Solar Panel Calculator (Rooftop Size)
Rooftop solar size in kW from your monthly units, number of panels, roof area, generation, PM Surya Ghar subsidy and payback.
Result
How to use
- 1
Enter your average monthly electricity units from your bill.
- 2
Adjust the generation, panel size, rate and cost if you know them.
- 3
See the system size, panels, roof area, yearly generation, subsidy and payback.
Questions
How many units does a 1 kW solar system generate in India?
About 3.5–4.5 units a day, or roughly 1,300–1,500 units a year, for a shadow-free south-facing roof. It is lower in the monsoon and higher in summer. This calculator assumes 4 units/kW/day by default.
How much subsidy does PM Surya Ghar give?
For residential rooftop solar: ₹30,000 per kW for the first 2 kW, ₹18,000 for the 3rd kW, capped at ₹78,000 for 3 kW and above (central financial assistance, as listed on the scheme portal in October 2026). Apply on pmsuryaghar.gov.in through a registered vendor.
How much roof space is needed?
About 100 sq ft (10 m²) of shadow-free area per kW. A 3 kW system needs roughly 300 sq ft.
About this Solar Size tool
Solar Panel Calculator (Rooftop Size) — Rooftop solar size in kW from your monthly units, number of panels, roof area, generation, PM Surya Ghar subsidy and payback. It is one of 200 free tools on namasivayam.in, made by software engineer Namasivayam Vadivelan for everyday use in India.
Everything is calculated instantly in your browser: nothing you type or upload is sent to any server, there is no sign-up, and it works on mobile and desktop. Enter your average monthly electricity units from your bill.
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Results are estimates to help you plan. They are not financial, tax or medical advice.