Useful Notes on “Geothermal Energy”

The word geothermal comes from the Greek words geo (earth) and therme (heat). So, geothermal energy is heat from within the earth. We can use the steam and hot water produced inside the earth to heat buildings or generate electricity. Geothermal energy is a renewable energy source because the water is replenished by rainfall and the heat is continuously produced inside the earth.

Geothermal energy is generated in the earth’s core, about 4,000 miles below the surface. Temperatures hotter than the sun’s surface are continuously produced inside the earth by the slow decay of radioactive particles, a process that happens in all rocks. The earth has a number of different layers (from inner to outer):

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i. The core itself has two layers: a solid iron core and an outer core made of very hot melted rock, called magma;


ii. The mantle which surrounds the core and is about 1,800 miles thick. It is made up of magma and rock; and

iii. The crust is the outermost layer of the earth, the land that forms the continents and ocean floors. It can be three to five miles thick under the oceans and 15 to 35 miles thick on the continents.

Most geothermal reservoirs are deep underground with no visible clues showing above ground. Geothermal energy can sometimes find its way to the surface in the form of:


i. Volcanoes and fumaroles (holes where volcanic gases are released)

ii. Hot springs and

iii. Geysers.

The most active geothermal resources are usually found along major plate boundaries where earthquakes and volcanoes are concentrated. Most of the geothermal activity in the world occurs in an area called the Ring of Fire. This area rims the Pacific Ocean.


When magma comes close to the surface it heats ground water found trapped in porous rock or water running along fractured rock surfaces and faults. Such hydrothermal resources have two common ingredients: water (hydro) and heat (thermal). Naturally occurring large areas of hydrothermal resources are called geothermal reservoirs.

Uses of Geothermal Energy:

Some applications of geothermal energy use the earth’s temperatures near the surface, while others require drilling miles into the earth. The three main uses of geothermal energy are:

Direct Use of Geothermal Energy:

The direct use of hot water as an energy source has been happening since ancient times. The Romans, Chinese, and Native Americans used hot mineral springs for bathing, cooking and heating. Today, many hot springs are still used for bathing, and many people believe the hot, mineral-rich waters have natural healing powers.

After bathing, the most common direct use of geothermal energy is for heating buildings through district heating systems. Hot water near the earth’s surface can be piped directly into buildings and industries for heat.

A district heating system provides heat for 95 per cent of the buildings in Reykjavik, Iceland. Examples of other direct uses include: growing crops, and drying timber, fruits, and vegetables.


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