The German geothermal energy industry
The available geothermal energy in the Earth’s crust originates mainly from radioactive decay and is a remnant from the time of our planet’s formation. A portion of the sun’s energy is also stored in the uppermost layers (up to 2 m deep) and adds to the ground temperature. Already in many countries around the world, geothermal energy is being used to generate electricity or to directly supply heating networks with heat. The ecological and economical advantages of geothermal are particularly clear in regions where the geological conditions are especially favourable (i. e. regions of volcanic activity, temperatures > 200 °C). In countries such as Germany, Italy, Indonesia, Mexico and the USA geothermal energy has been an integral part of energy concepts for years now. Aside from making efficient use of available high temperature regions, the German geothermal industry places a lot of emphasis on technologies which can work efficiently at lower temperature ranges (approx. 120 – 200 °C).
An overview of the technology
Geothermal activities generally fall into two categories; deep geothermal energy and sub-surface or shallow geothermal energy. Shallow geothermal energy is perfect for cooling and heating buildings. Through deep geothermal on the other hand, electricity can be generated by power stations and heat can be fed directly into heating networks for industrial applications or to heat buildings.
Deep geothermal energy is further subdivided into hydro-geothermal or HDR systems and deep bore hole heat exchangers.
In hydro-geothermal energy, high temperature water is tapped at great depths from subsurface reservoirs. Depending on the temperature, hydro-geothermal energy can be used for heat or electricity generation.
The HDR (hot dry rock) process utilises the geothermal energy in the hot dry rock deep underground (approx. 3,000 to 7,000 m) where there are little or no natural sources of water. In this process, water is circulated via a deep borehole through a system of fissures created in a controlled manner. Through a second borehole, the hot water is returned to the surface as steam, where it drives a turbine to generate electricity or is alternatively fed into the heating network.
In order to effectively utilise lower temperature ranges German companies offer a wide range of solutions. As well as the Kalina Cycle, the ORC (Organic-Rankine Cycle) also offers good conditions for the utilisation of low temperatures between 120 and 200 °C in electricity production. Downstream integration of such systems can considerably increase returns from high-enthalpy locations.
Shallow geothermal energy uses energy obtained from the uppermost layers of the Earth at depths of up to 400 metres. Average temperatures range from seven to twelve degrees Celsius in the first 100 to 150 metres below the surface. Heat pumps, geothermal heat collectors, borehole heat exchangers, energy piles or ground-contact concrete structures are used in order to take advantage of this energy in the shallow subsurface. Heat pumps are used to increase these low temperatures to levels which are of use inside buildings. This is done by extracting ground heat in a cyclic process.
If heat pumps are by-passed the constant temperatures present below the surface can also be used to cool buildings. If the ground is not able to provide adequate cooling, heat pumps can be operated in the opposite direction thus providing support for cooling.
Geothermal heat collectors are normally laid horizontally at a depth of 80 – 160 cm and are subject to local climatic conditions at the surface. A heat transfer medium flows through the collectors, which take heat from the ground.
Borehole heat exchangers are the most common type of system in Central and Northern Europe. They are used in shallow, sub-surface applications at a depth of between 50 and 400 metres. The area required is small and they use a constant temperature level. Synthetic piping is laid, which is integrated with the circuits and connected with the cooling and heating system of the building. This is then used to circulate a heat transfer medium, which takes heat from the surroundings and transfers it to the heat pumps.
In energy piles, deep concrete piles, diaphragm walls or other static, subterranean structures are fitted out with synthetic piping that utilise the geothermal heating and cooling, using water as the main medium. The cold water is warmed in the concrete piles by the geothermal heat. The warm water, interconnected with the heat pump, heats the building. Through a simple reversal, the system can be used in summer for cooling.
Market developments in Germany and abroad
Around the world, more than 33,000 MW of geothermal power are set up in more than 75 countries. A large part of installed systems are currently used for heat generation. More than 10,000 MW of electric energy are provided by geothermal power stations.Iceland, with its excellent geological conditions, gets a quarter of its energy needs from geothermal.
German systems generally utilise deeper geothermal energy for the production of heat but also for co-generation; the production of heat and electricity. For example a geothermal power station in Landau produces an electrical output of 3.0 MW and a thermal output of 6 – 8 MW. This power station produces electricity for around 6,000 households and heat for 300. Numerous other projects have also been planned or are currently under way in construction. There are currently around 150 prospecting fields for geothermal electricity production.
Around 28,500 geothermal heat pumps were sold in 2006, allowing commercial and residential property to be efficiently provided with heat supply.
The basic conditions for making use of geothermal energy
Shallow geothermal energy can be utilised in many regions around the world and is perfect for residential and commercial property applications.
Aside from favourable geological conditions, deep geothermal projects require stable political conditions too. Questions concerning bore holes and the use and return of extracted thermal water are of particular relevance.
Electricity generation by geothermal power station requires a clearly defined legal framework to cover the supply of national grid networks with electricity – this is of particular importance.
In Germany, electricity production from geothermal sources is dependent on plant sizes laid down by the EEG or Renewable Energy Laws. Aside from reimbursement for supplying electricity to grid networks, plant operators can also benefit from a state loan at favourable interest rates. The German government supports the installation of environmentally friendly heat pumps in private houses with a market initiative programme.
Outlook
Geothermal energy is available around the clock and is not subject to seasonal changes, the weather or climatic conditions. Geothermal energy is increasingly becoming a hot topic in political discussions concerning the future of our energy supply. Against a background of climbing fossil fuel prices, the long-term, secured availability of geothermal energy together with a flexible range of possible applications such as heating, cooling and electricity generation, is ensuring that an ever increasing number of plants are being built worldwide. Alone in the heating sector, an annual increase of 20 % to 30 % is expected in installed capacity.
Heat pump applications concerning commercial and residential property are becoming ever more attractive because, when used together with geothermal energy, heat pumps can both heat and cool. An optimal configuration of heat pumps can improve room climate and provide considerable savings in heating and cooling costs.
German specialists for large-scale, geothermal applications are listed on the following pages. You will also find information on companies which have many years experience in constructing and installing heat pumps.
