Solar panels needed for 900 kWh per month
21 panels
of 400 W (8.3 kW) cover 900 kWh/month at 4.5 peak sun hours · about $23,333 before the 30% credit at $2.80/W
System size by peak sun hours
| Peak sun hours | System size | 400 W panels | Roof area |
|---|---|---|---|
| 3 h | 12.5 kW | 32 | 688 sq ft |
| 3.5 h | 10.7 kW | 27 | 580 sq ft |
| 4 h | 9.4 kW | 24 | 516 sq ft |
| 4.5 h | 8.3 kW | 21 | 452 sq ft |
| 5 h | 7.5 kW | 19 | 408 sq ft |
| 5.5 h | 6.8 kW | 18 | 387 sq ft |
| 6 h | 6.2 kW | 16 | 344 sq ft |
kW = monthly kWh ÷ 30 ÷ sun hours ÷ 0.8 (inverter, wiring, soiling and temperature losses). Southwest US ~5.5-6.5 h, Midwest/Northeast ~3.5-4.5 h.
FAQ
How many solar panels for 900 kWh a month?
About 21 panels of 400 W (8.3 kW) with 4.5 peak sun hours; 16 in a 6-hour sunny climate and 27 at 3.5 hours.
What does a 8.3 kW system cost?
At a typical $2.50-$3.20 per watt installed: $20,833-$26,667 before incentives.