Solar Panel System GuideSolar tool
Solar System Size Calculator
Estimate solar system size in kilowatts from your annual electricity use, peak sun hours, and a system derate factor before getting a professional assessment.
Estimate only.Confirm with a pro and get a real quote. A professional solar site assessment and a written installer quote are authoritative for final system size, production, and cost.
Screening result
Fine Print and Sources
Estimate only. These tools use only the values you enter and simple planning math. Confirm with a pro and get a real quote. A professional solar site assessment and a written installer quote are authoritative for system sizing, production, and final purchase decisions.
Method: system kW equals annual kWh divided by 365, then divided by peak sun hours, then divided by the derate factor. Peak sun hours and derate vary by roof, shading, orientation, and equipment. NREL PVWatts is a more detailed production model.
- EnergySage solar sizing guide: explains how annual electricity use, peak sun hours, and panel wattage drive system size and panel count.
- NREL PVWatts calculator: a detailed production model that accounts for location, orientation, shading, and system losses.