Full-load hours
The number of hours per year a plant would need to run at rated power to deliver its actual annual output; equal to capacity factor multiplied by 8,760.
Full-load hours (also equivalent full-load hours, FLH, or in German practice Volllaststunden) express annual production as a time instead of a percentage. They are common in European wind and solar reporting and in project finance models.
A 5 MW turbine producing 15,000 MWh in a year has 3,000 full-load hours, equivalent to a 34% capacity factor. For solar PV the number is numerically identical to specific yield in kWh/kWp.
Indicative ranges:
- Solar PV, Germany: 900–1,100 h; southern Spain 1,600–1,900 h; Atacama with trackers above 2,800 h
- Onshore wind, Germany: roughly 1,600–2,200 h fleet average, 2,500–3,200 h for modern low-specific-power turbines at good sites
- Offshore wind, North Sea: 3,500–4,500 h
- Nuclear: 7,000–8,000 h
The metric is convenient because energy yield follows by simple multiplication: a 10 MW solar park at 1,000 h produces about 10 GWh per year. When comparing figures, check whether hours are stated on AC or DC capacity, gross or net of losses and curtailment, and for the first year or averaged over the asset life, since degradation reduces them over time.
Related terms
All terms →- Capacity factor
The ratio of the energy a power plant actually produces over a period to the energy it would produce running at full nameplate capacity for the whole period.
- Specific yield
Annual energy produced per unit of installed PV capacity, expressed in kWh/kWp per year; combines solar resource and system performance.
- Peak sun hours
Daily solar irradiation expressed as the equivalent number of hours at 1,000 W/m²; numerically equal to kWh/m² per day.
- Power curve
The relationship between hub-height wind speed and a turbine's electrical output, used with a wind speed distribution to estimate annual energy production.
- Load factor
The ratio of average demand to peak demand over a period, indicating how evenly a consumer or system uses electricity.