Solar panels needed for 400 kWh per month
10 panels
of 400 W (3.7 kW) cover 400 kWh/month at 4.5 peak sun hours · about $10,370 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 | 5.6 kW | 14 | 301 sq ft |
| 3.5 h | 4.8 kW | 12 | 258 sq ft |
| 4 h | 4.2 kW | 11 | 236 sq ft |
| 4.5 h | 3.7 kW | 10 | 215 sq ft |
| 5 h | 3.3 kW | 9 | 194 sq ft |
| 5.5 h | 3.0 kW | 8 | 172 sq ft |
| 6 h | 2.8 kW | 7 | 150 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 400 kWh a month?
About 10 panels of 400 W (3.7 kW) with 4.5 peak sun hours; 7 in a 6-hour sunny climate and 12 at 3.5 hours.
What does a 3.7 kW system cost?
At a typical $2.50-$3.20 per watt installed: $9,259-$11,852 before incentives.