How Many Solar Panels for 1,800 kWh per Month?
To cover 1,800 kWh per month you need about 16.4 kW of solar, or 42 panels of 400 W, assuming 4.5 peak sun hours a day. Depending on where you live that ranges from 31 panels (Southwest) to 53 panels (Northeast). The array needs roughly 882 sq ft of roof.
Solar panels for 1,800 kWh by region
| Region | Sun hours | System size | 400 W panels | Roof space |
|---|---|---|---|---|
| Northeast / Pacific Northwest | 3.5 | 21.14 kW | 53 | 1,113 sq ft |
| Midwest / Mid-Atlantic | 4.5 | 16.44 kW | 42 | 882 sq ft |
| Southeast / Texas | 5 | 14.79 kW | 37 | 777 sq ft |
| Southwest | 6 | 12.33 kW | 31 | 651 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 16.4 kW system
| Region | System size | At $2.50/W | At $3.00/W | At $3.50/W |
|---|---|---|---|---|
| Northeast / Pacific Northwest | 21.14 kW | $52,838 | $63,405 | $73,973 |
| Midwest / Mid-Atlantic | 16.44 kW | $41,096 | $49,315 | $57,534 |
| Southeast / Texas | 14.79 kW | $36,986 | $44,384 | $51,781 |
| Southwest | 12.33 kW | $30,822 | $36,986 | $43,151 |
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)
1,800 kWh × 12 = 21,600 kWh per year (59.2 kWh per day)
21,600 ÷ (4.5 × 365 × 0.8) = 16.44 kW
16,438 W ÷ 400 W = 41.1 → 42 panels
42 × 21 sq ft = 882 sq ft of roof
Tips at 1,800 kWh per month
- Check your roof space – 42 panels need about 882 sq ft of usable, unshaded roof. Many roofs cannot fit this on one side, so a split east/west layout or a ground mount may be needed.
- Look for the big loads – Usage this high often comes from electric heating, a pool pump, an EV or central air. Check those before sizing – a heat pump water heater or EV charge timing can shrink the system.
- Batteries – Batteries are sized separately from panels. At this usage, backing up the whole home is expensive; most owners back up essential circuits with one or two batteries.
Frequently asked questions
How many solar panels do I need for 1,800 kWh per month?
About 42 panels of 400 W (16.44 kW) in a region with 4.5 peak sun hours. That ranges from 31 panels in the Southwest to 53 in the Northeast and Pacific Northwest.
How big a solar system do I need for 1,800 kWh a month?
1,800 kWh a month is 21,600 kWh a year. Divided by 4.5 sun hours × 365 days × 0.8 system efficiency, that gives a 16.44 kW system. It is 12.33 kW with 6.0 sun hours and 21.14 kW with 3.5.
How much does solar cost for 1,800 kWh per month?
At 4.5 sun hours the system costs about $41,096 to $57,534 installed ($2.50–$3.50 per watt), or $49,315 at $3.00. The federal 25D credit ended for systems installed after December 31, 2025, so check state and utility rebates separately.