Solar Potential Calculator: System Size and Yearly Production

Enter your address or ZIP, roof details and electricity use to estimate the solar system size you need and how much it would produce in a year at your location, using the National Laboratory of the Rockies' PVWatts model.

Solar potential calculator

How big a solar system would cover your electricity use, and how much would it make where you live? Enter your location, a few roof details and your usage. We run the numbers with PVWatts, the free solar model from the National Laboratory of the Rockies (formerly NREL).

ZIP code or street addressUsed to look up sunshine data. Saved with your result to improve our tools.Usable roof area for panels, sq ft (optional)The sunny faces, minus edges and vents. Leave empty if unsure.

Which way does the roof face?Roof pitch

Shade on that roof None or very little Some (trees part of the day) Heavy

Your electricity use I know my kWh Use my monthly bill

Electricity use (kWh)Look for "kWh used" on your bill. U.S. average: about 10,800 a year.Per

We save what you enter and your result to improve our tools (privacy policy).

Assumptions and limits

Production: NLR PVWatts v8 (NSRDB typical-year weather nearest your location), standard modules, fixed roof mount, DC-to-AC ratio 1.2, inverter 96% (PVWatts defaults).
Losses: 14% (PVWatts default, which already includes 3% for shade; PVWatts Version 5 Manual (Dobos, 2014)). “Some shade” uses 10% shade loss (≈ 20% total) and “heavy shade” 25% (≈ 34% total). These shade levels are our assumptions; a site survey measures real shade.
Location: a ZIP code uses the center of its 3-digit ZIP area; a street address is looked up with the U.S. Census Bureau Gazetteer and Geocoder. We save what you enter and your result (including the address) to improve these tools; see our privacy policy.
Panels: 400 W each; a 400-watt-class panel is about 21 sq ft (Qcells Q.TRON BLK M-G2+ data sheet). We allow about 23 sq ft per panel for gaps, so about 17 W per sq ft of usable roof. Fire-code setbacks can reduce usable area; Berkeley Lab finds panels typically cover 16–41% of total roof area (Berkeley Lab, Distributed Solar and Storage 2025 Data Update).
Usage from a bill: bill ÷ price per kWh. This ignores fixed charges, so it slightly overstates use. The average U.S. home used about 10,800 kWh a year (EIA).
State prices: residential average Jan–Jul 2026, EIA Electric Power Monthly, Table 5.6.B (Sept 2026).
Production also changes year to year with the weather (often ±5–10%), and panels lose a little output each year.
This is an estimate, not a design. A licensed installer must confirm sizing, wiring and permits.

Learn more in our Solar guide, or see all calculators.