How Many kW of Solar Does Your Home Need? A Bill-Based Guide

A ₹3,000 electricity bill does not tell an installer how much solar your home needs. Two households can pay the same amount while using different numbers of units, because tariffs and fixed charges differ. Start with the kWh on the bill. Then ask when you use that electricity and what you expect the system to do.

A sensible first estimate gives you a capacity range to discuss. It cannot settle the roof layout, inverter design or backup requirement. Those decisions need a site survey and a clear account of your household loads.

Read twelve months of units before comparing packages

Write down billed kWh for each available month, covering a full year if possible. Add them and divide by twelve for average monthly use. Keep unusually high summer months visible rather than treating one pleasant winter month as your normal demand. If a bill covers more than a month, compare its dates before using it.

For an illustrative household using 300 kWh per month, annual consumption is 3,600 kWh. Suppose the planning assumption is 4 net kWh per kWp per day, after system losses. One kWp would then produce 1,460 kWh in the model. Dividing 3,600 by 1,460 gives approximately 2.47 kWp. The assumed yield is not a promise for Gorakhpur, Delhi or any other location; shade, orientation, season and system design change it.

Panel counts turn a decimal into a real layout

If you are evaluating 550 W modules, five modules total 2.75 kWp. Under the same illustrative yield, they produce about 4,015 kWh per year. This is why an annual-energy calculation may not land on the familiar 2 kW or 3 kW package a seller advertises.

Ask for the exact module dimensions and a roof drawing showing access routes, water tanks, parapets and shadows. NDMC's FAQ gives an approximate area allowance, but a rule of thumb cannot show whether five particular modules fit your terrace safely. Do not remove maintenance access merely to squeeze in one extra panel.

Annual matching does not mean the bill becomes zero

Your solar system produces during daylight. A refrigerator, evening lights and night-time air conditioning have a different use pattern. Electricity consumed directly and electricity exported to the grid may receive different economic treatment. Ask your DISCOM how imports, exports, settlement periods and fixed charges apply to your connection.

Try a lower annual-energy target if your roof or budget is limited. At 70% of this household's annual demand, the target would be 2,520 kWh. With the same yield assumption, the mathematical capacity is about 1.73 kWp before whole-module choices. Compare the resulting quotations on their complete scope, rather than assuming that maximum capacity is always the best purchase.

Backup needs a separate load list

A kWp figure describes panel capacity. It does not say how many hours your fans will run during a power cut. Write a separate list of essential appliances, their running power and desired backup hours. Starting loads and simultaneous use matter too. The installer must match the backup inverter, usable battery energy and supported circuits to that requirement.

Do not add a battery solely because a sizing calculator returns a particular number. Equally, do not accept a bill-saving grid-tie quotation as a complete answer to a frequent-outage problem. Ask the supplier to state which requirement the design actually covers.

Take these questions to the survey

Request the proposed DC panel capacity, inverter AC rating, module count, expected annual generation with its assumptions, and a roof layout. Ask what shade losses were allowed, whether sanctioned load or local approval limits affect the proposal, and who handles metering paperwork. Keep the battery and backup scope separately identified.

Before comparing prices, use Solarower's system-sizing calculator with your actual units and a cautious yield assumption. Save both a base case and a lower-generation case. The useful outcome is a set of questions a supplier can answer in writing, followed by a design that fits your roof and usage.

System-sizing calculator →

Sources and editorial notes

• NDMC rooftop solar FAQs: generation and roof area; local rules are not national rules
• Fronius Primo GEN24 operating instructions: operating modes and backup limits

Research checked 16 October 2026. Calculations are illustrative assumptions, not a site assessment, guaranteed output or quotation. Equipment examples describe functions, not endorsements. Illustration created with AI; it does not show a Solarower installation.