How Many Solar Panels Do You Need? (2026 Guide)
By Sunfinder Editorial Team · April 2026 · 7 min read
The average US home uses 10,632 kWh/year. A standard 400W solar panel produces 400–700 kWh/year depending on where you live. Divide one by the other and you get a number — but the right answer for your home requires three pieces of information: your annual electricity usage, your location's solar yield, and how much of your bill you want to offset.
The Formula
Step 1: Find Your Annual Usage
Your electricity bill shows monthly kWh usage. Add up 12 months for your annual total. If you only have one bill, multiply by 12 — but seasonal variation matters. A home in Minnesota uses 3× more electricity in January than July. A home in Arizona uses 3× more in August than December.
If you are adding an EV, add approximately 3,000–4,500 kWh/year for average driving. If you are switching to electric heating or cooking, add 2,000–6,000 kWh/year. Size for your future usage, not just today's bill.
Step 2: Find Your Local Yield
Solar yield (kWh per kWp per year) is how much electricity one kilowatt of solar capacity produces in your location. It varies from about 900 kWh/kWp in Seattle to 1,900 kWh/kWp in Phoenix. The national average is 1,400 kWh/kWp. Use your city page on Sunfinder for the exact PVGIS figure for your location.
Panel Count by State (10,800 kWh/yr household)
| State | Annual yield | Peak sun hrs | System size | Panels (400 W) |
|---|---|---|---|---|
| California | 1622 kWh/kWp | 5.7 hrs/day | 6 kW | 15 panels |
| Texas | 1580 kWh/kWp | 5.5 hrs/day | 6.4 kW | 16 panels |
| Florida | 1490 kWh/kWp | 5.2 hrs/day | 6.8 kW | 17 panels |
| New York | 1190 kWh/kWp | 4.2 hrs/day | 8.8 kW | 22 panels |
| Arizona | 1820 kWh/kWp | 6.4 hrs/day | 5.2 kW | 13 panels |
| Washington | 1050 kWh/kWp | 3.7 hrs/day | 10 kW | 25 panels |
Offset Percentage: 80%, 90%, or 100%?
Most installers size for 90–100% offset. But 100% offset is not always the best financial decision. If your utility has net metering at full retail rate, sizing for 100% makes sense — you get full credit for every kWh exported. If your utility has reduced export rates (California NEM 3.0, avoided-cost states), sizing for 80–90% and keeping a smaller system is often smarter.
A practical rule: if export credits are less than 50% of your import rate, size your system for 80–85% offset. You'll maximize self-consumption and avoid oversizing for electricity you'll sell back at a loss. If export rate equals import rate (full retail net metering), go to 100% or slightly over.
Panel Sizes in 2026
| Panel wattage | Type | Panels for 8 kW | Roof space needed | Cost range |
|---|---|---|---|---|
| 400 W | Mono PERC | 20 | 380 sq ft | $0.30–$0.45/W |
| 440 W | TOPCon | 19 | 360 sq ft | $0.35–$0.50/W |
| 480 W | TOPCon XL | 17 | 325 sq ft | $0.40–$0.55/W |
| 500 W | HJT / IBC | 16 | 305 sq ft | $0.50–$0.70/W |
Roof Space: The Real Constraint
A 400W panel occupies roughly 19 sq ft. An 8 kW system needs about 380 sq ft of usable south-facing roof space. Obstructions (vents, chimneys, skylights), north-facing sections, and shading all reduce available area. If your roof is limited, choose higher-wattage panels (440–500W) to fit more power in less space. Premium TOPCon and HJT panels deliver 15–20% more power per square foot than standard mono PERC panels at roughly 20–40% higher panel cost.