PV Annual Energy, Specific Yield, and Capacity Factor
The first question a solar customer asks, answered with the NREL PVWatts energy model: annual kWh = DC nameplate x peak-sun-hours x 365 x performance ratio, plus the two benchmarks every designer compares systems by - specific yield (kWh per kW installed) and capacity factor. The same hardware makes a quarter more energy at a desert site than an average one, so the estimate starts from the site's plane-of-array irradiation, not a rule-of-thumb kWh-per-kW. The performance ratio (default 0.77) rolls up soiling, shading, mismatch, wiring, and inverter losses. A pre-design estimate, not a bankable production model.
Formula and source
annual_kwh = dc_kw x psh x 365 x perf_ratio; specific_yield = annual_kwh / dc_kw; capacity_factor = annual_kwh / (dc_kw x 8760); monthly_kwh_avg = annual_kwh / 12.
NREL PVWatts energy model (E_annual = P_dc x PSH x 365 x PR) and the standard specific-yield and capacity-factor definitions, by name; the relations are public.
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