To cover 500 kWh a month (6,000 kWh a year) at a typical U.S. location (median state, 1,340 kWh per kW a year), you need about 4.8 kW — 11 × 440-W panels on roughly 296 sq ft of roof.
| Panel | Panels | System | Roof area |
|---|---|---|---|
| 400 W | 12 | 4.8 kW | 294 sq ft |
| 420 W | 11 | 4.62 kW | 283 sq ft |
| 440 W | 11 | 4.84 kW | 296 sq ft |
| 460 W | 10 | 4.6 kW | 281 sq ft |
| State | kWh per kW | System kW | Panels | Roof sq ft |
|---|---|---|---|---|
| Arizona | 1,755 | 3.5 | 8 | 215 |
| California | 1,677 | 4 | 9 | 242 |
| Texas | 1,421 | 4.4 | 10 | 269 |
| Florida | 1,455 | 4.4 | 10 | 269 |
| North Carolina | 1,446 | 4.4 | 10 | 269 |
| New York | 1,291 | 4.8 | 11 | 296 |
| Massachusetts | 1,302 | 4.8 | 11 | 296 |
| Illinois | 1,265 | 4.8 | 11 | 296 |
| Washington | 1,077 | 5.7 | 13 | 350 |
Location changes the answer by about 63%: the same 500 kWh takes 8 panels in Arizona but 13 in Washington. At 4.8 kW this is smaller than the 7.7 kW median U.S. install (Berkeley Lab, 2025).
Sun-hours check: 500 kWh a month is 16.4 kWh a day. With 4.93 peak sun hours and the 0.74 derate factor implied by the modeled yield (losses, inverter, heat), 16.4 ÷ (4.93 × 0.74) = 4.48 kW — the same answer.
Where exports earn less than retail (California, Arizona, Utah, Georgia and others), many installers size to about 70% of use: 3.5 kW here. Run the numbers in the solar payback calculator.
The full method, material data and tips are on the main solar panel calculator page.