Geothermics

Geothermal energy is the energy stored in the form of heat underneath the solid surface of the Earth. Enormous temperatures of up to 6,000 degrees Celsius reign in the Earth's interior, visible in volcanoes, hot springs and geysers. This warmth heats up layers of rock and soil as well as underground water reservoirs and can be used for providing heat, cooling, for generating electricity and for desalinating seawater. The constant warming of the Earth's surface by the sun can be used for heating purposes by means of heat pumps. Geothermal heat is particularly interesting when it comes to generating electricity as it is available at all times, irrespective of the season, weather or climatic conditions. Geothermal heat is one of the world's richest sources of renewable energy.

Technology
In order to make geothermal heat in deep layers of rock usable, a medium is required for transporting it to the surface. There are two basic options for this:

1. The medium is already available underground in the form of steam or hot water. This is brought to the surface by means of a borehole, is cooled off through use and then fed back in again.

2. There are hot rocks underground. In order to be able to extract heat from these, water is pumped down deep, where it is heated and brought up to the surface again (e.g. in so-called "hot dry rock" processes).

There are various technological developments available for using the energy to provide heat or to generate cooling or electricity. These include heat pumps, geothermal collectors, geothermal probes, energy piles and also concrete construction components that are in contact with the soil.

The principle of heat pumps is used daily in refrigeration engineering, with the difference that the heat which arises incidentally during the cooling process is released as waste into the environment. The heat pump uses heat from various media (e.g. soil or water). It cools these and transfers the heat which arises to the heating system. The action of the heat pumps is based on applying the physical principle that liquid absorbs heat when evaporating and then releases it again when it changes back from a gas into a liquid. The refrigerator developed by Carl von Linde over 100 years ago used this very principle. During the cooling process, the heat inside of a cold room is absorbed via a cooling agent acting as a medium and is pumped out. The heat pump uses the "refrigerator principle" in the opposite direction - it takes heat that is circulating outside of a house and pumps it into the closed living areas. Energy is needed to compress the cooling agent - approx. four kilowatt hours of heat can be extracted with one kilowatt hour of electrical energy. The yields fluctuate depending on the capacity of the system and the ratio between the internal and external temperatures. The lower the temperature is in the heating system itself and the higher the average temperature is in the heat source that is being tapped the better (source: www.hol-dir-die-sonne-ins-haus.de).

Domestic sector
Sales of heat pumps in Germany rose in 2006 to around 28,000 systems, some 60 percent more than in 2005 (source: AGEE-Stat, as of April 2007). In total, almost two billion kilowatt hours of heating energy were provided from geothermal energy in 2006 (source: AGEE-Stat/Federal Ministry of the Environment). The largest plants are in Neubrandenburg, Waren/Müritz, Neustadt-Glewe (all in Mecklenburg-Western Pomerania), Erding and Straubing (Bavaria). The generation of electricity from geothermal energy has been limited to a single power plant in Neustadt-Glewe to date which came into operation at the end of 2003. It brings hot water with a temperature of around 97 degrees Celsius up from a depth of 2,250 meters for electricity and heat generation. The power plant has an output of up to 230 kilowatts (source: Erdwärme-Kraft GbR). In 2006, the amount of electricity generated from geothermics in Germany was around 400,000 kilowatt hours (source: AGEE-Stat/Federal Ministry for the Environment). GeoForschungsZentrum Potsdam, Germany's National Research Centre for Geosciences in the Brandenburg city of Groß-Schönebeck, is working on making geothermal energy sources in the lowlands of northern Germany usable for electricity generation. New procedures for tapping deep sandstone in a 4,300-metre deep former gas borehole are being developed. In order to prove that this reservoir will be suitable for operating geothermal energy power plants, a second borehole was drilled at the beginning of May 2006. This was supported by the Federal Ministry for the Environment and the state of Brandenburg.

International markets
Across the globe, plants with a capacity of around 28 GW were installed for the direct use of geothermal energy in 2005 (source: RWE AG). Together, they have supplied more than 70,000 GW hours of thermal energy. In addition to this, there is some eight GW of installed capacity for electricity generation. The most important countries are China, Sweden, the USA, Iceland, Turkey, Hungary, Italy, New Zealand and the Philippines.