Is there a simple definition for geothermal energy?
Katharina Aubele: The term geothermal energy comes from the Greek, literally translated it means geothermal energy. And that is also true: the heat that is stored inside the earth. Temperatures in the interior of the earth are currently around five to six thousand degrees Celsius. Of course, the further out you go, the cooler it gets. According to geothermal gradients, the temperature, starting from the earth’s surface, increases by an average of three degrees Celsius for every hundred meters of depth. In use, a distinction is made between near-surface and deep geothermal energy. Near-surface geothermal energy refers to everything down to a depth of 400 meters below ground level. From there, deep geothermal energy begins.
What are the differences?
Aubele: Near -surface geothermal energy is generally used in single-family homes or in office buildings to generate hot water locally. Heat pumps are used here. This means that an additional source of energy is required to bring the relatively low temperature level that the geothermal collectors absorb to a level that, for example, heats the hot water circuit in a connected building. In deep geothermal energy, it is usually the case that temperatures are reached that can be used directly. At temperatures of over 100 degrees Celsius, it is also sufficient for conversion into electricity. The Geothermal Alliance is all about deep geothermal energy.
How did the GAB come about?
Aubele: The Bavarian Geothermal Alliance was created as an interdisciplinary research project as a result of an initiative by the Bavarian state government. The consortium consists of the Friedrich Alexander University in Nuremberg, the University of Bayreuth and the TUM. There is close cooperation with the plant operators.
UNIQUE GEOLOGICAL FORMATION
Why is the geological condition in Bavaria so suitable for using deep geothermal energy?
Aubele: In Bavaria, hydrothermal geothermal energy is primarily used. This means that existing deep groundwater, which has a very high temperature, is pumped. In Bavaria we have a geological situation that strongly favors this method. There are deposits from the southern German Molasse Basin in the subsoil. The Molasse Basin refers to the foreland basin that arose in front of the mountain belt of the Alps. Below the deposits of the Molasse Basin there is a deep Upper Jurassic aquifer called the Malm.
This limestone tends to weather in a karstic manner, usually resulting in very large cavities. This means that this rock has a very good water flow. The Alps push this layer further down. In turn, the temperature is higher at depth. This means that at a depth of 3000 to 5000 meters there is an aquifer. If this is drilled and the hot groundwater is pumped, it can be used directly. There are 33 deep geothermal plants in Germany, 21 of which are in Bavaria.
How is this heat conveyed and used?
Aubele: The hydrothermal plant usually works via a doublet. Duplicate because there are two holes. The first is the so-called production well, through which the hot groundwater is brought to the top. This usually works with the help of submersible centrifugal pumps. As soon as the hot water is on the surface, it is decided whether it is hot enough to generate electricity from it. If it is not hot enough, district heating is generated via heat exchangers. The cooled thermal water is returned to the reservoir through the re-injection well, so that the water balance in the aquifer is balanced. The thermal water is guided in a closed circuit on the surface and does not come into contact with the environment.
SUSTAINABLE AND RELIABLE
What advantages does geothermal energy have over other forms of energy?
Aubele: It can be counted among the renewable forms of energy. Of course, over long periods of time, we extract heat from the earth’s crust. However, if you now consider that the earth is 4.6 billion years old and the temperature in the earth’s core is still several thousand degrees Celsius, this is a cooling process that has not yet occurred on a large scale in our lifetime or in that of our grandchildren will show effects. Another advantage of geothermal energy is that it is independent of the time of day or season, in contrast to photovoltaics or wind energy.
The GAB is to research open questions in the use of geothermal energy. Could you give examples of planned projects?
Aubele: An example of a research topic is the so-called scaling education. We have very calcareous water here in Bavaria. If these are conveyed from the depths to the surface, they cool down on the one hand and there is also a drop in pressure on the other. This means that the minerals previously dissolved in the water are deposited. Here in the Molasse Basin, these are mainly lime deposits, which then spread throughout the entire complex. These are of course harmful to seals, risers and pumps. Descaling takes a long time and is very expensive for the system operator. In the GAB, the formation mechanisms of the scalings are researched in order to successfully avoid them. We were also recently awarded a project by the Federal Environment Agency to investigate
CITIZEN PARTICIPATION ON GEOTHERMAL ENERGY
A course on geothermal energy is planned. What should this look like exactly?
Aubele: The geothermal/geoenergy course will be set up as part of the GAB. It is expected to begin in the 2017/18 winter semester. The Friedrich Alexander University takes over the coordination here. She will also supervise most of the courses. The course is clearly aimed at engineers and geoscientists. However, it should also impart skills that are particularly important for geothermal energy and renewable energies. Something like this is relatively rare in Germany at the moment. In addition to the natural sciences and geoscientific disciplines, students are taught skills in business administration, legal principles in the field of renewable energies and aspects of citizen participation.
Citizen participation also plays a role at GAB …
Aubele: Such a technology can only be established if you have the people on your side. There are always fears. People ask themselves, for example: What is happening underground, will my property sag or will my house break through? These are fears that must be taken seriously. After all, there are always incidents in connection with geothermal drilling. Another fear is whether earthquakes will be triggered. In Bavaria we are fortunate to live in a region that has little geological prestressing underground. There are also plans to set up an urban monitoring network to address this concern. In general, I have found that many fears can be clarified if you explain everything openly and honestly.
About the project:
The Geothermie Allianz Bayern (GAB) was created to answer research questions in the field of deep geothermal energy and to bundle and network the operating experiences of the operators. Seven chairs, junior research groups and working groups from the Technical University of Munich (TUM) are involved in the research network, as well as the GeoZentrum Nordbayern of the FAU Nuremberg-Erlangen and a chair from the University of Bayreuth . The project coordination takes place at the Munich School of Engineering (MSE) of the TUM. The joint research project is funded by the Bavarian State Ministry for Education and Culture, Science and Art.
Bilder zum Download: mediatum.ub.tum.de/1338056
Technical University of Munich
Dr. Katharina Aubele
Phone: +49 (89) 289 10641