Rooftop Solar Calculator
Rooftop solar size, PM Surya Ghar subsidy, net cost, payback and 25-year savings
| Year | Tariff per unit | Saving | Total saved | Gain after cost |
|---|---|---|---|---|
| 1 | ₹7.00 | ₹25,200 | ₹25,200 | -₹55,800 |
| 2 | ₹7.21 | ₹25,956 | ₹51,156 | -₹29,844 |
| 3 | ₹7.43 | ₹26,735 | ₹77,891 | -₹3,109 |
| 4 | ₹7.65 | ₹27,537 | ₹1,05,427 | ₹24,427 |
| 5 | ₹7.88 | ₹28,363 | ₹1,33,790 | ₹52,790 |
| 6 | ₹8.11 | ₹29,214 | ₹1,63,004 | ₹82,004 |
| 7 | ₹8.36 | ₹30,090 | ₹1,93,094 | ₹1,12,094 |
| 8 | ₹8.61 | ₹30,993 | ₹2,24,087 | ₹1,43,087 |
| 9 | ₹8.87 | ₹31,923 | ₹2,56,009 | ₹1,75,009 |
| 10 | ₹9.13 | ₹32,880 | ₹2,88,890 | ₹2,07,890 |
Runs entirely in your browser. Nothing you type or upload is sent to us or stored.
Results are for general guidance. Please check anything important before relying on it. Terms of use
How to Use
- Enter your average monthly units from your electricity bill, or switch to Monthly bill and enter the amount. Set your electricity rate per unit.
- Pick your state. It sets the average sunshine and the subsidy rate. Turn on Use my own generation figure if your installer gave you one.
- Enter the shadow-free roof area in sq ft. The recommended size is capped by what fits, or choose I'll choose to try your own size.
- Check the cost per kW against your vendor's quote and keep Claim the PM Surya Ghar subsidy on if you qualify.
- Read the size, subsidy, net cost, payback and 25-year savings. The chart shows when your savings pass what you paid, and the table gives each year. Everything updates as you type.
How this rooftop solar calculator sizes your system
A rooftop solar plant is sold by its peak capacity in kilowatts (kW). How many units it makes in a year depends on how much sun your area gets, so the calculator starts from your bill: it works out the units you use in a year and divides by what 1 kW makes in your state. The answer is rounded to the nearest 0.5 kW and then capped by your roof, because each kW needs about 10 sq m (roughly 108 sq ft) of shadow-free space according to MNRE's consumer guidance.
Roof limit (kW) = shadow-free area (sq ft) ÷ 108
Yearly saving = units you use from solar × your rate per unit
MNRE says 1 kW can make 4 to 5.5 units on a clear sunny day. Over a whole year, with cloudy and monsoon days, most of India averages less than that, so the state figures here range from 3.5 units a day in the north-east to 4.5 in Rajasthan and Ladakh. They are our estimates, not official numbers. If your installer or a neighbour's meter gives you a better figure, switch on "Use my own generation figure".
PM Surya Ghar subsidy
Under PM Surya Ghar: Muft Bijli Yojana, the central government pays a fixed subsidy (central financial assistance) to residential consumers who install a grid-connected plant through a registered vendor, using solar modules made in India from Indian cells. The rates below are from the scheme's guidelines as amended in 2025 and were unchanged when we checked in October 2026. Apply through pmsuryaghar.gov.in.
| System size | Most states | Special category states and UTs |
|---|---|---|
| First 2 kW | ₹30,000 per kW | ₹33,000 per kW |
| Third kW | ₹18,000 | ₹19,800 |
| 3 kW and above (maximum) | ₹78,000 | ₹85,800 |
Special category means the north-eastern states, Himachal Pradesh, Uttarakhand, Jammu and Kashmir, Ladakh, Andaman and Nicobar Islands and Lakshadweep. Some states, Delhi among them, add a subsidy of their own on top; this calculator counts only the central amount. The scheme's own guide suggests 1 to 2 kW for homes using up to 150 units a month, 2 to 3 kW for 150 to 300 units, and above 3 kW beyond that.
Worked example
A family in Pune uses 300 units a month and pays about ₹7 a unit. With 4.2 units per kW per day, they need 3,600 ÷ 1,533 = 2.35 kW, so a 2.5 kW plant. It makes about 3,830 units a year.
- Cost at ₹60,000 per kW: ₹1,50,000
- Subsidy: 2 × ₹30,000 + 0.5 × ₹18,000 = ₹69,000
- Net cost: ₹81,000
- First-year saving: 3,600 units × ₹7 = ₹25,200
With the tariff rising 3% a year, the savings cover the ₹81,000 in a little over 3 years and add up to about ₹9.2 lakh over 25 years. The extra 230 or so units go to the grid under net metering. DISCOMs usually credit exported units at a lower rate than they charge, so the calculator leaves them out of the savings.
Before you sign
- Get two or three quotes from vendors registered on the portal. Prices depend on the panel brand, inverter, mounting structure and how high the roof is.
- Use your average rate per unit (total bill ÷ units), not just the top slab, or the savings will look bigger than they are.
- Panels slowly lose output over the years and an inverter may need replacing once, so treat the 25-year figure as an upper estimate.
- The CO₂ figure uses CEA's grid emission factor of 0.727 kg per unit for 2023-24. You can change it if CEA publishes a newer number.