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Geothermal Energy is low –temperature heat (compared to energy from soil, sandstone and underground water in thermostat layer) reserved under the surface layer formed under the combined effect of solar energy and heat energy from the earth’s core. There is no big change to the temperature of the thermostat layer in different seasons or regions: slightly lower in winter and slightly higher during the summer. It is always under 25℃, which is the result of the combination of solar energy and the heat energy of the earth’s core. As indicated by geological surveys, due to the great influence of heat energy of the earth’s core, there is temperature gradient under the thermostat layer. Temperature will increase by 3-4℃underground for every 100 meters in depth underground. However, solar energy has great influence and top 100 meters below the earth's surface can be exploited to harvest the geothermal energy stored within. Chart 1 is schematic view of shallow geothermal energy.
Balance of shallow geothermal energy is indicated by chart1. Shallow geothermal energy is regenerative energy which mainly uses the indirect solar energy. 30% of solar energy is reflected by cloud layer and the earth’s surface.15% is absorbed by the cloud and the rest absorbed by land and sea. In this way, the thermostat layer is formed in the 100 meters under the surface layer. However, the absorbed solar energy is released to the atmosphere and space in different forms.
Indicated by chart 2, every year radiation from sun amounts to the heat released by 95000 billion tons of raw coal, which is 6500 times of the energy consumption of the world in 2004. The radiation is the major supply source of the shallow geothermal energy in underground 400 meters.
Chart3 indicates that shallow geothermal energy is mainly reserved in the thermostat layer ( in 400 meters underground ) under which heat energy of the earth’s core starts to make great influences. This is not included in the geothermal energy.
Shallow geothermal energy features in rich reservation, swift regeneration, wide distribution, constant temperature in the whole year and inexhaustible. It is a huge treasury of green energy.
