Panel Count firstOpen the prefilled roof-fit calculator
Savings nextCompare the bill impact
Battery laterCheck backup sizing after panel fit
9.13 kWrequired capacity at 4.5 sun hours
23 x 400Wrounded installed capacity: 9.20 kW
431 / 575 sq ftmodule surface / gross roof at 75% usable
Panel count by sun level and panel wattage
| Peak sun hours/day | 350W | 400W | 450W |
|---|---|---|---|
| 3.5 low-sun | 34 panels / 11.90 kW | 30 panels / 12.00 kW | 27 panels / 12.15 kW |
| 4.5 medium-sun | 27 panels / 9.45 kW | 23 panels / 9.20 kW | 21 panels / 9.45 kW |
| 5.5 high-sun | 22 panels / 7.70 kW | 19 panels / 7.60 kW | 17 panels / 7.65 kW |
All rows target 12,000 kWh/year and use 20% aggregate losses. Panel count is rounded up, so installed DC capacity is slightly above the unrounded requirement.
Formula and worked calculation
1,000 x 12 / (365 x 4.5 x 0.80) = 9.13 kW
Divide 9.13 kW by 0.40 kW per panel: 22.83. Since part of a panel cannot be installed, round up to 23 panels. The result is a 9.20 kW DC array. Using the current PVSize 400W module footprint of 18.7 sq ft, the panels themselves occupy about 431 sq ft.
Country and regional parameters to replace
- United States: test roughly 3.5-5.5 peak sun hours, then verify local net metering, snow, shading, setbacks, and utility data.
- Australia: test roughly 4.0-5.5 hours and verify export limits, inverter sizing, orientation, and network requirements.
- United Kingdom: test roughly 2.5-3.5 hours and use a wider seasonal production check before treating annual average output as winter coverage.
Error boundary: this is an annual energy-offset estimate, not a guarantee that every monthly bill reaches zero. Seasonal production, self-consumption, export compensation, shade, panel degradation, clipping, roof geometry, and utility rules can change the result.
Run the estimate through the project flow
The first link opens a prefilled roof-fit calculation. Automatic replay may show a result, but it does not count as a human calculator start or completion. Edit an input or click Calculate for a human action.
Continue with related evidence
Full comparison tableCompare 500-3,000 kWh/month
Battery next stepSize an 8-hour outage load
System rangeCompare 5 kW and 10 kW
Last reviewed July 18, 2026. Planning estimate only; no price, rebate, installation, or engineering result is promised.