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How to calculate the amount of kilowatt hours (kWh) your solar panel system will produce

A calculator and a solar panel system

Interested to know how many kilowatt hours (kWh) your new solar panel system will kick out per year? It’s pretty simple to come up with a ballpark number. All you gotta do is look at the map below, which is labeled with an estimate of the number of kWh you can generate with one kilowatt (kW) of solar panels in every part of the United States.

If you haven’t gotten solar yet and you want to skip the ballpark estimates and have a professional use their high-tech software to give you an more exact estimate, connect with one of our trusted solar installer partners today.

If you’re ready for the ballpark, multiply the size of your system in kW by the number that is written in the shaded region where you live in the map below. Then multiply the result by 78%, to account for losses due to wiring and conversion from DC to AC power. Simple!


Map Source

For example, let’s say you live in Nevada and are thinking about installing a 5-kW solar system. Most Nevadans live in the Las Vegas metro area, which is located in the shaded region labeled “2000.”

Take that 2000 and multiply by the 5 kilowatts of your system size to get 10,000 kWh. Multiply that by .78 to get 7,800 kWh, which is a good estimate of how much electricity your 5-kW system will produce in a year.

How much money can you save with solar panels?

Ah, here’s the tricky part. Electricity costs different amounts depending on your utility company. To make it more complicated, some utility companies charge a flat fee for electricity, while some charge different prices based on the time of day or season.

Let’s look at a simple example, using the data from above. People in Las Vegas get their electricity from NV Energy, which currently (no pun intended) offers a flat-rate of $.12/kWh for home customers.

Take the 7,800 solar kWh from the last step and multiply it by $.12/kWh, and you end up with $936 of savings per year. Pretty good!

You could further divide that $936 into 12 equal amounts to see that you’ll save an average of $78 per month. Note, that’s just an average, because solar panels don’t make the same amount of electricity all year round.

Unless you live at the equator, the angle of the sun in the sky changes based on the time of year. It’s low in the winter and high in the summer. Changes to weather patterns also affect how much sun your panels will get, though maybe not as much in the desert of southern Nevada as in the blue hills of northern Wisconsin.

How to estimate your own solar savings

Follow the steps above to see how much a 5-kW solar system could save you. Multiply the number in your area of the USA map by the size of your solar system in kW, then multiply the result by .78. Finally, multiply that by the price you pay per kWh from your utility company, and you’ve got an estimate of your annual savings!

To see how much you’d save with solar panels in Santa Ana, California, for example, you first have to discover that you pay $.25/kWh for electricity. Then, find that the Los Angeles area lies within the 1,900 number on the map, so the calculation for a 5-kW system would be: 5 kW x 1900 kWh/kW x 78% output x $.25, or $1,850 per year!

Or in Massachusetts, where electricity costs $.20/kWh, and a kW of solar panels makes about 1,500 kWh per year, the panels save you $1,170 per year. But Massachusetts has other great solar incentives, including the SMART Solar program, which will save you hundreds of dollars more every year.

Every state offers different electricity prices and incentives, and every roof is different, too. If you’re ready to bypass the guessing game using estimated numbers, get multiple solar quotes for your home from trusted professional installers, and check the math based on our site.

Last modified: December 14, 2018

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Thank you for your explanations concerning radiance charts and the 0.78 conversion factor. I have a 17 panel system, each panel at 305W, in Las Vegas, and the calculation is right on the money. 2000 x 5.185 kW = 10,370 kWh x 0.78 = 8089 kWh/year x $0.12/kW = $970 savings/year. The Fed Tax rebate was 30% on the total install cost, and NV Energy rebated $1100. My payback in full will take 10 years. The panels are rated for 25 years minimum.


“Unless you live at the equator, the angle of the sun in the sky changes based on the time of year.” *blink, blink* The earth is still tilted, even if you live at the equator.




Beginning stages (with a solar expert) of planning a 20-Megawatt solar array on family farm in SE Nebraska. I have calculations based on 1700 irradex, for 5 hrs at using a .15 efficiency index for the panels. What will be the estimated total potential annual output considering the reductin tion (78%)? Looking for a preliminary corroboration of my calcs only..


I see a lot of questions from people asking for help to calculate what they need for their specific situation. You can estimate this yourself using the info on this page. I recently had a solar system installed so I will share the related calculations for my actual system which may help others do the same for their specific scenario. I live in NJ and my town has its own electric company. The rates are fairly expensive so that made our decision to install a solar system a little easier. However, I’m skeptical by nature and didn’t fully believe the… Read more »


Don’t get sucked into this price per/watt install prices these companies would have you believe.. nonsense! It’s now 2018, solar gear and tech is cheap. Branded LiFePO4 batteries last for 20 years as with these new 300w panels. If you can install yourself do it! save thousands.. but just don’t get ripped off by these horrible companies.

Rusty J

What a great idea, spending $28,000 to save $78 per month, let’s see, that would take only 29 years to pay it off. And then I wonder what Solar technolongy will be available then….

tolenna joe

base on the radiance chart, what would be the number for kosrae, micronesia please help

Lynn Harding (@Lynn9711SATX)

Thank you for this informative article! It helped provide a frame of reference for determining what to expect each month when our 6.36kW grid-tied solar panel system is fully functioning!


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