Geothermal Energy introduction

GEOTHERMAL ENERGY:

Geothermal comes from Greek words Geo meaning earth and thermal meaning heat. Geothermal energy is primarily heat energy from earth's own interior. 

INTRODUCTION: It is classified as renewable because it comes from the earth's interior which is almost inexhaustible as like solar and wind energy, so long as its sources are actively sought and economically tapped. As we travel down earth's surface radially, there exists a temperature gradient of 0.03 deg c per meter. Thus a 30 deg c increase in temperature can be obtained per km depth from the earth crust. There are many local hot spots just below the surface where the temperatures are much higher than expected. Ground water, when comes into contact with hot spots, either dry or wet steam is formed. By drilling holes to these locations, hot water and steam can be tapped and these can be used for power generation or space heating. 

Heat transfer from the earth's interior is by three means 1. Direct heat conduction 2. Rapid injection of ballistic magma along natural rifts penetrating deep into earth's mantles. 3. Bubble like magma that buoys upwards towards the surface.

IMPORTANT ASPECTS OF GEOTHERMAL ENERGY 

FORM OF ENERGY Thermal energy in the form of hot water, steam, geothermal brine, mixture of these fluids. 

AVAILABILITY Generally available deep inside the earth at a depth more than about 80 km. Hence, generally not possible to extract. In a few locations in the world, deposits are at depths of 300 to 3000 m. Such locations are called geothermal fields. 

METHOD OF EXTRACTION: Deep production wells are drilled in the geothermal fields. The hot steam/water/brine is extracted from the geothermal deposits by production wells, by pumping or by natural pressure. 

GEOTHERMAL FLUIDS Hot water Hot brine Wet steam Mixture of above 

RANGE OF GEOTHERMAL POWER PLANTS INSTALLED CAPACITY 5 MW to 400 MW 

AVERAGE GEOTHERMAL GRADIENT 30 deg c  per 1000 m length 

GEOTHERMAL ENERGY RELEASED THROUGH EARTH'S CRUST About 0.06 W/m 

TOTAL GEOTHERMAL RESERVES IN THE EARTH 4x(10^15) MJ (estimated) 

RATE AT WHICH THE RENEWABLE ENERGY CAN BE TAPPED FOR PRODUCTION OF ELECTRICITY 2x10^12 to 10x10^12 MJ/year (estimated) 

TYPES OF GEOTHERMAL ENERGY DEPOSITS 

Hydro thermal: hot water and steam, hot brine. 

Petro thermal: hot dry rock (HDR)