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The net capacity factor is the
unitless A dimensionless quantity (also known as a bare quantity, pure quantity, or scalar quantity as well as quantity of dimension one) is a quantity to which no physical dimension is assigned, with a corresponding SI unit of measurement of one (or 1) ...
ratio of actual electrical energy output over a given period of time to the theoretical maximum electrical energy output over that period. The theoretical maximum energy output of a given installation is defined as that due to its continuous operation at full nameplate capacity over the relevant period. The capacity factor can be calculated for any electricity producing installation, such as a
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 b ...
consuming
power plant A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many ...
or one using
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 wind or the sun. The average capacity factor can also be defined for any class of such installations, and can be used to compare different types of electricity production. The actual energy output during that period and the capacity factor vary greatly depending on a range of factors. The capacity factor can never exceed the
availability factor 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 deduc ...
, or uptime during the period. Uptime can be reduced due to, for example, reliability issues and maintenance, scheduled or unscheduled. Other factors include the design of the installation, its location, the type of electricity production and with it either the fuel being used or, for renewable energy, the local weather conditions. Additionally, the capacity factor can be subject to regulatory constraints and market forces, potentially affecting both its fuel purchase and its electricity sale. The capacity factor is often computed over a timescale of a year, averaging out most temporal fluctuations. However, it can also be computed for a month to gain insight into seasonal fluctuations. Alternatively, it can be computed over the lifetime of the power source, both while operational and after decommissioning. A capacity factor can also be expressed and converted to full load hours.


Sample calculations


Nuclear power plant

Nuclear power plants are at the high end of the range of capacity factors, ideally reduced only by the
availability factor 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 deduc ...
, i.e. maintenance and refueling. The largest nuclear plant in the US,
Palo Verde Nuclear Generating Station The Palo Verde Generating Station is a nuclear power plant located near Tonopah, Arizona, in western Arizona. It is located about due west of downtown Phoenix, Arizona, and it is located near the Gila River, which is dry save for the rainy seas ...
has between its three reactors a nameplate capacity of 3,942 MW. In 2010 its annual generation was 31,200,000 MWh, leading to a capacity factor of: :\frac=0.904= Each of Palo Verde’s three reactors is refueled every 18 months, with one refueling every spring and fall. In 2014, a refueling was completed in a record 28 days, compared to the 35 days of downtime that the 2010 capacity factor corresponds to. In 2019, Prairie Island 1 was the US unit with the highest factor and actually reached 104.4%.


Wind farm

The Danish offshore wind farm Horns Rev 2 has a nameplate capacity of 209.3 MW. it has produced 6416 GWh since its commissioning 7 years ago, i.e. an average annual production of 875 GWh/year and a capacity factor of: :\frac=0.477 = 47.7\% Sites with lower capacity factors may be deemed feasible for wind farms, for example the onshore 1 GW
Fosen Vind Fosen Vind is a complex of six onshore wind farms in Fosen, Norway, commissioned in 2018-20. With a nameplate capacity of 1  GW the project is Europe's second largest onshore wind farm (second to the Markbygden Wind Farm); it more than doubl ...
which is under construction in Norway has a projected capacity factor of 39%. Feasibility calculations may be affected by seasonality. For example in Finland, capacity factor during the cold winter months is more than double compared to July. While the annual average in Finland is 29.5%, the high demand for heating energy correlates with the higher capacity factor during the winter. Certain onshore wind farms can reach capacity factors of over 60%, for example the 44 MW Eolo plant in Nicaragua had a net generation of 232.132 GWh in 2015, equivalent to a capacity factor of 60.2%, while United States annual capacity factors from 2013 through 2016 range from 32.2% to 34.7%. Since the capacity factor of a wind turbine measures actual production relative to possible production, it is unrelated to Betz's coefficient of 16/27 \approx 59.3%, which limits production vs. energy available in the wind.


Hydroelectric dam

the
Three Gorges Dam The Three Gorges Dam is a hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has been the world' ...
in China is, with its nameplate capacity of 22,500 MW, the largest power generating station in the world by installed capacity. In 2015 it generated 87 TWh, for a capacity factor of: :\frac=0.45 = 45\%
Hoover Dam Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on S ...
has a nameplate capacity of 2080 MW and an annual generation averaging 4.2 TW·h. (The annual generation has varied between a high of 10.348 TW·h in 1984, and a low of 2.648 TW·h in 1956.). Taking the average figure for annual generation gives a capacity factor of: :\frac=0.23 = 23\%


Photovoltaic power station

At the low range of capacity factors is the
photovoltaic power station A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building ...
, which supplies power to the electricity grid from a large-scale
photovoltaic system A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and ...
(PV system). An inherent limit to its capacity factor comes from its requirement of
daylight Daylight is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected by Earth and terrestrial objects, like landforms and buildings. Sunligh ...
, preferably with a sun unobstructed by clouds, smoke or
smog Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words '' smoke'' and ''fog'' to refer to smoky fog due to its opacity, and odor. The word was then int ...
, shade from trees and building structures. Since the amount of sunlight varies both with the time of the day and the seasons of the year, the capacity factor is typically computed on an annual basis. The amount of available sunlight is mostly determined by the
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
of the installation and the local cloud cover. The actual production is also influenced by local factors such as dust and ambient temperature, which ideally should be low. As for any power station, the maximum possible power production is the nameplate capacity times the number of hours in a year, while the actual production is the amount of electricity delivered annually to the grid. For example, Agua Caliente Solar Project, located in
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
near the 33rd
parallel Parallel is a geometric term of location which may refer to: Computing * Parallel algorithm * Parallel computing * Parallel metaheuristic * Parallel (software), a UNIX utility for running programs in parallel * Parallel Sysplex, a cluster o ...
and awarded for its excellence in renewable energy has a nameplate capacity of 290 MW and an actual average annual production of 740 GWh/year. Its capacity factor is thus: :\frac= 0.291 = 29.1\%. A significantly lower capacity factor is achieved by Lauingen Energy Park located in
Bavaria Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total l ...
, near the 49th parallel. With a nameplate capacity of 25.7 MW and an actual average annual production of 26.98 GWh/year it has a capacity factor of 12.0%.


Determinants of a plant capacity factor

There are several reasons why a plant would have a capacity factor lower than 100%. These include technical constraints, such as availability of the plant, economic reasons, and availability of the energy resource. A plant can be out of service or operating at reduced output for part of the time due to equipment failures or routine maintenance. This accounts for most of the unused capacity of base load power plants. Base load plants usually have low costs per unit of electricity because they are designed for maximum efficiency and are operated continuously at high output. Geothermal power plants,
nuclear power plant A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces ...
s, coal-fired plants and bioenergy plants that burn solid material are almost always operated as base load plants, as they can be difficult to adjust to suit demand. A plant can also have its output curtailed or intentionally left idle because the electricity is not needed or because the price of electricity is too low to make production economical. This accounts for most of the unused capacity of
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 powe ...
s and load following power plants. Peaking plants may operate for only a few hours per year or up to several hours per day. Many other power plants operate only at certain times of the day or year because of variation in loads and electricity prices. If a plant is only needed during the day, for example, even if it operates at full power output from 8 am to 8 pm every day (12 hours) all year long, it would only have a 50% capacity factor. Due to low capacity factors, electricity from peaking power plants is relatively expensive because the limited generation has to cover the plant fixed costs. A third reason is that a plant may not have the fuel available to operate all of the time. This can apply to fossil generating stations with restricted fuels supplies, but most notably applies to intermittent renewable resources. Solar PV and wind turbines have a capacity factor limited by the availability of their "fuel", sunshine and wind respectively. A hydroelectricity plant may have a capacity factor lower than 100% due to restriction or scarcity of water, or its output may be regulated to match the current power need, conserving its stored water for later usage. Other reasons that a power plant may not have a capacity factor of 100% include restrictions or limitations on air permits and limitations on transmission that force the plant to curtail output.


Capacity factor of renewable energy

For
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 ...
sources such as
solar power Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovolta ...
,
wind power Wind power or wind energy is mostly the use of wind turbines to generate electricity. Wind power is a popular, sustainable, renewable energy source that has a much smaller impact on the environment than burning fossil fuels. Historically ...
and
hydroelectricity Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...
, the main reason for reduced capacity factor is generally the availability of the energy source. The plant may be capable of producing electricity, but its "fuel" (
wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...
,
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when ...
or
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
) may not be available. A hydroelectric plant's production may also be affected by requirements to keep the water level from getting too high or low and to provide water for
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
downstream. However, solar, wind and hydroelectric plants do have high
availability factor 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 deduc ...
s, so when they have fuel available, they are almost always able to produce electricity. When hydroelectric plants have water available, they are also useful for load following, because of their high ''dispatchability''. A typical hydroelectric plant's operators can bring it from a stopped condition to full power in just a few minutes.
Wind farm A wind farm or wind park, also called a wind power station or wind power plant, is a group of wind turbines in the same location used to produce electricity. Wind farms vary in size from a small number of turbines to several hundred wind turb ...
s are variable, due to the natural variability of the wind. For a wind farm, the capacity factor is determined by the availability of wind, the swept area of the turbine and the size of the generator. Transmission line capacity and electricity demand also affect the capacity factor. Typical capacity factors of current wind farms are between 25 and 45%. In the United Kingdom during the five year period from 2011 to 2019 the annual capacity factor for wind was over 30%.
Solar energy Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essen ...
is variable because of the daily rotation of the earth, seasonal changes, and because of cloud cover. For example, the Sacramento Municipal Utility District observed a 15% capacity factor in 2005. However, according to the SolarPACES programme of the
International Energy Agency The International Energy Agency (IEA) is a Paris-based autonomous intergovernmental organisation, established in 1974, that provides policy recommendations, analysis and data on the entire global energy sector, with a recent focus on curbing car ...
(IEA), solar power plants designed for solar-only generation are well matched to summer noon peak loads in areas with significant cooling demands, such as
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...
or the south-western United States, although in some locations solar PV does not reduce the need for generation of network upgrades given that air conditioner peak demand often occurs in the late afternoon or early evening when solar output is reduced. SolarPACES states that by using thermal energy storage systems the operating periods of solar thermal power (CSP) stations can be extended to become dispatchable (load following).Thomas R. Mancini and Michael Geyer (2006)
Spain Pioneers Grid-Connected Solar-Tower Thermal Power
SolarPACES, OECD/ IEA, p. 3.
Geothermal has a higher capacity factor than many other power sources, and geothermal resources are generally available all the time.


Capacity factors by energy source


Worldwide

*Nuclear power 88.7% (2006 - 2012 average of US's plants). * Hydroelectricity, worldwide average 44%, range of 10% - 99% depending on water availability (with or without regulation via storage dam). * Wind farms 20-40%. * CSP solar with storage and Natural Gas backup in Spain 63%, California 33%. * Photovoltaic solar in Germany 10%, Arizona 19%, Massachusetts 13.35% (8 year average as of July 2018).


United States

According to the US Energy Information Administration (EIA), from 2013 to 2017 the capacity factors of utility-scale generators were as follows: , - ! colspan="8", Non-fossil fuels !! Coal !! colspan="4" , Natural Gas !! colspan="3" , Petroleum Liquids , - !Nuclear !! Hydro !!Wind !!Solar PV !!Solar CSP !!Landfill Gas
and !!Other Biomass
including Wood !! Geothermal !! !! !! !! !! !! !! !! , - , 89.9% , , 38.9% , , 32.4% , , NA , , NA , , 68.9% , , 56.7% , , 73.6% , , 59.8% , , 48.2% , , 4.9% , , 10.6% , , 6.1% , , 12.1% , , 0.8% , , 2.2% , - , 91.7% , , 37.3% , , 34.0% , , 25.9% , , 19.8% , , 68.9% , , 58.9% , , 74.0% , , 61.1% , , 48.3% , , 5.2% , , 10.4% , , 8.5% , , 12.5% , , 1.1% , , 1.4% , - , 92.3% , , 35.8% , , 32.2% , , 25.8% , , 22.1% , , 68.7% , , 55.3% , , 74.3% , , 54.7% , , 55.9% , , 6.9% , , 11.5% , , 8.9% , , 13.3% , , 1.1% , , 2.2% , - , 92.3% , , 38.2% , , 34.5% , , 25.1% , , 22.2% , , 69.7% , , 55.6% , , 73.9% , , 53.3% , , 55.5% , , 8.3% , , 12.4% , , 9.6% , , 11.5% , , 1.1% , , 2.6% , - , 92.2% , , 43.1% , , 34.6% , , 25.7% , , 21.8% , , 68.0% , , 57.8% , , 74.0% , , 53.7% , , 51.3% , , 6.7% , , 10.5% , , 9.9% , , 13.5% , , 0.9% , , 2.3% , - , 92.6% , , 42.8% , , 37.4% , , 26.1% , , 23.6% , , 73.3% , , 49.3% , , 77.3% , , 54.0% , , 57.6% , , 11.8% , , 13.7% , , NA , , 13.9% , , 2.5% , , NA However, these values often vary significantly by month.


United Kingdom

The following figures were collected by the Department of Energy and Climate Change on the capacity factors for various types of plants in UK grid:


See also

* Demand factor * Intermittent power source


References

{{Authority control Power station technology