The availability factor of a power plant is the amount of time that it is able to produce electricity over a certain period, divided by the amount of the time in the period. Occasions where only partial capacity is available may or may not be deducted. Where they are deducted, the metric is titled ''equivalent availability factor'' (EAF). 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 plant is run at less than full capacity, in which case the capacity factor is less than the availability factor. The availability of a power plant varies greatly depending on the type of

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...

, the design of the plant and how the plant is operated. Everything else being equal, plants that are run less frequently have higher availability factors because they require less maintenance and because more inspections and maintenance can be scheduled during idle time. Most thermal power stations, such as

coal Coal is a combustible black or brownish-black sedimentary rock, formed as stratum, rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen ...

, geothermal and nuclear power plants, have availability factors between 70% and 90%. Newer plants tend to have significantly higher availability factors, but preventive maintenance is as important as improvements in design and technology. Gas turbines have relatively high availability factors, ranging from 80% to 99%. Gas turbines are commonly used for

peaking power plant Peaking power plants, also known as peaker plants, and occasionally just "peakers", are power plants that generally run only when there is a high demand, known as peak demand, for electricity. Because they supply power only occasionally, the power ...

s, co-generation plants and the first stage of combined cycle plants. 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 Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space * Nuclear ...

. The emergence of

renewable energy Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most 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. By convention, such zero production periods are counted against the capacity factor but not against the availability factor, which thus remains defined as depending on an active, controlled supply of fuel, along with factors concerning reliability and maintenance. 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%. Photovoltaic power stations which have few or no moving parts and which can undergo planned inspections and maintenance during night have an availability factor approaching or equal to 100% when the sun is shining.

References

*Institute of Electrical and Electronics Engineers
Std 762-2006 - IEEE Standard Definitions for Use in Reporting Electric Generating Unit Reliability, Availability, and Productivity
{{Electricity generation Power station technology ar:معامل الجهوزية

See also

References