Peaking power plant

Peaking power plant

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 United States, this often occurs in the afternoon, especially during the summer months when the air conditioning load is high. The peak power load generally occurs between 4pm and 5pm when people return home from work, start cooking dinner, and turn up the air conditioning. During this time many workplaces are additionally still open and consuming power.

The time that a peaker plant operates may be many hours a day or as little as a few hours per year, depending 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 or highly 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 petroleum-derived liquids, such as diesel oil and jet fuel, but they are usually more expensive than natural gas, so their use is limited. However, many peaker plants are able to use petroleum as a backup fuel. The thermodynamic efficiency of single-cycle gas turbine power plants ranges from 20 to 42%, with between 30 to 42% being average for a new plant.

For greater efficiency, a Heat Recovery Steam Generator (HRSG) is added at the exhaust. This is known as a combined cycle plant. Cogeneration uses waste exhaust heat for process or other heating uses. Both of these options are used only in plants that are intended to be operated for longer periods than usual. Reciprocating engines are sometimes used for smaller peaker plants.

Larger peaking plants that operate for extended periods of time are almost always required to have emissions controls and monitoring equipment. Smaller plants in the 3 MW range or less are often excluded from controlling their emissions due to the low number of hours they accumulate per year.

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.

The opposite of a peaking plant are base load power plants, which operate continuously, stopping only for maintenance or unexpected outages. Intermediate load following power 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.

Environmentally Friendly Methods

Nominally more environmentally-friendly alternative methods to meeting demand for electrical power with quick-starting fossil fueled plants are grid energy storage techniques and vehicle to grid technologies.

See also

* Base load power plant


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