A thermal power station is a power station in which heat energy is converted to electric power. In most of the places in the world the turbine is steam-driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle.
The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use coal, while others turn to natural gas, nuclear power, solar energy or geothermal energy. Almost all coal, nuclear, geothermal, solar thermal electric and waste incineration plants, as well as many natural gas power stations are thermal. Natural gas is frequently combusted in gas turbines as well as boilers. The waste heat from a gas turbine, in the form of hot exhaust gas, can be used to raise steam by passing this gas through a heat recovery steam generator (HRSG) or heat exchanger. This is called a Combined Cycle Power Plant.