Here is a simple equation that you can use to determine the size of your potential solar electric system:
Divide your average daily kilowatt-hour use by the number of sun hours per day (see ESH chart below). Medford, Oregon averages 4.5 sun hours a day. If you're averaging 10 kWh a day, divide that figure by the 4.5 sun hours and you end up with 2,222.22, which represents the kilowatt-size system you'll need to "zero out your bill." Your utility company can provide the average daily electrical use information. Solarman recommends that you get it for the past year, not just one month. Feel free to call or email us if you have further questions.
| State | City | High | Low | Avg | State | City | High | Low | Avg | |
| AK | Fairbanks | 5.87 | 2.12 | 3.99 | MO | Columbia | 5.50 | 3.97 | 4.73 | |
| AK | Matanuska | 5.24 | 1.74 | 3.55 | MO | St. Louis | 4.87 | 3.24 | 4.38 | |
| AL | Montgomery | 4.69 | 3.37 | 4.23 | MS | Meridian | 4.86 | 3.64 | 4.43 | |
| AR | Bethel | 6.29 | 2.37 | 3.81 | MT | Glasgow | 5.97 | 4.09 | 5.15 | |
| AR | Little Rock | 5.29 | 3.88 | 4.69 | MT | Great Falls | 5.70 | 3.66 | 4.93 | |
| AZ | Tuscon | 7.42 | 6.01 | 6.57 | MT | Summit | 5.17 | 2.36 | 3.99 | |
| AZ | Page | 7.30 | 5.65 | 6.36 | NM | Albuquerque | 7.16 | 6.21 | 6.77 | |
| AZ | Pheonix | 7.13 | 5.78 | 6.58 | NB | Lincoln | 5.40 | 4.38 | 4.79 | |
| CA | Santa Maria | 6.52 | 5.42 | 5.94 | NB | N. Omaha | 5.28 | 4.26 | 4.90 | |
| CA | Riverside | 6.35 | 5.35 | 5.87 | NC | Cape Hatteras | 5.81 | 4.69 | 5.31 | |
| CA | Davis | 6.09 | 3.31 | 5.10 | NC | Greensboro | 5.05 | 4.00 | 4.71 | |
| CA | Fresno | 6.19 | 3.42 | 5.38 | ND | Bismark | 5.48 | 3.97 | 5.01 | |
| CA | Los Angeles | 6.14 | 5.03 | 5.62 | NJ | Sea Brook | 4.76 | 3.20 | 4.21 | |
| CA | Soda Springs | 6.47 | 4.40 | 5.60 | NV | Las Vegas | 7.13 | 5.84 | 6.41 | |
| CA | La Jolla | 5.24 | 4.29 | 4.77 | NV | Ely | 6.48 | 5.49 | 5.98 | |
| CA | Inyokern | 8.70 | 6.87 | 7.66 | NY | Binghampton | 3.93 | 1.62 | 3.16 | |
| CO | Grandby | 7.47 | 5.15 | 5.69 | NY | Ithica | 4.57 | 2.29 | 3.79 | |
| CO | Grand Lake | 5.86 | 3.56 | 5.08 | NY | Schenetady | 3.92 | 2.53 | 3.55 | |
| CO | Grand Junction | 6.34 | 5.23 | 5.85 | NY | Rochester | 4.22 | 1.58 | 3.31 | |
| CO | Boulder | 5.72 | 4.44 | 4.87 | NY | New York City | 4.97 | 3.03 | 4.08 | |
| DC | Washington | 4.69 | 3.37 | 4.23 | OH | Columbus | 5.26 | 2.66 | 4.15 | |
| FL | Apalachicola | 5.98 | 4.92 | 5.49 | OH | Cleveland | 4.79 | 2.69 | 3.94 | |
| FL | Belie Is. | 5.31 | 4.58 | 4.99 | OK | Stillwater | 5.52 | 4.22 | 4.99 | |
| FL | Miami | 6.26 | 5.05 | 5.62 | OK | Oklahoma City | 6.26 | 4.98 | 5.59 | |
| FL | Gainsville | 5.81 | 4.71 | 5.27 | OR | Astoria | 4.76 | 1.99 | 3.72 | |
| FL | Tampa | 6.16 | 5.26 | 5.67 | OR | Corvallis | 5.71 | 1.90 | 4.03 | |
| GA | Atlanta | 5.16 | 4.09 | 4.74 | OR | Medford | 5.84 | 2.02 | 4.51 | |
| GA | Griffin | 5.41 | 4.26 | 4.99 | PA | Pittsburg | 4.19 | 1.45 | 3.28 | |
| HI | Honolulu | 6.71 | 5.59 | 6.02 | PA | State College | 4.44 | 2.79 | 3.91 | |
| IA | Ames | 4.80 | 3.73 | 4.40 | RI | Newport | 4.69 | 3.58 | 4.23 | |
| ID | Boise | 5.83 | 3.33 | 4.92 | SC | Charleston | 5.72 | 4.23 | 5.06 | |
| ID | Twin Falls | 5.42 | 3.42 | 4.70 | SD | Rapid City | 5.91 | 4.56 | 5.23 | |
| IL | Chicago | 4.08 | 1.47 | 3.14 | TN | Nashville | 5.20 | 3.14 | 4.45 | |
| IN | Indianapolis | 5.02 | 2.55 | 4.21 | TN | Oak Ridge | 5.06 | 3.22 | 4.37 | |
| KN | Manhattan | 5.08 | 3.62 | 4.57 | TX | San Antonio | 5.88 | 4.65 | 5.30 | |
| KN | Dodge City | 4.14 | 5.28 | 5.79 | TX | Brownsville | 5.49 | 4.42 | 4.92 | |
| KY | Lexington | 5.97 | 3.60 | 4.94 | TX | El Paso | 7.42 | 5.87 | 6.72 | |
| LA | Lake Charles | 5.73 | 4.29 | 4.93 | TX | Midland | 6.33 | 5.23 | 5.83 | |
| LA | New Orleans | 5.71 | 3.63 | 4.92 | TX | Fort Worth | 6.00 | 4.80 | 5.43 | |
| LA | Shreveport | 4.99 | 3.87 | 4.63 | UT | Salt Lake City | 6.09 | 3.78 | 5.26 | |
| MA | E. Wareham | 4.48 | 3.06 | 3.99 | UT | Flaming Gorge | 6.63 | 5.48 | 5.83 | |
| MA | Boston | 4.27 | 2.99 | 3.84 | VA | Richmond | 4.50 | 3.37 | 4.13 | |
| MA | Blue Hill | 4.38 | 3.33 | 4.05 | WA | Seattle | 4.83 | 1.60 | 3.57 | |
| MA | Natick | 4.62 | 3.09 | 4.10 | WA | Richland | 6.13 | 2.01 | 4.44 | |
| MA | Lynn | 4.60 | 2.33 | 3.79 | WA | Pullman | 6.07 | 2.90 | 4.73 | |
| MD | Silver Hill | 4.71 | 3.84 | 4.47 | WA | Spokane | 5.53 | 1.16 | 4.48 | |
| ME | Caribou | 5.62 | 2.57 | 4.19 | WA | Prosser | 6.21 | 3.06 | 5.03 | |
| ME | Portland | 5.23 | 3.56 | 4.51 | WI | Madison | 4.85 | 3.28 | 4.29 | |
| MI | Sault Ste. Marie | 4.83 | 2.33 | 4.20 | WV | Charleston | 4.12 | 2.47 | 3.65 | |
| MI | E. Lansing | 4.71 | 2.70 | 4.00 | WY | Lander | 6.81 | 5.50 | 6.06 | |
| MN | St. Cloud | 5.43 | 3.53 | 4.53 |