What is Geothermal Energy?

The word geothermal comes from the Greek words geo (Earth) and therme (heat). Geothermal energy is heat from within the Earth.Geothermal energy is generated in the Earth’s core, almost 4,000miles beneath the Earth’s surface. The double-layered core is made up of very hot magma (melted rock) surrounding a solid iron center.Very high temperatures are continuously produced inside the Earth by the slow decay of radioactive particles. This process is natural in all rocks. Surrounding the outer core is the mantle,which is about 1,800 miles thick and made of magma and rock. The outermost layer of the Earth, the land that forms the continents and ocean floors, is called the crust. The crust is three to five miles thick under the oceans and 15 to 35 miles thick on the continents.
The crust is not a solid piece, like the shell of an egg, but is broken into pieces called plates. Magma comes close to the Earth’s surface
near the edges of these plates. This is where volcanoes occur. The lava that erupts from volcanoes is partly magma. Deep underground,
the rocks and water absorb the heat from this magma. We can dig wells and pump the heated, underground water to the surface. People around the world use geothermal energy to heat their homes and to produce electricity.
Geothermal energy is called a renewable energy source because the water is replenished by rainfall and the heat is continuously produced deep within the Earth. We won’t run out of geothermal energy.

Finding Geothermal Energy

What are the characteristics of geothermal resources? Some visible features of geothermal energy are volcanoes, hot springs, geysers,
and fumaroles. But you cannot see most geothermal resources. They are deep underground. There may be no clues above ground that a geothermal reservoir is present below.
Geologists use different methods to find geothermal reservoirs. The only way to be sure there is a reservoir is to drill a well and test the
temperature deep underground. 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 borders the Pacific Ocean.

Characteristics and Applications of Geothermal Energy

Geothermal energy is an enormous, underused heat and power resource that is clean (emits little or no greenhouse gases), reliable (average system availability of 95%), and homegrown (making us less dependent on foreign oil). Geothermal resources range from shallow ground to hot water and rock several miles below the Earth’s surface, and even farther down to the extremely hot molten rock called magma. Mile-or-more-deep wells can be drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface for use in a variety of applications.
The general characteristics of geothermal energy that make it of significant importance for both electricity production and direct use include:
  •   Extensive global distribution; it is accessible to both developed and developing countries.
  • Environmentally friendly nature; it has low emission of sulphur, CO2 and other greenhouse gases.
  • Indigenous nature; it is independent of external supply and demand effects and fluctuations in exchange rates.
  • Independence of weather and season.
  • Contribution to the development of diversified power sources.

Potential

It has been estimated from geological, geochemical, shallow geophysical and shallow drilling data it is estimated that India has about 10,000 MWe of geothermal power potential that can be harnessed for various purposes. Rocks covered on the surface of India ranging in age from more than 4500 million years to the present day and distributed in different geographical units. The rocks comprise of Archean, Proterozoic, the marine and continental Palaeozoic, Mesozoic, Teritary, Quaternary etc., More than 300 hot spring locations have been identified by Geological survey of India (Thussu, 2000). The surface temperature of the hot springs ranges from 35 C to as much as 98 C. These hot springs have been grouped together and termed as different geothermal provinces based on their occurrence in specific geotectonic regions, geological and strutural regions such as occurrence in orogenic belt regions, structural grabens, deep fault zones, active volcanic regions etc., Different orogenic regions are – Himalayan geothermal province, Naga-Lushai geothermal province, Andaman-Nicobar Islands geothermal province and non-orogenic regions are – Cambay graben, Son-Narmada-Tapi graben, west coast, Damodar valley, Mahanadi valley, Godavari valley etc.
  • Puga Valley (J&K)
  • Tatapani (Chhattisgarh)
  • Godavari Basin Manikaran (Himachal Pradesh)
  • Bakreshwar (West Bengal)
  • Tuwa (Gujarat)
  • Unai (Maharashtra)
  • Jalgaon (Maharashtra)
    courtesy: www.need.org, www.eai.in
    Posted by
    Mahesh ( MGIT ECE 4th yr)