Average Peak Sun Hours By State (+ 50 State Winter, Summer Averages)

Whenever we are calculating if solar panels pay off, we use the average peak sun hours at your location. To help with numerous calculations we made on The Green Watt, we have summarized the average sun peak hours by state. On top of that, we have also looked at how many sun peak hours all 50 states get in the summer vs. how many do they get in the winter.

Namely, let’s first explain what sun peak hours actually are:

We all know that sunny states will get more sun than colder states, right? The sun peak hours is how we measure and express how much useful sun (for electricity generation) we actually get.

As we will see in the average sun peak hours chart further on, the yearly average sun peak hours range from 3 to almost 7 sun peak hours per day (Alaska with 2.99 sun peak hours per day is a bit of an exception). This data is measured by National Renewable Energy Laboratory. Here is one example of these solar irradiance maps:

average peak sun hours by state
National Renewable Energy Laboratory measures average peak sun hours across the US. Source: NREL 2018 October solar data.

What does 1 sun peak hour mean? Well, it means that the amount of sun is enough for the solar system to generate its specified electricity production.

Example: Let’s say that we have a 5kW solar system. Here is how much electricity will be generated per day for locations with different peak sun hours:

  • 1 peak sun hour = 5 kWh per day.
  • 2 peak sun hours = 10 kWh per day.
  • 3 peak sun hours = 15 kWh per day.
  • 4 peak sun hours = 20 kWh per day.
  • 5 peak sun hours = 25 kWh per day.
  • 6 peak sun hours = 30 kWh per day.
  • 7 peak sun hours = 35 kWh per day.

More peak sun hours = more electricity generated. Here are two cases, 1st for sunny California, and the 2nd one for cloudy New York:

  • California gets an average of 5.38 peak sun hours per day (year-round average). That means a 5kW solar system will generate 26.90 kWh of electricity per day in California.
  • New York gets an average of 3.79 peak sun hours per day (year-round average). That means a 5kW solar system will generate 18.95 kWh of electricity per day in New York.

As we can see, the same-size solar system in California will generate about 42% more electricity than a PV solar system in New York (year-round average).

Here is the full average sun peak hour chart state-by-state, with year-round average (2nd column), summer average (3rd column), and winter average (4th column):

State-By-State Peak Sun Hours Chart

US State: Average Peak Sun Hours (Hours/Day): Avg. Summer Peak Sun Hours (Hours/Day): Avg. Winter Peak Sun Hours (Hours/Day):
Alabama 4.32 Hours Per Day 4.69 Hours Per Day 3.37 Hours Per Day
Alaska 2.99 Hours Per Day 3.87 Hours Per Day 1.78 Hours Per Day
Arizona 6.57 Hours Per Day 7.42 Hours Per Day 6.01 Hours Per Day
Arkansas 4.69 Hours Per Day 5.29 Hours Per Day 3.88 Hours Per Day
California 5.38 Hours Per Day 6.19 Hours Per Day 3.42 Hours Per Day
Colorado 4.87 Hours Per Day 5.72 Hours Per Day 4.44 Hours Per Day
Connecticut 3.84 Hours Per Day 4.27 Hours Per Day 2.99 Hours Per Day
Delaware 4.23 Hours Per Day 4.69 Hours Per Day 3.37 Hours Per Day
Florida 5.67 Hours Per Day 6.16 Hours Per Day 5.26 Hours Per Day
Georgia 4.74 Hours Per Day 5.16 Hours Per Day 4.09 Hours Per Day
Hawaii 6.02 Hours Per Day 6.71 Hours Per Day 5.59 Hours Per Day
Idaho 4.92 Hours Per Day 5.83 Hours Per Day 3.33 Hours Per Day
Illinois 3.14 Hours Per Day 4.08 Hours Per Day 2.47 Hours Per Day
Indiana 4.21 Hours Per Day 5.02 Hours Per Day 2.55 Hours Per Day
Iowa 4.55 Hours Per Day 5.05 Hours Per Day 2.99 Hours Per Day
Kansas 5.79 Hours Per Day 6.14 Hours Per Day 5.28 Hours Per Day
Kentucky 4.94 Hours Per Day 5.97 Hours Per Day 3.60 Hours Per Day
Louisiana 4.92 Hours Per Day 5.71 Hours Per Day 3.63 Hours Per Day
Maine 4.51 Hours Per Day 5.20 Hours Per Day 3.56 Hours Per Day
Maryland 4.47 Hours Per Day 4.71 Hours Per Day 3.84 Hours Per Day
Massachusetts 3.84 Hours Per Day 4.27 Hours Per Day 2.99 Hours Per Day
Michigan 4.00 Hours Per Day 4.71 Hours Per Day 2.70 Hours Per Day
Minnesota 4.53 Hours Per Day 5.43 Hours Per Day 3.53 Hours Per Day
Mississippi 4.44 Hours Per Day 4.86 Hours Per Day 3.64 Hours Per Day
Missouri 4.73 Hours Per Day 5.50 Hours Per Day 3.97 Hours Per Day
Montana 4.93 Hours Per Day 5.70 Hours Per Day 3.66 Hours Per Day
Nebraska 4.79 Hours Per Day 5.40 Hours Per Day 4.38 Hours Per Day
Nevada 6.41 Hours Per Day 7.13 Hours Per Day 5.83 Hours Per Day
New Hampshire 4.61 Hours Per Day 5.30 Hours Per Day 3.66 Hours Per Day
New Jersey 4.21 Hours Per Day 4.76 Hours Per Day 3.20 Hours Per Day
New Mexico 6.77 Hours Per Day 7.16 Hours Per Day 6.21 Hours Per Day
New York 3.79 Hours Per Day 4.57 Hours Per Day 2.29 Hours Per Day
North Carolina 4.71 Hours Per Day 5.05 Hours Per Day 4.71 Hours Per Day
North Dakota 5.01 Hours Per Day 5.48 Hours Per Day 3.97 Hours Per Day
Ohio 4.15 Hours Per Day 5.26 Hours Per Day 2.66 Hours Per Day
Oklahoma 5.59 Hours Per Day 6.26 Hours Per Day 4.98 Hours Per Day
Oregan 4.03 Hours Per Day 5.71 Hours Per Day 1.90 Hours Per Day
Pennsylvania 3.91 Hours Per Day 4.44 Hours Per Day 2.78 Hours Per Day
Rhode Island 4.23 Hours Per Day 4.69 Hours Per Day 3.58 Hours Per Day
South Carolina 5.06 Hours Per Day 5.72 Hours Per Day 4.23 Hours Per Day
South Dakota 5.23 Hours Per Day 5.91 Hours Per Day 4.56 Hours Per Day
Tennessee 4.45 Hours Per Day 5.20 Hours Per Day 3.14 Hours Per Day
Texas 4.92 Hours Per Day 5.49 Hours Per Day 4.42 Hours Per Day
Utah 5.26 Hours Per Day 6.09 Hours Per Day 3.78 Hours Per Day
Vermont 4.13 Hours Per Day 5.35 Hours Per Day 3.77 Hours Per Day
Virginia 4.13 Hours Per Day 4.50 Hours Per Day 3.37 Hours Per Day
Washington 3.57 Hours Per Day 4.83 Hours Per Day 2.60 Hours Per Day
West Virginia 3.56 Hours Per Day 4.12 Hours Per Day 2.47 Hours Per Day
Wisconsin 4.29 Hours Per Day 4.85 Hours Per Day 3.28 Hours Per Day
Wyoming 6.06 Hours Per Day 6.81 Hours Per Day 5.50 Hours Per Day

Source: Global Solar Atlas, National Renewable Energy Laboratory, and Turbine Generator.

As we can see from the chart, the number of peak sun hours in the summer can reach over 7 per day in the sunniest states (Arizona, Nevada, New Mexico). In the winter, the sun’s peak hours can be anywhere from 7% to 42% below the 12-month average.

Looking at the yearly average, here are the 5 best US states for solar panels:

  1. New Mexico. Here we get 6.77 peak sun hours per day on average. In the winter, the average falls to 6.21 peak sun hours per day (8.3% reduction). In the summer, the average increases to 7.16 peak hours per day (5.8% increase). We can see that amount of sun irradiance is quite constant in New Mexico and you can make a lot of electricity via solar panels year round.
  2. Arizona. In sunny Arizona, we get 6.57 peak sun hours per day on average. In the winter, the average falls to 6.01 peak sun hours per day (8.5% reduction). In the summer, the average increases to 7.42 peak hours per day (12.9% increase).
  3. Nevada. In cities like Las Vegas, we get 6.41 peak sun hours per day on average. In the winter, the average falls to 5.83 peak sun hours per day (9.0% reduction). In the summer, the average increases to 7.13 peak hours per day (11.2% increase).
  4. Wyoming. Here we get 6.06 peak sun hours per day on average. In the winter, the average falls to 5.50 peak sun hours per day (9.2% reduction). In the summer, the average increases to 6.81 peak hours per day (12.4% increase).
  5. Hawaii. Of course, we get a lot of sun in Hawaii. How much exactly? According to solar irradiance maps, we get 6.02 peak sun hours per day on average. In the winter, the average falls to 5.59 peak sun hours per day (7.2% reduction). In the summer, the average increases to 6.71 peak hours per day (11.5% increase).

Alright, in these states, you can easily use the solar panel year round.

Now let’s have a look at the 5 worst US states to install solar panels in:

  1. Alaska. Of course, Alaska gets the least amount of sun. The yearly average is 2.99 peak sun hours. In the winter, the average falls to only 1.78 peak sun hours per day (40.5% reduction). In the summer, the average increases to 3.87 peak hours per day (29.4% increase).
  2. Ilinois. Cities like Chicago get very little sunlight. The yearly average is 3.14 peak sun hours. In the winter, the average falls to only 2.47 peak sun hours per day (21.3% reduction). In the summer, the average increases to 4.08 peak hours per day (30.0% increase).
  3. Washinton. The yearly average in this state is 3.57 peak sun hours. In the winter, the average falls to only 2.60 peak sun hours per day (27.2% reduction). In the summer, the average increases to 4.83 peak hours per day (35.3% increase).
  4. West Virginia. The yearly average in this state is 3.56 peak sun hours. In the winter, the average falls to only 2.47 peak sun hours per day (30.6% reduction). In the summer, the average increases to 4.12 peak hours per day (15.7% increase).
  5. New York. New York is also one of the states that get below-average sun exposure. The yearly average in New York is 3.79 peak sun hours. In the winter, the average falls to only 2.29 peak sun hours per day (39.6% reduction). In the summer, the average increases to 4.57 peak hours per day (20.6% increase).

We see quite clearly that states with lower yearly sun irradiance have big swings in peak sun hours in the winter vs. in the summer. This is because they are located farther north, and are thus impacted by changing seasonal solar irradiance angle.

Having all these solar irradiance data expressed in average peak sun hours summarized will come very useful for numerous calculations. We will use this average peak sun hours by state data to calculate the financial viability of installing solar panels.

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