Storage power stations
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Main article: Grid energy storage
It is possible to store energy and produce electrical power at a later time as
in pumped-storage hydroelectricity, thermal energy storage, flywheel energy
storage, battery storage power station and so on.
Pumped storage
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Main article: Pumped-storage hydroelectricity
The world's largest form of storage for excess electricity, pumped-storage is
a reversible hydroelectric plant. They are a net consumer of energy but
provide storage for any source of electricity, effectively smoothing peaks and
troughs in electricity supply and demand. Pumped storage plants typically
use "spare" electricity during off peak periods to pump water from a lower
reservoir to an upper reservoir. Because the pumping takes place "off peak",
electricity is less valuable than at peak times. This less valuable "spare"
electricity comes from uncontrolled wind power and base load power plants
such as coal, nuclear and geothermal, which still produce power at night
even though demand is very low. During daytime peak demand, when
electricity prices are high, the storage is used for peaking power, where
water in the upper reservoir is allowed to flow back to a lower reservoir
through a turbine and generator. Unlike coal power stations, which can take
more than 12 hours to start up from cold, a hydroelectric generator can be
brought into service in a few minutes, ideal to meet a peak load demand.
Two substantial pumped storage schemes are in South Africa, Palmiet
Pumped Storage Scheme and another in the Drakensberg, Ingula Pumped
Storage Scheme.
Typical power output
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See also: List of largest power stations
The power generated by a power station is measured in multiples of
the watt, typically megawatts (106 watts) or gigawatts (109 watts). Power
stations vary greatly in capacity depending on the type of power plant and
on historical, geographical and economic factors. The following examples
offer a sense of the scale.
Many of the largest operational onshore wind farms are located in China. As
of 2022, the Roscoe Wind Farm is the largest onshore wind farm in the world,
producing 8000 MW of power, followed by the Zhang Jiakou (3000 MW). As of
January 2022, the Hornsea Wind Farm in United Kingdom is the largest
offshore wind farm in the world at 1218 MW, followed by Walney Wind
Farm in United Kingdom at 1026 MW.
In 2021, the worldwide installed capacity of power plants increased by 347
GW. Solar and wind power plant capacities rose by 80% in one year. [27] As of
2022, the largest photovoltaic (PV) power plants in the world are led
by Bhadla Solar Park in India, rated at 2245 MW.
Solar thermal power stations in the U.S. have the following output:
Ivanpah Solar Power Facility is the largest of the country with an output of
392 MW
The Koeberg Nuclear Power Station, South Africa
Large coal-fired, nuclear, and hydroelectric power stations can generate
hundreds of megawatts to multiple gigawatts. Some examples:
The Koeberg Nuclear Power Station in South Africa has a rated capacity of
1860 megawatts.
The coal-fired Ratcliffe-on-Soar Power Station in the UK has a rated capacity
of 2 gigawatts.
The Aswan Dam hydro-electric plant in Egypt has a capacity of 2.1 gigawatts.
The Three Gorges Dam hydro-electric plant in China has a capacity of 22.5
gigawatts.
Gas turbine power plants can generate tens to hundreds of megawatts.
Some examples:
The Indian Queens simple-cycle, or open cycle gas turbine (OCGT), peaking
power station in Cornwall UK, with a single gas turbine is rated 140
megawatts.
The Medway Power Station, a combined-cycle gas turbine (CCGT) power
station in Kent, UK, with two gas turbines and one steam turbine, is rated
700 megawatts.[28]
The rated capacity of a power station is nearly the maximum electrical power
that the power station can produce. Some power plants are run at almost
exactly their rated capacity all the time, as a non-load-following base load
power plant, except at times of scheduled or unscheduled maintenance.
However, many power plants usually produce much less power than their
rated capacity.
In some cases a power plant produces much less power than its rated
capacity because it uses an intermittent energy source. Operators try to
pull maximum available power from such power plants, because
their marginal cost is practically zero, but the available power varies widely—
in particular, it may be zero during heavy storms at night.
In some cases operators deliberately produce less power for economic
reasons. The cost of fuel to run a load following power plant may be
relatively high, and the cost of fuel to run a peaking power plant is even
higher—they have relatively high marginal costs. Operators keep power
plants turned off ("operational reserve") or running at minimum fuel
consumption[citation needed] ("spinning reserve") most of the time. Operators feed
more fuel into load following power plants only when the demand rises above
what lower-cost plants (i.e., intermittent and base load plants) can produce,
and then feed more fuel into peaking power plants only when the demand
rises faster than the load following power plants can follow.
Output metering
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Not all of the generated power of a plant is necessarily delivered into a
distribution system. Power plants typically also use some of the power
themselves, in which case the generation output is classified into gross
generation, and net generation.
Gross generation or gross electric output is the total amount of
electricity generated by a power plant over a specific period of time. [29] It is
measured at the generating terminal and is measured in kilowatt-
hours (kW·h), megawatt-hours (MW·h),[30] gigawatt-hours (GW·h) or for the
largest power plants terawatt-hours (TW·h). It includes the electricity used in
the plant auxiliaries and in the transformers.[31]
Gross generation = net generation + usage within the plant (also known as
in-house loads)
Net generation is the amount of electricity generated by a power plant that
is transmitted and distributed for consumer use. Net generation is less than
the total gross power generation as some power produced is consumed
within the plant itself to power auxiliary equipment such as pumps, motors
and pollution control devices.[32] Thus
Net generation = gross generation − usage within the plant (a.k.a. in-house
loads)
