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

  1. Anonymous says:

    “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.

  2. SREE says:


  3. John says:

    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..

    1. Ben Zientara says:

      Back-of-the-envelope, you’re looking at between 27,000 and 30,000 MWh of electricity per year.

  4. anonymous says:

    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 estimates. My system was just turned on a couple of weeks ago and I’m very happy to report that the estimates were accurate and we’re seeing decent power production on sunny days. When I use the calculations on this page they were very close to my actuals (so far) so that’s encouraging as well. NJ is a 1600 zone based on the map above.

    I have 42 Panasonic 320W panels (the all black models, look as nice as possible but definitely not invisible). The front of house faces south and we were told by 3 different installers that our house was ideally located for solar (we were still skeptical as I assumed they say that to everyone..) The system size is 13.44 kilowatts (42 panels X 320W per panel).

    System size of 13.44 x 1600 for NJ yields 21,504. Now take 21,504 X 0.78 to get 16,773 which is the projected annual kilowatt hours (KWH) the system should produce. So 16,773 KWH X 0.1929 which is the cost per KWH that my electric company charges and that equals $3,235 worth of electricity per year.

    The solar installation was part of a major home remodeling project and while I know how much electricity I used before I don’t know how much I will use going forward. The house is fairly large (4,000 sqft) which is twice the size as before but we have new appliances, furnace, hot water heater and A/C units all of which are energy efficient. Also, recessed lighting in every room with LED bulbs will be a big improvement as well.

    The electric company in my town “buys” the excess power my system produces at the same rate that I would need to buy from them (I think this 1 for 1 is a requirement in NJ but not certain). This is tracked on my new meter and will get reconciled each year so I have produced more than I use they will pay me 19 cents for every KWH. Based on my usage projection it’s unlikely I’ll have any excess but good to know it’s a possibility.

    I’ll be taking advantage of the federal tax rebate and I’ve secured a 10 year loan at $315 per month. NJ has a state tax credit program (SRECs) which should cover about $250 per month of the loan amount for the next 10 years. Hopefully this is a good financial decision and if I’m only paying $65 of the loan out of pocket plus any excess electricity we use (which we would have had to pay for anyway) then it’s definitely worth it.

    I will say that it feels great to be generating electricity for “free” each day. It was a sunny day in NJ yesterday and the system produced 59 KWH which is close to peak output for 13.44 system (AFAIK) so not bad for late October when the days are shorter. Very interested to see how this performs over time, especially through the summer.

    1. Ben Zientara says:

      Wow, thanks for writing! We’re really glad everything worked out for you like your installer said. We’d say it’s a testament to the hard work the solar industry has done to make sure our estimates are on the up-and-up and we communicate clearly and effectively. Good job getting in on the SREC market, and cheers to being able to fully pay off your system in just 10 years! That nice big tax credit should provide some warmth in the dark winter/early spring of 2019, too.

      We’d love for you to come back in a year or so and report how well things are working out! Again, congratulations on going solar!

  5. Earl says:

    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.

  6. Rusty J says:

    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….

    1. Ben Zientara says:


      It really depends on your state and how much energy you need. At today’s highest average installed prices ($3.50/watt), a system that costs $28,000 before any tax credits or other incentives would be about 8-kW in size, and produce around 9,500 kWh of electricity even in the cloudiest of places in the lower 48 states. Even if you were paying $.11/kWh (one of the cheapest electricity prices in the U.S.), the system would save you around $90 per month, or $1,080 in the first year.

      Each year, as electricity prices rise, your solar panels will still be kicking out the kilowatts, saving you around 3% more per year for their 25-year lifespan. At that rate, it would take around 21 years for the panels to pay off their original cost.

      But of course, if you pay income taxes, you can take advantage of the federal tax credit to reduce that cost by 30% after the first year, bringing cost after the tax credit and energy savings to $18,520, which will be paid off after year 15. And if there are any other incentives available, as there are in many states, that payback time can be further reduced. And most people don’t live in states with the cheapest electricity bills.

      A lot of people pay $.15-$20/kWh, and some pay up to $.30/kWh, bringing the payback times for 8-kW system near them down to single digits.

      If you don’t have a steady income, and live in a state with lots of cheap fossil-fuel power and no incentives, solar power can be tough to make pencil, financially. But it’s far from expensive for most people in the US, right now.

  7. tolenna joe says:

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

  8. Lynn Harding (@Lynn9711SATX) says:

    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!

  9. joey says:

    hello, i just want to know what is kwh and kw?? very difficult to understand about these things. energy and power?? is anyone want to explain??

  10. sheldon says:


    1. Ben Zientara says:


  11. I want to buider a solar farm in NJ approx 240,000 Sq ft. How much electricit will it produce? Annual income at 20 cents kwH?

  12. matt says:

    Great infomration here. 1 question, why am I multiplying by 78%? I dont understand where that 78% is coming from.

    1. Ben Zientara says:

      Great question, Matt-

      The numbers on the map represent kilowatt-hours per kilowatt of solar panels. Each panel is rated to produce a number of watts under laboratory testing, directly from its junction box. Once you’ve got the panel hooked up in a string, feeding into an inverter and then to your electric meter, about 78% of that lab testing number is available to use.

      So 78% is an estimate of the amount of solar energy that’s available after losses through the inverter, wires, etc. Here’s a link that’ll explain a little further, and even offers a solar calculator for you:

  13. Shiv Baghel says:

    i want to produce 1kilowatt eelectricity per hour….how many solar plate used in production and details of solar panels like daimeter length etc..

  14. Lloyd says:

    How many Solar kilowatts (or kwh) does Indiana produce annually?

  15. saurav upadhyay says:

    if my electricity bill cost for 163 kwh units in one month ,what cost charged is be for solar panel system for my 163 units cosumption in solar panel ,please calculate and tell me which is cheap

  16. mayur says:

    i want to get information about will home solar system work in mansoon season? give me quatation of 50 kw to 100 kw panel on my mail id

  17. Essam moqbel says:

    I consume an average of 4.5kw/day to run a 200w fridge and a100w TV for 10hours plus total of 500w/d lighting.What size of solar panels(KW/h) do i require to give me this daily capacity; please note that i live in the middlest,Yemen therefore need the solar system not for annual savings for my electricity bill rather than providing alternitive source of power which is currently upsent in our region ,also what type&size of batterries are required to store the power needed during the night which is about 60% of the daily4.5kw.your kind help would be very apprecieted.

  18. Junior Madjani says:

    I am an engineer currently working for a Gold mine. i am currently looking at a cost saving project of installing solar panel systems for our Mills. Our mills generate approximately 4500 Kwh, how many solar panel do need to install in order to generate that? please help.

  19. tophermiller says:

    Very helpful. But one question: Does this calculation assume AC kw or DC kw for the system size parameter?

  20. Anonymous says:

    If I am charged .09 per kwh and the monthly bill is roughly $15,000, how many kwh would I need to produce in order to reduce my bill to zero?

  21. Anonymous says:

    GaelanClark writes….Solar City is selling their services in Colorado. Their contract shows a price per kwh of $0.109. The price per kwh of electricity from non-renewable energy in Colorado is $0.112. A difference of $0.003 per kwh!!! So under the above assupmtions we can calculate the actual “savings” a solar customer would realize. Colrado is in the “1900” region…1900*78%=1482…1482/12(*5)=617.5 kwh per month. 617.5*.003=$1.85 dollars per month!!!! WOW!!! AMAZING SAVINGS!!!! And, you would still need to be plugged into the grid and you would still be receiving a bill from your local power provider, so in fact, your bill would be greater when getting shilled by Solar City.

  22. Anonymous says:

    You can use the light generated by light bulbs or led lights to generate energy with solar panels, but the power you get out of the panels will be way less than the power you use to run the light bulb

  23. Anonymous says:

    I have a monthly bill of 900kw used. How much panels sys , will I needed for that . I am living in Turks and Caicos Islands.

  24. Anonymous says:

    Which is better 3.57 kw for $17,493 or 3.71 kw for $18,179? How many panels is for 3.57 and 3.71?

    1. Ben Zientara says:

      Well, they’re both $4,900/kW of panels, so whichever you can best afford would be best. Depending on the modules they use, it could be the same number of panels, or the larger one might even be fewer panels! My guess is each system would be around 20 panels.

      If that system size produces more than you use, the only other concern would be your state’s net metering laws, which may allow the utility to pay you less than the retail rate for energy above your usage. Depending on the rate, it could make the extra expense less desirable. AGAIN, that’s a concern only if your system would produce more power than you use per year.

  25. Anonymous says:

    Hello..can we generate power through light bulbs or high light emitting bulbs like traffic lights using solar pannels

  26. Anonymous says:

    its very useful to me thanks a lot

  27. Anonymous says:

    this is great info. dont forget that our energy companies usually charge for alot more than just the generation amount. there’s usually transmission, distribution, and other customer and gov fees. if you’re looking to see how much you’ll offset, make sure to include these especially if they’re charged on a per kwh basis. for instance in PA, my generation charges are only 8.2c /kwh but after all the other fees I end up paying about 12c/kwh.

  28. Anonymous says:

    I live in the 200 region and the numbers appear close based on what I see. I might add if you live in CA its about $.20 /KWH average not anywhere near $.11.

  29. Anonymous says:

    Help me figure this out. Using SRP’s time of use plans gets my electric cost down to $0.07 kWh from 10 am to 1pm which allows me to keep my AC off for the rest of the daylight hours. Doesn’t that drop the annual figure of 7800 kWh in half? Even if it’s 4000 kWh, my annual savings would only amount to $280, right? ($0.07 X 4000)

  30. Anonymous says:

    DOE stands for “Depratment of Energy” (US). While I didn’t find the exact map on the DOE website, here is another US government website with the solar radiance data. YOu will see that the maps look pretty similar:

  31. Anonymous says:

    DOE stands for “Depratment of Energy” (US). While I didn’t find the exact map on the DOE website, here is another US government website with the solar radiance data. YOu will see that the maps look pretty similar.

  32. Wynn says:

    Dan: Very helpful stuff here. Thank you. Can you explain what those numbers (2000 for AZ) from the radiance chart actually mean?

  33. deependra says:

    i have read many articles about set up of solar system, initial coast have heavy amount. i have land for agriculture and i want electricity through solar for every operation.but i cant understand about role of my indian govt.

  34. fakhrul says:

    how did you come up with 78% and where did you get the map? how was the map developed?

    1. Dan Hahn says:

      Hi Fakhrul,

      The map is a solar radiance chart from DOE. 78% reflects the total assumed energy delivered by your solar system accounting for three specific losses:

      PV Energy delivered as % of manufacturers rating: 95%
      Wiring & power point tracking losses: 9% (91% delivered)
      Inverter Efficiency: 90%
      Total Energy Delivered 95% x 91% x 90% = 78%

      1. eunoia16 says:

        Can you cite your source please? What’s DOE?

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