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Capacity Factor

The capacity factors are calculated as follows:

Quarterly capacity factor = (energy produced during quarter) / (quarterly capacity * 2190)

Annual capacity factor = (energy produced during year) / (Q4 capacity * 4 * 2190)

The annual capacity factor as computed from the above equation does not take into account any changes in capacity during the year. Most projects have a constant capacity throughout the entire year, but a few projects do increase/decrease their capacity.

An average of the quarterly capacity factors may be a better assessment of the annual capacity factors.

The Capacity Factor is a measure of efficiency, which is defined as the ratio of actual energy output to the amount of energy a project would produce if it operated at full rated power for 24 hours per day within a given time period. Although variations exist with wind turbine ratings based on widely differing test conditions, procedures and non-standardized miles-per-hour specifications, the capacity factor is still considered a strong indicator of wind project performance. Voluntary standards for testing wind turbines, however, have been developed by the American Wind Energy Association.

The annual capacity factor is typically computed based on annual production figures and turbine capacity for the year, or it can be computed as the average of quarterly capacity factors calculated for each group of turbines reported in that quarter. With WPRS quarterly data available from operators, only operating turbines are used to calculate the capacity factor so that performance results are not skewed by non-operational capacity. With significant re-powering and new capacity installation during the period of 1996 to 1999, changes to the capacity are only included in the capacity factor calculation during the quarter of installation. Although new turbines are not likely to operate for the entire quarter in which they are installed, this method provided the most consistent method for calculating CF without randomly interpreting when new turbines are operational or nonoperational.

Cumulative Capacity

Cumulative capacity = (total number of turbines) * (rated power)

Turbine specific energy

The wind turbine specific energy is the total amount of energy produced by a wind turbine(s) divided by the total rotor swept area of the turbine(s). As a normalized value, it provides a basis for comparison of dissimilarly sized wind turbines. It is calculated as follows:

Quarterly energy per swept area = (energy produced during quarter) / (number of turbines * swept area)

Annual energy per swept area = (energy produced during year) / (number of turbines in Q4 * swept area)

As with the capacity factor, an average of the quarterly values may be a better assessment of the annual value.

Energy production

The amount of energy produced is reported by project operators. The database reports it as is.

Individual turbine model outputs submitted by wind operators are included for each quarter along with an annual total. An annual total for the entire project follows. Individual turbine model outputs may not always equal total project output because individual turbine production is usually read from meters owned by project operators, while total project output is measured from utility substation meters. Line losses and calibration differences between meters account for some of these differences.

New capacity

New capacity = (number of new turbines) * (rated power for turbine)

All query results are zeros because the number of new turbines is zero.

Number of new turbines

Total number of turbines installed

The total number of turbines installed is equivalent to the cumulative number of turbines installed as reported by project operators.

Project operator

Any developer or operator who directly receives payments for electricity from the wind power purchaser.

Results show that within the 1996-1999 period, several of the larger operators restructured and consolidated. Before 1997, the major operators included Kenetech, SeaWest, Zond, Flowind and Cannon. By 1998, Zond was purchased by Enron Corporation, Green Ridge took over operations of the Kenetech, and Flowind facilities and FPL Energy took over Cannon and Cameron Ridge operations.

Resource area

During the period from 1996-1999, wind performance data were received from operators with projects located in the following resource areas but are by no means limited to only these resource areas:

All five resource areas are narrow mountain passes leading into hot valley or desert regions. These regions account for nearly 95% of all of California's wind-generated electricity in 1999.


Statewide is not a sorting parameter per se, but a total of the queried data for the entire state of California.

Swept area

Turbine manufacturer

The seven largest wind turbine manufacturers are Bonus, Flowind, Kenetech, Moerup, Vestas, Nagasaki, and Nordtank.

Turbine origin

Turbine rated power

The kW size rating is listed for each turbine model.


The quarters are defined as follows: