ABSTRACT

There is sufficient geothermal heat underground to serve the energy need of human society for a long time. Geothermal heat is also environmentally acceptable and dispatchable. A major issue is the viable, economical, and sustainable means to capture this energy. The temperature of geothermal energy generally increases with the depth underground, and its possible usages depend on the level of temperature. So far, most geothermal energy is recovered from low-depth hydrothermal sources which are generally at low temperatures. These sources can generate power with the use of organic Rankine cycle, although efficiency is not as large as the power generated from high-temperature sources. The present chapter describes in detail the use of ORC for geothermal power generation. The chapter points out that ORC can also be used for co and polygeneration. The use of Kalina binary cycle for power generation from low-temperature geothermal sources is also briefly evaluated. The chapter points out that, in principle, there are four other methods for geothermal heat recovery for power production. Enhanced geothermal systems require recovering heat from deeper but softer and wet sources. Generally, this is carried out at the depth of 3–5 km using advanced drilling and fracturing methods. This can be done anywhere in the world. Geothermal heat can also be recovered from super hot dry rock by fracturing it and recovering released heat. This is known as Super hot rock geothermal (HDR). This is also carried out at high depth. The third method is called advanced geothermal systems. This is a novel approach being pursued by Eavor company in Canada and the technique is called Eavor-loop. This is a closed loop and it uses deep and horizontal drilling technologies to generate loops undergrounds where heat recovering fluids are not in direct contact with the soil surroundings. This technique is in the development stage. The fourth method is to recover heat under supercritical and high enthalpy conditions. The chapter describes seven projects that are investigating this method of heat recovery. Finally, the chapter also examines the roles of supercritical CO2 cycle and nano technology on geothermal power generation.