Steam turbines are a mature technology and have been used since the 1880s for electricity production. Most of the electricity generated in the United States is produced by steam turbines integrated in central station power plants, and steam turbines are also commonly used for combined heat and power (CHP) installations. There are 699 sites in the United States that are using steam turbines for CHP operation. These steam turbine CHP installations have an average capacity of 37 MW and a combined capacity of 26 GW, representing 32% of the total installed CHP capacity. The majority of these CHP steam turbines are at industrial plants, commercial buildings with high thermal loads, and district heating sites.