In engineering, energy conversion is any process of converting energy from one form to another. Energy found in fossil fuels, solar radiation, or nuclear fuels needs to be converted into other energy forms such as electrical, propulsive, or cooling to be useful. Machines are used to convert energy from one form to another. The efficiency of a machine characterizes how well it can convert the energy from one form to another.

Energy is converted so that it may be used by other machines or to provide an energy service to society. An internal combustion engine converts the chemical energy in the gasoline to the propulsive energy that moves a car. A solar cell converts the solar radiation into the electrical energy that can then be used to light a bulb or power a computer.

The steam engine illustrates the energy conversion process. In a steam engine, burning coals heat water (the fluid), which expands and moves a piston. The water is then cooled and once again brought near the hot coals in a cycle that keeps the steam engine moving. The steam engine uses the temperature difference between the hot and cold water to move the piston. This conversion is never perfect, and some of the energy of the burning coals is lost as heat. Only the exergy part of energy can be converted without limitations. The operation of the steam engine is described from an energy perspective by the machine cycles of thermodynamics, from the fluid flows by fluid mechanics, and from the heat flow by the science of heat transfer.

Energy conversion machines

There are many different machines that convert one energy form into another:

• Alternator,
• Fuel cells,
• Geothermal power,
• Heat engines, such as the internal combustion engine used in cars or the steam engine,
• Hydroelectric dams,
• Jet engine,
• Nuclear reactor,
• Nuclear fusion,
• Ocean thermal power,
• Solar cells,
• Solar thermal,
• Steam engine,
• Wave power,
• Windmills

See also

• Energy economics,
• Energy storage,
• Renewable energy