The working figure is 80 to 100 square feet of clear, shadow-free roof per kilowatt. That gives you a straightforward table.
A 1 kW system needs roughly 80 to 100 square feet. A 2 kW system needs 160 to 200. A 3 kW system, the most common residential size in India, needs 250 to 300 square feet. A 5 kW system needs 400 to 500 square feet. A 10 kW system needs 800 to 1,000 square feet.
Those numbers assume standard 550W to 590W monocrystalline panels laid out with the spacing installers actually use, which includes walkways for maintenance and clearance for tilt.
The word doing the real work in that sentence is shadow-free. This is where most roofs fail, and it is the single most common reason a system underperforms its quotation. Area occupied by a water tank is not usable. Area that falls into shadow from a parapet wall by mid-afternoon is not usable. Area shaded by a neighbouring building for part of the day is partially usable at best.
How to check this properly, and it takes one day. Stand on your terrace at ten in the morning, at noon, and at three in the afternoon. Note where shadows fall each time. The usable area is the part that is sunlit at all three. Do this in winter if you can, when the sun is lower and shadows are longest, because a roof that works in June may not in December.
Why shading matters more than people expect. On a standard string inverter system, panels are wired in series, and the string performs to its weakest member. Shade on one panel drags down the output of the whole string, not just that panel. Microinverters or power optimisers mitigate this, at extra cost. It is cheaper to lay panels only where the sun actually reaches.
Structure and access matter too. Your roof needs to carry the load, which for residential systems is modest but not nothing, particularly on older buildings or sheet roofs. There must be a route for cabling down to your meter. And there should be enough clearance around panels for someone to walk safely when cleaning, which in Delhi NCR happens more often than in cleaner-air cities.
Elevated mounting as a solution. If your usable area is limited by a water tank or an obstruction, raising the structure above it can recover space. This adds meaningful cost and needs structural assessment, but on a constrained roof it is sometimes what makes the system viable.
Working the other way, from roof to system. If you have 300 square feet of genuinely clear terrace, you are looking at roughly 3 kW, which conveniently is where the central subsidy caps. If you have 500 square feet you could fit 5 kW, but remember the subsidy still caps at Rs 78,000, so those extra two kilowatts are at full price.
Sheet roofs and tin sheds. These can work with appropriate structure, but need more careful assessment for load and fixing method. Expect a higher structure cost and insist on a proper site survey.
Our roof area tool converts your available space into installable capacity, and the solar calculator works the other way from your electricity bill. Running both gives you two independent estimates, and where they disagree tells you whether your roof or your consumption is the binding constraint.
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Last updated 27 July 2026 · Reviewed by the RenSetu team