Autor: Mario Kogler , 23.07.2018

Bayerische Landeskraftwerke GmbH recently commissioned the flagship project Eixendorf II in Bavaria, Germany. This involved installing, in addition to the existing power plant at Eixendorf reservoir, ...

... on the existing concrete auxiliary dam for Eixendorf Lake, the movable power plant type from the German hydropower specialist HSI with fish-friendly power plant technology. Following a design and pre-project planning phase lasting around five years, the eco-power plant, which was controversial in some areas, was fully installed in January of last year after just five months of construction, and was able to start trial operation in March. It now supplies green electricity to around 800 people. The costs of this project amounted to approximately 1.8 million euros.

Eixendorf Lake nestles gently in the beautiful Schwarzach Valley and is a popular haunt with anglers and nature lovers. The reservoir is renowned well beyond the local region for its abundance of predatory fish and is also very popular with cyclists and campers. The River Schwarzach has been dammed there since 1975. At the time, the flooding caused by the creation of the reservoir swallowed up the adjacent villages of Eixendorf, Höllmühle, Obermühle, Seebarnhammer and even a section of the former Bodenwöhr-Rötz railway line. The dam was required for reasons of flood protection and water regulation. The plan was also to make it possible to utilise the hydroenergetic power, and it was in this context that the Eixendorf Dam power plant project was implemented. Following an overhaul almost five years ago, today it delivers a standard capacity of 3.8 million kWh per year. As the head of Eixendorf Lake was regularly exposed when the water level was low, the muddy bottom of the lake created a considerable nuisance with unpleasant odours in the immediate surroundings. The lake’s value as a place of recreation was heavily constrained as a result. This was why in 1987 a 60-metre-long concrete weir was constructed as a regulating auxiliary dam, resulting in a level difference of 5 m between the auxiliary dam and reservoir. This ensures that the water level stays at the same level all year round and the sludgy sediments from the nutrient-rich River Schwarzach settle upstream of the auxiliary dam.

With its “Ecological hydropower” business segment, Bayerische Landeskraftwerke GmbH has devoted itself to utilising hydropower in a sustainable and ecological way. Under the premise of better exploiting existing power potential, a new, special hydropower plant has now been integrated into the auxiliary dam.
“The 5-metre height difference can now be utilised to produce energy at the new Eixendorf II eco-power plant,” explains qualified engineer Jochen Zehender, project manager from Bayerische Landeskraftwerke GmbH – a fully owned subsidiary of the Free State of Bavaria based in Nuremberg. The background to this is the 10-point plan of the
Bavarian State Government to mark the energy revolution which instructed Bayerische Landeskraftwerke GmbH to implement hydropower plants which are particularly environmentally sustainable.
“For us the ecological aspect is very clearly the focus of our projects, and we are very keen to find the best solutions for all parties involved,” says Zehender. As was the case with the Eixendorf Dam power plant, the priority for Eixendorf II is flood protection and nature conservation. This means that the generation of power at the eco-power plant is based on the water regulation measures and dictated by the amount of water in the River Schwarzach.

“When it came to choosing the right technology, there were not many manufacturers to consider. The movable hydropower plant type from HSI Hydro Engineering GmbH features engineering that is designed for the situation at our location. This means the concept per se is ideally suited to retrofitting on existing horizontal structures,” explains Zehender. The movable hydropower plant was developed by the hydropower specialist HSI Hydro Engineering GmbH in collaboration with the expert in special electrical machines Krebs & Aulich GmbH specifically for locations with low drops and a fluctuating water level, and has been patented since 2002. An integral part of the concept is not to use components such as gears or converters in order to prevent any negative effects on the level of efficiency. This ensures that the level of efficiency can be kept high both in the partial load range and in the full load range, and when water levels fluctuate greatly. The twin-regulated Kaplan bulb turbine with a diameter of 1 m was configured in a “Bulb” design. The directly coupled synchronous generator is permanently magnetically excited. With an extraction water quantity of 4.5 m³/s and the drop of 5 m, the plant delivers a power output of approximately 190 kW. With these conditions, the plant delivers an annual average output of around 0.8 million kWh.

The power plant components were mounted in the steel frame by HSI at the factory and thoroughly tested. At the construction site, the all-in-one power plant module, which had a hefty weight of 22.5 tonnes and was supplied ready for operation, was lifted into its final intended location by mobile crane. The installation work was completed via plug & play in around two days. To prevent the module from floating up, the construction company then filled its hollow cavities with 15 m³ of special concrete. This gives the power plant module a total weight of around 66 t. The module for Eixendorf II with a length of 10 m and measuring 2.5 m in height and width is currently the smallest of all 19 modules that have been deployed to date. Another important aspect of the movable hydropower plant from HSI is the screen system which was developed specifically for it: A round arch screen with a gap width of just 18 mm, which shields the turbine in a semi-circular arch upstream of the generator housing, ensures that fish and other aquatic organisms are protected. The automatically traversing screen cleaner is deployed twice a day and, in combination with the regulating weir gate, it safeguards the optimum transfer of floating debris from the head water to the lower water. However, this is not sufficient during flooding events. The solution at once illustrates the particular quality of a movable hydropower plant: Mounted on a fixed pivot point at the height of the generator, the entire power plant unit can be hydraulically raised up. In this way, sediment and debris can continue to be transported on under the plant even during a major flood, which proves to be a great advantage for rivers which carry a significant amount of debris.

What makes the structural concept of the movable power plant so special is the fact that – in contrast to almost all conventional hydropower plants – this plant can be integrated directly into an existing weir system. Separate infeed and discharge channels, bypass channels and surrounding structures, such as gravel traps, screens or machine buildings, are not required. This means that the level of intervention in the existing periphery/weir system is kept to a minimum and there is a significant improvement to the overall ecological situation. With this design, water permanently flows over the power plant components. This is one of the most important criteria when it comes to the risks of flooding at the location. This aspect was particularly evident during the recent once-in-a-century flood in 2015 when the level rose to around 5 m above the level of water in the auxiliary dam. It was not least for this reason that the power plant building with all the control units was positioned on a nearby elevation – so on safe terrain. The new power plant control system was quickly integrated into the existing one, thus ensuring an optimum balance between water regulation and energy generation.

When it comes to deciding on the best possible turbine technology to create an ecological hydropower plant, the plant’s suitability for fish is regarded as the central criterion. Bayerische Landeskraftwerke GmbH deliberately opted for the fish-friendly turbine technology from HSI Hydro Engineering GmbH. “For us criteria such as the turbine, the close-meshed trashrack, the permanent fish bypass via a slot in the back-up flap of the power plant module, but also the low level of structural impact on the natural surroundings were the decisive factors,” explains Jochen Zehender in summary. Fish monitoring in order to evaluate the fish-friendly measures is already in full swing. This involves around 30 budding scientists examining around 30,000 fish, eight species of fish per power plant, on different dates. The monitoring has been scheduled to take place over a total of three years. What can be concluded from the investigations conducted so far is that the fish bypass located on the side of the back-up flap should be shifted into the middle and thus modified. In addition, the dam operator is currently examining various possibilities for a future fish ladder in the form of a vertical slot pass. The planning approval procedure for this is currently ongoing at the Schwandorf Administrative District Office. In the discharge area of the turbine, a large-scale surrogate spawning ground has been heaped up. A base substrate with different granulations was introduced for the different species of fish. “The spaw­ning ground is a stroke of luck for the fish,” explains project manager Zehender. The surrogate spawning ground is in principle a sandbank located exactly in the discharge area of the turbine. This means that the spawning ground will be flushed through and available for the fish for a long period of time.

With the commissioning of the Eixendorf II eco-power plant, Bayerische Landeskraftwerke GmbH now operates 23 hydropower plants and generates an average of 55.8 million kWh per annum. This amount of power is enough to supply roughly 55,000 people with CO2-free energy. The local supervision is undertaken by the Bavarian water resource management authorities, which also operate the state dam facilities. Three eco-power plant projects with corresponding technology began operating back in 2016 and 2017 – two of them with regional partners. The water rights consent process is currently ongoing at three more power plant projects on the Regen, Saalach and Amper Rivers; the power plant on the Wertach is still in the planning phase. In addition to the construction of new hydropower plants, Bayerische Landeskraftwerke GmbH also demonstrates its commitment to exhausting the existing potential for performance with extensive upgrades of existing power plants.
In October 2014, Bayerische Landeskraftwerke GmbH was presented with the “Shaper of the Energy Revolution 2014” award by the Bavarian Ministry of Economic Affairs in recognition of its innovative approaches in the ecological utilisation of hydropower.

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The plant is deployed between the head water and the lower water, and water flows over the top of it. The fact that the plant is mounted on a pivot point means it can pivot. It therefore serves as a weir opening during flooding. Debris and sediment can be flushed through under the plant.  Another aspect is the fish-friendly design, with the round arch screen with a gap width of 18 mm representing a safe barrier for fish and other aquatic organisms.

graphic: Bayerische Landeskraftwerke

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Bayerische Landeskraftwerke GmbH is pursuing the aim of making better use of performance potential. With this in mind, the movable hydropower plant was integrated into the existing concrete auxiliary dam.

photo credits: Bayerische Landeskraftwerke

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A bird’s-eye view of the Eixendorf Dam recreation area.

photo credits: www.oberpfalz-luftbild.de

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In addition to the fish-friendly turbine technology, other measures for improving the ecology of Eixendorf Lake were also implemented. Examples include the surrogate spawning ground, which was created directly in the discharge area of the plant, and the fish monitoring scheduled for a period of three years.

photo credits: Bayerische Landeskraftwerke