Geothermal Energy: The Energy of the Future?

Abstract

In general terms, geothermal energy is the thermal energy stored in the Earth’s crust. Geothermal energy is used nowadays to indicate that part of the earth’s heat that can be recovered and exploited by man. The total heat flow through the surface of the Earth has been calculated by several authors. The total value obtained by Jaupart et al (2007) is 46 X 1012W. The estimate for continental heat loss is 14 X 1012W, and for the heat loss through the oceans they found 32 X 1012W. The thermal energy of the Earth is immense, but only a fraction can be utilized by mankind. Geothermal energy can be used in two main applications. The first is on a large scale – generating electricity by injecting water into a geothermal heat source and using the resulting steam to drive turbines. The second is on a building or household scale: using a loop of tubing that goes into the ground, to extract heat from the house and pump that heat into the ground, or to extract heat from the ground and pump it into the house. Installed geothermal electric capacity at 2005 was 9064 MWe. Worldwide direct utilization of geothermal energy in 2005 was 273 372 X 1012 J/year (Lund et al,2005). The number of countries with direct uses has increased since than, as well as total installed capacity and energy use. The distribution of thermal energy by category was 32% for geothermal heat pumps, 30% for bathing and swimming, 20% for space heating and 18% for other uses. Unlike fossil fuel power plants, no smoke is emitted from geothermal power plants; only steam is emitted from geothermal facilities. Emissions of nitrous oxide, hydrogen sulfide, sulfur dioxide, particulate matter, and carbon dioxide are extremely low, especially when compared to fossil fuel emissions. The binary geothermal plant, along with the flash binary plant, produce near zero air emissions. Even dry steam plants, which are considered to have the highest levels of air emissions, are considered environmentally benign, compared with fossil fuels. Noise from normal operation of geothermal power plants comes from cooling tower fans and is very low, A variety of noise muffling techniques and equipment are available for geothermal facilities. Geothermal heating and cooling using geothermal pumps only causes pollution to the extent that the electricity source required to run a geothermal heat pump may come from a polluting source such as coal or oil. However the amount of electricity used for geothermal heating and cooling is typically about a quarter the electricity that would be required to heat or cool the same place with electrical heaters and conventional air conditioning.