It's always dark in front of the hoe - Kirsten Fust, Managing Director of Hamburger Energiewerke, uses this old adage from mining to describe why the company will in future no longer pump thermal water from a depth of 3000 meters under Wilhelmsburg. It was planned to be able to supply around 5,000 households in the vicinity with district heating from the year 2024.
But in front of the hoe – to stay with the picture – the geologists did find a rock layer during their test drilling in January through which water with a temperature of more than 100 degrees flows, but further investigations at the borehole would have shown that it would not be worthwhile to pump the thermal water from the depths, explained State Councilor for the Environment Michael Pollmann, who visited the drilling site at the Old Lock in Wilhelmsburg on Thursday. The amount of energy that could have been extracted would have been too small.
Together with Fust and the managing director of Hamburg Wasser, Ingo Hannemann, Pollmann explained how the project, which is crucial for Hamburg, will now proceed. Because it will continue. During drilling at the beginning of the year, the companies involved accidentally discovered another layer of rock at a depth of around 1,300 meters, which turned out to be a possible geothermal source. Subsequent investigations showed that water with a temperature of around 50 degrees could be pumped there and that the quantity could also be sufficient to produce district heating for Wilhelmsburg.
On Thursday, a second test drilling started, which will reach exactly into the 1300 to 1400 meter deep rock. It is intended to show how much water can be brought to the surface and exactly how many degrees the water will have. "Final results" are expected in the fall, said Fust. This also includes the answer to the question of how the water – if the quantity is sufficient – could be brought to the temperatures of 80 to 130 degrees Celsius required for district heating. The use of a heat pump seems most likely to those involved in the project. But their operation must also fit into the eco-heating concept that Hamburg wants to pursue with the geothermal project in Wilhelmsburg.
The planned geothermal funding is part of the "Integrated Heat Transition Wilhelmsburg" (IW3 for short) project, which aims to achieve an almost CO₂-free heat supply for large parts of the district. As a "real laboratory of the energy transition", the Federal Ministry of Economics is funding the project with a total of around 22.5 million euros. The plant is intended to provide "green" heat and thus contribute to Hamburg's exit from fossil heat supply.
As part of its climate plan, Hamburg wants to phase out the use of coal for heating by 2030. Should the second test drilling deliver successful results, the borehole would also serve directly as a well for the thermal water. The heat would then be extracted from the pumped water in a heat exchanger and the cold water would be pumped back underground. The drill hole from the first test well could be used for this.
She was very hopeful that the rock layer at a depth of 1,300 meters could be used to supply geothermal energy in the future, said Fust and was almost enthusiastic about the form of energy. It is generated by the heat in the Earth's core. "This will shine for a long time, when there are no more people," explained Fust. The heat from the earth is therefore considered inexhaustible by human standards. In addition, unlike the sun and wind, it is always present.
There are currently 42 systems with deep geothermal energy in Germany. The experts speak of deep geothermal energy from boreholes of 400 meters. In northern Germany, however, the technology is not very common, explained Fust. Energy suppliers from the entire region therefore looked at the Hamburg project "with eagle eyes". State Councilor for the Environment Pollmann made it clear that additional geothermal sites in the Hanseatic city could also be envisaged if the project continued successfully. Compared to wind turbines, for example, geothermal systems only need a small amount of space.
Thanks to the scientific monitoring of the project by geologists in the mesoTherm project, the project participants now also know why the previously unknown rock layer lies under Wilhelmsburg. Around 45 million years ago, the North Sea stretched deep into what is now inland. The layer of rock found now was probably the beach of the young North Sea.
"Even in the 21st century, real discoveries are still possible," said Inga Moeck, professor of geothermal energy at the Georg-August University of Göttingen, who heads the accompanying program mesoTherm. Like everyone involved, she too hopes to “supply as many people as possible with renewable heat” with the thermal water from the newly discovered layer. According to Pollmann, it is not yet possible to say how many households there will be in the end.
