Capacity factor

Worldwide Nuclear Power Capacity Factors

Nuclear power plants are at the high end of the range of capacity factors, ideally reduced only by the availability factor, i.e. maintenance and refueling. The largest nuclear plant in the US, Palo Verde Nuclear Generating Station has between its three reactors a nameplate capacity of 3,942 MW. In 2010 its annual generation was 31,200,000 MWh,[2] leading to a capacity factor of:

${\displaystyle {\frac {31,200,000\ {\mbox{MW·h}}}{(365\ {\mbox{days}})\times (24\ {\mbox{hours/day}})\times (3942\ {\mbox{MW}})}}=0.904={90.4\%}}$

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,[3] compared to the 35 days of downtime that the 2010 capacity factor corresponds to.

In 2019, Prairie Island 1 was the best US unit and actually reached 104.4%.[4]

The Danish offshore wind farm Horns Rev 2 has a nameplate capacity of 209.3 MW. As of January 2017 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:

${\displaystyle {\frac {875,000\ {\mbox{MW·h}}}{(365\ {\mbox{days}})\times (24\ {\mbox{hours/day}})\times (209.3\ {\mbox{MW}})}}=0.477=47.7\%}$[5]

Sites with lower capacity factors may be deemed feasible for wind farms, for example the onshore 1 GW Fosen Vind which as of 2017 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.[6] While the annual average in Finland is 29.5%,[6] 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%,[7] while United States annual capacity factors from 2013 through 2016 range from 32.2% to 34.7%.[8]

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 ${\displaystyle \approx }$ 59.3%, which limits production vs. energy available in the wind.

As of 2017 the Three Gorges Dam 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:

${\displaystyle {\frac {87,000,000\ {\mbox{MW·h}}}{(365\ {\mbox{days}})\times (24\ {\mbox{hours/day}})\times (22,500\ {\mbox{MW}})}}=0.45=45\%}$

Hoover Dam has a nameplate capacity of 2080 MW[9] and an annual generation averaging 4.2 TW·h.[9] (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.[9]). Taking the average figure for annual generation gives a capacity factor of:

${\displaystyle {\frac {4,200,000\ {\mbox{MW·h}}}{(365\ {\mbox{days}})\times (24\ {\mbox{hours/day}})\times (2,080\ {\mbox{MW}})}}=0.23=23\%}$

At the low range of capacity factors is the photovoltaic power station, which supplies power to the electricity grid from a large-scale photovoltaic system (PV system). An inherent limit to its capacity factor comes from its requirement of daylight, preferably with a sun unobstructed by clouds, smoke or smog, 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 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 near the 33rd parallel 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:

${\displaystyle {\frac {740,000\ {\mbox{MW·h}}}{(365\ {\mbox{days}})\times (24\ {\mbox{hours/day}})\times (290\ {\mbox{MW}})}}=0.291=29.1\%}$.

A significantly lower capacity factor is achieved by Lauingen Energy Park located in Bavaria, 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%.

According to the US Energy Information Administration (EIA), from 2013-2017 the capacity factors of utility-scale generators were as follows:[21]

However, these values often vary significantly by month.

• Nuclear power 88.7% (2006 - 2012 average of US's plants).[22]
• Hydroelectricity, worldwide average 44%,[23] range of 10% - 99% depending on water availability (with or without regulation via storage dam).
• Wind farms 20-40%.[24][25]
• CSP solar with storage and Natural Gas backup in Spain 63%.[26]
• CSP solar in California 33%.[27]
• Photovoltaic solar in Germany 10%, Arizona 19%.[28][29][30]
• Solar PV in Massachusetts is 13.35%, 8 year average as of July 2018.[31]

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:[32][13][33][14][34][15][35][16][36][37]