Calculator

Solar System Size Calculator

By NerdVolt Editorial TeamJune 16, 2026Estimate tool

Accuracy note: The arithmetic on this page is deterministic from your inputs. Solar production, code, utility, incentive, and savings outputs are estimates unless you supply exact equipment specs, tariffs, shade data, and local requirements.

Use annual or monthly usage, target offset, panel wattage, and either a PVWatts 1 kW production value or the built-in rough fallback.

Inputs

Annual electricity use (kWh)Target offset (%)Annual kWh from 1 kW solarLatitude for PVWattsLongitude for PVWattsTilt (degrees)Azimuth (180 = south)Panel wattage (W)System losses (%)

Result

How this is calculated

Target annual production = annual kWh × offset. Required DC kW = target annual kWh ÷ modeled annual kWh per 1 kW DC. Panel count = ceiling(required kW × 1000 ÷ panel watts).

Sources

DOE: planning a home solar electric system
NREL: PVWatts API