500-3,000kWh/month covered
350W / 400W / 450Wpanel ratings compared
3.5 / 4.5 / 5.5peak sun hours/day
How to read each cell: recommended panel count, rounded-up DC system capacity, and approximate module footprint. The roof number is panel surface only. PVSize's roof-fit calculator assumes 75% of gross roof area is usable, so divide the table footprint by 0.75 for a first gross-roof check before local setbacks, access paths, obstructions, tilt, and layout.
Low-sun reference: 3.5 peak sun hours/day
| Monthly use | 350W panels | 400W panels | 450W panels |
|---|---|---|---|
| 500 kWh | 17 panels5.95 kW / 330 sq ft | 15 panels6.00 kW / 281 sq ft | 14 panels6.30 kW / 297 sq ft |
| 1,000 kWh | 34 panels11.90 kW / 660 sq ft | 30 panels12.00 kW / 561 sq ft | 27 panels12.15 kW / 573 sq ft |
| 1,500 kWh | 51 panels17.85 kW / 990 sq ft | 45 panels18.00 kW / 842 sq ft | 40 panels18.00 kW / 848 sq ft |
| 2,000 kWh | 68 panels23.80 kW / 1,320 sq ft | 59 panels23.60 kW / 1,104 sq ft | 53 panels23.85 kW / 1,124 sq ft |
| 2,500 kWh | 84 panels29.40 kW / 1,630 sq ft | 74 panels29.60 kW / 1,384 sq ft | 66 panels29.70 kW / 1,400 sq ft |
| 3,000 kWh | 101 panels35.35 kW / 1,960 sq ft | 89 panels35.60 kW / 1,665 sq ft | 79 panels35.55 kW / 1,675 sq ft |
Medium-sun reference: 4.5 peak sun hours/day
| Monthly use | 350W panels | 400W panels | 450W panels |
|---|---|---|---|
| 500 kWh | 14 panels4.90 kW / 272 sq ft | 12 panels4.80 kW / 225 sq ft | 11 panels4.95 kW / 234 sq ft |
| 1,000 kWh | 27 panels9.45 kW / 524 sq ft | 23 panels9.20 kW / 431 sq ft | 21 panels9.45 kW / 446 sq ft |
| 1,500 kWh | 40 panels14.00 kW / 776 sq ft | 35 panels14.00 kW / 655 sq ft | 31 panels13.95 kW / 658 sq ft |
| 2,000 kWh | 53 panels18.55 kW / 1,029 sq ft | 46 panels18.40 kW / 861 sq ft | 41 panels18.45 kW / 870 sq ft |
| 2,500 kWh | 66 panels23.10 kW / 1,281 sq ft | 58 panels23.20 kW / 1,085 sq ft | 51 panels22.95 kW / 1,082 sq ft |
| 3,000 kWh | 79 panels27.65 kW / 1,533 sq ft | 69 panels27.60 kW / 1,291 sq ft | 61 panels27.45 kW / 1,294 sq ft |
High-sun reference: 5.5 peak sun hours/day
| Monthly use | 350W panels | 400W panels | 450W panels |
|---|---|---|---|
| 500 kWh | 11 panels3.85 kW / 214 sq ft | 10 panels4.00 kW / 187 sq ft | 9 panels4.05 kW / 191 sq ft |
| 1,000 kWh | 22 panels7.70 kW / 427 sq ft | 19 panels7.60 kW / 356 sq ft | 17 panels7.65 kW / 361 sq ft |
| 1,500 kWh | 33 panels11.55 kW / 641 sq ft | 29 panels11.60 kW / 543 sq ft | 25 panels11.25 kW / 530 sq ft |
| 2,000 kWh | 43 panels15.05 kW / 835 sq ft | 38 panels15.20 kW / 711 sq ft | 34 panels15.30 kW / 721 sq ft |
| 2,500 kWh | 54 panels18.90 kW / 1,048 sq ft | 47 panels18.80 kW / 879 sq ft | 42 panels18.90 kW / 891 sq ft |
| 3,000 kWh | 65 panels22.75 kW / 1,261 sq ft | 57 panels22.80 kW / 1,066 sq ft | 50 panels22.50 kW / 1,060 sq ft |
Formula and assumptions
required kW = monthly kWh x 12 / (365 x peak sun hours x 0.80)
The panel count is required kW x 1,000 / panel watts, always rounded up to a whole panel. Installed DC capacity is the rounded panel count multiplied by panel wattage. All tables use 20% aggregate system losses, equal to an 80% planning efficiency.
- Module footprints: 19.4 sq ft for 350W, 18.7 sq ft for 400W, and 21.2 sq ft for 450W.
- No battery, export limit, demand charge, incentive, snow, shade, or seasonal mismatch is modeled.
- Peak sun hours are annual planning averages, not daylight duration.
- Final roof design must account for fire setbacks, walkways, vents, orientation, structure, local code, and inverter limits.
Worked example: 1,000 kWh/month, 4.5 sun hours, 400W panels
Required capacity = 12,000 / (365 x 4.5 x 0.80) = 9.13 kW. Dividing by 0.40 kW per panel gives 22.83, so the planning count rounds up to 23 panels. Installed DC capacity is 9.20 kW and module footprint is about 431 sq ft.
Regional parameter check
| Planning context | Starting sun-hours | Loss range to test | What to verify locally |
|---|---|---|---|
| United States | 3.5-5.5 | 14%-22% | Utility interval data, shading, net metering, snow, roof setbacks. |
| Australia | 4.0-5.5 | 14%-20% | Export limits, inverter sizing, orientation, DNSP requirements. |
| United Kingdom | 2.5-3.5 | 18%-25% | Seasonal yield, roof direction, shading, DNO/export constraints. |
Check roof fit, then continue the project flow
The table answers the energy target. The Panel Count calculator checks how many selected modules fit the available roof and produces a shareable Solar Project Summary.
Related specific questions
1,000 kWh/monthSee the complete worked answer
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Method note: values are deterministic planning calculations from the formula above, not measured production or installer quotes. Last reviewed July 18, 2026.