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


Interested to know how many kilowatt hours (kWh) your new solar panel system will kick out per year? All you gotta do is multiply the size of your system in kW by 78% of the number in the shaded region you live in the map below. Then, bingo you’re good to go!


Map Source

For example, let’s say you live in Arizona and are thinking about installing a 5kW solar system.

For the sake of the example, lets say you’re living in the “2000” shaded region.

Next, multiply 5 (since you’re considering a 5kw system) by 1560 (78% of “2000” is 1560) to arrive at 7800 kWh.

That means on average your system will offset 650kWh from your monthly electric bill (7800 divided by 12 months equals 650 kWh).

If you’re paying $0.11/kWh, that amounts to $71.50 saved per month ($0.11 x 650 kWh = $71.50)!

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

  1. tolenna joe says:

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

  2. 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!

  3. 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??

    1. Ben Zientara says:


  4. says:

    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?

  5. 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:

  6. 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..

  7. Lloyd says:

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

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. tophermiller says:

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

  13. 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?

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. Anonymous says:

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

  19. Anonymous says:

    its very useful to me thanks a lot

  20. 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.

  21. 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.

  22. 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)

  23. 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:

  24. 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.

  25. Wynn says:

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

  26. 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.

  27. 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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