Average Peak Sun Hours in All States

The U.S. averages about 4.98 peak sun hours per day. Arizona tops the list at 6.54, while Alaska sits lowest at 3.17. Most states fall between 4.5 and 5.5 peak sun hours daily.

What Are Peak Sun Hours

A peak sun hour is not the same as an hour of daylight. It refers to one hour during which sunlight intensity averages 1,000 watts per square meter, the standard reference level used by the National Renewable Energy Laboratory to rate solar panels.

A location with 5 peak sun hours a day might have 12 hours of actual daylight, but only a portion of that daylight is strong enough to count. Morning and evening light is weaker and spread across more atmosphere, so it contributes less to the total.

This number matters because it directly determines how much energy a solar system produces. Multiply your system’s size in kilowatts by your area’s peak sun hours and a standard loss factor, and you get an estimate of daily output.

Average Peak Sun Hours by State

Below is the average peak sun hours by state, ranked from highest to lowest, based on standard PVWatts modeling assumptions for a south-facing residential rooftop.

These figures are annual averages measured at each state’s largest city. Actual output at a specific address can differ by 15 to 25 percent in states with strong elevation or coastal variation.

The Sunniest States for Solar

Four factors explain why certain states consistently top these rankings:

• Elevation: thinner air scatters less sunlight before it reaches the ground.
• Low humidity: dry air lets more direct sunlight through instead of diffusing it.
• Fewer cloudy days: deserts and high plains see far less persistent cloud cover.
• Latitude: states closer to the equator see the sun sit higher in the sky for more of the year.

Arizona, New Mexico, and Nevada dominate the top of the list for exactly these reasons. Interestingly, Florida ranks 8th rather than 1st despite its sunny reputation, because humid, subtropical air scatters more sunlight than the dry desert Southwest does.

The Cloudiest States for Solar

Washington, Oregon, and Alaska sit near the bottom, largely due to Pacific storm systems and high latitude. Alaska’s swing is the most extreme of any state, with December averaging under half a peak sun hour per day in Anchorage while June nears 6.

It’s worth noting that state averages can be misleading here. Eastern Washington and eastern Oregon, on the far side of the Cascade mountains, regularly see 5 or more peak sun hours daily, closer to the national average than their state’s coastal number suggests.

How Peak Sun Hours Affect Solar Panel Output

The relationship is simple: fewer peak sun hours means more panels are needed to hit the same energy target. A household that needs a 6 kilowatt system in Arizona might need closer to 9 or 10 kilowatts of panels to produce the same annual energy in Washington or Alaska, since the average U.S. home uses roughly 10,800 kWh per year according to federal energy usage data.

This is one reason system size, and therefore project cost, varies so much by region, something worth understanding before comparing quotes with a solar cost calculator.

Peak Sun Hours vs Daylight Hours

These two terms get mixed up often, but they measure different things. Daylight hours count how long the sun is above the horizon, regardless of intensity. Peak sun hours count only the sunlight strong enough to matter for energy production.

A summer day in Phoenix might bring 14 hours of daylight but only 7 to 8 peak sun hours. A winter day in Seattle might offer 9 hours of daylight yet barely more than 1 peak sun hour, since so much of that daylight is weak and diffused by cloud cover.

Seasonal Changes in Peak Sun Hours

Every state sees some seasonal swing between summer and winter output, though the size of that swing depends heavily on latitude.

• Desert Southwest states typically see a 1.5 to 2x swing between summer and winter.
• Mid-Atlantic and Midwest states often see a 2.5 to 3x swing.
• Northern New England and the Pacific Northwest can see swings of 3.5x or more.
• Alaska sees the most extreme swing in the country, often exceeding 10x between summer and winter.

For grid-tied homes with net metering, this swing usually matters less, since summer overproduction offsets winter shortfalls over the course of a year. For off-grid or battery-reliant systems, though, sizing for the worst month rather than the annual average becomes important.

Why Your Exact Address Matters More Than the State Average

State-level numbers are a useful starting point, but they’re calculated from one representative city, usually the state capital or largest metro area. Homeowners outside that specific location can see meaningfully different results.

California is the clearest example. The state average sits at 6.08, based on Sacramento, but coastal San Francisco often sees closer to 5.3 while inland areas near Bakersfield can exceed 6.6. That’s roughly a 25 percent spread within a single state. This kind of gap is also worth keeping in mind when reviewing hidden costs in a solar contract, since underperforming systems relative to sales estimates are a common source of dispute.

Peak Sun Hours and Contract Expectations

Production estimates written into a sales agreement are only as good as the peak sun hour assumption behind them. If a signed agreement promises output that doesn’t match your state or specific address, it’s worth understanding the gap before committing. This matters whether you’re weighing a solar lease versus a solar loan or reviewing an escalator clause tied to expected annual production.

Homeowners who later find their system consistently underperforms the number they were quoted sometimes look into options to get a refund from a solar company, particularly when the original estimate ignored shading, roof orientation, or local microclimate factors that a peak sun hour average alone can’t capture.

Bottom Line on Solar Sun Hours by State

Most U.S. states fall between 4.5 and 5.5 peak sun hours per day, with the desert Southwest well above that range and the Pacific Northwest and Alaska well below it. Knowing your state’s number, and ideally your exact address’s number from a tool like the Department of Energy’s solar resources, is the starting point for sizing any solar system accurately and setting realistic expectations for what it will produce.

Frequently Asked Questions

What state has the most peak sun hours?

Arizona leads at 6.54 peak sun hours per day, followed closely by New Mexico at 6.42 and Nevada at 6.41, all desert states with high elevation and low humidity.

What state has the fewest peak sun hours?

Alaska has the fewest at 3.17 peak sun hours per day, followed by Washington at 3.95 and Oregon at 4.06, largely due to high latitude and Pacific storm patterns.

What is a good number of peak sun hours for solar?

Most solar professionals consider 4 or more peak sun hours per day sufficient for a worthwhile residential system, though even lower numbers can work well with the right system size and local incentives.

Does more peak sun hours always mean better solar savings?

Not necessarily. Electricity rates and incentives often matter as much as sunlight. Some lower-sun states with high electricity costs see faster paybacks than sunnier states with cheap power.

How much do peak sun hours change between seasons?

Most states see a 2 to 3 times difference between their sunniest and cloudiest months, though far northern states like Alaska can see swings of 10 times or more between summer and winter.

This article is for general informational purposes only and does not constitute financial, legal, or engineering advice. For an exact production estimate, consult a licensed solar installer or use a location-specific solar calculator.