Systems in which combined production of electrical power and useful thermal energy is achieved by the sequential use of a fuel or fuels. The electrical power is produced by a generator that is most often powered by a prime mover such as a steam turbine, gas turbine, or reciprocating (piston) engine. Examples of useful thermal energy include hot exhaust gases, hot water, steam, or chilled water. Other names for cogeneration systems are combined heating and power (CHP), district heating, and total energy.