Pumping Heat in Hamburg

The German port city plans to store hot water underground and bring it up to heat homes in the winter

- Josefine Fokuhl

Five miles east of the German port city of Hamburg lies Tiefstack, a massive coal power plant that local officials want to shut down. While replacing its output will require a patchwork of smaller solutions, one piece is warming water with so-called waste heat from steel mills and aluminum foundries and storing it almost a mile underground. “The idea has been around since the thermos,” says Kirsten Fust, chief engineer at Energiewerke Hamburg, the local power utility.

The experimental technology, called aquifer thermal energy storage, pumps hot water 1,300 meters below the surface, then brings it back up for use in municipal systems known as district heating when it’s needed. If all goes as planned, by next year the technology will be able to provide heat to more than 13,000 households.