The Koepchenwerk is a historic pumped storage power plant on the Hengsteysee in Herdecke, which was put into operation in 1930. It is considered one of the first large pumped storage power plants in Germany and was named after the engineer Arthur Koepchen, who developed the idea for this type of electricity storage. The power plant was designed to use excess electricity in times of low demand to pump water into a higher storage basin. When energy demand increased, this water could then be fed back through turbines to generate additional electricity.