To cover 750 kWh a month (9,000 kWh a year) at a typical U.S. location (median state, 1,340 kWh per kW a year), you need about 7 kW — 16 × 440-W panels on roughly 431 sq ft of roof.
| Panel | Panels | System | Roof area |
|---|---|---|---|
| 400 W | 17 | 6.8 kW | 416 sq ft |
| 420 W | 16 | 6.72 kW | 411 sq ft |
| 440 W | 16 | 7.04 kW | 431 sq ft |
| 460 W | 15 | 6.9 kW | 422 sq ft |
| State | kWh per kW | System kW | Panels | Roof sq ft |
|---|---|---|---|---|
| Arizona | 1,755 | 5.3 | 12 | 323 |
| California | 1,677 | 5.7 | 13 | 350 |
| Texas | 1,421 | 6.6 | 15 | 404 |
| Florida | 1,455 | 6.6 | 15 | 404 |
| North Carolina | 1,446 | 6.6 | 15 | 404 |
| New York | 1,291 | 7 | 16 | 431 |
| Massachusetts | 1,302 | 7 | 16 | 431 |
| Illinois | 1,265 | 7.5 | 17 | 457 |
| Washington | 1,077 | 8.4 | 19 | 511 |
Location changes the answer by about 58%: the same 750 kWh takes 12 panels in Arizona but 19 in Washington. At 7 kW this is smaller than the 7.7 kW median U.S. install (Berkeley Lab, 2025).
Sun-hours check: 750 kWh a month is 24.7 kWh a day. With 4.93 peak sun hours and the 0.74 derate factor implied by the modeled yield (losses, inverter, heat), 24.7 ÷ (4.93 × 0.74) = 6.72 kW — the same answer.
Where exports earn less than retail (California, Arizona, Utah, Georgia and others), many installers size to about 70% of use: 4.8 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.