Capacity Factor

Capacity factor is the ratio of a solar system’s actual energy output over a period to its maximum possible output if it ran at full nameplate capacity 24 hours a day, 365 days a year. It is expressed as a percentage and reflects how effectively a system utilizes its rated capacity.

For residential solar, capacity factors in the US typically range from 15% to 25%, depending on location, weather, and system design. A 10 kW system running at 100% capacity for a full year would produce 87,600 kWh (10 kW × 8,760 hours). If it actually produces 15,000 kWh, its capacity factor is about 17%. This may sound low, but it’s normal — solar panels only produce during daylight hours and output varies with clouds, seasons, and panel orientation. Southwest states like Arizona and Nevada achieve higher capacity factors (20–25%) due to more sunlight hours, while northern or cloudier states may see 12–18%. Capacity factor is more commonly used for utility-scale solar projects and comparisons between energy technologies than for individual residential systems, where annual kWh production is the more practical metric.