Energy from Heat

Energy means power—the power to do work. And thermal, or heat, energy can do a lot of work. When heat is applied to water, for instance, it makes the water boil. Boiling water then changes to vapor, or steam, which can apply great force as it escapes a container. Large quantities of steam powered the earliest train engines.
The most important source of thermal energy for our Earth is the Sun’s rays. This “solar energy” is used to heat houses, water, and, in some countries, ovens used for cooking. Solar power can even be converted to electricity and stored for later use.
To human beings the second most important source of thermal energy is the store of natural fuels on and in the Earth. When these fuels—mainly coal, oil, gas, and wood—are burned, they produce heat. This heat can be used for warmth, made to power a machine directly, or converted into electricity. For example, a car engine burns gasoline (an oil product) for direct thermal power. In some areas coal is burned to produce the electricity that powers people’s homes.
In a very few parts of the world, an interesting third form of heat energy comes from “living” heat inside the Earth itself. This “geothermal energy” comes from such sources as natural hot springs and the heat of active volcanoes (“geo-” means “earth”). Naturally escaping steam and hot water are used to heat and power homes and businesses in Reykjavik, Iceland. And though volcanoes are mostly too hot to tap directly, worldwide experiments continue as other major fuel supplies dwindle.