The Glems pumped-storage power plant is located on the edge of the Swabian Alb. Due to the steep slope between the artificially created upper reservoir and the powerhouse, the pumped-storage power plant can utilize a head of almost 300 m.
In Glems, two sets of machines, each consisting of a Francis turbine, a pump, and an electric motor, produce energy. The machines operate as generators in turbine mode and as motors in pump mode. The turbine output is regulated as needed via adjustable blades of the guide vanes. With a maximum output of 45 MW, the turbines require little more than six hours to fill the upper reservoir (810,000 m³), producing 560,000 kilowatt hours of electricity. Within eleven hours, with a maximum output of 34 MW per pump, the water can be pumped from the lower reservoir back to the upper reservoir via the pipeline.
The special feature of the Glems pumped-storage power plant is that it can provide control power not only in turbine mode but also in pump mode. This is made possible by a process known as hydraulic short-circuit operation. In hydraulic short-circuit operation, the pump extracts water from the lower reservoir and pumps it toward the upper reservoir. Depending on demand, more or less water is diverted to the turbine, thus making more or less power available to the grid. Given the current grid situation, this so-called control power is very valuable, as fluctuations in the grid can be compensated for immediately.