Calculate How Much Solar

Calculate How Much Solar

First, you need to know the power consumption for the property. You can find this using the power bills for 12 months. Add the monthly kilo-watt hours (kWh) for an annual total. If you don't have power bills, there are other ways to create an estimate. Order the solar design service and we can help. Once you know the kWh desired, use the calculator here to determine the kilo-watts (kW) of solar power you will need to generate kWh.

Solar Power Calculator

1. Enter the kWh used per year:         
2. Find the Solar Hours per Day (see table below)          
3. Enter the % of Electricity Bill you want to cover          
4. Click Calculate        
5. This is the Solar Array Size in kW          

The NEXT STEP, now that you have an estimate for the desired kW, VIEW SOLAR KIT SIZES to compare prices, brands and, options.

Remember, you decide how much solar to get based on the need, available space, and budget. There is no rule that you have to offset 100% of current energy use. Utilities will generally allow grid-connected systems up to 120% of the previous 12 months consumption. They will also allow for consumption increases from an electric vehicle, home expansion or other needs.

How to Calculate Your Solar Video Tutorial

Watch this video to learn how much solar power in kilo-watts or kW is needed to generate the kilo-watt hours or kWh of energy used at your property.


The following table provides a lookup for the solar hours per day in the biggest cities in each state of the USA. Use the solar hours per day in the calculator above. If you know the annual kWh consumed at the property, then divide it by the kWh per 1kW to determine the solar array size needed for the project.

          Maine Augusta 4.52 1,276
Alabama Birmingham 5.26 1,422   Maryland Baltimore 4.83 1,437
Alabama Huntsville 5.08  1,418   Massachusetts Boston 4.72 1,339
Alabama Mobile 5.49 1,540   Massachusetts Springfield 4.88 1,391
Alabama Montgomery 5.43 1,513   Michigan Detroit 4.60 1,325
Alaska Anchorage 3.40 1,053   Michigan Grand Rapids 4.48 1,280
Arizona Flagstaff 6.21 1,695   Minnesota Duluth 4.37 1,278
Arizona Phoenix 6.52 1,753   Minnesota Mpls/St Paul 4.62 1,320
Arizona Tucson 6.54 1,807   Mississippi Jackson 4.47 1,277
Arkansas Little Rock 5.18 1,401   Missouri Kansas City 5.04 1,414
Arizona Flagstaff 6.21 1,695   Missouri Springfield 5.16 1,412
Arizona Phoenix 6.52 1,753   Missouri St. Louis 4.99 1,387
Arizona Tucson 6.54 1,807   Nebraska Lincoln 5.02 1,436
Arkansas Little Rock 3.40 1,401   Nebraska Omaha 5.02 1,425 
California Bakersfield 6.16 1,714   Nevada Las Vegas  6.37 1,764
California Fresno 5.96 1,636   Nevada Reno  5.99 1,697 
          New Hampshire Concord 4.83 1,303
California Los Angeles 6.13 1,708   New Jersey Newark 4.74 1,313
California Modesto 5.96  1,652    New Mexico Albuquerque 6.41 1,805
California Oakland 5.62  1,598   New York Buffalo 4.34 1,221
California Oxnard 6.04  1,702    New York New York City 4.58 1,310
California Riverside 6.28  1,790   New York Syracuse 4.21 1,159
California Sacramento 5.83  1,620    North Carolina Charlotte 5.18 1,419
California Salinas 5.61  1,598   North Carolina Wilmington 5.29 1,493
California San Bernardino 6.20  1,714    North Dakota Bismark 4.72 1,364
California San Diego 5.70 1,627    Ohio Cincinnati 4.68 1,301
California San Francisco 5.56 1,593    Ohio Cleveland 4.68 1,290
California San Jose 5.86 1,667    Ohio Columbus 4.57 1,296
Colorado Colorado Springs 5.72 1,614   Ohio Dayton 4.70 1,330
Colorado Denver 5.69 1,59   Ohio Toledo 4.62 1,326
Colorado Fort Collins 5.19  1,455    Oklahoma Oklahoma City 5.54 1,579
Connecticut Bridgeport 4.63 1,307   Oregon Portland 4.09 1,118
Connecticut Hartford 4.68  1,273    Pennsylvania Philadelphia 4.78 1,334
DC Washington 4.87 1,391   Pennsylvania Pittsburgh 4.46 1,210
Florida Fort Lauderdale  5.74 1,662   Rhode Island Providence 4.74 1,334
Florida Jacksonville 5.52  1,478    South Carolina Charleston 5.38 1,489
Florida Miami 5.77  1,623    South Dakota Sioux Falls 4.88 1,441
Florida Orlando 5.64  1,570    Tennessee Clarksville 4.48 1,394
Florida Tallahassee 5.41  1,446    Tennessee Knoxville 5.00 1,397
Florida Tampa 5.76 1,610    Tennessee Memphis 5.18 1,470
Georgia Atlanta 5.26 1,470    Tennessee Murfreesboro 4.97 1,404
Georgia Savannah 5.34  1,459    Tennessee Nashville 4.91 1,390
Hawaii Honolulu 5.87 1,683   Texas Amarillo 6.08 1.735
Idaho Boise 5.17 1,439   Texas Dallas 5.50 1.552
Illinois Chicago 4.55 1,307   Texas Houston 5.33 1.476
Illinois  Springfield 4.62 1,331   Texas San Antonio 5.54 1.545
Indiana Fort Wayne 4.61 1,317   Utah Salt Lake City 5.32 1,554
          Vermont Montpelier 4.30 1,219
Indiana Indianapolis 4.72 1,342   Virginia Richmond 5.06 1,360
Iowa Des Moines 4.79 1,362   Washington Seattle 3.97 1,157
Kansas Kansas City 5.04 1,464   Washington Spokane 4.38 1,228
Kansas Wichita 5.38 1,553   Wisconsin Milwaukee 4.62 1,339
Kentucky Louisville 4.81 1,389   Wyoming Cheyenne  5.46 1,574
Louisiana New Orleans 5.41 1,524   Wyoming Cody 5.00 1,478
Louisiana Shreveport 5.38 1,454          

The solar hours per day table uses PV Watts calculations for each location using these input standards:

  • Module Type - Premium 19% or greater efficiency
  • Array Type - Fixed (roof mount)
  • System Losses - 12% standard or 15% snow county
  • Tilt - 20 degrees
  • Azimuth - 180 degrees
  • Inverter Efficiency - 98

Actual results will vary for each project.

Solar Power Map of the United States

Find your Solar Hours per Day using the color-coding on this map. Enter the value for your location into the solar calculator.

solar-radiation-map of the USA

The solar map uses insolation, a measure of solar radiation energy received on a given surface area in a given time. This is typically measured in kilo-watt hours per square meter per day (kWh/m2/day). The map shows the average daily total solar radiation throughout the United States. The U.S. Department of Energy, National Renewable Energy Laboratory (NREL) developed it.

Steps to calculate how much solar you need

At SunWatts, we make solar simple, and calculating how much solar you need has never been easier. On our Calculate How Much Solar page, you will learn how much solar power in kilo-watts or kW is needed to generate the kilo-watt hours or kWh of energy used at your property.

To estimate your solar system size, you will need three pieces of information to calculate the solar kilowatts.

  1. Your utility power bill for the last 12 months
  2. The solar hours per day for your location
  3. The percentage amount of the power bill you want to be covered

Now, let's look at each item in more detail.

It would be best if you had a year's worth of monthly power bills. On each power bill, locate the kilo-watt hours or kWh for each month. That is how much energy you consumed. Some power bills have a summary chart. You might find your kWh there. The summary chart may show the average daily kWh used for the past 12 months. If so, you can enter the total kWh for the year.

If no total is provided, then add the kilo-watt hours for each month and enter the total into #1 on our Solar Power Calculator. Do NOT include comma or decimal point. As an example, the average home in the USA uses 30 kWh per Day. Multiply that by 365 days, and the average home in the USA uses 11,000 kWh of electricity per year. So let's enter 11000 into field #1.

The next piece of information to look at are the solar hours per day for your location. In the USA, the average solar hours per day is between 4-6 hours. The AVERAGE solar hours per day. It's longer in the summer, shorter in winter. Now, scroll down the page to find your state and nearest city for the solar hours. For our example, let's use the first location on the list. Birmingham Alabama has 5.26 solar hours per day. Enter this number into #2, Solar Hours per Day.

The final piece of information is the amount of your electricity bill you want to cover. 50%, 80%, 100%, 150%; It’s up to you. But let's start with 100. Enter the whole number into #3, Do NOT include the % symbol. For our example, you should enter #1 11000, #2 5.26 and #3 100 You're ready to click calculate!

The example answer should be 7.64. This means that 7.64 kW or 7,640 watts of solar should generate 11,000 kilo-watt hours per year in Birmingham Alabama. You now know how to calculate the kW size you will need for a solar kit that will generate the kWh you consume. To find the price and more details for a solar kit, click the red link to VIEW SOLAR KIT SIZES, or use the menu by choosing Solar Kit, then Solar Kit Sizes.

You will see that we have many different size solar kits, from 1,000 to 1 million watts. SunWatts. Solar Made Simple.