• WES250

    WES250 turbines in the UK show an annual average PV-performance of 112%

Availability Explained

WES250 turbines in the UK show an annual average PV-performance of 112% and an annual average Availability of 98% between 2017 – 2019.

2020 has been an average good wind year in the UK: the annual wind index showed a 2,5% above-long-term-average value, and 7% higher than the annual average wind speed between 2017 – 2019.

The WES250 turbines in the UK have made the most of it during this period, though. Between January 2017 and December 2019 the turbines have reached an annual average PV-performance of 112% and an annual average Availability of 98%. The WES250 turbines in the UK were ready to go, practically any time of the year.


The term “availability” as used in the wind industry, is a measure of the potential for a wind turbine or wind farm to generate electrical power. If the turbine is “available” and grid-connected, and the wind and other conditions are within the turbine specification, then power will be generated.

The availability factor of a wind turbine is the amount of time that the turbine is able to produce electricity over a certain period, divided by the amount of the time in the period. The availability factor should not be confused with the capacity factor. The capacity factor for a given period can never exceed the availability factor for the same period. The difference arises when the turbine runs at less than full capacity, in which case the capacity factor is less than the availability factor.

The availability of a wind turbine varies greatly depending on the design of the turbine and how the turbine is operated. Everything else being equal, wind turbines that run less frequently have higher availability factors because they require less maintenance and because more inspections and maintenance can be scheduled during idle time.

PV performance WES250 2017-2019
Availability WES250 2017-2019

Originally the term availability factor was used only for power plants that depended on an active, controlled supply of fuel, typically fossil or later also nuclear. The emergence of renewable energy such as hydro, wind and solar power, which operate without an active, controlled supply of fuel and which come to a standstill when their natural supply of energy ceases, requires a more careful distinction between the availability factor and the capacity factor.

A wind turbine cannot operate in wind speeds above a certain limit, which counts against its availability factor. With this definition, modern wind turbines which require very little maintenance, have very high availability factors, up to about 98%.

More information

Sjoerd Overpelt

Project Developer