Estimate only. Your roof's direction, tilt and shade change the real production. An installer's site survey gives the final number.
How it works
- Your area's solar production: what a standard 1 kW roof system produces in a year in your ZIP code area, from PVWatts, the solar calculator of the National Laboratory of the Rockies (formerly NREL). It is calculated at the center of your 3-digit ZIP prefix, from the 2020 Census ZIP code areas (Census Bureau).
- Your usage: monthly bill ÷ your state's average residential electricity price (EIA, Table 5.6.B).
- System size: yearly usage × the share you want to cover ÷ your area's production per kW.
- Panels: system size ÷ panel wattage, rounded up.
The reference system faces south at a 20° tilt with 14% losses. Puerto Rico, U.S. territories and military ZIP codes are not covered.
Why the ZIP code matters
Sun varies within a state: coastal fog, mountains and latitude change how much a panel produces. The 3-digit ZIP prefix narrows the estimate to your region instead of the state average. Since the federal Residential Clean Energy Credit does not apply to systems placed in service after December 31, 2025 (IRS), getting the size right matters more for the cost.
If you know your yearly kWh from your bills, use the solar system size calculator.