Study in Germany on flexibility of combined geothermal heat and power generation

Geothermal power plant by Turboden in Bavaria, Germany (source: Turboden)
Alexander Richter 7 Aug 2020

The German Federal Environment Agency released study on options for the flexibility of power and heat generation with geothermal energy within an energy system that is dominated by intermittent resources.

The Federal Environment Agency (Umweltbundesamt) of Germany has shared a new study on deep geothermal energy on its website. It examines the extent to which geothermal-based electricity and heat systems can be used to flexibly cover electricity requirements and, above all, to provide control power without this having a negative impact on the heat supply.

The scientists from the Technical University of Munich and the University of Bayreuth come to differentiated results in their study on flexibility options for electricity and heat generation with geothermal energy (study in German). The technical analysis as well as the simulation of the geothermal systems showed that the technical potential of the permanent provision of positive and negative control reserve for almost all technical flexibility options, especially for existing systems, is low. The exception is the technical flexibility potential for the provision of positive control power through hot water or thermal water storage tanks. The technical potential here is medium to large, but the technical effort is also increasing.

The technical potential of the positive and negative provision of control reserve with limited time availability (i.e. in time slices), on the other hand, is medium to large for almost all flexibility options. However, the overall potential of balancing power provision remains at a low level.

Compared to conventional combined heat and power (CHP), geothermal energy, according to the study, shows a very variable power figure, which guarantees a very high degree of flexibility between power and heat generation. The CO2 emissions per unit of energy generated are lower than with fossil CHP.

Under the current economic framework, the plants could only provide limited economic control power. Existing systems with the support of the peak load heating plant can already generate additional (small) profits by providing positive secondary control power. This is not the case for existing systems without modification or expansion with heat storage.

The reduction in the value to be applied for electricity from geothermal energy enables greater use of the flexibility potential. Existing systems and systems with a peak load heating plant could provide economically negative and positive secondary control power. A provision of flexibility through deep geothermal power plants, whose power generation is remunerated according to the EEG, is not to be expected in the medium term without additional incentives.

A temporal decoupling of the electricity production from the heat demand with the help of heat storage enables a more electricity price-oriented driving style of the geothermal based electricity heating system. The more flexible energy system reduces the total costs through higher revenues because electricity can be fed in at times of higher electricity prices. “In summary, it can be stated that the provision of control power through geothermal-based electricity-heat systems is currently possible with restrictions from a hydrogeochemical and technical point of view,” is the conclusion.

The potential of deep geothermal energy is still too little known. In order to facilitate their application and to make knowledge available, the Leibniz Institute for Applied Geophysics (LIAG) has started to develop an interactive e-learning portal for deep geothermal energy as part of the GeoFaces research project. The new GeotIS portal is available free of charge with the first e-learning modules.

Sources: Federal Environment Agency, LIAG, pgl via