How much sun does your area get?
2024 measured data · verified 2026-08-08 · runs entirely in your browser
Type a ZIP code (or pick a state) — you get the measured 2024 daily solar radiation for that state's capital: a 12-month curve, the annual average, and a rough model of what a roof would make of it. Nothing you type is uploaded anywhere.
Measured 2024 · reference city:
– kWh/m²/day average daily sun
Each bar is one month's average daily solar radiation (GHI) measured on a horizontal surface at the state's capital in 2024 — the same number installers call “peak sun hours.” Your roof is not the capital: real output depends on your exact site. Open the full state guide →
What that means on a roof — rule-of-thumb model
Model: state annual average × tilt × orientation × shade derates × 0.75 real-world performance ratio. Multipliers are typical PV-modeling rules of thumb (PVWatts-style), not a production audit — an installer's shading study beats this page every time.
The honest print
This tool gives you a real, dated measurement — and then it stops being precise on purpose.
- What's measured: daily solar radiation (GHI, kWh/m²/day) at each state's capital during 2024, from the Open-Meteo archive (ERA5 re-analysis). Each monthly bar is the average of that month's measured days.
- What's estimated: everything on a real roof. Tilt, orientation, shading and local weather move the number ±30% — the model uses typical PV derates (PVWatts-style), not a production audit.
- Your exact address: use NREL NSRDB or Google Project Sunroof for a site-specific estimate.
- ZIP look-up: the first three digits map to the state that holds most ZIPs with that prefix; a few cross-state ZIPs exist. If your ZIP misses, pick the state manually.