Berlin’s underground car parks are producing so much heat they could power thousands of homes with clean geothermal electricity, according to a new study.
The heat given off by car engines makes the city’s car parks hotter than the surrounding earth, which in turn raises the temperature of the groundwater. This could pose a threat to water quality but also presents an opportunity — using heat pumps to extract the energy and use it to heat homes. In Berlin alone, enough energy is transferred to the groundwater to supply 14,660 households with heat, based on modelling from over 5,000 underground car parks.
“This would have the advantage of extracting energy from the groundwater and thus cooling it down and improving its quality,” explains Maximilian Noethen, a geoscientist from Martin Luther University Halle-Wittenberg.
The researchers didn’t just look at Berlin to come to their conclusions, but 31 underground car parks in various cities throughout Germany, Austria, and Switzerland. Their investigations consistently showed that these car parks heat up the groundwater throughout the year. The volume of traffic in the underground car parks, their proximity to the groundwater, and ambient groundwater temperatures were the biggest factors influencing how much heat was produced.
“Public underground car parks heat up the groundwater more than private facilities as they are often deeper and the cars park there for shorter periods of time,” explains Noethen.
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Groundwater temperatures in European cities have been rising for decades as a result of global warming, which could affect the quality of the groundwater from which we draw large parts of our drinking water. “This development needs to be controlled through a variety of measures,” cautions Professor Peter Bayer from the Institute of Geosciences and Geography at MLU.
While the heat from groundwater alone is not enough to cover the heating needs of a city like Berlin, the researchers believe that the potential for geothermal energy goes well beyond this and that it could make a significant contribution to supplying sustainable heat.
Elsewhere in Europe, Croatia is building a 16MW geothermal plant boosted by €30mn in funding, while Hungary aims to replace about 1-1.5 billion cubic metres of natural gas with geothermal energy per year. And Europe’s largest geothermal heating plant, in the city of Aarhus in Denmark, is expected to be completed by 2030, with the capacity to cover 30% of the district’s energy needs.