Chapter 9 - Geothermal energy

Abstract

Geothermal energy is natural energy in the form of heat that is produced and preserved within the Earth. The term “geothermal energy” is taken from the Greek words, “geo” and “therme”—earth and heat respectively—whereas “energos” means active. Hence, the overall term may be referred to as the movement of active heat energy within the Earth. The temperature of the Earth increases with its depth and this geothermal gradient allows continuous heat conduction from the Earth’s core to the surface. This is also called “terrestrial heat-flow.” If the heat flow rate is high and energy extraction is economical, then humans can utilize this heat for multiple purposes, that is, electricity generation, heating, and agriculture use. The average heat flow to the surface of the Earth is 50mW/m2. The temperature increase 25°C–30°C with every kilometer of the Earth’s depth, with some regions having this gradient as high as 150°C. It is the only source of energy that can be used to supply baseload or dispatchable power without weather constraints. Due to the increasing demand for switching to clean energy production, the need for research and development in engineered geothermal systems is becoming critical. Recently the development in geothermal systems has enabled the elimination of the need for natural hydrothermal resources. It can be done by fracturing the subsurface rocks and injecting water. The water is heated when it comes in contact with the rocks, and production wells are then utilized to send it to the surface.