Geothermal energy utilizes the energy present in the geothermal gradient (i.e) the difference in the energy level between earth's core and surface. The immense heat of the earth's core is due to the radioactive decayed which could produce heat up to 4000 degree Celsius. The geothermal energy is extracted by sweeping cold water in to the core of the earth where it will get heated up and converted in to stream. This stream is then propelled out of the earth crust with high speed, which is used to rotate the turbine in order to produce electricity. The heated stream is then cooled down and sent back to earth's core again.