Operation and Control of Renewable Energy Systems

Chapter 9Geothermal Energy

9.1 The Origin of Geothermal Energy

The geothermal energy is basically thermal energy stored in the Earth's crust. It is clean and sustainable. It is one of the less-recognized forms of renewable energy, and this is the only form of renewable energy which is not dependent on the Sun. Geothermal energy comes from the natural generation of heat primarily due to the decay of the naturally occurring radioactive isotopes of uranium, thorium and potassium within the Earth. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface and even deeper down to the extremely high temperatures of molten rock called magma. It is estimated that the annual energy due to the internal heat generation and flowing from the interior of the Earth to the surface is about 10²¹ J per year.

Geothermal energy has been used by the Romans, Japanese, Turks, Icelanders, Central Europeans and the Maori of New Zealand for bathing, cooking and space heating. Baths in the Roman Empire, the middle kingdom of the Chinese and the Turkish baths of the Ottomans were some of the early users of geothermal energy [1, 2].

Geothermal energy is present everywhere below the Earth's surface, but the most desirable resources are concentrated in the regions of active or geologically young volcanoes. Most geothermal reservoirs are deep underground with no visible sign of it available on the Earth's surface. But sometimes, geothermal ...