Thermal Structure of the Earth
The term “renewable energy” is used for a source of energy from a reservoir that can be restored on a “short time scale” (in human time scales). Renewable energy includes geothermal energy and several forms of solar energy such as bio-energy (bio-fuel), h
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Thermal Structure of the Earth
Island of Vulcano, southern Italy
I. Stober and K. Bucher, Geothermal Energy, DOI: 10.1007/978-3-642-13352-7_1, © Springer-Verlag Berlin Heidelberg 2013
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1 Thermal Structure of the Earth
1.1 Renewable Energies, Global Aspects The term “renewable energy” is used for a source of energy from a reservoir that can be restored on a “short time scale” (in human time scales). Renewable energy includes geothermal energy and several forms of solar energy such as bio-energy (bio-fuel), hydroelectric, wind-energy, photovoltaic and solar-thermal energy. These sources of energy are converted to heat or electricity for utilization. An example: The “renewable” aspect of burning firewood in a cooking stove lies in the relatively short period of time required to re-grow chopped down forests with solar energy and the process of photosynthesis. In contrast, it will take much more time to “renew” coal beds when burning coal for the same purpose, although geological processes will eventually form new coal beds. The “renewable” aspect of geothermal energy will be explained and discussed in detail in this chapter. The International Geothermal Association (IGA) wrote in a recent press release on “Renewable Energy Policy Network for the 21st Century” that the global production of renewable energies increased by 16 % from 2007 to 2008 and amounts to a total of 280 GW (IGA 2009; www.geothermal-energy.org). The growth in renewable energy consumption is larger than the increase in fossil fuel consumption in Europe and the US. Political and financial programs support the development and use of renewable energies in more than 60 countries. Large hydroelectric systems had the largest share in electricity production from renewable energy sources in 2008 with 860 GWel followed by wind energy with 121 GWel, small hydroelectric systems with 85 GWel and biomass conversion with 52 GWel. Photovoltaic systems (13 GWel) and geothermal systems (10 GWel) follow with a large gap. Thermal energy production from renewable sources is dominated by biomass (250 GWth), followed by solar thermal systems (145 GWth) and geothermal systems (50 GWth) (Bertani 2007, 2010). Geothermal energy has the potential to become a significant source of energy in the future because it is available everywhere and withdrawals are continuously replenished. From a human perspective the resource is essentially unlimited. Heat and electricity can be continuously produced and therefore it is a base load resource. The utilization is friendly to the environment and the land consumption for the surface installations is small. The coming years will show how the optimistic expectations and the positive perception of geothermal energy utilization will succeed in regions with low-enthalpy geothermal resources.
1.2 Internal Structure of the Earth Geothermal energy is the thermal energy stored in the Earth body, geothermal energy is underground heat. 99 % of the Earth is hotter than 1,000 °C and only 0.1 % is colder than 100 °C. The average temperature a
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