If you have more space than you need power — a big terrace, a warehouse roof, a shed, or a small idle plot — you can fill it with solar and sell what you don't use. Here's how the economics actually work, and the constraint that trips most people up.
Your own consumption might need 3 kWp. But your roof has room for 12 kWp. Those extra 9 kWp generate power you'll never use yourself — so it goes to the grid, and the DISCOM pays you for it. Instead of sizing solar to your bill, you size it to your space.
Self-consumed units are worth your full retail tariff (₹5–7.5/kWh) because you avoid buying them. Exported units earn the buyback rate (₹2–3.5/kWh), which is always lower. So the economics are strongest when you use as much as you can and sell the remainder.
| Scale | Space | Capacity | Notes |
|---|---|---|---|
| Spare rooftop | 500–1,500 sq ft | 5–15 kWp | Still residential, subsidy up to 10 kWp. Same installer and paperwork, just a bigger array. |
| Commercial roof | 2,000–10,000 sq ft | 20–100 kWp | Commercial net metering. No residential subsidy, but accelerated depreciation if you have business income. |
| Small ground mount | 0.25–2 acres | 50–400 kWp | Needs land conversion and a full DISCOM application. A genuine business, not a bill-offset. |
1. Sanctioned load cap. Most states cap your rooftop system at 100–150% of your sanctioned load. If your connection is 5 kW, you may not be allowed to install 15 kWp without upgrading the connection first. Check this before anything else — it kills more projects than cost does.
2. Subsidy ceiling. PM Surya Ghar caps at ₹78,000 for 3 kW and tapers to ₹1,41,000 at 10 kW. Beyond 10 kWp there is no residential subsidy at all.
3. Buyback isn't cash everywhere. Some DISCOMs credit units against future bills rather than paying cash. If you export far more than you consume, those credits may expire unused at the financial year end.
A 10 kWp rooftop in a ₹7/kWh state with 50% self-consumption returns roughly 14–16% annually and pays back in 5–6 years. Push self-consumption higher and it improves sharply. The yield also rises every year as grid tariffs climb ~3% annually while your cost stays fixed — and because avoided electricity bills aren't income, the return is effectively tax-free.
Choose Earn from Surplus Space in the calculator, enter your area and sanctioned load, and get capacity, cost, and annual yield — with the load cap checked for you.
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