Forbach Pumped Storage Power Plant: Breakthrough
to the Main Tunnel – Cavern Excavation Completed
The conversion of the Rudolf Fettweis plant in Forbach into a modern pumped storage power plant is progressing rapidly. Since the beginning of 2024, Porr Tunnelbau has been modernizing the plant on behalf of EnBW Energie Baden-Württemberg AG with the aim of making a key contribution to the energy transition and grid stability in Baden-Württemberg. Pumped storage power plants are a technology that has been used for energy storage for over 100 years. However, in view of the energy transition, they have once again come into focus as they offer a flexible and sustainable solution for electricity supply.
Breakthrough in the Schwarzenbach Headrace Tunnel in August 2025
As part of the conversion, Porr is responsible for the construction of caverns, water reservoirs, and tunnels using mining techniques, the shell construction of the power plant cavern, and the construction of two headrace tunnels. The total excavation volume will be approximately 400 000 m3. Around 200 000 m3 of storage volume is planned for water storage in the main and secondary tunnels.
In August 2025, the construction team made significant progress in Forbach. After the breakthrough from the cavern to the Schwarzenbach tunnel marked another step forward in the middle of the month, raise boring work on the Murg tunnel began just a few days later. This was completed in less than three weeks.
Excavation of the Cavern Completed
At the same time, work is continuing on the power plant cavern, which will measure approximately 123 m in length, 20 m in width, and 42 m in height when completed. Concrete work has been underway there since the beginning of September. Another highlight followed in mid-September when the breakthrough of the main tunnel between the cavern water reservoir and the outlet structure was successfully completed. At 1010 m length, it is the longest tunnel in the project. By the end of September, excavation in the cavern had also been completely finished.
Thanks to the dedicated efforts of all those involved, the project remains on schedule. From 2027, the completed new pumped storage power plant will make a decisive contribution to the flexible supply of electricity in Baden-Württemberg and to the stability of the power grid.
