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An electricity storage facility for the energy transition

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Hydropower is the oldest renewable energy source. Besides being able to generate climate-neutral power, its main advantage is that it can store large amounts of energy and, if necessary, feed it back into the grid within a matter of seconds – a factor critical to the success of the energy transition. That’s because electricity storage facilities not only buffer the natural fluctuations in generation from wind power and photovoltaics, but also help to keep the power grid balanced at all times. We are using the climate-friendly type of storage and realizing a unique project by expanding our hydropower plant in Forbach.



Storage volume virtually doubled
Expanding the pumped storage power plant
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With the topographical features of the traditional power plant and the overwhelming approval of the local people, Forbach offers ideal conditions for expanding the site. The project is designed to reflect sustainable activity in every respect. The impact on nature and the population is minimal during the construction period due to the underground construction method. Extensive measures have already been taken to compensate for the few effects – in the area of species protection, for example, by resettling native lizards

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From planning to operation, the project is being monitored by environmental planning officers and nature experts. An underground cavern storage facility and a cavern power plant are being built. The existing machines, which are up to 100 years old, are being taken out of service and replaced by new, more efficient machines. Together with the existing equalizing reservoir, these components form the new lower level. The Schwarzenbach Dam serves as the upper reservoir.

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EnBW extension video Forbach (available only in German)

New power plant in the mountain increases capacity by 10 MW

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In this concept, the water collected via the Schwarzenbach Dam reaches the newly built cavern power plant, where the new Schwarzenbach power plant (with one pump turbine) and the new Murg plant as a run-of-river power plant (with two turbines) are located. Due to its new position in the mountain, the water flows almost vertically onto the turbine, increasing the output currently generated by 10 megawatts

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Quickly available power in the event of grid fluctuations

The power plant is connected to the equalizing reservoir in Forbach via a main tunnel. A further six tunnels provide additional storage space. After being used in the cavern power plant, the water is collected in the cavern storage facility and equalizing reservoir. If necessary, it can be transported from here via the cavern power plant’s pump turbine back to the Schwarzenbach Dam and used again later to generate electricity. The advantage of this setup is that if too much electricity generated from renewable energies ends up in the grid it can be easily moderated by the pumping operation – and is immediately available again when needed.

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Larger reservoirs allow seven hours of nonstop power generation

The new cavern storage facility will increase the power plant’s storage volume by 200,000 cubic meters – the existing equalizing reservoir has a useful volume of 204,000 cubic meters. The new lower level – consisting of a cavern storage facility and an equalizing reservoir – will thus have enough storage capacity for seven hours’ continuous turbine operation. For economic reasons and due to its status as a historic place, however, the venerable power plant building for the Murg and Schwarzenbach works cannot be integrated into the new concept.

  • On 11 May, the Supervisory Board confirmed the investment decision for the expansion project. Construction work is expected to begin in late 2023.
  • EnBW’s project management team invites you to an information evening at the Murghalle, Forbach, in late autumn. Here, citizens and interested parties will have the opportunity to ask questions and find out more about the planned construction work.
  • You can find further information in our press portal (only available in German).
Do you have any questions about our expansion project in Forbach?

Get in touch with us now at:

The Rudolf Fettweis plant
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Forbach hydropower plant is truly exceptional in many respects. In addition to its traditional history, it can be described as a run-of-river, storage and pumped storage power plant. This is due to the location of the Rudolf Fettweis plant (shortened in German to RFW), which is characterized by considerable differences in elevation, an optimal water supply and topographically ideal conditions for reservoirs.

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Four power plants for full power

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The RFW is made up of a total of four individual power plants that were built in two construction phases: In the first phase, between 1914 and 1918, the Murg plant and the low-pressure hydropower plant were built. The Raumünzach plant (1921 to 1923) and the Schwarzenbach plant (1922 to 1926) were added a little later. The five turbines of the Murg plant and the two of the Schwarzenbach plant are housed together in the Forbach powerhouse. Altogether, they produce around 105 million kilowatt-hours of renewable electricity per year from natural tributaries with a total output of 71 MW. This amount of electricity is enough to supply around 30,000 households with carbon-free electricity.

At the heart of the RFW is the Schwarzenbach Dam, a storage reservoir popular with locals and tourists. The water flows along tunnels and a pressure pipe to reach the RFW, located 357 meters below, where it is used to generate electricity. The Schwarzenbach Dam’s storage reservoir has previously been completely emptied three times for repair and maintenance work: in 1935, 1952 and most recently in 1997. It takes two and a half months to completely empty the reservoir from the time the bottom outlet is opened.

The hydro fish lift at the low-pressure hydropower plant
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Power plants that are built on a river always encroach on nature. In order to make them as nature-friendly as possible, the German Environment Agency adopted the EC Water Framework Directive (WFD) in 2000. This specifies the amount of water that must be present in the river at any given time and may not be used to generate electricity. Furthermore, the waterway must remain unobstructed for fish.

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State-of-the-art fish migration aid

Construction of the hydro fish lift at the low-pressure hydropower plant in Forbach.

At the low-pressure hydropower plant in Forbach, the amount of water discharged has always corresponded to the natural outflow of the Murg. In order to ensure that fish can swim unobstructed both upstream and downstream, EnBW has worked on a unique project in conjunction with the Karlsruhe Institute of Technology (KIT) and the company Baumann Hydrotec to develop a so-called hydro fish lift. This space-saving concept allows the fish in the Murg to migrate without having to make any major structural alterations to the existing historic buildings. One particular advantage of the fish lift is that it works independently of water level fluctuations in the upper reservoir and the water discharged via the fish migration aid can also be used to generate energy by means of an installed residual flow turbine.

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How the hydro fish lift works

The fish are lured by a current into a kind of elevator cab (the so-called floating piston). Once the elevator cab is closed, the elevator shaft is flooded with water from below. The power of the water drives the elevator car upward within the tube. Once it reaches the top, the exit opens and the fish swim out. When the shaft is emptied, the elevator car moves back down. The lift allows the fish to climb, but it is also used to help them descend.

A lift with a timetable

The lift always remains in the entry area for half an hour. It takes about five minutes for the lift to travel to the top and empty itself. While the elevator car remains at the bottom, there is a constant flow of water through it. The aim is to simulate and create the natural countercurrent for the fish swimming upstream so that they remain in the elevator car until it goes up. When fish are descending, experience shows that the ideal length of time the elevator car spends in the upstream water is 15 minutes before the descent begins. However, the lift’s travel intervals can be adjusted at any time.

How a pumped storage plant works
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The water carried to the top in pumped storage power plants acts as a kind of battery. The idea is not new, but the ability to store energy that is not needed is becoming ever more important. That’s because wind turbines and solar parks, which generate a great deal of electricity from renewable energy sources, do not produce power on demand, but rather when the wind blows and the sun shines. This sounds (and is) trivial, but it presents a key challenge on the journey toward the climate-neutral energy world of tomorrow and beyond. And potential energy from water is currently the only way of storing large amounts of electricity..

One spectacular example is the international NordLink project, which has cost billions. At its core is a high-voltage cable in the North Sea, which has been connecting Schleswig-Holstein with the southern coast of Norway since 2021. If more wind power is produced in and off the coast of northern Germany than is needed (or can be transported to the south of the country), it can be consumed in Norway. Production at Norwegian hydropower plants can then be reduced or shut down altogether, enabling water to be stored for later generation, more or less creating a transnational, virtual storage power plant.

The history of the power plant
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The Forbach site represents the beginning of electrification in Baden. That is why the chronicle published to mark the RFW’s 100th anniversary had the title “Power Plant of the Century.” “The Rudolf Fettweis plant is a solid testimony to a real pioneering spirit and the realization of great plans in difficult times,” wrote Kathrin Buhrke, the Mayor of Forbach at the time.

In the first construction phase from 1914 to 1918 ...

… construction teams working “on behalf of the state” embarked on the project’s first expansion stage – consisting of the Murg high-pressure hydropower plant and the Murg low-pressure plant. The low-pressure plant started operations in 1917, followed by the high-pressure plant in 1918.

At the start of work on the dam in 1922 …

… 60 hectares of forest were cleared. Three houses were demolished, the people were relocated and a dedicated railroad line was laid to the local stone quarry at Schneiderskopf for transporting materials.

The completion of many elements in 1925 …

… included the pressure tunnel, the apparatus house, the pressure pipes and the power plant extension with machines six and seven in Forbach.

RFW renovation works in 1952

The history of the Rudolf Fettweis plant in the second half of the 20th century is primarily a story of value retention and continuous optimization.

Complete modernization in 1969

In 1969/70, the machines in the low-pressure hydropower plant above Forbach were fully modernized.

Dam updated in 1997

In the mid-1990s, the turbine in the Raumünzach plant was adapted to changed inflow conditions and its output was reduced to 50 percent of its previous level.

100th anniversary in 2018

Since 2010, conversion plans have been underway to create a modern pumped storage power plant. At the beginning of 2018 – in the power plant’s anniversary year – the approval application was submitted.

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Historical film footage shows the construction of the Rudolf Fettweis factory in Forbach.

At the time, the Schwarzenbach plant was the first power plant in Europe capable of storing energy for power generation on an industrial scale. The man behind the idea and largely responsible for drawing up the construction plans was hydraulic engineer Theodor Rehbock. However, his thoughts on how hydropower could be used in the upper Murg valley, which were put forward in as early as 1903, initially focused on a paper mill near Forbach rather than on electricity generation. Only after the Grand Duchy of Baden announced its intention to establish a state electricity supply did the plans fall into the hands of EnBW’s predecessor company Badische Landes-Elektrizitäts-Versorgungs AG (later Badenwerk AG). From the start of construction in 1922 until its completion in 1926, Rudolf Fettweis oversaw the work on the Schwarzenbach Dam. The entire power plant complex was ultimately named after him.