The German geothermal energy industry
Geothermal energy can be used to heat and cool buildings, as well as for industrial and agricultural purposes. It is particularly interesting for electricity generation, as the source is available around the clock, independent of the season, weather or climatic conditions.
The technology at a glance
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
so-called HDR (hot dry rock) process utilises the geothermal energy in the hot dry rock deep underground. In this process, water is circulated via a deep borehole through a natural or newly created system of cracks and crevices. 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. Due to the extremely high temperatures, HDR systems have a higher level of efficiency than other geothermal processes. The cost-effectiveness of such a system depends on the type of rock and its permeability. Sample calculations indicate that using the HDR process can bring electricity generation costs down to around ten cents/kWh. Geothermal energy in this form is generally still in the testing phase, but is already being used in practice to a limited extent.
Shallow geothermal energy uses energy obtained from the uppermost layers of the earth at depths of up to 200 metres. In order to utilise temperatures of eight to twelve degrees Celsius in the shallow subsurface, heat pumps, geothermal heat collectors, borehole heat exchangers, energy piles or ground-contact concrete structures are used.
Heat pumps are employed to make optimal use of the low temperature levels of geothermal energy near the surface. For example, heat pumps can use the environmental heat in the ground in close proximity to houses. In a circuit process, heat is taken from the ground and made usable for heating and water heating. Running the process in the reverse direction can also provide cooling in the summer. What is more, the principle is applicable at low temperatures too; even ground temperatures of 0 degrees Celsius allow for the use of heat pumps. Power is required for operating the heat pumping process. A medium (brine, water or air) circulates in a piping system and extracts heat from the surroundings through pressure change and changes to the condition of aggregation. A refrigerator, for instance, functions on the same principle, though in the opposite direction. It takes heat from its interior, emits this heat to its surroundings and thus provides the desired cooling in the interior.
Running the process in the reverse direction can also provide cooling in the summer. The principle is also applicable at low temperatures; what is more, even ground temperatures of zero degrees Celsius allow for the use of heat pumps. Heat pumps are suitable for combination with solar thermal systems (refer to the brochure “Renewables made in Germany: solar thermal – biogas – solid biomass and biofuels”). Energy costs incurred during the operation of the heat pumps are up to 60 % below those of other heating systems for the same heating requirement. Since the majority of the heat provided through the heat pumps is derived from renewable energy, energy resources and the environment are preserved.
Geothermal heat collectors are normally laid horizontally at a depth of 80 – 160 cm. A heat transfer medium flows through the collectors, which take heat from the ground. They are subject to the effects of the prevailing weather conditions on the surface. A heat pump is therefore forced, when combined with a geothermal heat collector, to manage with particularly unfavourable heat-source temperatures when heat requirements are at their greatest.
Borehole heat exchangers are the most common type of system in Central and Northern Europe. They can be laid at a depth of between 50 and 400 metres; for private households however the average depth is up to 100 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 or diaphragm walls 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.
Development in Germany
Geothermal energy in Germany currently contributes 630 megawatts (MW) of thermal energy and 0.23 MW of electrical energy to overall energy production. Worldwide thermal capacity exceeds 28,000 MW. Some EUR 250 million was invested in Germany in 2005 to increase the use of geothermal energy. According to the German heat pump association (Bundesverband Wärmepumpe), a total of some 44,000 heat pumps were sold last year, meaning that sales more than doubled in 2006. For 2007 too, there are indications of strong consumer interest throughout Europe for this cost-effective and environmentally friendly energy source.
The use of hydro-geothermal energy for heating and electricity generation has been successfully tested for many years in Germany, in Neustadt-Glewe (Mecklenburg-Western Pomerania). In May of this year, the foundation stone for the first industrial geothermal energy plant in Germany was laid in Landau in the south of the German federal state of Rhineland-Palatinate. From October on, the plant will supply power for some 6,000 households and local heating for 300 households. Additional projects are being planned or are currently in the construction phase. There are presently around 100 prospective sites for geothermal power supply.
Regulatory framework
The realisation of deep-geothermal research projects requires continuous research funding and a stable political regulatory framework.
Depending on the plant size, electricity generation from geothermal energy in Germany is funded under the German renewable energy sources act (EEG). In addition to the feed-in compensation, plant manufacturers can also make use of state support in the form of a loan at reduced rates of interest.
Through its Market Incentive Programme, the German federal government supports the installation of environmentally friendly heat pumps in private dwellings. The renewable heat legislation planned by the government will initiate a further investment drive. More citizens may decide to install heat pumps through the introduction of a bonus programme, by which a subsidy is paid for environmentally friendly heat production via a small surcharge on fuel oil and gas. A directive for the promotion of renewable heat is currently being negotiated at EU level.
In many countries governments are financing information campaigns and successfully fostering support for heat pump technology. The development of shallow geothermal energy also requires intensive public relations work to inform the public of the possible effects, since test boreholes can cause harmless but nevertheless noticeable earth tremors.
