What are peak sun hours?

Learn what they mean and why they matter

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“Peak sun hours” represent the time each day when a solar energy system can generate electricity at maximum efficiency. Because a solar panel’s electricity production depends on the availability and intensity of direct sunlight, peak sun hours are a vital metric for estimating the amount of solar power a solar panel system can generate each day.

Keep reading to learn everything you need to know about peak sunlight hours, including when they occur, why they matter and how you can estimate your own potential solar energy production using the average peak sun hours in your area.

Key insights

  • Solar panels produce electricity most efficiently during peak sun hours.
  • Technically speaking, a peak sun hour is one hour when an area receives at least 1,000 watts of sunlight per square meter.
  • The number of peak sun hours a property receives varies based on its geographic location and the time of year, but a yearly average is accurate enough for most residential uses.
  • Most locations in the U.S. average between four and six peak sun hours daily, occurring around midday.

Peak sun hours explained

Peak sun hours, sometimes also called “daily peak sun hours,” “peak irradiance hours” or “solar radiation hours,” occur when the sun is at or near its highest position in the sky. That’s because sunlight can reach your solar panels using the most direct path possible for several hours before and after this zenith.

Across the United States, most areas will receive between four and six peak sun hours each day, usually falling somewhere between 10 a.m. and 4 p.m. As Ty Sauer, a development manager with global renewable energy company the RES Group, explained to us, peak sun hours are ”typically between midday and the afternoon when the sun is angled directly at the solar modules.”

How peak sun hours are measured

Peak sun hours are most often measured by looking at a location’s sun irradiance or intensity.

You don’t necessarily need to know all of the technical details of solar power production to benefit from solar panels, but if you’re curious, just know that the strength of the sunlight is recorded in terms of watts (or kilowatts) per square meter. One peak sun hour is equal to 1000 W/m² (or 1 kW/m²) of sunlight per hour.

Why peak sun hours matter

Peak sun hours are critical when designing a solar panel system because they are directly related to the amount of potential solar power that can be generated in any given location.

Simply put, with more peak sun hours each day, your system can generate a larger amount of electricity, offsetting more of your utility power consumption and saving you more money.

How to estimate your peak sun hours

There are a few different ways to estimate how many peak sunlight hours your property receives, depending on how accurate you want your estimate to be. We’ve included instructions for three different methods below.

Check the average peak sun hours in your state

Looking at the average peak sunlight hours in your state should give you a decent idea of your home’s solar potential, but keep in mind that estimates for larger states may be less relevant to your individual property since they have so much extra ground to cover.

While states that share a border with Canada fall on the lower end of the spectrum, states in the Southwest tend to receive the highest number of daily peak sun hours. For example, Arizona, New Mexico and California have the most solar potential in the continental U.S., while Alaska, Michigan and Washington receive some of the lowest amounts of peak sun hours in the country.

StateAverage peak sun hours*
Alabama 3.5-4
Alaska 2-3
Arizona 7-8
Arkansas 3.5-4
California 5-7.5
Colorado 5-6.5
Connecticut 2.5-3.5
Delaware 3-3.5
Florida 3.5-4.5
Georgia 4-4.5
Hawaii 5.5-6.5
Idaho 4-4.5
Illinois 3-4
Indiana 2.5-4
Iowa 3.5-4.5
Kansas 4-5.5
Kentucky 3-4
Louisiana 4-4.5
Maine 3-3.5
Maryland 3-4
Massachusetts 2.5-3.5
Michigan 2.5-3.5
Minnesota 3.5-4.5
Mississippi 4-4.5
Missouri 4-4.5
Montana 4-5
Nebraska 4.5-5
Nevada 6-7.5
New Hampshire 3-3.5
New Jersey 3.5-4
New Mexico 6-7
New York 3-3.5
North Carolina 4 4.5
North Dakota 4-4.5
Ohio 2.5-3.5
Oklahoma 4.5-5.5
Oregon 3-5
Pennsylvania 2.5-3.5
Rhode Island 3-4
South Carolina 4-4.5
South Dakota 4.5-5
Tennessee 3.5-4.5
Texas 4.5-6
Utah 6-7
Vermont 3-3.5
Virginia 3.5-4
Washington 2.5-5
West Virginia 2.5-3.5
Wisconsin 3-4
Wyoming 5.5-6
*According to Palmetto

» MORE: Where your solar savings go the furthest

Check the average peak sun hours in a nearby city

If you live in one of North America’s major metropolitan areas, your property will likely receive between 3.5 and 7 hours of peak sunlight on any given day of the year. Here are the year-round daily peak sun hour averages for some of the United States’ most notoriously sunny (and not so sunny) cities.

CityAverage peak sun hours*
Seattle 3.92
New York 4.46
Minneapolis 4.47
Chicago 4.57
Washington, D.C. 4.86
Atlanta 5.13
Dallas 5.41
Denver 5.62
Los Angeles 6.04
Phoenix 6.50
*According to the NREL’s PVWatts calculator

Look up your property’s peak sun hours online

For a precise measurement of your property’s average peak sun hours, the National Renewable Energy Laboratory’s PVWatts calculator is a great, free resource with highly accurate solar irradiance data for both residential and commercial properties all across the United States.

To use this tool, simply enter your address (or city) into the calculator and click “Go.” After reviewing the resource data to confirm you’ve input the correct information, the “Results” tab will display your annual average solar radiation per day, as well as your peak sun hours month-to-month throughout the entire year.

For additional insight into how your solar panels may perform, you can also add your system’s total wattage to the table on the “System Info” tab of the PVWatts calculator. This will let you see your approximate monthly and annual kilowatt-hour (kWh) production in the “Results” tab.

» CALCULATE: How many kWh does a solar panel produce?

How many peak sun hours do you need to go solar?

There is no set number of peak sun hours necessary for you to benefit from a solar energy installation. However, you or your solar installer will need to consider your property’s solar potential when designing your system and deciding how large it needs to be.

Because peak sun hours vary, the exact same solar panel system can yield dramatically different results in different locations. For example, a six-kilowatt (kW) solar array will produce more energy in Phoenix than it will in Washington, D.C., which also means people in Phoenix can meet similar energy needs with smaller, cheaper systems.

Once you know how much energy your home uses and how many peak sun hours you can expect each day, you can calculate how large your solar energy system needs to be to achieve your goals.

» LEARN: How many solar panels do I need for my house?

To find out more about peak sun hours and other aspects of your solar installation, consider working with a reputable solar energy company. They should be able to answer any questions you have about peak sun hours, energy savings and the process of going solar before you commit to a purchase, and many even offer site assessments to help you understand what you can expect from your system once it’s installed.

(If you want to see how accurate these estimates can be, check out this review from Jack, a ConsumerAffairs reviewer from Arizona, who calculated that SunPower’s peak-sun-hour estimate was only about 8% off after a year of production.)

Find a Solar Energy partner near you.


    Are peak sun hours the same as hours of sunlight?

    Peak sun hours and hours of sunlight are different. “Peak sun hours” only refer to the hours of the day when sunlight is at its most intense — from late morning to midafternoon. So, while there may be 12 or more hours of sunlight throughout an entire day, most locations in the U.S. only get four to six peak sun hours daily.

    How do peak sun hours vary during the year?

    When the days get longer in the summer, so do the number of peak sun hours. Conversely, peak sun hours are harder to come by during the winter.

    You can theoretically try to account for these fluctuations, but most people use a yearly average as shorthand for their property’s power potential.

    How are Global Horizontal Irradiance (GHI) and Global Tilted Irradiance (GTI) different?

    Global Horizontal Irradiance (GHI) and Global Tilted Irradiance (GTI) are both measures of sunlight intensity used to calculate solar potential. However, GTI refers to the sun’s intensity on a tilted surface (i.e., a solar panel on a normal residential roof), while GHI references the sun’s intensity on a horizontal surface parallel to the ground.

    ConsumerAffairs writers primarily rely on government data, industry experts and original research from other reputable publications to inform their work. Specific sources for this article include:
    1. Unbound Solar, “Sun Hours Map: How Many Sun Hours Do You Get?” Accessed July 19, 2023.
    2. The National Renewable Energy Laboratory (NREL), “Global Horizontal Solar Irradiance.” Accessed July 19, 2023.
    3. The National Renewable Energy Laboratory (NREL), “PV Watts Calculator.” Accessed July 19, 2023.
    4. Palmetto, “What are Peak Sun Hours?” Accessed July 19, 2023.
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