Sizing2 min read
The right system size depends on how much electricity you use, not on how big your house is. A small flat with two ACs can need more solar than a large house with none.
Start with your electricity bill
Look for the units (kWh) on your last few bills. Summer bills are higher because of ACs and coolers, so take an average across the year rather than using your highest month.
Turn units into kilowatts
In Gujarat, each 1 kW of rooftop panels produces about 4 units a day, or roughly 120 units a month. Divide your average monthly units by 120 to get the system size.
For example, a home using 250 units a month needs about 2 kW, and one using 360 units needs about 3 kW.
Turn kilowatts into panels
Modern panels are usually around 540–550 watts each, so every kilowatt takes about two panels. A 3 kW system is typically 5–6 panels; the exact count depends on the panel model.
Check your roof space
Plan for about 100 sq ft of shadow-free roof per kilowatt. Water tanks, stair rooms, trees and taller neighbouring buildings all cast shade, and shaded panels produce much less.
Quick guide
- 0–150 units a month: 1–2 kW
- 150–300 units a month: 2–3 kW
- Above 300 units a month: above 3 kW
