Geothermal heat – an underestimated factor in the energy mix

Geothermal heat is inexhaustible by human standards. In contrast to wind and solar energy, it is independent of the weather and is available around the clock. At a rate of 2.2% in the German energy mix, geothermal heat plays only a minor role. Yet, it is expected to undergo more rapid expansion in the coming years. With the right technology, the country could be supplied with energy and heat from the depths for thousands of years and without any hazardous waste on top of that.

Depending on the drilling depth, two types of geothermal heat are available, that is, near-surface and deep geothermal energy. Near-surface drilling up to depths of 400 m is used mainly by homeowners and contractors in order to heat or cool buildings and plants. Heat is generated by circulating water or another liquid in a closed pipe system. A heat pump on the surface absorbs the energy and adjusts it to the required temperature levels.

Geothermal system Munich Riem for municipal distant heating systems of the Munich public works department (Photo: GtV-Bundesverband Geothermie)

Currently, approximately 265,000 near-surface geothermal systems are being operated in Germany. The inventory of the particularly effective and environmentally-friendly heat pumps is experiencing a steep upward development. This also offers opportunities for drilling specialists as well as suppliers and tube producers. In 2006, more than 28,000 ground source heat pumps were installed in Germany. “By the year 2017, the number of the brine-water and water-water heat pumps sold in Germany will rise to a volume of approximately 65,000 systems sold per year and will level out at this figure,” forecasts Michael Platt, one of the authors of a study sponsored by the International Geothermal Center, GZB.

FastLink is a pre-insulated installation kit developed by Armaflex Company. It was designed specifically to connect heat pump cycles. The corrugated stainless steel pipes can be installed in seconds without the need for special tools, and the quick couplings guarantee leak-proof insulation of the tubes. The brass fittings provide exact fit, and thanks to their micro-cell structure, the Armaflex FastLink conduits are protected from moisture penetration. Afriso, a producer of measuring, control and monitoring devices, has expanded its product range and has added a complete product family of flow meters that, among other things, monitor the heating and cooling water in geothermal applications.

Experts expect further potential from deep geothermal systems, which could cover a significant amount of the overall energy requirements in future. By the year 2020, the Federal Environment Ministry expects an installed output of 500 to 750 MW, while the Bundesverband Geothermie (Federal Geothermal Association) even forecasts 1 GW. Deep geothermal applications are particularly interesting for power generation, since the heat is not subject to fluctuations and could thus help to cover the base load in Germany.

In technical terms, geothermal applications either pump hot thermal water directly from the water table (hydrothermal systems) or press cold water into hot intrusive rock and then pump it back (petrothermal systems). Currently, the use of petrothermal resources is still very limited, while the hot springs in the Upper Rhine Rift, the Molasse Basin and the North German Basin are already being tapped.

Drilling with a geothermal probe (Photo: TRACTO-TECHNIK)

For deep geothermal energy in particular, the challenges and opportunities for tube products are significant, as complex pipe systems are required to pump the groundwater to the surface. In addition, the cycle in hydro-geothermal energy systems requires high pressure to prevent the escape of gases dissolved in the thermal water. This means high stress on feed pumps, pressure retention valves and safety valves. In addition, large pipe networks that guarantee best-possible energy retention are required on the surface in order to connect entire towns or municipal districts to the distant heating system. In this connection, local heat specialist Thermaflex has developed a pre-insulated compact building connection that can already be delivered with individually tailored pipes for individual connections. Therefore, the connection can be installed much faster and simpler. As a result, residential streets can be closed again up to 70% faster than before.

According to the ambitious target of the Federal government, Germany shall be supplied completely with power from renewable energy sources by the year 2050. The Federal Environment Ministry and European Union programmes therefore support various scientists, universities, research centres and companies in their research, development and improvement activities. For example, a pilot project is currently underway at the RWTH Aachen University. Thanks to a 2,500-metre-deep drill hole with a geothermal probe, project SuperC will cover about 80% of the heating and cooling requirements of a university building.

Targeted investments into the technology are expected to bring forward geothermal energy. However, according to the Fraunhofer Institute for Wind Energy and Energy Systems Technology, this is not enough. The lack of capacities for exploration measures and drilling capacities are currently slowing down the industry. The institute considers the number of nation-wide projects (19 in operation, 18 under development and 66 planned) as comparatively low and adds that the opportunities in this regard have not been exhausted by far. Currently, investors are shying away because of the costs. After all, expensive initial drilling operations are often unsuccessful. As a result, the Bundesverband Geothermie (Federal Geothermal Association) demands better funding conditions for interested companies and states that, in contrast to other renewable energies, the field of geothermal energy continues to remain at a disadvantage.

- All information on the research projects of the Ministry and the
- Forschungszentrum Jülich
- Research Agenda for Geothermal Energy
- Brochure: Deep Geothermal Energy – Options for Use in Germany (german)
- Brochure: Ground source heat pumps (german)