Peaking power plant

Peaking power plants, also known as peaker plants, and occasionally just 'peakers', are power plants that generally run only when there is a high demand, known as peak demand, for electricity. Because they supply power only occasionally, the power supplied commands a much higher price per kilowatt hour than base load power. Peak load power plants are dispatched in combination with base load power plants, which supply a dependable and consistent amount of electricity, to meet the minimum demand. Peaking power plants, also known as peaker plants, and occasionally just 'peakers', are power plants that generally run only when there is a high demand, known as peak demand, for electricity. Because they supply power only occasionally, the power supplied commands a much higher price per kilowatt hour than base load power. Peak load power plants are dispatched in combination with base load power plants, which supply a dependable and consistent amount of electricity, to meet the minimum demand. Although historically peaking power plants were frequently used in conjunction with coal baseload plants, peaking plants are now used less commonly. Combined cycle gas turbine plants have two or more cycles, the first of which is very similar to a peaking plant, with the second running on the waste heat of the first. That type of plant is capable of rapidly starting up, at reduced efficiency, and then transitioning over some hours to a more efficient baseload generation mode. Combined cycle plants have similar capital cost per watt to peaking plants, but run for much longer periods and hence give cheaper electricity. Peak hours usually occur in the morning or late afternoon/evening depending on location. In temperate climates, peak hours often occur when household appliances are heavily used in the evening after work hours. In hot climates, the peak is usually late afternoon when air conditioning load is high, during this time many workplaces are still open and consuming power. In cold climates, the peak is in the morning when space heating and industry are both starting up. A peaker plant may operate many hours a day, or it may operate only a few hours per year, depending on the condition of the region's electrical grid. Because of the cost of building an efficient power plant, 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 are rarely, if ever, operated as peaker plants. For countries that are trending away from coal-fired base load plants and towards intermittent energy sources such as wind and solar, there is a corresponding increase in the need for peaking or load following power plants and the use of a grid intertie. Peaker plants are generally gas turbines that burn natural gas. A few burn biogas or petroleum-derived liquids, such as diesel oil and jet fuel, but they are generally more expensive than natural gas, so their use is limited to areas not supplied with natural gas. However, many peaker plants are able to use petroleum as a backup fuel, as storing oil in tanks is easy. The thermodynamic efficiency of simple-cycle gas turbine power plants ranges from 20 to 42%, with between 30 and 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, district heating or other heating uses. Both of these options are used only in plants that are intended to be operated for longer periods than usual. Natural gas and diesel generators with reciprocating engines are sometimes used for grid support using smaller plants. Another option for increased efficiency and power output in gas turbines is installing a turbine inlet air cooling system, that cools down the inlet air temperature increasing mass flow ratio. This option, in combination with a thermal energy storage tank, can increase the turbine power output in on-peak periods up to 30%. Hydroelectric dams are intentionally variable; they can generate less during off-peak and quickly respond to peak demands, consequently hydroelectricity may function as load following or a peaking plant and with sufficient water, a base-load plant. Natural gas turbines or pumped storage are often used where there is not enough hydroelectricity to respond to daily and weekly variations in generation and consumption. It is not unusual for a dam to be built with more capacity than can be sustained by the water supply, allowing for a higher peak output. Upgrading equipment at existing dams can be one of the least expensive ways of increasing peak generation. The ability to vary the amount of electricity generated is often limited by the requirement that minimum or maximum flows downstream are satisfied.