Tool 04 · Sun
How much sun does your area get?
Type a ZIP or pick a state — measured 2024 daily solar radiation for that state's capital, a 12-month curve, and a rough roof model. Nothing uploaded.
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
Illustrative model: state-capital annual average × tilt × orientation × shade factors × 0.75 performance assumption. These fixed factors are not PVWatts output, a roof measurement or a weather forecast. ZIP selects a state, not local weather. Obtain a roof-specific annual yield including shade and orientation, then enter it in the panel-count or Solar calculator instead of this regional approximation.
Use this free solar sun look-up to see measured 2024 solar radiation for a state and a practical roof-production frame. Enter a ZIP or choose a state to view seasonal sun context before sizing a system.
No email required. Instant browser-based planning math with clear assumptions.
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.
Questions homeowners ask
Why a ZIP code and not my address?
What does kWh/m²/day mean?
Is this my roof's number?
Where does the data come from?
What this tool estimates
Use this free solar sun look-up to see measured 2024 solar radiation for a state and a practical roof-production frame. Enter a ZIP or choose a state to view seasonal sun context before sizing a system.
No email required. Results are calculated in your browser; use them as a planning estimate, not a guaranteed quote or savings forecast.
How the math works
The tool reports annual and monthly average daily solar radiation from the stated source, then applies transparent tilt, orientation, shade and performance assumptions for a roof-production frame. It is not a site survey or a production guarantee.
Key variables that change your result
Solar radiation
Measured radiation is a resource indicator; it is not the exact energy output of a particular roof.
Roof orientation and tilt
South-facing, well-tilted arrays often produce differently from east-west or shaded arrays.
Shading and losses
Trees, chimneys, inverter losses and local conditions can materially change a final design.
Questions homeowners ask
How much sun does my state get for solar panels?
Can I use a ZIP code for a solar estimate?
Does more sun always mean faster solar payback?
State context matters
Find your state solar guide
Costs, incentives, export rules and payback inputs vary by state. Open your state guide before treating any calculator result as a buying decision.