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Calculating Solar Power Potential with PV Watts


Washington State PV Array 

I like solar calculators, and this is an interesting one to explore.

The PV Watts1 calculator from the National Renewable Energy Laboratory (NREL) is a simple solar calculator that can help you figure out how much electricity you can generate with a PV system at many locations around the world. (Disclaimer here.)

When you use the calculator, it gives you a measurement of solar radiation in kilowatt-hours per square meter, which is also known as peak sun hours. (Here’s a very detailed explanation of that concept from the U.S. Department of Energy.)  

I used the calculator to compare peak sun hours and kWh of electricity generated for several different locations. You should know that I used all the default settings on the calculator, so the measurements below assume a 4 kilowatt PV system and a fixed tilt, south-facing PV array.

OK, here we go!

  • According to this calculator, here in Topeka, Kan., we get an average of 4.95 peak sun hours per day. Over the course of a year that would add up to 5,238 kWh a year, which is worth $403.33 at local electricity prices.

  • How about a sunnier location? Well, it looks like Albuquerque, N.M., has 6.48 peak sun hours per day, which produces 6,726 kWh a year for a value of $585.16 in electricity. 

  • Or, for less sun, we could look at the Northwest. Famously rainy Seattle, Wash., gets 3.76 peak sun hours a day for 3,879 kWh a year, and $248.26 worth of electricity.

  • What about outside the United States? Stockholm, Sweden gets 2.98 peak sun hours a day, and generated 3102 kWh a year. Cairo, Egypt gets 5.66 peak sun hours, and generates 5727 kWh a year.

You can take a look at your location and see how it compares. There’s also a PV Watts 2 calculator, which is more complicated to use, but will allow you to select any location in the United States.


Pictured Above: A PV array in Manchester, Wash., near Seattle. Photo by DOE/NREL/JOHN GROBLER