Origin and Types of Geothermal Energy

1. Million’s year ago, the planet earth’s formation took place from gravitational collapse of the sun. The earth’s interior having the mass of hot liquids, gases and steam is cooling slowly and the temperature of the earth’s core is estimated to be about 4000°C.
2. As the fluids are cooled by loosing heat, the outer solid crust of about 30 km depth, ocean, lakes were formed. The average geothermal heat dissipation from land is about 0.06 W/m² as compared to solar heat energy of 1 kW/ m².
3. Below the solid crust is the molten mass called magma which is still in the process of cooling. The earth’s tremors, caused the magma to come closure to earth’s surface in certain places and the crust fissures were opened up.
4. The hot magma near the earth surface thus causes active volcanoes, hot springs and geysers where water exists. It also causes steam to vent through the fumaroles.
5. Figure shows the typical geothermal field. The hot magma near the surface (1) solidifies into igneous rock (2) The heat of magma is conducted upwards into this rock.
6. The ground water that finds its way down to this rock through fissures in it will be by the heat of the rock or by mixing with hot gases and steam emanating from the magma. The heated water will then rise upwards by convection into a porous and permeable reservoir (3) above the igneous rock (2).
7. It is covered by the layer of solid impermeable rock (4). It traps the hot water in the reservoir called hydrothermal field.
8. However, the solid rock (4) has the fissures (5). It acts as vents of this giant hydrothermal field which acts as underground boiler. The vents show up as geysers fumaroles (6) or hot springs (7).
9. A well made by drilling hole in the upper crest in the region of geothermal field can be used to trap steam for use in a conventional power plant. The steam originating from magma is called meteoritic steam which is the largest source of geothermal steam.

The types of geothermal energy resources are :

1. Hydrothermal
2. Hot dry rock (HDR)
3. Geo-pressurised
4. Magma

However, only the hydrothermal energy is being presently utilized since the technology for commercial utilization of other geothermal energy sources is not available.