The short answer
To cover an average Missouri home's 1,041 kWh a month, you need about a 8.8 kW solar system, 22 panels of 400 W. For 1,000 kWh a month it takes about 18 panels in sunny Arizona and 28 in Washington, from NLR PVWatts sun data.
The same home in every state
System size and 400 W panels to cover 100% of 1,041 kWh a month at each state's largest city.
| Alabama Huntsville | 3A | 9.2 | 23 |
|---|---|---|---|
| Alaska Anchorage | 7 | 13.6 | 34 |
| Arizona Phoenix | 2B | 7.2 | 18 |
| Arkansas Little Rock | 3A | 9.2 | 23 |
| California Los Angeles | 3B | 7.6 | 19 |
| Colorado Denver | 5B | 8 | 20 |
| Connecticut Bridgeport | 5A | 9.6 | 24 |
| Delaware Wilmington | 4A | 9.2 | 23 |
| District of Columbia Washington | 4A | 9.2 | 23 |
| Florida Jacksonville | 2A | 8.8 | 22 |
| Georgia Atlanta | 3A | 9.2 | 23 |
| Hawaii Honolulu | 1A | 8 | 20 |
| Idaho Boise | 5B | 8.8 | 22 |
| Illinois Chicago | 5A | 9.6 | 24 |
| Indiana Indianapolis | 4A | 9.6 | 24 |
| Iowa Des Moines | 5A | 9.2 | 23 |
| Kansas Wichita | 4A | 8.4 | 21 |
| Kentucky Louisville | 4A | 9.6 | 24 |
| Louisiana New Orleans | 2A | 8.8 | 22 |
| Maine Portland | 6A | 9.6 | 24 |
| Maryland Baltimore | 4A | 9.2 | 23 |
| Massachusetts Boston | 5A | 9.6 | 24 |
| Michigan Detroit | 5A | 10 | 25 |
| Minnesota Minneapolis | 6A | 9.6 | 24 |
| Mississippi Jackson | 3A | 9.2 | 23 |
| Missouri Kansas City | 4A | 8.8 | 22 |
| Montana Billings | 6B | 9.6 | 24 |
| Nebraska Omaha | 5A | 8.8 | 22 |
| Nevada Las Vegas | 3B | 7.2 | 18 |
| New Hampshire Manchester | 5A | 10 | 25 |
| New Jersey Newark | 4A | 9.6 | 24 |
| New Mexico Albuquerque | 4B | 7.2 | 18 |
| New York New York | 4A | 10 | 25 |
| North Carolina Charlotte | 3A | 8.8 | 22 |
| North Dakota Fargo | 6A | 10 | 25 |
| Ohio Columbus | 4A | 9.6 | 24 |
| Oklahoma Oklahoma City | 3A | 8.4 | 21 |
| Oregon Portland | 4C | 11.2 | 28 |
| Pennsylvania Philadelphia | 4A | 9.2 | 23 |
| Rhode Island Providence | 5A | 10 | 25 |
| South Carolina Charleston | 3A | 8.8 | 22 |
| South Dakota Sioux Falls | 6A | 8.8 | 22 |
| Tennessee Nashville | 3A | 9.6 | 24 |
| Texas Houston | 2A | 8.8 | 22 |
| Utah Salt Lake City | 5B | 8.8 | 22 |
| Vermont Burlington | 6A | 10.4 | 26 |
| Virginia Virginia Beach | 3A | 8.8 | 22 |
| Washington Seattle | 4C | 11.6 | 29 |
| West Virginia Charleston | 4A | 10.4 | 26 |
| Wisconsin Milwaukee | 5A | 9.6 | 24 |
| Wyoming Cheyenne | 5B | 8.4 | 21 |
How it works
The formula
panels = kW × 1,000 ÷ panel watts, rounded up
Assumptions
- Sun: NLR PVWatts 8.5.0 (the National Laboratory of the Rockies, formerly NREL) for standard panels on a fixed roof mount, 20° tilt, facing south, 14% losses, at your state's largest city. PVWatts lets you model your own roof.
- Use: EIA's average monthly residential use for your state fills in until you type yours. Your bill shows your real yearly use, which is better.
- Panels are counted whole, so the system you buy is a little bigger than the exact need.
Worked example: an average Missouri home
- 1,041 kWh × 12 = 12,492 kWh a year
- ÷ 1,433 kWh per kW = 8.72 kW
- × 1,000 ÷ 400 W → 22 panels, 8.8 kW
Too big or too small
- Too big: under net billing, extra power earns little; you pay for panels that don't pay back.
- Too small: fine if it's what fits the roof or budget; every panel still saves its share.
- Plan for changes: an EV or heat pump adds a lot of use; size for it now if it's coming.
Questions people ask
How many solar panels do I need?
Divide your yearly use by what 1 kW of panels makes in your state, then by the panel size. For 1,000 kWh a month: about 22 panels of 400 W at the U.S. average of 1,394 kWh per kW, 18 in Arizona and 28 in Washington.
What size solar system do I need for 1,000 kWh a month?
About 8.6 kW at the U.S. average sun, from 6.8 kW in Arizona to 11 kW in Washington, for a south-facing roof at a 20° tilt.
Should I cover 100% of my use?
Under full net metering, covering your yearly use is the usual target. Where exports earn less (net billing), a smaller system sized to what you use while the sun is up often pays back faster; the solar payback calculator on WattSums shows the difference.
How much roof space do I need?
Check the panel's spec sheet: a typical residential panel is about 18 to 22 sq ft, and installers leave fire-code setbacks around the edges. Shade, an east-west roof or a steep pitch means more panels for the same power.