Compare calculators

Both calculators run independently — change the inputs on either side to compare results.

Solar Panel System Sizing Calculator

Size a rooftop solar PV system from your real electricity usage, local peak sun hours, system losses, and your target offset — and get the number of panels you actually need.

Average monthly electricity use (kWh)

Peak sun hours (daily average) (h/day)

Share of usage to offset (%)

System losses (inverter, wiring, soiling, heat) (%)

Panel power rating (W)

Solar Energy

Solar Payback Period Calculator

Calculate how many years a solar PV system takes to pay back its net upfront cost through annual electricity bill savings. Use it as the primary financial test when evaluating whether to install solar.

Total System Cost ($)

Annual Savings ($/year)

Tax Incentives ($)

Key differences

	Solar Panel System Sizing Calculator	Solar Payback Period Calculator
Category	Solar Energy	Solar Energy
Inputs required	5	3
Result	Solar panels needed (panels)	Payback Period (years)
What it does	Size a rooftop solar PV system from your real electricity usage, local peak sun hours, system losses, and your target offset — and get the number of panels you actually need.	Calculate how many years a solar PV system takes to pay back its net upfront cost through annual electricity bill savings. Use it as the primary financial test when evaluating whether to install solar.