Availability

For most electricity generators, availability is the same as capacity value, i.e., the percentage of time that a plant can be reliably called on to provide power in response to demand, i.e. how much of the time it is not shut down (e.g., for maintenance or repair).

Wind turbines, on the other hand, have a capacity value of zero, yet they are typically “available” over 90% of the time. However, they are available only to the wind (should it blow), not the actual needs of customers on the grid.