Capacity factor


Capacity factor

The net capacity factor of a power plant is the ratio of the actual output of a power plant over a period of time and its output if it had operated at full nameplate capacity the entire time. To calculate the capacity factor, total the energy the plant produced during a period of time and divide by the energy the plant would have produced at full capacity. Electrical energy is usually measured in kilowatt hours, or megawatt-hours in the electrical industry. Kilowatts or megawatts alone are not units of energy. They are units of power. Energy is power multiplied by time. Capacity factors vary greatly depending on the type of fuel that is used and the design of the plant. The capacity factor should not be confused with the availability factor.

Sample calculation

A base load power plant with a capacity of 1,000 MW might produce 648,000 megawatt-hours in a 30-day month. The number of megawatt-hours that would have been produced had the plant been operating at full capacity can be determined by multiplying the plant's maximum capacity by the number of hours in the time period. 1,000 MW X 30 days X 24 hours/day is 720,000 megawatt-hours. The capacity factor is determined by dividing the actual output with the maximum possible output. In this case, the capacity factor is 0.9 (90%). [ [http://www.nrc.gov/reading-rm/basic-ref/glossary/capacity-factor-net.html Glossary Capacity factor (net)] ]

Reasons for reduced capacity factor

There are two main reasons why a plant would have a capacity factor lower than 100%. The first reason is that it was 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 have the lowest costs per unit of electricity because they are designed for maximum efficiency and are operated continuously at high output. Geothermal plants, nuclear plants, coal plants and bioenergy plants that burn solid material are almost always operated as base load plants.

The second reason that a plant would have a capacity factor lower than 100% is it that output is curtailed 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 plants. Peaking plants may operate only a few hours per year or up to a several hours per day. Their electricity is relatively expensive. It is uneconomical, even wasteful, to make a peaking power plant as efficient as a base load plant because they do not operate enough to pay for the extra equipment cost, and perhaps not enough to offset the embodied energy of the additional components.

Load following power plants

Load following power plants, also called intermediate power plants, are in between these extremes in terms of capacity factor, efficiency and cost per unit of electricity. They produce most of their electricity during the day, when prices and demand are highest. However, the demand and price of electricity is far lower during the night and intermediate plants shutdown or reduce their output to low levels overnight.

Capacity factor and renewable energy

When it comes to several renewable energy sources such as solar power, wind power and hydroelectricity, there is a third reason for unused capacity. The plant may be capable of producing electricity, but its fuel (wind, sunlight or water) 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 downstream. However, solar, wind and hydroelectric plants do have high availability factors, so when they have fuel available, they are almost always able to produce electricity. [ [http://www.awea.org/faq/basicen.html How Does A Wind Turbine's Energy Production Differ from Its Power Production?] ]

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 farms are highly intermittent, due to the natural variability of the wind, but because a wind farm may have hundreds of widely-spaced wind turbines, the farm as a whole tends to be robust against the failure of individual turbines. In a large wind farm, a few wind turbines may be down for planned or unplanned maintenance at a given time, but the remaining turbines are generally available to capture power from the wind. Wind farms have typical capacity factors of 35%.

Solar power plants are intermittent because of the daily rotation of the earth and because of cloud cover. Solar power has a typical capacity factor of about 20%.

See also

*Intermittent power source
*Energy storage

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • capacity factor — UK US noun [C] ► PRODUCTION a measure of the relationship between the amount a machine or factory produces and the amount it could produce if it operated as effectively as possible: »The capacity factor of energy delivered by wind turbines is… …   Financial and business terms

  • Capacity factor — См. Коэффициент использования мощности Термины атомной энергетики. Концерн Росэнергоатом, 2010 …   Термины атомной энергетики

  • capacity factor — apkrautumo faktorius statusas T sritis radioelektronika atitikmenys: angl. capacity factor; load factor; loading factor vok. Belastungsfaktor, m; Belastungsverhältnis, n; Lastfaktor, m rus. коэффициент нагрузки, m pranc. facteur de charge, m …   Radioelektronikos terminų žodynas

  • capacity factor — noun : the ratio of the average load carried by a power station or system for a given period to the rated capacity of the station or system for the same period compare load factor …   Useful english dictionary

  • Capacity Factor —   The ratio of the average load on (or power output of) a generating unit or system to the capacity rating of the unit or system over a specified period of time.   ***   The ratio of the electrical energy produced by a generating unit for the… …   Energy terms

  • capacity — ca·pac·i·ty n pl ties 1: a qualification, power, or ability (as to give consent or make a testament) created by operation of law 2: an individual s ability or aptitude; esp: mental ability as it relates to responsibility for the commission of a… …   Law dictionary

  • Capacity — is the ability to hold, receive or absorb, or a measure thereof, similar to the concept of volume.Capacity may also refer to: *Capacity (economics), the point of production at which a firm or industry s average (or per unit ) costs begin to rise …   Wikipedia

  • factor — [fak′tər] n. [ME factour < OFr facteur < L factor, doer, maker < pp. of facere, DO1] 1. a) a person who carries on business transactions for another; commission merchant; agent for the sale of goods entrusted to his possession b) an… …   English World dictionary

  • factor loco tutoris — in the family law of Scotland, formerly a person appointed to a pupil without a tutor until a tutor could be appointed. The post vanished with the coming into force of the Age of Legal Capacity (Scotland) Act 1991 and the role is now carried… …   Law dictionary

  • factor — 1 *agent, attorney, deputy, proxy 2 constituent, *element, component, ingredient Analogous words: determinant, *cause, antecedent: *influence: agency, agent, instrument, instrumentality, *mean …   New Dictionary of Synonyms


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.