A traditional heat pump extracts heat from the air - even very cold air - and uses it to warm an interior space and then conversely pulls heat from the inside air and exports it to cool the space, a geothermal heating/cooling system. Operating on the same principals a thermal heat pump (or EGS, enhanced geothermal systems) takes an ancient concept and makes it feasible for use throughout the world.
Geothermal energy is a huge potential source of power from the earth's core. Nature exhibits this energy in the hot springs and geysers in places like Yellowstone Park, and vents it spectacularly in the form of volcanoes. The heat is generally thought to be generated by radioactive decay that goes on deep in the earth's crust.
This natural resource has been used for centuries - in ancient Rome the hot water and steam that exists near the surface was used to heat buildings and spas - and is used in a similar way today, most famously in Iceland where 89 percent of the homes are heated by geothermal means. Geothermal energy is also widely used in Japan, California, and New Zealand.
Directly tapping underground water is not a viable method of energy capture in most parts of the world where water does not exist close enough to the earth's surface. Even in Iceland there are several other methods used to extract and use the earth's heat. One (and this is a highly simplified description) is to pump water through injection wells to where it passes through the joints in hot rocks and is recovered, brought to the surface and converted to steam which is piped to steam turbines to generate electricity.
Icelanders not only heat and power their homes with geothermal energy, it is also used for fish farming, timber drying, animal husbandry, and most famously for its Blue Lagoon which draws tourists from all over the world to bath in its reportedly therapeutic waters.
The hot rocks method is also limited as to areas where sufficient heat exists close to the surface to make direct recovery economically feasible. However, the heat pump can be used to extract heat from the ground almost everywhere and is opening up geothermal energy to most of the world and its environmental benefits are enormous and we will talk about these benefits and EGS recovery in another article.