fictional yield assumption, not automatically 3,600 kWh used by the workshop.
Even bill A consumes only 3,000 kWh over the whole month. A 3,600 kWh generation estimate therefore needs careful overlap and surplus analysis. In bill B, more closed days can further reduce overlap. A 30 kWp case is useful for learning, but that does not make it the right size for this workshop. The bill provides an energy quantity; operations and site evidence complete the preliminary assessment.
Keep these ideas
Use meter readings to establish units.
Explain energy, charge and account-balance changes separately.
A candidate capacity needs timing checks even when its monthly generation looks close to consumption.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
HT bill examples bring together kWh, kVAh, multiplication factors, demand and time-of-day lines. Keep each quantity connected to its own charge.
By the end of this topicReproduce an HT total and explain why equal kWh can coexist with different billed energy charges.
FICTIONAL AP-STYLE TEACHING BILL
HT bill C · daytime production
Original simplified training layout. All rates, charge amounts, demand inputs and adjustments are invented for arithmetic practice.
Connection and account
HT business · TRAIN-HT-01A fictional high-tension supply; category and voltage come from connection records.
Billing period
1–30 April · 30 daysEnergy and demand refer to this billing period.
Active energy register
50,000 → 50,375 · MF 80375 × 80 = 30,000 kWh. MF is the stated meter multiplication factor.
Apparent energy register
8,000 → 8,400 · MF 80400 × 80 = 32,000 kVAh. This example bills energy on kVAh.
Contract / recorded demand
300 kVA / 240 kVAThe contracted quantity differs from the largest recorded demand.
Billing demand
270 kVA · given teaching inputUse the billed quantity for the worked total; it is not inferred from recorded demand alone.
Bill line
Working / meaning
Amount
Energy
32,000 kVAh × fictional ₹7.50/kVAh
₹2,40,000
Demand charge
270 kVA × fictional ₹400/kVA/month
₹1,08,000
Time-of-day adjustment
A separately supplied teaching line
+ ₹3,000
Illustrative duty
30,000 kWh × fictional ₹0.06/kWh
₹1,800
Period adjustment
A supplied teaching adjustment
₹1,200
Current-period charges
2,40,000 + 1,08,000 + 3,000 + 1,800 + 1,200
₹3,54,000
Previous balance
An unpaid earlier balance
+ ₹10,000
Credit already recorded
An account credit; not solar export
− ₹4,000
Amount payable₹3,60,000
This example intentionally bills energy on kVAh. Billing demand and the ToD adjustment are supplied teaching inputs. The amount payable is ₹3,54,000 + ₹10,000 − ₹4,000.
Trace the energy calculation first
The active register difference is 375; with MF 80, the consumption is 30,000 kWh. The apparent register difference is 400; with MF 80, it is 32,000 kVAh. The energy charge uses 32,000 kVAh × ₹7.50, not 30,000 kWh × ₹7.50. Using the wrong register would understate this energy line by ₹15,000.
The ₹1,800 illustrative duty is based on kWh here, showing why each line’s unit must be read individually. The following invented band breakdown explains the ToD adjustment; the real applicable bands and rates must come from the connection’s tariff.
Unpack bill C’s ₹3,000 ToD adjustment
Fictional band
Billed kVAh
Adjustment to base rate
Adjustment amount
Higher-rate band
4,000
+ ₹1/kVAh
+ ₹4,000
Lower-rate band
2,000
− ₹0.50/kVAh
− ₹1,000
Remaining hours
26,000
₹0/kVAh
₹0
Total
32,000
Base ₹7.50 was already applied to all units
+ ₹3,000
The energy base is ₹2,40,000. Adding the net band adjustment gives ₹2,43,000 for energy plus ToD. Do not charge the full adjusted band rates again after already charging the base. A bill showing full band rates would instead calculate 4,000 × ₹8.50 + 2,000 × ₹7 + 26,000 × ₹7.50 = the same ₹2,43,000. These quantities and rates are fictional; no actual AP clock slots are prescribed.
FICTIONAL AP-STYLE TEACHING BILL
HT bill D · contrasting night-heavy operation
Original simplified training layout. All rates, charge amounts, demand inputs and adjustments are invented for arithmetic practice.
Account and period
TRAIN-HT-02 · 30 daysA different fictional business with the same monthly active energy.
Active / apparent energy
30,000 kWh / 37,500 kVAhMatching period registers; ratio = 0.80 in this teaching example.
Contract / billing demand
300 kVA / 270 kVABilled demand is deliberately held constant for comparison.
Operational information
Night-heavy operationThe daily pattern comes from supplied operations information, not from the energy total.
Bill line
Working / meaning
Amount
Energy
37,500 kVAh × ₹7.50
₹2,81,250
Demand
270 kVA × ₹400
₹1,08,000
ToD adjustment
Given input for this example
+ ₹6,000
Illustrative duty
30,000 kWh × ₹0.06
₹1,800
Period adjustment
Given input
₹1,200
Current charges
2,81,250 + 1,08,000 + 6,000 + 1,800 + 1,200
₹3,98,250
Prior balance / credit
Neither included
₹0
Amount payable₹3,98,250
Night-heavy usage does not cause low power factor by itself. Timing and active/apparent energy relationship are two independent assumptions in this case; each must be examined separately.
Separate the causes of the higher bill
Compared with bill C, current charges are ₹44,250 higher. Of that, ₹41,250 comes from 5,500 extra billed kVAh × ₹7.50. The other ₹3,000 comes from the changed ToD adjustment. Demand, duty and the period adjustment were held constant. This example does not show that night operation always costs more; its rates and adjustments are fictional.
The two businesses each use 30,000 kWh, yet they have different bills and may use different fractions of solar generation on site. Do not use bill value alone to size solar. Also do not calculate a post-solar HT bill by subtracting solar kWh directly from billed kVAh: the required electrical and tariff quantities must be assessed.
Keep these ideas
Follow MF, register and billing unit together.
Equal active energy does not guarantee equal bill charges.
Timing and power factor are separate inputs.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
A single month can hide seasonality, shutdowns and changing business activity. Build one consistent energy history before treating it as a sizing input.
By the end of this topicNormalise billing periods, recognise unusual months and distinguish known explanations from assumptions.
Fictional HT case · active energy
Twelve months, one connection
Bars show kWh per billing period. Use the table below to compare daily averages.
Apr
30,000
May
34,100
Jun
31,500
Jul
27,900
Aug
29,450
Sep
30,000
Oct
26,350
Nov
24,000
Dec
27,900
Jan
29,450
Feb
26,600
Mar
32,750
Annual total: 350,000 kWh across 365 days. This is an illustrative non-leap-year history; it is not measured site data.
Period
Days
Active energy (kWh)
kWh / calendar day
Apr
30
30,000
1,000.0
May
31
34,100
1,100.0
Jun
30
31,500
1,050.0
Jul
31
27,900
900.0
Aug
31
29,450
950.0
Sep
30
30,000
1,000.0
Oct
31
26,350
850.0
Nov
30
24,000
800.0
Dec
31
27,900
900.0
Jan
31
29,450
950.0
Feb
28
26,600
950.0
Mar
31
32,750
1,056.5
Total / weighted average
365
350,000
958.9
Read the pattern before choosing an average
The annual total is 350,000 kWh. Its calendar-day average is 350,000 ÷ 365 ≈ 958.9 kWh/day, while the average calendar month is 350,000 ÷ 12 ≈ 29,166.7 kWh. These are different averages with different denominators.
February has 26,600 kWh and only 28 days: 950 kWh/day. August has 29,450 kWh and 31 days: also 950 kWh/day. Their unequal monthly totals do not show different daily intensity. In contrast, May’s 1,100 kWh/day and November’s 800 kWh/day still differ after correcting for period length.
Investigate, then label the explanation
Pattern
Useful follow-up evidence
Seasonal rise
Cooling load, production records, occupancy or seasonal operating hours.
Low month
Shutdown/holiday calendar, reduced production, meter status or missing billing days.
Sudden jump
New equipment, additional shifts, changed register/MF, estimated readings or later adjustments.
Recent business change
Dated expansion or closure information; last year may no longer represent the proposed operating condition.
For this case, assume the site confirms a November production slowdown and a May production peak. Without that confirmation, they would remain hypotheses. Keep unusual but real months in the history; explain them rather than deleting them to make the result look smooth.
Make the annual record usable
Use the same connection and the same active-energy basis throughout. Keep kVAh and demand in their own columns.
Record the actual start/end dates, number of days and actual/estimated status. Resolve overlaps and gaps instead of silently calling them twelve full months.
Keep billed grid import separate from total site demand when existing solar or other generation is present. A post-solar import bill alone understates total site use.
Retain period demand, tariff/category changes and relevant operational notes. For sizing, pair this history with interval demand and a site assessment.
Keep these ideas
Compare kWh/day when period lengths differ.
Use a weighted daily average: total energy ÷ total days.
Annual totals still do not reveal daytime overlap.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
Monthly energy answers “how much”. Solar overlap also requires “when”. Two businesses with identical annual bills can use very different shares of the same solar generation.
By the end of this topicExplain daylight overlap, closed-day effects and the evidence needed to turn a rough profile into a reliable input.
Operating-day shapes · same daily energy
When the business uses electricity
Each bar is one hour’s share of daily energy. All three graphs use the same scale: baseline = 0%; top = 10% of the day’s energy in one hour.
Daytime production
Most demand occurs during working daylight hours; some standby load remains.
10% of daily energy
00:0006:0012:0018:0024:00
Night-heavy operation
Most energy is required after sunset; limited daylight demand can leave more solar surplus.
10% of daily energy
00:0006:0012:0018:0024:00
Continuous operation
This simplified case distributes demand evenly through all 24 hours. Real seven-day businesses still vary.
10% of daily energy
00:0006:0012:0018:0024:00
Illustrative profiles, not meter readings. Taller bars indicate a larger energy share in that hour. Each row totals 100%. The interactive worksheet provides exact hourly values.
Match energy within the same time interval
On-site solar use = the smaller of solar generation and site loadIn one illustrative hour, 120 kWh solar and 80 kWh load gives 80 kWh on-site use and 40 kWh surplus. In another hour, 20 kWh solar and 80 kWh load gives 20 kWh on-site use and 60 kWh import.
Add these matches hour by hour. Matching total monthly solar against total monthly use skips the timing information. For an on-grid plant without storage, noon surplus does not physically power the building at midnight. Any bill credit or energy-accounting treatment is a separate metering/settlement question.
A closure is a different load day
Solar may generate on Sundays, holidays and shutdown days even when the main process stops. Standby equipment, security, refrigeration or other loads may continue. Estimate or measure that baseline separately. Setting closed-day load to zero without evidence can overstate surplus; treating closed days as full production can overstate on-site use.
Our worksheet separates operating days and closed days. It assumes each closed day uses 15% of an operating day’s energy, evenly through 24 hours. This is a visible teaching assumption, not a default for real factories. Choosing 30 operating days represents a seven-day schedule in the fictional 30-day month.
Know the strength of the input
Input
What it can establish
What remains uncertain
Monthly bill
Period energy, recorded demand and listed charge data.
Exact hour-by-hour demand and solar overlap.
Operating-hours interview / schedule
Likely working periods and closures.
Actual equipment loading, cycling and standby use.
Authorised interval meter / logger data
Measured load over dated intervals, with units and gaps checked.
Whether the measured period represents other seasons or future operations.
Production and equipment changes
Reasons the future pattern may differ.
Magnitude until the change is quantified.
A daylight percentage estimated from business hours should be labelled as an estimate. Even measured hourly averages can hide variation within an hour: simultaneous matching using finer intervals may change the result. Use suitable data and technical modelling for a real design.
Keep these ideas
Hold monthly energy constant to isolate the effect of timing.
Count closed-day generation and standby load.
A business schedule is useful evidence, but it is not an interval meter.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
A preliminary capacity is a candidate to investigate. Begin with an energy calculation, then check timing, usable space and the connection.
By the end of this topicCalculate an energy-based starting size and explain why it is not the final design.
Follow the quantities
From bill history to a candidate
01
Establish demand
Check twelve months, billing days, operational changes and interval data.
02
State the generation assumption
Use a dated site-specific yield estimate; show the assumed losses and basis.
03
Test the candidate
Assess hourly use, surplus, roof constraints and the actual connection.
Document the input source and uncertainty at every step. A numerical answer can still depend on weak information.
What a yield means
Specific yield expresses generated energy per installed DC kWp over a stated period. For this lesson, assume 4 kWh/kWp/day of usable AC solar generation. At this assumed yield, 200 kWp produces 800 kWh on the illustrative day. It does not produce 200 kW continuously or guarantee 800 kWh every day.
A real estimate depends on location and weather, orientation, tilt, shading, temperatures, equipment, losses, availability and the modelling period. A monthly or annual yield should reflect seasonal variation; a repeating average day is only a teaching shortcut. The 4 figure here already represents AC generation after assumed aggregate losses. Do not subtract an arbitrary second loss factor.
Starting capacity = target annual solar energy ÷ assumed annual specific yieldIf the teaching target is 280,000 kWh/year and the assumed yield is 1,460 kWh/kWp/year: 280,000 ÷ 1,460 ≈ 191.8 kWp DC. A 200 kWp candidate can then be examined. The 280,000 target is an illustrative choice, not a required offset percentage.
Use the annual HT case carefully
Its consumption is 350,000 kWh/year. At the assumed 1,460 kWh/kWp/year, matching that whole annual energy would give approximately 239.7 kWp. This annual equality does not mean all solar would be used on site or all grid imports would disappear. The night load and closed days still exist.
At 200 kWp, the same assumed yield gives 292,000 kWh/year. That is generation, not on-site use or avoided billed energy. The interactive topic uses a separate 30-day teaching month with 30,000 kWh demand; do not multiply its result by twelve and present it as the detailed annual history above.
Candidate
Generation in the 30-day example at yield 4
What the calculation leaves open
30 kWp
30 × 4 × 30 = 3,600 kWh
How much overlaps the small business’s actual load?
200 kWp
200 × 4 × 30 = 24,000 kWh
What happens at midday and on closed days?
750 kWp
750 × 4 × 30 = 90,000 kWh
Does a larger site need this generation when it occurs, and can it accommodate the system?
kWp is the module array’s DC rating. Inverter AC capacity and the DC/AC ratio are design choices, not interchangeable labels. The engineer’s design and simulated output determine clipping and other effects; this simplified worksheet does not size inverters or strings.
Keep these ideas
Keep energy target, yield period and units consistent.
Treat the first capacity as a candidate.
Final feasibility and design require technical confirmation.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
Use one controlled change at a time to see cause and effect, then compare different business cases. The workings are visible so you can explain every result.
By the end of this topicDistinguish generated energy, on-site use, surplus and imports across capacity and usage scenarios.
TEACHING MODEL · 30 DAYS · NO STORAGE
Change a capacity. Inspect the overlap.
All scenarios use a repeating hourly solar shape. Grid availability is assumed throughout. Surplus is potential excess generation before any export limit or curtailment; it has zero financial credit in this example.
20–950 kWp, in 10 kWp steps. Candidate capacities are not connection-eligibility bands.
Total site demand for all 30 calendar days, including closed days. Zero explores a no-load boundary.
Changing the pattern redistributes the same monthly energy in time.
Remaining days use 15% of operating-day energy, evenly across 24 hours.
An illustrative AC-energy yield per DC kWp after aggregate losses. The 1–6 input range is a teaching control, not a forecast range.
Solar generation—
Solar used on site—
Potential surplus—
Remaining grid import—
Site loadSolar
Inspect the hourly energy table (kWh)
Each row is a one-hour interval. Solar is the same on operating and closed days. Closed-day surplus = solar − closed-day on-site use; closed-day imports = closed-day load − closed-day on-site use.
Hour
Load
Solar
On site
Surplus
Import
Closed load
Closed on site
Follow the calculation
Compare three capacities with these same inputs
Capacity
Generation kWh
On-site kWh
Surplus kWh
Import kWh
Illustrative bill impact
A separate, flat kWh teaching bill: ₹8 per imported kWh + ₹12,000 unchanged other charges. No export credit, tax, adjustment, arrears or ToD rates. This does not reproduce the HT kVAh bills in Topic 4.5 or prescribe AP settlement.
Limits: repeated average days; no outages, seasonal weather, within-hour variation, equipment limits or changing power factor. No battery or virtual time-shifting. Actual exports require an applicable approved arrangement. If export is constrained, some potential surplus may be curtailed. No inputs or progress are stored.
Begin with a controlled comparison
Start at 200 kWp, 30,000 kWh/month, 26 operating days and yield 4. Keep those inputs fixed and change only the usage pattern. Solar generation stays at 24,000 kWh; the on-site fraction changes because the load moves in time. This isolates timing. Next keep the pattern fixed and vary capacity: total generation changes, but on-site use is limited by load in each hour.
The fixed 30/200/750 comparison table deliberately applies all three capacities to the same current inputs. A large surplus from 750 kWp on a small load is useful evidence that the candidate needs reconsideration, not evidence that the excess will earn money.
A continuous base load improves overlap, but the midday solar peak still needs checking.
These are contrasting examples, not recommendations. The voltage class, sanctioned/contract capacity and approval route are not determined by the three solar sizes. After comparing cases, change just one input within a case so you can identify why its result moves.
Read the two balances
Generation = on-site use + potential surplusThe second balance is site demand = on-site use + grid import. The model checks overlap within each hour and then totals operating and closed days. Small differences between displayed sums can arise from rounding.
If you reduce the number of operating days while holding monthly kWh fixed, the same energy is concentrated into fewer operating days. The model increases operating-day load accordingly. That is a controlled assumption; it is different from a real shutdown that reduces monthly production and energy, as in LT bill B. Change monthly kWh too when studying that different scenario.
Keep these ideas
Change one input to isolate its effect.
On-site use cannot exceed either generation or load in an interval.
Potential surplus is not automatically permitted export or a credit.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
An energy calculation is only one boundary on a solar project. A credible preliminary assessment shows the candidate, the supporting evidence and the questions still open.
By the end of this topicExplain how roof, electrical and operational constraints change a candidate capacity and record input confidence.
Follow the quantities
Three checks around the candidate
01
Demand and timing
Will generation overlap the business’s current and expected load?
02
Usable roof and site
Can the candidate fit with safe access, structural suitability and acceptable shading?
03
Connection and operation
Can the electrical connection and applicable operating arrangement accommodate it?
A constraint can change the capacity, layout, design or project feasibility. Do not label a project approved because one of these checks looks favourable.
Gross roof area is not usable solar area
A roof footprint includes tanks, skylights, equipment, shade zones, setbacks, access and maintenance routes. Layout depends on module dimensions, mounting, tilt and spacing. Structural condition and loads need engineering review even when the measured area appears sufficient.
Illustrative area check: 1,200 m² usable ÷ 6 m²/kWp = 200 kWpThe 6 m²/kWp is an invented preliminary space allowance, not a universal standard. If only 900 m² is usable under that same assumption, the space-based candidate falls to 150 kWp.
Neither result proves structural suitability or supplies a layout. A 200 kWp energy-based candidate and a 150 kWp space-based candidate create an open design question, rather than permission to ignore the smaller boundary.
Connection information has its own evidence
Confirm supply voltage, category, sanctioned load/contract demand and current account records. Resolve inconsistent bills or proposed connection changes.
Check existing solar, generators, metering and electrical infrastructure with the technical team. Imported energy is not necessarily total site load.
Confirm the applicable metering/export arrangement and any limits. Do not derive permission from a candidate size, an online example or a tariff label alone.
Account for actual grid availability. The worksheet assumes uninterrupted grid availability; ordinary on-grid solar is not outage backup.
Keep a short assumption register
Input
Example source/status
Next confirmation
30,000 kWh/month
Actual bill for one period; annual record incomplete.
Obtain missing periods and explain anomalies.
Daytime operation
Reported working hours; no interval data.
Check representative load data and closures.
Yield 4
Fictional teaching assumption.
Use a dated site-specific estimate with loss assumptions.
Usable roof 1,200 m²
Preliminary marked area.
Engineering layout, shading and structural review.
Export treatment
Unconfirmed for the actual connection.
Verify applicable approvals, meter arrangement and settlement terms.
What a preliminary result should communicate
Record the candidate kWp, period energy, timing assumption, generation estimate, expected on-site use/surplus under that assumption, space check and unresolved connection questions. State which inputs are measured, reported, estimated or missing. This makes the estimate useful to engineering and project coordination without turning it into a final design or guaranteed bill outcome.
Keep these ideas
Usable area, energy and connection checks address different questions.
A precise number can still be based on uncertain inputs.
Carry open assumptions into technical review.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
Solar changes physical electricity flows first. The bill then applies the connection’s charging and settlement rules to the relevant measured quantities.
By the end of this topicBuild a transparent bill comparison and explain why on-site use, export and demand charges need separate treatment.
Begin with a small, fully worked energy balance
Use a separate fictional 30-day business example: total site demand is 30,000 kWh; solar generation is 24,000 kWh; interval matching establishes 18,000 kWh on-site use. These are supplied example totals, not the default worksheet result.
Grid import = 30,000 − 18,000 = 12,000 kWhPotential surplus = 24,000 − 18,000 = 6,000 kWh. The site still imports because its demand and solar output differ in time.
Charge component
Before solar
After solar
Example assumption
Imported-energy charge
30,000 × ₹8 = ₹2,40,000
12,000 × ₹8 = ₹96,000
Flat kWh rate; on-site use reduces imports.
Other charge
₹12,000
₹12,000
Held constant. No demand reduction is assumed.
Export credit
₹0
₹0
This comparison assigns no financial value to surplus.
Other adjustments / tax / arrears
₹0
₹0
Omitted to keep the mechanism visible.
Illustrative current charges
₹2,52,000
₹1,08,000
Reduction = ₹1,44,000 = 18,000 × ₹8.
Why all generation is not a bill reduction
Multiplying all 24,000 generated kWh by ₹8 would give ₹1,92,000, overstating this example’s charge reduction by ₹48,000. Only the 18,000 kWh used on site displaces imports under the stated assumptions. The 6,000 kWh surplus is counted physically but receives no credit here.
This zero-credit assumption is a modelling choice. It is not an AP export rule. If a real approved arrangement values exported energy, calculate that credit using its actual eligible quantity, rate, period, carry-forward and settlement rules. Do not automatically value exports at the retail import rate or assume all surplus can be exported.
Follow the quantities
Keep three records separate
01
Physical flows
Measured or modelled generation, on-site use, import and permitted export.
02
Bill quantities
The relevant kWh/kVAh, time bands, demand and charge bases.
03
Settlement
Credits, offsets, carry-forward and payments under the applicable arrangement.
AP-specific arrangements require the current applicable regulation, amendments, tariff category and supply/metering records. A teaching model cannot establish their applicability.
Which lines may change?
Bill line
What to assess after solar
Energy
Import reduction and its timing, the correct billing unit and applicable rates.
Demand / fixed
Actual recorded peak, billing minima, authorised capacity and applicable terms. Do not assume proportional reduction with kWh.
ToD
Imports/exports in the actual defined time bands, not a whole-month average.
Duty / adjustment
Whether and how the calculation basis changes under its actual rule.
Arrears / payments
Account history. Solar generation does not clear an old balance by itself.
For HT bill C, do not reuse the flat ₹8 worksheet to claim its after-solar bill. It bills energy in kVAh and has demand and ToD components. Its post-solar bill needs those quantities and applicable treatment, not just solar kWh.
Use a fair before/after comparison
Compare like periods and the same production/operating basis. Weather, tariffs, occupancy, new equipment, shutdowns or delayed adjustments can also change a bill. A lower bill after commissioning is not, on its own, a measured solar saving. Reconcile meter and generation records and explain changes in the business load.
The worksheet shows current-charge mechanics only. Investment cost, maintenance expenditure, loans and payback are separate topics in Section 6.
Keep these ideas
Energy balance comes before charge arithmetic.
Apply the correct billing units and actual settlement terms.
Separate solar effects from business and tariff changes.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.
Consumption history and energy charges billed in kWh.
kVAh
Apparent-energy register difference × multiplier.
Energy charges when the tariff bills kVAh.
kW or kVA
Sanctioned load, contract demand, recorded maximum demand or billing demand.
Fixed or demand charges. Use the billed quantity to reproduce the charge.
Amount payable (₹)
Current-period charges plus account movements such as arrears and credits.
Payment. It is not a measure of consumption.
Solar generation (kWh)
Capacity × assumed specific yield × days.
An energy-based starting estimate, not on-site use or a bill reduction.
On-site use, surplus and import
Solar and load matched in each time interval.
Explaining which energy displaces imports and which is potential surplus.
Work with the quantities
Keep a separate line for kWh, kVAh, kW/kVA and rupees. State the period and teaching assumptions next to each calculation. These are practice questions; no score or progress is stored.
Topic by topic
Each question tests one topic from this section. If an explanation is unclear, return to that topic and try again.
Topic 4.1 · Bill anatomy and meter readings
A kWh register rises from 8,200 to 8,575 and MF is 80. What is the period energy?
Show explanation
(8,575 − 8,200) × 80 = 375 × 80 = 30,000 kWh. Confirm that these are raw readings requiring the multiplier; do not multiply an already scaled consumption value again.
Topic 4.2 · Demand and power factor on a bill
Contract demand is 300 kVA, recorded maximum is 240 kVA and the supplied billing demand is 270 kVA. At the fictional ₹400/kVA rate, what is the demand charge?
Show explanation
270 × ₹400 = ₹1,08,000. Use billing demand for the arithmetic. The applicable tariff and agreement must explain its derivation; the recorded maximum alone is not the supplied billing quantity.
Topic 4.3 · How charges form the total
Current charges are ₹25,330, arrears ₹1,200 and an already recorded credit ₹200. What is payable?
Show explanation
₹25,330 + ₹1,200 − ₹200 = ₹26,330. The ₹1,000 net balance is not part of this period’s energy consumption. Do not use the resulting blended ₹/kWh as an avoided-energy tariff.
Topic 4.4 · LT worked bills
Bill A uses 3,000 kWh; bill B uses 2,400 kWh. At ₹8 energy + ₹0.06 duty + ₹0.05 adjustment per kWh and unchanged fixed charges, how much do current charges fall?
Show explanation
600 × (8 + 0.06 + 0.05) = ₹4,866. Bill A’s net prior balance changes the difference in payable amounts, but does not change this current-charge reduction.
Topic 4.5 · HT worked bills
An HT example has 30,000 kWh and 32,000 kVAh. Its energy rate is ₹7.50/kVAh. Which quantity gives the energy charge?
Show explanation
Use 32,000 kVAh: 32,000 × ₹7.50 = ₹2,40,000. Using kWh would produce ₹2,25,000, a ₹15,000 understatement. Solar kWh cannot simply be subtracted from kVAh.
Topic 4.6 · Twelve months of consumption
February has 26,600 kWh in 28 days; August has 29,450 kWh in 31 days. Which has higher calendar-day use?
Show explanation
Neither: 26,600 ÷ 28 = 950 and 29,450 ÷ 31 = 950 kWh/day. Compare consistent period lengths before attributing different totals to a change in business activity.
Topic 4.7 · Daily usage patterns and closures
One hour has 120 kWh solar and 80 kWh load. A later hour has 20 kWh solar and 80 kWh load. Find total on-site use, surplus and imports.
Show explanation
First hour: on site 80, surplus 40, import 0. Second: on site 20, surplus 0, import 60. Totals: solar 140; load 160; on site 100; surplus 40; import 60 kWh. Simply taking min(140,160) would wrongly claim 140 kWh on-site use.
Topic 4.8 · Preliminary sizing step by step
A teaching energy target is 280,000 kWh/year and assumed yield is 1,460 kWh/kWp/year. What does the quotient establish?
Show explanation
280,000 ÷ 1,460 ≈ 191.8 kWp. It establishes an energy-based starting candidate under that yield, not a final design. Interval overlap, usable area, structural/electrical suitability and connection conditions still need review.
Topic 4.9 · Compare capacities and usage
At 200 kWp, yield 4 and a 30-day month, you switch only from daytime to night-heavy use. Which quantity is unchanged, and why?
Show explanation
Generation remains 200 × 4 × 30 = 24,000 kWh. Monthly site demand also remains at the chosen input. On-site use, surplus and imports change because consumption moves between hours.
Topic 4.10 · Constraints and missing information
The energy estimate suggests 200 kWp. Preliminary usable area is 900 m² with an assumed 6 m²/kWp allowance. Can 200 kWp be confirmed?
Show explanation
The simple area check gives 900 ÷ 6 = 150 kWp under that assumption. Record the conflict and obtain technical assessment/layout; neither estimate establishes structural or electrical feasibility. Do not silently treat 200 kWp as approved.
Topic 4.11 · Before-and-after solar bills
Load is 30,000 kWh, solar is 24,000 kWh and on-site use is 18,000 kWh. With ₹8/kWh imports, unchanged ₹12,000 other charge and no export credit, calculate after-solar charges.
Show explanation
Imports = 12,000 kWh and surplus = 6,000 kWh. After = 12,000 × ₹8 + ₹12,000 = ₹1,08,000. Before = ₹2,52,000. Reduction = ₹1,44,000. This fictional model does not establish AP settlement or an HT kVAh bill.
Across the section
These questions connect ideas from several topics.
Practice
1. The annual total is 350,000 kWh across 365 days. What are the daily and monthly averages, and what important input is still missing?
Show explanation
Daily average = 350,000 ÷ 365 ≈ 958.9 kWh/day. Average calendar month = 350,000 ÷ 12 ≈ 29,166.7 kWh. Neither reveals the hourly profile or closed-day demand; representative timing data is still needed.
Practice
2. In the worksheet you reduce operating days but leave monthly kWh unchanged. Is that the same as the LT workshop consuming less during a holiday month?
Show explanation
No. The worksheet redistributes the same monthly energy into fewer operating days while applying its closed-day assumption. A holiday that lowers actual monthly demand requires changing the monthly kWh input too.
Practice
3. At the fictional yield of 4, a 750 kWp plant generates 90,000 kWh in 30 days. Can it eliminate the grid bill for a business consuming 90,000 kWh?
Show explanation
Monthly equality does not establish hourly overlap. Night-time imports and daytime surplus can coexist. Fixed/demand charges and actual export settlement may also remain relevant; roof and connection feasibility are separate checks.
Practice
4. A business reports “we operate 9 to 6”, but supplies only one monthly bill. Can you state its exact solar self-consumption percentage?
Show explanation
No. Operating hours are useful, but actual equipment loading, standby loads, weekends and seasonal patterns remain unknown. Mark a rough profile as estimated and obtain representative interval data and fuller bill history.
Practice
5. Solar reduces imported kWh by 40%. May you reduce the HT kVAh charge and demand charge by 40% too?
Show explanation
No. kVAh, peak kVA and billing demand have their own electrical quantities and tariff treatment. Solar timing, reactive power and applicable billing minima matter. The kWh percentage does not establish those changes.
Put it together: from one bill to a candidate
Worked example
The daytime workshop and a 30 kWp candidate
Return to LT bill A: 3,000 kWh in a 30-day period, a 25 kW sanctioned load and ₹25,330 current charges. The site reports daytime work on 26 of those days. The team studies the course’s 30 kWp teaching capacity at the fictional yield of 4 kWh/kWp/day.
Enter 30 kWp, 3,000 kWh, daytime production, 26 operating days and yield 4 in the Topic 4.9 worksheet. Then answer the three questions below.
Practice
A. How much does 30 kWp generate in the 30-day example, and how much of that energy does the workshop use on site?
Show explanation
30 × 4 × 30 = 3,600 kWh generated. The worksheet matches about 2,480.4 kWh to the workshop’s load hour by hour. The other 1,119.6 kWh is potential surplus, and 519.6 kWh is still imported when solar output is lower than the load, mainly at night and around sunrise and sunset. Generating more than the month’s 3,000 kWh does not remove imports.
Practice
B. The worksheet’s bill panel uses its own flat teaching bill, so work this one by hand with bill A’s structure: ₹8 energy, ₹0.06 duty and ₹0.05 adjustment per imported kWh, the same ₹1,000 fixed charge and no export credit. Estimate current charges before and after solar.
Show explanation
Before: 3,000 × ₹8.11 + ₹1,000 = ₹25,330, which reproduces bill A. After: 519.6 × ₹8.11 + ₹1,000 ≈ ₹5,214. The reduction of about ₹20,116 equals the 2,480.4 kWh used on site × ₹8.11, not all 3,600 generated kWh. The duty and adjustment are assumed to apply to imported kWh here; their actual basis must be checked, and arrears or credits remain account history.
Practice
C. Why is 30 kWp still only a candidate for this workshop?
Show explanation
About 31% of its generation, 1,119.6 of 3,600 kWh, is potential surplus with no value assigned in this example, and export needs an applicable approved arrangement. The daytime profile is reported rather than measured, the closed-day load of 15% of an operating day and yield 4 are teaching assumptions, and one bill is not a twelve-month history. Usable roof area and whether the 25 kW LT connection can accommodate the plant need confirmation. Compare a smaller capacity in the worksheet too; engineering review decides the design.
Keep these ideas
Read the bill’s units and period.
Match solar and demand within time intervals.
Make assumptions and unresolved constraints visible.
Sources and teaching notes · online references
Prepared 22 September 2026. The official APEPDCL FY 2026–27 schedule was reviewed for distinctions between connection categories, voltage, kWh/kVAh billing, fixed/demand charges and time-of-day treatment. The examples intentionally simplify those structures. Bills, rates, profiles, capacities and arithmetic here are original fictional teaching examples, not current AP tariffs, an eligibility decision or a quotation. Real bills depend on the applicable category, supply agreement, tariff order and amendments. The core lesson works offline; the following background links need internet access.