Power is energy per cycle. The power or capacity of a power plant can be expressed in units of megawatts of electricity (MWe). As a percentage of the value of heating oil produced on factory buses as marketable energy (in MWe), the electrical efficiency of a standard power plant is considered an efficiency of 33% to 48%. This efficiency is limited because all heat engines obey the laws of thermodynamics (see: Carnot cycle). The remaining energy must leave the plant in the form of heat. This waste heat can be removed by passing it through a cold water tank or cooling tower. If the waste heat is used for district heating, it is called combined heat and power generation. An important part of power generation is related to salt generation; These are usually located in desert countries with high natural gas reserves, and the production of clean water and electricity in these plants is an equally important product.
Since generating efficiency is essentially limited by the ratio of absolute steam temperature at the turbine inlet and outlet, increasing efficiency requires the use of high temperature and high pressure steam. In the past, other fluids such as mercury were used for testing in mercury steam turbine power plants because they can reach higher temperatures than water at lower operating pressures. However, the obvious risk of toxicity and poor heat transfer properties have eliminated mercury as a liquid.