Updated 24 March 2026
How Many Solar Panels Do I Need?
The answer depends on three things: how much electricity you use, where you live, and how efficient your panels are.
Quick Reference Table
| Monthly Usage | System Size | Panels (400W) | Estimated Cost |
|---|---|---|---|
| 500 kWh (small home) | 4 kW | 10 | $8,000-$12,000 |
| 750 kWh (medium home) | 6 kW | 15 | $12,000-$18,000 |
| 886 kWh (US average) | 7 kW | 18 | $14,000-$21,000 |
| 1,200 kWh (large home) | 10 kW | 25 | $20,000-$30,000 |
| 1,500 kWh (large home + EV) | 12 kW | 30 | $24,000-$36,000 |
| 2,000 kWh (large home + pool + EV) | 16 kW | 40 | $32,000-$48,000 |
Based on national average of 4.5 peak sun hours/day and 400W panels. Your location may get more or less sun.
Peak Sun Hours by Region
Peak sun hours measure how much usable sunlight your area gets. More sun = fewer panels needed.
| Region | Peak Sun Hours | Panels for 886 kWh/mo |
|---|---|---|
| Arizona / Nevada | 6.5-7.5 | 12-14 |
| California / Texas | 5.5-6.5 | 14-17 |
| Florida / Southeast | 5.0-5.5 | 16-18 |
| Midwest / Mid-Atlantic | 4.0-4.5 | 18-22 |
| Pacific Northwest | 3.5-4.0 | 22-25 |
| Northeast | 3.5-4.5 | 20-25 |
Roof Space Required
Each 400W panel needs about 18 sq ft of roof space. Here is how many panels fit on different roof sizes:
| Usable Roof Area | Max Panels | Max System Size |
|---|---|---|
| 200 sq ft | 11 | 4.4 kW |
| 300 sq ft | 16 | 6.4 kW |
| 400 sq ft | 22 | 8.8 kW |
| 500 sq ft | 27 | 10.8 kW |
| 700 sq ft | 38 | 15.2 kW |
Usable roof area is typically 40-60% of total roof area after accounting for vents, chimneys, shade, and setback requirements.
Planning for the Future
Electric vehicle: An EV adds 300-500 kWh/month to your usage. If you plan to get an EV in the next 5 years, add 3-5 extra panels now.
Heat pump: Switching from gas to electric heating adds 200-400 kWh/month in winter. Size your system for this if planning electrification.
Battery storage: A battery does not change how many panels you need. It changes when you use the power, not how much you generate.
Pro tip: Always size slightly larger than your current needs. Solar panels degrade about 0.5% per year, and your electricity usage tends to increase over time. An extra 2-3 panels today costs $600-$900 and provides a buffer for 20+ years.
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