The Azimuth Project
Capacity factor of wind power



For wind power, capacity factor can be anywhere from one tenth to half of it’s nameplate rating, and is usually about one fifth to one third of the nameplate capacity. Currently wind power has a capacity factor of 25% to 30% in the U.S. and slightly over 20% in Europe. New wind power installations are estimated to have a capacity factor around 35% in the United States.

“Firm Capacity”

The output of a farm can vary between nothing and it’s nameplate rating depending on weather regardless of it’s capacity factor. Because of this it becomes harder to count on wind power in the same way we count on current baseload or load following generation. To examine this, the “Firm capacity”, defined as the fraction of installed wind capacity that is online at the same probability as that of a coal-fired power plant, of an interconnected group of operating wind farms was examined. When farms are connected with sufficient transmission over a large geographic area, about half of the group’s total output can be counted on as baseload with roughly the same availability as other forms of baseload like coal. In that context, the “firm capacity” factor would likely be one sixth to one tenth of a group of wind farm’s nameplate rating provided there was sufficient transmission capacity and area between the farms.

Economic influences on capacity factor

In at least some regions, wind farms may be sited in certain locations that lead to the farm having a lower capacity factor if a sufficient amount of generation can compete with other generators that tend to charge much more than the national average. In California during the summer, wind power tends to ramp up in the late afternoon. This is economically beneficial for the wind farm owners because demand for electricity is extremely high at that time and they are generally competing with simple cycle natural gas generators who have rates from 20c to 80c per kWh. A side effect of this tends to be a lower capacity factor than if wind power was located in other parts of the state, but as long as the increase in the value of their electricity is greater than the loss in revenue from lower overall output, it is economically beneficial. If wind penetration grows and it starts competing with other less expensive generators it’s capacity factor will probably increase. Along those lines, all estimates regarding capacity factor should be examined critically because they may have a significant number of economic and other factors associated with them.


This paper examines the idea of the “firm capacity” of wind power.

The latter paper focuses on the capacity factor of wind farms. The author claims that the capacity factor of wind has been overestimated to lie in the 30-35% range while the mean realized value for Europe in the five year period preceding the paper was below 21%.

Data on wind power generation during summer in California.

This book comments on the time of the day and year that wind power tends to be available in California among other regions.

Data on electricity generation costs.

category: energy