ABSTRACT
Geothermal energy is renewable heat energy from deep in the earth which is generated in many places, such as hot spring areas. Geothermal power generation based on geothermal energy is quite attractive, even compared with other renewable energies, because the energy is hardly affected by weather, thus allowing a stable energy supply. For example, there are currently 18 operational geothermal power plants in Japan, providing 0.2% of total electricity supply. Since geothermal energy is a renewable resource with very low CO2 emissions, electricity providers are planning to construct several more geothermal power plants in the next decade, to increase the contribution up to 1% of electricity supply (Yoshizuka et al., 2010).
