Calculate Solar Array Size and Cost

Image of a calculator and a pencil.What size solar system do I need for my home? Though this is a complicated question, we have simplified it for you below. It’s actually pretty easy to calculate solar. Follow the 4 steps to estimate your solar power system needs. Then calculate how much it might cost to install the solar system!

Step 1: Yearly Electricity (kWh) Usage

Look at your electricity bills and average out your usage to find your annual electricity usage. Look for ‘kWh’.

  • kWh = Kilowatt Hours; a measure of electricity
  • Your bill may tell you your kWh/month. If your bill is ~$100/month, you might use ~1,000 kWh/month. If your bill is ~$200, maybe closer to 1,800 kWh/month.

Step 2: Average Sun Hours at your house

Look at the chart below to get the number of hours per day the Sun shines on your house.

 Just find the closest big city.

Show/Hide City Sun Hours Chart

State City Avg State City Avg
AK Fairbanks 3.99 MO Columbia 4.73
AK Matanuska 3.55 MO St. Louis 4.38
AL Montgomery 4.23 MS Meridian 4.43
AR Bethel 3.81 MT Glasgow 5.15
AR Little Rock 4.69 MT Great Falls 4.93
AZ Tuscon 6.57 MT Summit 3.99
AZ Page 6.36 NM Albuquerque 6.77
AZ Pheonix 6.58 NB Lincoln 4.79
CA Santa Maria 5.94 NB N. Omaha 4.90
CA Riverside 5.87 NC Cape Hatteras 5.31
CA Davis 5.10 NC Greensboro 4.71
CA Fresno 5.38 ND Bismark 5.01
CA Los Angeles 5.62 NJ Sea Brook 4.21
CA Soda Springs 5.60 NV Las Vegas 6.41
CA La Jolla 4.77 NV Ely 5.98
CA Inyokern 7.66 NY Binghampton 3.16
CO Grandby 5.69 NY Ithica 3.79
CO Grand Lake 5.08 NY Schenetady 3.55
CO Grand Junction 5.85 NY Rochester 3.31
CO Boulder 4.87 NY New York City 4.08
DC Washington 4.23 OH Columbus 4.15
FL Apalachicola 5.49 OH Cleveland 3.94
FL Belie Is. 4.99 OK Stillwater 4.99
FL Miami 5.62 OK Oklahoma City 5.59
FL Gainsville 5.27 OR Astoria 3.72
FL Tampa 5.67 OR Corvallis 4.03
GA Atlanta 4.74 OR Medford 4.51
GA Griffin 4.99 PA Pittsburg 3.28
HI Honolulu 6.02 PA State College 3.91
IA Ames 4.40 RI Newport 4.23
ID Boise 4.92 SC Charleston 5.06
ID Twin Falls 4.70 SD Rapid City 5.23
IL Chicago 3.14 TN Nashville 4.45
IN Indianapolis 4.21 TN Oak Ridge 4.37
KN Manhattan 4.57 TX San Antonio 5.30
KN Dodge City 5.79 TX Brownsville 4.92
KY Lexington 4.94 TX El Paso 6.72
LA Lake Charles 4.93 TX Midland 5.83
LA New Orleans 4.92 TX Fort Worth 5.43
LA Shreveport 4.63 UT Salt Lake City 5.26
MA E. Wareham 3.99 UT Flaming Gorge 5.83
MA Boston 3.84 VA Richmond 4.13
MA Blue Hill 4.05 WA Seattle 3.57
MA Natick 4.10 WA Richland 4.44
MA Lynn 3.79 WA Pullman 4.73
MD Silver Hill 4.47 WA Spokane 4.48
ME Caribou 4.19 WA Prosser 5.03
ME Portland 4.51 WI Madison 4.29
MI Sault Ste. Marie 4.20 WV Charleston 3.65
MI E. Lansing 4.00 WY Lander 6.06
MN St. Cloud 4.53

Step 3: Input the numbers

Input the numbers in the calculator below. For those calculating by hand, the formula is:

Array Size (kW) = (Annual kWh usage) / (365 days/year) / (Solar Hours/day) / (0.82 derate factor)
  • Example: My electricity bill is ~$110/mo and I use about 900kWh/month. I live in SoCal near LA, so I get about 5.62 solar hours/day.
  • (10,800 kWh/year) / (365 days/year) / (5.62 kWh/day) / (0.82) = 6.4 kW Array
  • Due to real world efficiency losses (irradiance, dust, temperature, and wiring), you should expect your system power output (AC power) to be about 82% of the system (DC power) size. This is the 0.82 efficiency constant included.

Step 4: Calculate solar size and cost!

Step 5: Get a free quote (or 2)

Now that you have an idea of the cost, get a free estimate from one of the top solar installers in the nation.

Image of Sungevity logo.
Map of the US with states where Sungevity is active highlighted.Get a free solar quote from SungevityBenefits of Sungevity:

  • free personalized iQuote online
  • quote from designer, not salesperson
  • compare options online
  • $750 discount if you choose to install

Do You Live in One of These States?

AZ, CA, CO, CT, DC, DE, HI, MA, MD, NC, NH, NJ, NM, NV, NY, OR, PA, RI, TX, VT, or WA

Image of SolarCity logo.
Map of the US with states highlighted where SolarCity is active.

Get a free solar quote from SolarCity

Benefits of SolarCity:

  • #1 solar provider in America
  • high-efficiency solar panels
  • $0 down
  • maintenance included

Referrals: Yes, if you choose to have solar panels installed from one of these installers, I will earn a referral fee. It’s at no cost to you and you will get an additional discount in some cases. Thank you for your support.