Solar Panel Output by Location

Annual solar production is calculated as system size (kW) × peak sun hours (per day) × 365 days × (1 − system loss). NREL's standard 14% system loss factor accounts for inverter efficiency, wiring losses, soiling, and shading.

Monthly seasonal distribution uses standard Northern Hemisphere irradiance factors, normalized so the monthly average equals the annual average. Production peaks May–July and dips November–January.

The 25-year output total applies a 0.5% annual degradation rate, which is conservative for modern Tier 1 panels.

Solar production varies dramatically by location. The fundamental driver is peak sun hours per day — a measure NREL has mapped in detail for the entire U.S. The Southwest leads with 6+ peak sun hours; the Pacific Northwest and Northeast trail at 3.5–4 peak sun hours.

For any system, annual production roughly equals system size × peak sun hours × 365 × 0.86 (after standard losses). An 8 kW system in Phoenix produces about 16,000 kWh per year. The same system in Seattle produces about 9,000 kWh.

Production also varies seasonally. Summer months produce 1.5–2× as much as winter months because of longer days and higher sun angles. This seasonality matters for system sizing — most installers size systems against annual usage rather than worst-month usage, relying on net metering credits to balance summer surplus against winter deficit.

Note that low sun hours don't disqualify solar — they just shift the economics. A homeowner in Massachusetts with high electricity rates ($0.28/kWh) can have better solar economics than a homeowner in low-rate sunny states because each kWh produced is worth so much more.