Peaking power plant
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Peaking power plants, also known as peaker plants, are power plants that generally run only when there is a high demand, known as peak demand, for electricity. In the U.S., this occurs in the afternoon, especially during the summer months when the air conditioning load is high. In contrast, base load power plants operate continuously, stopping only for maintenance or unexpected outages. Intermediate plants operate between these extremes, curtailing their output in periods of low demand, such as during the night. Base load and intermediate plants are used preferentially to meet electrical demand because the lower efficiencies of peaker plants make them more expensive to operate.
The time that a peaker plant operates may be many hours a day or as little as a few hours per year. It depends on the condition of the region's electrical grid. It is expensive to build an efficient power plant, so if a peaker plant is only going to be run for a short and variable time, it does not make economic sense to make it as efficient as a base load power plant. In addition, the equipment and fuels used in base load plants are often unsuitable for use in peaker plants because the fluctuating conditions would severely strain the equipment. For these reasons, nuclear, geothermal, waste-to-energy, coal and biomass plants are rarely, if ever, operated as peaker plants.
Peaker plants are generally gas turbines that burn natural gas. A few burn diesel oil, but it is usually more expensive than natural gas, so its use is limited. However, many peaker plants are able to use diesel oil as a backup fuel. The thermodynamic efficiency of gas turbine power plants ranges from 20 to 40%, with about 30 to 35% being average for a new plant. The most efficient gas turbines combined cycle plants are generally used for load cycling, cogeneration plants, or peaker plants that are intended to be operated for longer periods than usual. Reciprocating engines are sometimes used for smaller peaker plants.
Although gas turbine plants dominate the peaker plant category, other plants may provide power on a peaking basis. Some hydroelectric plants are operated this way. Storage technologies like pumped storage can be used to provide peak load power. Photovoltaic arrays deliver most of their energy during peak load hours, so sometimes they are also included in the peaker class of power plants.
