<P> The initially developed reciprocating steam engine has been used to produce mechanical power since the 18th Century, with notable improvements being made by James Watt . When the first commercially developed central electrical power stations were established in 1882 at Pearl Street Station in New York and Holborn Viaduct power station in London, reciprocating steam engines were used . The development of the steam turbine in 1884 provided larger and more efficient machine designs for central generating stations . By 1892 the turbine was considered a better alternative to reciprocating engines; turbines offered higher speeds, more compact machinery, and stable speed regulation allowing for parallel synchronous operation of generators on a common bus . After about 1905, turbines entirely replaced reciprocating engines in large central power stations . </P> <P> The largest reciprocating engine - generator sets ever built were completed in 1901 for the Manhattan Elevated Railway . Each of seventeen units weighed about 500 tons and was rated 6000 kilowatts; a contemporary turbine set of similar rating would have weighed about 20% as much . </P> <P> The energy efficiency of a conventional thermal power station, considered salable energy produced as a percent of the heating value of the fuel consumed, is typically 33% to 48% . As with all heat engines, their efficiency is limited, and governed by the laws of thermodynamics . Other types of power stations are subject to different efficiency limitations, most hydropower stations in the United States are about 90 percent efficient in converting the energy of falling water into electricity while the efficiency of a wind turbine is limited by Betz's law, to about 59.3% . </P> <P> The energy of a thermal power station not utilized in power production must leave the plant in the form of heat to the environment . This waste heat can go through a condenser and be disposed of with cooling water or in cooling towers . If the waste heat is instead utilized for district heating, it is called cogeneration . An important class of thermal power station are associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas and in these plants, freshwater production and electricity are equally important co-products . </P>

Fuel and ash circuit in thermal power plant