How we calculate your solar production
This calculator uses NREL PVWatts, the industry-standard solar performance model from the U.S. Department of Energy — the same tool professional installers use. When you enter your ZIP code, we find the nearest weather station in the National Solar Radiation Database and model hour-by-hour panel performance for your exact location, tilt, and orientation.
Location matters enormously: a 1 kW system produces roughly 1,800 kWh/year in Phoenix versus about 1,100 kWh/year in Seattle. Savings are calculated from your state's electricity rate for the power you use on-site (we default to 50% self-consumption), plus a conservative net-metering credit (9¢/kWh) for surplus you export. 25-year figures account for about 0.5% annual panel degradation.
Frequently asked questions
How accurate are these estimates?
PVWatts uses historical weather data and is validated against real installations — estimates are typically within 10–15% of actual output. Exact shading, panel quality, inverter efficiency, and soiling affect real-world performance.
Is there a federal solar tax credit in 2026?
No. The 30% residential credit (Section 25D) expired December 31, 2025. This calculator shows savings from bill reduction and net metering only — no tax credit. Some state and local incentives may still apply.
What is net metering?
It credits you for surplus solar sent to the grid. Policies vary by state — some pay full retail, others much less (California's NEM 3.0 is roughly 3–7¢/kWh). We default to a conservative 9¢/kWh; check your utility for the exact rate.
Why do results vary so much by location?
U.S. sunlight ranges from about 5.5–6.5 kWh/m²/day in the Southwest to 3.5–4.5 in the Pacific Northwest — so the same panels can produce ~70% more in Arizona than in Washington.
How many solar panels do I need?
It depends on your electricity use and roof. A typical US home installs about 15–25 panels (roughly 6–10 kW). Each modern panel is ~400 W, so a 7 kW system is around 18 panels. Use the slider above to match your usage — over-sizing past what you consume (plus modest export) rarely pays in 2026 without net metering at full retail.
Do solar panels work on cloudy days and in winter?
Yes, just less. Panels still generate on overcast days (often 10–25% of peak) and in winter, when shorter days and lower sun angles reduce output. Our estimate already accounts for this by modeling your location's full-year weather, so the annual figure reflects real seasonal variation.
How long do solar panels last?
Most panels are warrantied for 25 years and keep producing beyond that, losing roughly 0.5% of output per year. Inverters typically need replacing once in that span. Our 25-year savings figure already factors in this gradual degradation.
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