Solar panels needed for 1,800 kWh per month
42 panels
of 400 W (16.7 kW) cover 1,800 kWh/month at 4.5 peak sun hours · about $46,667 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 | 25.0 kW | 63 | 1,354 sq ft |
| 3.5 h | 21.4 kW | 54 | 1,161 sq ft |
| 4 h | 18.8 kW | 47 | 1,010 sq ft |
| 4.5 h | 16.7 kW | 42 | 903 sq ft |
| 5 h | 15.0 kW | 38 | 817 sq ft |
| 5.5 h | 13.6 kW | 35 | 752 sq ft |
| 6 h | 12.5 kW | 32 | 688 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 1,800 kWh a month?
About 42 panels of 400 W (16.7 kW) with 4.5 peak sun hours; 32 in a 6-hour sunny climate and 54 at 3.5 hours.
What does a 16.7 kW system cost?
At a typical $2.50-$3.20 per watt installed: $41,667-$53,333 before incentives.