Pumped storage power station, Forbach

On behalf of EnBW Energie Baden-Württemberg AG, PORR Tunneling is realising Lot 2 "Construction Trades" as part of the conversion of the Rudolf Fettweis Plant (RFW) Forbach from a storage and run-of-river power plant into a pumped storage power plant.

When the listed Forbach hydroelectric power plant was commissioned in 1914, it was crucial for electrification in the northern Black Forest. With the conversion to a pumped storage power plant, efficiency is now significantly increased. Until now, after passing the turbine wheels, the water from the Schwarzenbach and Murg dams first flowed into an equalisation basin and then into the Murg. Now an additional, underground sub-basin is being built, which will serve as an indirect power reservoir. From there, the water can be pumped up as often as desired and used to generate electricity.

Huge cavities and tunnels

Construction will start in autumn 2023. The work on Lot 2 includes, among other things, the cavity construction of caverns, water reservoirs and tunnels using mining tunnelling, the shell of the power plant cavern, the construction of two pressure shafts as well as special civil engineering work. Before the new power plants can go into operation in 2027,

the PORR team will have to blast and excavate huge cavities and galleries in the rock. An estimated 450,000 m³ of rock excavation material will be produced.

The tunnel system has a total length of 5,200 m. In addition, around 510 metres of shaft will be constructed using the raise-boring method. The volume of the underground water reservoirs is 200 million litres. The main tunnel alone will have a length of 946 m and a cross-section of up to 71.72 m² . In addition, there will be six side tunnels as well as access ‑tunnels, access tunnels and energy dissipation tunnels.

Balancing energy demand peaks

The conversion to a pumped-storage power plant is another building block for the energy transition. If, for example, surplus renewable energy is generated, such as wind energy at night, this is used to pump the water from the underground lower basin back into the day storage reservoir. If there is then an increased demand during the day, this day storage is used to generate energy. Since no start-up time is necessary, the power plants are ideal for balancing energy demand peaks. In day storage mode, it has a capacity of around 456 MWh.