Thermal energy is generated and measured by heat of any kind. It is caused by the increased activity or velocity of molecules in a substance, which in turn causes temperature to rise accordingly. There are many natural sources of thermal energy on Earth, making it an important component of alternative energy.

The laws of thermodynamics explain that energy in the form of heat can be exchanged from one physical object to another. For instance, putting fire under a pot of water will cause the water to heat up as a result of the increased molecular movement. In that way, the heat, or thermal energy, of the fire, is partially transmitted to the water.

Understanding the principles of thermodynamics has allowed human beings to harness natural sources of heat to create thermal energy out of a variety of sources. The sun, ocean, and geothermal sources such as geysers and volcanoes, can all be sources of thermal energy. As humans attempt to turn to sustainable forms of alternative energy instead as fossil fuel resources become depleted, much attention has been focused on improving methods of harnessing thermal energy to power human activity.

Solar thermal power is one of the most commonly used forms of thermal energy. Although gathering solar power is only available when the sun is visible in the sky, scientists have developed many different ways of storing and utilizing the power absorbed by solar devices. On a small level, a person can heat his or her pool by placing low-temperature collecting systems in or around the water. By absorbing sunlight and distributing it to the water, the temperature is increased throughout the day and even after the sun has set. Solar panels, evaporation pools, and other advanced systems can perform this function on a much more wide-spread level, creating enough stored power to run a factory or even city on solar thermal power.

The Earth is constructed around a molten core of incredible heat that lessens considerably as it reaches the surface or crust level. Yet by harnessing some of the heat generated below the surface of the planet, humans can extract enormous amounts of energy. The simplest way to do this is through geothermal energy sources such as geysers, or at the boundaries of tectonic plates. Geothermal wells pump out energy in the form of hot water or steam that can be converted into usable energy, or simply used directly.

Thermal energy is an awesome force that is just beginning to be fully understood. By creating new devices and methods to concentrate, store, and transport naturally-created thermal energy, human beings can reduce dependence on non-sustainable forms of energy. Thanks to the power of heat, hot baths, boiled water, and thermally-powered cities are all possible.