Unterhaching’s geothermal energy project

The municipality of Unterhaching (pop. 20,000) near Munich is drilling deep. Encouraged by geological reports, the city fathers are expecting to find water at a temperature of 100–120°C 3,400 m beneath the earth. Their aim is to obtain power from it in a geothermal power plant.

The geothermal power plant is expected to bring 150 l of hot water per second to the surface, where it will serve as an environmentally-friendly source of energy for a districtheating power plant that could supply around 3.7 MW of electricity and up to 16 MW of heat. At the same time, the municipal thermal energy company, Geothermie Unterhaching GmbH & Co KG, is carrying out the first large-scale trial of a new and more efficient technique called Kalina technology. This should make it possible to achieve a high energy yield even from lower water temperatures in the earth’s interior.

The geothermal project could become a showpiece project for the integration into a municipal energy concept: it proposes, amongst other things, a district-heating network supplying public institutions, enterprises, and residential buildings. This could replace fossil fuels and help cut annual emissions by up to 30,000 t of carbon dioxide, over 7 t of sulphur dioxide, and almost 11 t of nitrogen oxides. The combination of power and heat generation makes the project unique in Germany. One economically interesting aspect of the project, which will penetrate deep into the Bavarian Molasse Basin, is the revenue that will be generated from feeding power into the grid – the German Renewable Energy Law prescribes that electricity from geothermal energy may be fed into existing power grids and must be paid for by the power suppliers at specified rates.

For at least three months, the 70 t drilling rig will drill into the ground at a rate of about 2 m/h to produce Germany’s deepest geothermal borehole to date. The drill bit for the first 800 m measures 56 cm in diameter.

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