What Size Solar System for 100, 200, 300 or 500 Units?

What size solar system do I need for my monthly units bill?

Match roughly 1 kW of rooftop solar to every 100 units (kWh) you use in a month. The Delhi government's official sizing table puts monthly consumption of 0-150 units at 1-2 kW, 150-300 units at 2-3 kW and anything above 300 units at a plant larger than 3 kW, and the Prime Minister's Office release for PM Surya Ghar confirms the scale: a 3 kW system generates more than 300 units a month on average.

Sizing to your consumption matters more than sizing to your roof, because in most states surplus exported units are worth only a fraction of the retail tariff - or nothing at all. This guide gives the size, subsidy and area for each consumption band, with sources.

TL;DR: Use about 1 kW per 100 monthly units. A 100-unit home needs 1 kW, a 200-unit home 2 kW, a 300-unit home 3 kW and a 500-unit home about 5 kW. Central subsidy (PM Surya Ghar) is Rs 30,000/kW for the first 2 kW and Rs 18,000 for the third kW, capped at Rs 78,000 - so the subsidy jump stops at 3 kW. Each kW needs about 10 square metres of shadow-free roof.

Last verified: 12 November 2026

The quick sizing table

Costs are the MNRE benchmark cost under PM Surya Ghar: Rs 50,000/kW for the first 2 kW and Rs 45,000 for the additional kW - a benchmark, not a quote. Actual vendor prices, especially DISCOM-discovered L1 rates, are often lower; the National Portal FAQ advises residential consumers to pay according to DISCOM L1 rates. Area assumes the FAQ's rule of thumb of about 10 square metres of shadow-free area per kW.

How the 1 kW per 100 units rule works

The National Portal's FAQ states that on a clear sunny day a 1 kW rooftop plant generates 4 to 5.5 units. Across a month and a year - with monsoon clouds, winter haze and panel degradation - that averages out to roughly 100-120 units per kW per month in North India. The Prime Minister's Office gives the same arithmetic from the top down: 3 kW generating more than 300 units a month for a household under PM Surya Ghar.

Generation is not flat through the year: expect more in the April-June and autumn windows and less in monsoon and December fog. Our city-wise numbers for units generated per kW in North Indian cities show the local variation. When in doubt, size for your annual average units, not your worst summer bill - solar output peaks in the same months your air conditioner runs.

Size examples for common bills

100 units a month: 1 kW

A 1 kW system suits small households or low-usage connections. Subsidy: Rs 30,000. Benchmark cost: Rs 50,000, so roughly Rs 20,000 net after subsidy. It needs about 10 square metres and offsets most of a 100-unit bill, though fixed charges still apply.

200 units a month: 2 kW

A 2 kW system is the sweet spot for a typical family. Subsidy: Rs 60,000 (Rs 30,000/kW for both kilowatts). Benchmark cost: Rs 1,00,000, so roughly Rs 40,000 net. About 20 square metres of roof. Note that the subsidy per kW stops here - this is the last size where every kilowatt earns Rs 30,000.

300 units a month: 3 kW

A 3 kW system generates more than 300 units a month on average. Subsidy: Rs 78,000 - the scheme's maximum (Rs 30,000 x 2 kW plus Rs 18,000 x 1 kW). Benchmark cost: Rs 1,45,000 (Rs 50,000 x 2 plus Rs 45,000 x 1), so roughly Rs 67,000 net. About 30 square metres. This is also where the third kilowatt earns a smaller subsidy: Rs 18,000, not Rs 30,000.

500 units a month: 5 kW

A 5 kW system needs about 50 square metres and, at North India yields, generates around 500 units a month on average. Subsidy stays at Rs 78,000 - the MNRE guidelines allow no additional CFA beyond 3 kW - so the effective subsidy per kW falls from Rs 26,000 at 3 kW to about Rs 15,600 at 5 kW. Benchmark cost before subsidy: Rs 2,35,000. For bills this large, also check whether your state caps net metering eligibility by sanctioned load (see below).

Why you should not oversize: the 90 percent cap and surplus rates

Several states cap how much solar you can push into the grid. Haryana limits generation to 90% of your consumption per financial year and pays nothing for leftover credits, and Punjab treats generation above 90% of consumption as inadvertent injection with no payment (HERC regulations 2021; PSERC regulations). Where surplus is paid at all, it earns a fraction of the retail tariff: Rs 2/kWh in Uttar Pradesh, the DISCOM's average power purchase cost in Delhi. Our state-wise surplus export rate guide has the full table.

The practical rule: size to your consumption, with a small buffer if you expect consumption to grow (an EV, a second AC), not to your available roof.

Subsidy at each size under PM Surya Ghar

The central financial assistance is fixed by the MNRE guidelines and applies to residential consumers only - commercial and industrial installations get no CFA. The scheme runs until 31 March 2027.

Several states add a top-up on top of the central subsidy - see our state top-up guide and the step-by-step application process. If you are comparing financing, our solar loan guide for homeowners covers collateral-free loans for residential systems.

Worked example: a 250-unit home in Faridabad

Assumptions: monthly consumption of 250 units (a three-bedroom home with one AC in summer), DHBVN connection, shadow-free roof of at least 30 square metres. Sources: Delhi government sizing table (150-300 units -> 2-3 kW), MNRE benchmark costs and CFA.

• Recommended size: about 2.5 kW; round to 2 kW if the budget is tight, or 3 kW if you plan for rising consumption.
• Subsidy at 3 kW: Rs 78,000. Benchmark cost Rs 1,45,000, so roughly Rs 67,000 net of subsidy.
• Generation: about 300 units a month on average (PM Surya Ghar benchmark) - slightly above the 250-unit consumption, which matters in Haryana: generation above 90% of consumption is not paid at settlement, so a 2.5-2.7 kW plant is the cautious choice there.
• Area: about 30 square metres for 3 kW (10 sq m per kW).

Check the current 1 kW, 2 kW, 3 kW and 5 kW price guides for component-level costs, and the home solar guide for Delhi NCR for how subsidy, net metering and city-level rules fit together.

Frequently Asked Questions

How many solar panels do I need for 200 units per month?

About 2 kW of panels, which is four to five modern 500-550 W modules occupying roughly 20 square metres of shadow-free roof. That is based on 1 kW generating roughly 100-120 units a month on average in North India, per the National Portal's generation benchmark of 4-5.5 units per kW per clear day.

Is a 1 kW solar system enough for a home?

Only if you consume up to about 100-150 units a month. A 1 kW plant generates roughly 100-120 units a month on average, so heavier users will still draw most of their power from the grid. The Delhi government's own sizing table puts 0-150 units of monthly consumption at 1-2 kW.

How much subsidy do I get on a 3 kW solar system?

Rs 78,000 - the maximum central subsidy under PM Surya Ghar. It is the sum of Rs 30,000 per kW for the first 2 kW plus Rs 18,000 for the third kilowatt, per the MNRE guidelines. Systems larger than 3 kW get no additional central subsidy.

What size solar system do I need for a 500-unit bill?

About 5 kW. The subsidy is capped at Rs 78,000 regardless, so check the extra investment per kW against your slab tariff. Also confirm your state's net metering eligibility limits by sanctioned load, and note that in Haryana generation is only settled up to 90% of consumption.

Does solar cover my air conditioning load in summer?

Largely yes, if sized on your annual average consumption. Solar generation peaks in the same April-June window when AC load peaks, which is why sizing to the annual average rather than the peak bill works. Winter and monsoon generation dips, but net metering credits earned in high-generation months carry forward to offset those months in most states.

Should I size my system bigger than my consumption to sell power?

Usually no. Surplus units are paid at a fraction of the retail tariff - Rs 2/kWh in UP, the DISCOM's APPC in Delhi - or not paid at all in Haryana and Punjab above the 90% cap. Size to consumption first; our surplus export rates guide explains the state-wise settlement rules.