Quick answer: Solar PV size (kWp) = target daily generation (kWh) ÷ (peak sun hours × performance ratio). Number of panels = system kWp ÷ panel Wp. In India, peak sun hours ≈ 4.5–5.5 and performance ratio ≈ 0.75–0.8.
How to size rooftop solar
System kWp = Daily kWh / (PSH × PR)
Panels = System kWp / Panel Wp
Inverter kW ~ 0.8-1.0 × system kWp
Annual generation ~ kWp × PSH × 365 × PRWorked example
To generate 20 kWh/day at PSH 5 and PR 0.78: kWp = 20/(5×0.78) ≈ 5.1 kWp. With 545 Wp panels → ~10 panels. Inverter ~5 kW. Annual generation ≈ 5.1×5×365×0.78 ≈ 7,260 kWh/year.
Panels, inverter and generation estimate for India. Free tool.
Open the Solar PV Sizing Calculator →Frequently Asked Questions
How many solar panels do I need in India?
Divide the required system size in kWp by the panel wattage. System kWp equals daily kWh divided by peak sun hours (about 5 in much of India) times the performance ratio (~0.78).
What inverter size for a solar system?
Inverter rating is typically 0.8 to 1.0 times the array kWp, allowing a small amount of DC oversizing to capture more energy in real conditions without heavy clipping.