How Many Solar Panels for 900 kWh per Month?
To cover 900 kWh per month you need about 8.2 kW of solar, or 21 panels of 400 W, assuming 4.5 peak sun hours a day. Depending on where you live that ranges from 16 panels (Southwest) to 27 panels (Northeast). The array needs roughly 441 sq ft of roof.
Solar panels for 900 kWh by region
| Region | Sun hours | System size | 400 W panels | Roof space |
|---|---|---|---|---|
| Northeast / Pacific Northwest | 3.5 | 10.57 kW | 27 | 567 sq ft |
| Midwest / Mid-Atlantic | 4.5 | 8.22 kW | 21 | 441 sq ft |
| Southeast / Texas | 5 | 7.4 kW | 19 | 399 sq ft |
| Southwest | 6 | 6.16 kW | 16 | 336 sq ft |
Based on 100% offset, 400 W panels and about 21 sq ft per panel. Peak sun hours are regional averages.
Cost of a 8.2 kW system
| Region | System size | At $2.50/W | At $3.00/W | At $3.50/W |
|---|---|---|---|---|
| Northeast / Pacific Northwest | 10.57 kW | $26,419 | $31,703 | $36,986 |
| Midwest / Mid-Atlantic | 8.22 kW | $20,548 | $24,658 | $28,767 |
| Southeast / Texas | 7.4 kW | $18,493 | $22,192 | $25,890 |
| Southwest | 6.16 kW | $15,411 | $18,493 | $21,575 |
Installed cost before any rebates. Cost is system watts × price per watt. The federal 25D credit ended for systems installed after December 31, 2025.
How it is calculated (4.5 sun hours)
900 kWh × 12 = 10,800 kWh per year (29.6 kWh per day)
10,800 ÷ (4.5 × 365 × 0.8) = 8.22 kW
8,219 W ÷ 400 W = 20.55 → 21 panels
21 × 21 sq ft = 441 sq ft of roof
Tips at 900 kWh per month
- Typical home range – This is close to an average US household. A 21-panel array (about 441 sq ft) usually fits on one or two roof planes.
- Panel wattage choice – Higher-wattage panels cut the count: at 450 W the same system needs about 19 panels instead of 21, which helps on smaller roofs.
- Batteries – Panels alone do not give backup power in an outage. A battery is sized separately and mainly pays off with time-of-use rates or poor net metering.
Frequently asked questions
How many solar panels do I need for 900 kWh per month?
About 21 panels of 400 W (8.22 kW) in a region with 4.5 peak sun hours. That ranges from 16 panels in the Southwest to 27 in the Northeast and Pacific Northwest.
How big a solar system do I need for 900 kWh a month?
900 kWh a month is 10,800 kWh a year. Divided by 4.5 sun hours × 365 days × 0.8 system efficiency, that gives a 8.22 kW system. It is 6.16 kW with 6.0 sun hours and 10.57 kW with 3.5.
How much does solar cost for 900 kWh per month?
At 4.5 sun hours the system costs about $20,548 to $28,767 installed ($2.50–$3.50 per watt), or $24,658 at $3.00. The federal 25D credit ended for systems installed after December 31, 2025, so check state and utility rebates separately.