Calcvers
Solar Panel Calculator
Outdoor & Energy
Generated
September 24, 2026
Recommended system size
7.5 kW
to cover 900 kWh/month
Your inputs
- Monthly electricity usage
- 900 kWh
- Peak sun hours per day
- 5 h
- Panel wattage
- 400 W
- System losses
- 20 %
Breakdown
- Panels needed
- 19
- Roof area
- 32.3 m²
- Annual generation
- 10,800 kWh/yr
Panel output mix
| Item | Value |
|---|---|
| Monthly usage | 900 kWh |
| Solar output | 900 kWh |
What this means
A solar system is sized backwards from your usage. Your average daily usage (monthly ÷ 30) is divided by the peak sun hours your location gets — the hours per day when sunlight is strong enough for panels to produce at full rated power. Because inverters, heat, shading and wiring reduce real output by roughly 20%, we divide by (1 − losses) to arrive at the system size in kilowatts. Panel count is that size divided by each panel's wattage, and roof area follows at about 1.7 m² per panel.
Recommendations
- Use your highest-billing-month usage to avoid undersizing if you run heating or cooling.
- Size to match your daytime consumption — adding battery storage is a separate decision.
- Get a professional site survey; orientation, tilt and shading change output more than panel choice.
Watch out
- Peak sun hours vary by location and season — use your region's average, not the best month.
- This is a sizing estimate; a qualified installer must verify roof load, wiring and local regulations.