Average Peak Sun Hours By State — All 50 States + DC (2026 NREL Data)

The number on this page is the most important input to any U.S. solar calculation. Multiply your panel kilowatts by your state's PSH and the standard derate, and you get your daily energy production. Multiply by 365 and you get your annual production. Every other variable — panel efficiency, tilt, orientation, equipment cost — matters less than the difference between 6.5 and 4.0 peak sun hours.

I built a 6 kW array on my own house in 2024 and have logged production every day since. The number that comes off the inverter is exactly what these state averages predict — within about 5% — once you adjust for the local micro-conditions PVWatts can't see (your specific roof shading, your specific cell temperature curve, your specific tilt). For a national overview the state numbers are remarkably accurate.

What Are Peak Sun Hours?

A peak sun hour is one hour during which solar irradiance averages 1,000 W/m² — the same reference intensity used to rate solar panels at Standard Test Conditions (IEC 60904). It is not the same as hours of daylight. Phoenix gets about 14 hours of daylight on a summer day, but only 7–8 of those hours deliver enough intensity to be counted as peak sun hours.

The integrated daily total of solar irradiance, expressed in kWh/m²/day, is numerically identical to peak sun hours per day. So when NREL says Phoenix gets 6.54 PSH/day, they mean the same thing as "Phoenix gets 6.54 kWh/m²/day of usable solar energy averaged across the year."

The formula every solar calculator uses:

daily kWh = system kW × peak sun hours × derate (0.83 for PVWatts v8 default)

To find your exact number, use our peak sun hours calculator — it accepts your ZIP code or geolocation and returns NREL PVWatts v8 data for your specific coordinates. The numbers below are state averages measured at the largest city in each state.

Average Peak Sun Hours By State (Full Sortable Table)

Click any column header to sort. Click a state name to see its detailed page with monthly data, a production calculator, and worked examples.

All 51 States — Quick Reference Table

For users who want a single scannable list, here's the full ranking from sunniest to cloudiest, with the corresponding annual production for a 1 kW system. Multiply the kWh/year column by your system size (in kW) to get your estimated annual production.

Top 10 Sunniest States — And Why They Win

These ten states get the most peak sun hours per day in the U.S. The desert Southwest dominates the top 5, and the reason is climatology, not luck.

The pattern is clear: elevation + dry air + clear skies is the winning combination. Florida is the only state in the top 10 that's not elevated or arid — and it ranks 8th, not 1st, despite being famously "sunny." Atmospheric water vapor scatters direct beam radiation before it reaches the surface, which is why humid states underperform their reputation.

10 Cloudiest States — And Why

These ten get the lowest PSH in the country. Solar still works in all of them — even on cloudy days — it just takes more panels to produce the same energy.

Note that Washington and Oregon are ~25% lower than the U.S. average — but that's the state-capital number. Eastern Washington (Spokane, Yakima) gets 5.0+ PSH/day, only slightly below the national average. The Cascades create two completely different solar climates inside one state. Same for Oregon (eastern half is sunny). For city-level granularity, use the peak sun hours calculator.

Production Examples By State

To make the PSH numbers concrete, here's what a 6 kW residential system and a 10 kW system produce per year in 12 representative U.S. states. All calculated at the standard PVWatts v8 derate, then divided by the EIA average household use of 10,500 kWh/year to give a "% of average home" coverage.

What this means in practice:

• In Arizona, a 6 kW system covers an entire average household (100% offset). You don't need a bigger system unless you have an EV. For a worked example of the full sizing process, see how many solar panels to power a house.
• In California, a 6 kW system covers 96% — close enough that with net metering it's effectively 100%.
• In Massachusetts, you need an 8 kW system to fully cover an average home.
• In Washington, you need 9–10 kW to break 100%.
• In Alaska, even a 10 kW system only gets to 88% of average household use — and the seasonal swing is so extreme that you'd need a battery or grid backup for the dark winter months.

Try The Solar Output Calculator

Use the calculator below to estimate how much energy a solar panel produces at any PSH value. The default is set to the U.S. average of 4.98 peak sun hours.

For your exact PSH value, use the peak sun hours calculator — it geolocates you in one click and returns NREL data for your specific address.

Why State Averages Can Mislead

The state-capital numbers above are accurate for most users — but they hide significant internal variation in states with strong elevation gradients or coastal microclimates. A few examples:

• California: State average 6.08 PSH (Sacramento). Coastal San Francisco gets ~5.3 PSH; inland Bakersfield exceeds 6.6 PSH. Internal spread of about 25%.
• Colorado: State average 5.66 PSH (Denver). Western Grand Junction valley gets ~6.0 PSH; high-elevation Leadville exceeds that thanks to thin atmosphere.
• Washington: State average 3.95 PSH (Seattle). Eastern Spokane and Yakima get 5.0+ PSH. The Cascades create two different solar climates.
• Oregon: State average 4.06 PSH (Portland). Eastern Bend, Burns, and Pendleton all exceed 5.0 PSH.
• Hawaii: State average 5.82 PSH (Honolulu). Leeward (dry) sides of all islands exceed 6.5; windward (wet) sides drop below 5.0.
• Texas: State average 5.22 PSH (Houston). El Paso in the west gets 6.4+ PSH; Houston in the humid east is closer to 4.9.

The 4 km × 4 km NSRDB grid is fine enough to capture these microclimates. The state-level number is a starting point; the address-level number is the answer. If you live in any of the states above, don't size your system from the state number alone — use the peak sun hours calculator for the actual data at your roof.

Seasonal Variation By Region

Annual averages are useful for comparison, but your system experiences winter and summer very differently. The summer-to-winter swing depends on latitude:

For grid-tied homes with net metering, the annual average is what matters. Summer overproduction offsets winter underproduction; the meter just runs backwards. For off-grid systems, you must size for the worst month, not the average — otherwise you'll be running your generator all winter. In northern states, snow on panels is an additional winter factor to plan for. For battery-only systems, size for the worst-month daily output, which can be 50–90% lower than the annual average depending on your latitude.

Each state page (linked from the table above) includes a monthly PSH chart showing the full seasonal curve.

How Peak Sun Hours Affect System Sizing

The relationship between PSH and system size is straightforward: fewer peak sun hours means more panels to produce the same energy. The same household needing 10,000 kWh/year would need:

The Alaska number is misleading — you'd actually want significantly more capacity and a battery, because the worst-month December output is only 6% of June. For most U.S. states the calculation is straightforward: panel count scales linearly with the inverse of your PSH.

This is why location is the first question in any solar sizing conversation. You can adjust panel wattage, tilt, and orientation by 5–15%, but you cannot change your local PSH — and PSH varies by 2× across the country.

Methodology And Data Source

All PSH and kWh values on this page come from NREL PVWatts v8 using the National Solar Radiation Database (NSRDB), the U.S. Department of Energy's official solar irradiance dataset. For each state we simulated a 1 kW reference system at the largest city using these standard residential parameters:

• System capacity: 1 kW DC
• Tilt: 20° (typical residential)
• Azimuth: 180° (south-facing)
• System losses: 14% (PVWatts v8 default — covers inverter, soiling, shading, mismatch, wiring, connectors, light-induced degradation, nameplate tolerance, and availability)
• Array type: Fixed roof mount
• Module type: Standard monocrystalline silicon
• Data fetched: April 2026 (NSRDB historical 1998–2024 climatology)

These are NREL's standard defaults for residential rooftop solar, and they match the assumptions used across every calculator on this site. If your roof faces east or west, expect ~10% less. If your tilt matches your latitude (30–45° in the U.S.), expect ~3% more annual with bigger winter gains. For more on the underlying PVWatts methodology, see how to calculate solar panel output.

The NSRDB grid resolution is 4 km × 4 km, which captures coastal-vs-inland differences in California, elevation gradients in Colorado, and Cascade rain shadow effects in the Pacific Northwest. State-level numbers on this page are measured at one representative city per state — for address-level accuracy use the peak sun hours calculator, which calls the same NREL API for any U.S. coordinate.

Bottom Line

If you want a one-line answer: most U.S. states get 4.5 to 5.5 peak sun hours per day, with Arizona at the top (6.54) and Alaska at the bottom (3.17). The U.S. average is 4.98 PSH/day, which gives you about 1,367 kWh/year per 1 kW of installed solar after losses. To go from this number to your annual production, multiply by your system size in kW — a 6 kW residential system in an average U.S. location produces about 8,200 kWh/year, or roughly 78% of an average household's electricity use.

For your exact number, use the peak sun hours calculator. For the formula explanation, see how to calculate solar panel output. For panel-by-panel daily output, see how many kWh a solar panel produces per day.

Keep Reading

• Peak Sun Hours Calculator — Find PSH At Your Location
• How To Calculate Solar Panel Output
• How Many kWh A Solar Panel Produces Per Day
• Standard Solar Panel Sizes And Wattages (100W–600W)
• Solar Panel Watts Per Square Foot
• Rooftop Solar Calculator — How Many Panels Fit On Your Roof
• How Many Panels In A 1kW, 5kW, 10kW Solar System
• How Much Power A 5 kW Solar System Produces
• How Much Power A 10 kW Solar System Produces