Solar Panel Calculator
Home & ConstructionWork out how many solar panels and how many kW you need, and whether your roof is big enough.
Runs entirely in your browser — nothing is uploaded
Features
- System size in kW from your monthly consumption.
- Panel count for 350 W, 450 W or 550 W panels.
- Roof area needed, checked against what you have.
- Realistic performance ratio rather than a marketing figure.
- Runs in your browser.
How to use the Solar Panel Calculator
- 1Enter the units you use in a month, from your bill.
- 2Set the peak sun hours for your area — 4 to 5 across most of India.
- 3Enter your shade-free roof area to check the system fits.
Frequently asked questions
How many solar panels do I need?
It depends on consumption, not house size. As a rough guide, 1 kW generates about 4 units a day in most of India, so a home using 300 units a month needs roughly 2.5 kW — around five 550 W panels — and about 200 sq ft of shade-free roof.
What are peak sun hours?
Not daylight hours. It is the equivalent number of hours at full rated output, typically 4 to 5 across most of India. A twelve-hour day does not mean twelve hours of generation.
How much roof do I need per kW?
About 80 to 100 sq ft per kW for framed panels, and it must be free of shade for most of the day. Shade matters more than anything else: one shaded panel can drag down an entire string, so measure the unshaded area rather than the whole roof.