Estimate only. A solar installer will size your system from your actual usage, roof and shading.
How the calculator works
- Your usage: your monthly bill divided by the average residential electricity price in your state gives your estimated monthly kWh.
- System size: your yearly kWh, times the share you want to cover, divided by how much 1 kW of panels produces in a year in your state.
- Number of panels: the system size divided by the wattage of each panel, rounded up.
Where the numbers come from
- Electricity prices: average residential price by state from the U.S. Energy Information Administration (Electric Power Monthly, Table 5.6.B). The average includes fixed charges, so dividing your whole bill by it gives a consistent estimate.
- Solar production: PVWatts by the National Laboratory of the Rockies (formerly NREL), for a standard 1 kW roof system facing south at a 20° tilt with 14% losses, at each state's 2020 Census center of population.
Your result will change if your roof faces east or west, is heavily shaded or has a steeper pitch.
Federal tax credit
The federal Residential Clean Energy Credit does not apply to systems placed in service after December 31, 2025 (IRS), so this calculator shows the system size without incentives. Some states and utilities still offer rebates.