A heat source is any area, object or mechanism that creates heat. Heat is generated by the movement of energy from one area to another, whether it is in the same structure or separate ones. There are a number of heat sources that exist in nature, from the sun to the Earth's core, and some that are completely manmade. The most common use for a heat source is the commercial production of electricity.
Earth has a variety of natural heat sources available for use. One advantage to using a natural heat source is that no energy needs to be expended to create or maintain the heat. Another benefit is that natural heat sources tend to be either very long-lived or functionally infinite in their production of heat. The drawbacks can include inconsistent supply levels and complex or expensive requirements for capture. Different types of heat sources on Earth, however, are convenient, because they are accessible in nearly every area.
A geothermal heat source is under the surface of the Earth, where they may be found at incredibly high temperatures. These sources are a result of residual heat from the creation of the planet and new heat generated by the movement of the tectonic plates. Steam geysers are an example of geothermal heat that can be captured and used. The Earth itself is very warm under its surface, so digging down far enough will reach an area of intense heat that also can be harnessed.
The sun is another natural heat source. Both powerful and renewable, it is the primary provider of warmth to the planet. Through the use of solar panels, solar heat energy can be used to directly generate electricity. Large, focused mirrors can be used to concentrate the heat on certain areas to drastically increase the temperature of large amounts of water or gas. Disadvantages of solar heat include being unable to produce energy when there is heavy cloud cover and at night.
There also are alternative heat sources that exist but are not in widespread use. Heat-producing bacteria that are a natural part of the environment can be used. These bacteria decompose organic matter and through a biochemical process create heat as they grow and reproduce.
Manmade heat sources also are available. One of the most well known is a nuclear heat source. By refining specific compounds into a very pure form or creating substances that do not occur naturally, radioactive elements can be formed. The transfer of energy as the atoms decay causes a great amount of heat to be released. This heat is used to generate steam that operates turbines and creates electricity.