How many solar panels do you need?
Divide your yearly electricity use by what 1 kW of panels produces where you live, then by the rating of one panel. A home using 1,000 kWh a month needs about 17 panels of 400 W in New Mexico but 34 in Alaska, because the same panel produces less with less sun.
Calculator · solar output from PVGIS (NSRDB data)
Panels for your home
Panels needed
– panels
- System size
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- Output per year
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The formula
System size in kW = monthly kWh × 12 × share to cover ÷ yearly kWh per kW in your state. Number of panels = system size × 1,000 ÷ panel watts, rounded up. Yearly output per kW comes from PVGIS, the European Commission's solar model, run with US satellite weather data (NSRDB) for a south-facing roof at a 20° tilt with 14% system losses, in each state's largest city. A roof facing east or west, shade or a steeper pitch lowers output, so an installer's design for your roof can need more panels. Method.
Your monthly use is on your electric bill, in kWh. The default in the calculator is roughly what a $150 bill buys at Texas's average residential price of 16.1¢/kWh.
More panels are not always better. Under net billing, power you export earns less than the retail price, so covering 100% of your use can pay back slower than covering what you use during the day. Seenet metering vs net billing and your state's page for its rule.
Panels for 1,000 kWh a month, by state
With 400 W panels, covering all of a 1,000 kWh monthly use.
| State | kWh per kW a year | System size | 400 W panels |
|---|---|---|---|
| New Mexico | 1,810 | 6.6 kW | 17 |
| Arizona | 1,772 | 6.8 kW | 17 |
| Nevada | 1,770 | 6.8 kW | 17 |
| California | 1,676 | 7.2 kW | 18 |
| Hawaii | 1,669 | 7.2 kW | 18 |
| Colorado | 1,577 | 7.6 kW | 20 |
| Wyoming | 1,553 | 7.7 kW | 20 |
| Oklahoma | 1,545 | 7.8 kW | 20 |
| Kansas | 1,508 | 8.0 kW | 20 |
| South Carolina | 1,494 | 8.0 kW | 21 |
| Utah | 1,490 | 8.1 kW | 21 |
| Florida | 1,487 | 8.1 kW | 21 |
| Georgia | 1,467 | 8.2 kW | 21 |
| Idaho | 1,463 | 8.2 kW | 21 |
| Louisiana | 1,453 | 8.3 kW | 21 |
| Texas | 1,445 | 8.3 kW | 21 |
| Mississippi | 1,441 | 8.3 kW | 21 |
| North Carolina | 1,425 | 8.4 kW | 22 |
| Virginia | 1,424 | 8.4 kW | 22 |
| Alabama | 1,421 | 8.4 kW | 22 |
| Arkansas | 1,419 | 8.5 kW | 22 |
| Missouri | 1,393 | 8.6 kW | 22 |
| Nebraska | 1,378 | 8.7 kW | 22 |
| South Dakota | 1,362 | 8.8 kW | 23 |
| Iowa | 1,356 | 8.8 kW | 23 |
| Kentucky | 1,350 | 8.9 kW | 23 |
| Maryland | 1,337 | 9.0 kW | 23 |
| Tennessee | 1,333 | 9.0 kW | 23 |
| Montana | 1,329 | 9.0 kW | 23 |
| Connecticut | 1,327 | 9.0 kW | 23 |
| Delaware | 1,325 | 9.1 kW | 23 |
| New Jersey | 1,325 | 9.1 kW | 23 |
| Pennsylvania | 1,321 | 9.1 kW | 23 |
| Massachusetts | 1,315 | 9.1 kW | 23 |
| Rhode Island | 1,307 | 9.2 kW | 23 |
| Wisconsin | 1,302 | 9.2 kW | 24 |
| Indiana | 1,291 | 9.3 kW | 24 |
| Minnesota | 1,286 | 9.3 kW | 24 |
| Maine | 1,279 | 9.4 kW | 24 |
| New York | 1,279 | 9.4 kW | 24 |
| Ohio | 1,266 | 9.5 kW | 24 |
| New Hampshire | 1,264 | 9.5 kW | 24 |
| Michigan | 1,249 | 9.6 kW | 25 |
| West Virginia | 1,247 | 9.6 kW | 25 |
| North Dakota | 1,229 | 9.8 kW | 25 |
| Illinois | 1,196 | 10.0 kW | 26 |
| Vermont | 1,188 | 10.1 kW | 26 |
| Washington | 1,120 | 10.7 kW | 27 |
| Oregon | 1,115 | 10.8 kW | 27 |
| Alaska | 904 | 13.3 kW | 34 |
Solar output: PVGIS 5.2 (European Commission Joint Research Centre) with NSRDB solar radiation data; 1 kW peak, fixed, south-facing, 20° tilt, 14% system losses, 2005–2015 average at the city shown.