Solar Panel Size & Payback Calculator
Estimate how many solar panels and what system size (kW) you need to cover your electricity use, the yearly savings and the payback period.
How to use
- 1Enter your monthly electricity use (kWh) and your area's peak sun hours.
- 2Enter the panel wattage, system cost per watt, electricity price and any incentive.
How it's calculated
System kW = (monthly kWh × 12 ÷ 365) ÷ sun hours ÷ (1 − losses). Panels = kW × 1000 ÷ panel watts. Payback = net cost ÷ yearly savings.
Frequently asked questions
What are peak sun hours?
The average daily hours of 1,000 W/m² sunlight. They range from about 3 in cloudy northern regions to 6+ in deserts. NREL's PVWatts shows your local value.
What losses should I assume?
About 14% covers inverter, wiring, soiling and temperature losses (PVWatts default).
Is there a US solar tax credit?
The federal residential clean energy credit was 30% of system cost; recent legislation changes eligibility dates, so check the current IRS rules before relying on it.