Use our peak sun hours calculator — or jump to our peak sun hours map — to find out how many peak sunlight hours your location gets:
Peak Sun Hours Calculator
- Data source: National Renewable Energy Laboratory PVWatts Calculator
- The calculator does not take into account shading.
- The calculator assumes you will be using a solar array with a fixed tilt and azimuth angle, rather than one with 1-axis or 2-axis solar tracking.
What Are Peak Sun Hours?
Peak sun hours, also called peak sunlight hours, are a way to measure how much sunlight a location receives.
A peak sun hour is defined as one hour in which the intensity of sunlight (solar irradiance) averages 1,000 watts per square meter. For those of you who know a bit about electricity, you’ll recall this is equal to 1,000 watt hours of sunlight per square meter.
So we can write it as:
1 peak sun hour = 1 hour of sunlight at 1,000 W/m2 = 1,000 Wh/m2
And because 1,000 watts is equal to 1 kilowatt, we can also write it as:
1 peak sun hour = 1 hour of sunlight at 1 kW/m2 = 1 kWh/m2
Using historical data, we can estimate the amount of sunlight we expect a location to receive per day. Then we can express this value in peak sun hours.
So if, say, you live in Phoenix, AZ, you can expect to receive around 5.8 peak sun hours per day on average. Put another way, on an average day, the sun will pump out 5.8 kilowatt hours of sunlight per square meter.
Solar panels are usually rated at an input rating of 1,000 W/m2 (1 kW/m2), so during a peak sun hour you’d expect a 1 kW solar array to output 1 kWh of electricity before taking into account system losses.
This means knowing how many peak sun hours your location gets is useful because it lets you easily estimate how much energy a solar power system could produce.
To illustrate, let’s go back to the Phoenix example. Let’s say you’re considering putting a 5 kW solar array on your roof, and you want to estimate how much energy it could produce. You could get a rough estimate by multiplying the number of peak sun hours by the rated output of the solar array:
Estimated output = 5 kW * 5.8 peak sun hours per day = 29 kWh per day
So in an idealized scenario, your 5 kW solar array would output 29 kWh per day.
Note: This estimate is very rough and doesn’t take into account factors such as shading and system losses due to things like ambient temperature and inverter inefficiencies. It’s best used as a quick and dirty estimate.
Peak Sun Hours Map
Here is a peak sun hours map created by the National Renewable Energy Laboratory:
You’ll notice the map’s legend is in kWh/m2/day. Recall that 1 peak sun hour is equal to 1 kWh/m2, meaning these values are numerically identical. So although the map doesn’t say “peak sun hours” anywhere on it, it is in fact a map of average daily peak sun hours.
This next part is just for the solar nerds out there:
When sizing a solar power system, peak sun hours should be calculated using Global Horizontal Irradiance (GHI), or Global Tilted Irradiance (GTI) at the tilt angle of the solar panels. Many people mistakenly calculate peak sun hours using Direct Normal Irradiance (DNI).
If you don’t enter a tilt angle, our calculator uses the Global Horizontal Irradiance (GHI) at your location to calculate your peak sun hours. If you do enter a tilt angle, it uses the Global Tilted Irradiance at that angle.
How to Calculate Peak Sun Hours
I’ll run through 3 tools you can use to calculate peak sun hours:
- Our Peak Sun Hours Calculator
- PVWatts Calculator
- Global Solar Atlas
Let’s look at how to use each one:
1. Our Peak Sun Hours Calculator
Scroll up to our sun hours calculator at the top of this page.
In the first box, enter a location such as your address, city, or zip code. For example, if you live in Anaheim, CA and your zip code is 92804, you’d type “92804” into the box.
Select your location from the dropdown results. In this example you’d select “92804 Anaheim, CA, USA”.
If you know what angle your solar panels will be tilted at, you can enter a solar panel tilt angle (in degrees from horizontal). For example, if you’re putting solar panels on your roof and you know your roof angle is 30°, you’d enter “30”.
Note: If you don’t know your solar panel angle, you can leave the field blank or use our solar panel angle calculator to find the best angle for your location.
If you know what direction your solar panels will face, you can enter an azimuth angle (in degrees clockwise from north). If you’re putting panels on your house, your azimuth angle is limited to whichever direction your roof faces. Let’s say your sunniest roof faces southeast (135° clockwise from north). In that case, you’d enter “135”.
Click “Calculate Peak Sun Hours”.
The calculator will calculate the annual and monthly averages for your location:
If your tilt and azimuth angles are flexible, experiment with different angles to find the combo that results in the greatest number of peak sunlight hours.
2. PVWatts Calculator
The National Renewable Energy Laboratory’s PVWatts Calculator is an excellent tool for estimating how much solar energy your solar panels will produce. (In fact, it is the data source for our peak sun hours calculator.)
To use it to find peak sun hours, first enter your address in the search bar and click “Go”. I live in Atlanta, so for this example I just entered the address of Atlanta City Hall.
On the Solar Resource Data page, scroll down to the map to confirm that the calculator found the right location. If it did, click “Go to system info”. (If it didn’t, click “Change Location” and try again.)
On the System Info page, enter the details of your solar power system then click “Go to PVWatts results”. (The values that affect peak sun hours are array type, tilt, and azimuth.)
On the Results page, the peak sun hours for your location are listed in the Solar Radiation column. The daily averages are given for each month and for the entire year.
If you want, you can go back to the System Info page, change the values you entered, and see how they affect the number of peak sun hours your solar power system would receive.
3. Global Solar Atlas
The Global Solar Atlas is an interactive and searchable map that gives you free solar data for almost every spot on the globe. It’s a solar treasure trove.
To use it to find your peak sun hours, search your location in the search bar (or click on your location on the map). For example, if you live in Houston, TX, you can search “Houston” in the search bar and select “Houston, Texas, United States of America” from the dropdown results.
Locate “Global Horizontal Irradiation” (GHI) in the Site Info section. This is the number of total peak sun hours your location gets per year. In this example, I can see that Houston gets 1,705.4 peak sun hours per year.
To find your average daily peak sun hours, change the results from “Per year” to “Per day”.
When I do that, I see that Houston gets an average of 4.672 peak sun hours per day.
Tip: Locate “Optimum tilt of PV modules” in the Site Info section to find an estimate of your ideal solar panel tilt angle (“PV modules” is another way of saying “solar panels”). The first number is the tilt angle. So, in this example, the Atlas estimates the ideal solar tilt angle for Houston to be 26° from horizontal. (The second number is the azimuth angle, which the Atlas always lists as 180° in the northern hemisphere and 0° in the southern hemisphere.)
Peak Sun Hours by Zip Code
Here is a list of the average peak sun hours per day for 50 of the most populated zip codes in the US:
Note: The peak sun hour values in this table were all calculated using a tilt angle of 0° (horizontal) and an azimuth angle of 180° (south-facing).
|City||State||Zip Code||Average Daily Peak Sun Hours|
|New York City||NY||10025||4.14|
If you don’t see your zip code on this list, just enter it into our peak sun hours calculator at the top of this page.
Peak Sun Hours by State
Here is a list of average daily peak sun hours by state:
|State||Average Daily Peak Sun Hours|
To create this list, I used the Global Solar Atlas, which gives you solar data for specific regions around the world, including each US state.
I was surprised to learn that the places in the US with the most peak sun hours are in Hawaii. Some spots in Hawaii get upwards of 6.6 peak sun hours per day on average. That’s a lot of sun.
But, when you take into account the entire state, it’s sunny Arizona that has the highest average peak sun hours. According to the Atlas, the entire state has an average of nearly 5.7 peak sun hours per day.
And it comes as no surprise that Alaska is the state with the fewest peak sun hours. It’s so far north that neither the Global Solar Atlas nor PVWatts has solar data for most of the state. So the values for Alaska in the table above come from the parts of the state below 60° latitude.
More Solar Calculators
- Sengupta, M., Y. Xie, A. Lopez, A. Habte, G. Maclaurin, and J. Shelby. 2018. “The National Solar Radiation Data Base (NSRDB).” Renewable and Sustainable Energy Reviews 89 (June): 51-60.