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Researchers at the University of Siegen test the prototype of the new water wheel in the laboratory and research the fundamental performance characteristics.
© Universität Siegen
Hydro power

Schematic depiction of a traditional undershot water wheel (top) in comparison to StECon (bottom).
© Universität Siegen

Prototyp außerhalb des Wassers
© Universität Siegen

The planetary drive of the StECon consists of the outer gear wheels (yellow, 40 teeth), which are connected to the blades, the red gear wheels (18 teeth), which serve to transfer the force, and the central gear wheel, or sun wheel (green, 20 teeth), which is used to control the blade position.
© Universität Siegen

Water wheel with rotating blades

A newly developed water wheel is now able to generate power at locations where it had previously been technically almost impossible. The machine works fully submerged without weirs at a low flow speed and can move forwards and backwards. As a result, it can be used in rivers and also in tidal currents. A prototype has successfully passed the laboratory tests. At the moment, developers at the University of Siegen are optimising and testing the water wheel in field conditions.


Innovation is still possible even for technologies that mankind has known and used for thousands of years. Since the first advanced civilised societies, undershot water wheels have been used to convert the power of flowing water into mechanical energy or, more recently, into electric energy. The water may not reach higher than the hub of these wheels because the blades must be over the water surface due the distance that they travel against the flow direction. Otherwise opposing forces would arise and a breaking effect would come about. Furthermore, traditional water wheels are generally attached to natural watercourses by way of structural interventions, e.g., weirs. They place a burden on the ecological balance of rivers and streams.

The newly developed Stiller Energy Converter system, or StECon, manages without water management structures and works when it is fully submerged. Up to five blades mounted on a planetary gear make this possible. This gear effects a cycloidal movement sequence in which each blade rotates 180 degrees on its own axis during a complete turn of the wheel. In the meantime, one half of the blades absorbs the current force through a more upright orientation and the blades on the other half of the wheel rotate back to their original position to provide less resistance to the current. When moving against the flow direction, the blades are therefore almost parallel to the current and thus they minimise their resistance (see figure, centre left). As a result, when calculated the driving forces are always significantly larger than the breaking forces. The blades are designed symmetrically because both sides alternatively face the current.
The patented machine can be installed in all conceivable situations, it can work forwards and backwards and it can serve to generate energy and as a drivetrain. It is well suited for all application areas with low drop heights, including energy generation in flowing water, isolating channels and in ocean currents. Project coordinator, Professor Jürgen Jensen, from the Research Institute for Water and Environment at the University of Siegen explains, “Our water wheel makes it possible to tap the previously unused small and micro potential of hydropower. It is perfect for all locations on flowing water with sufficient current. Furthermore, smaller tributaries can also be considered.” In comparison to traditional water wheels and low pressure turbines, which can also be installed in locations with low drop heights of less than one metre, the StECon can process much higher flow rates and in this way it achieves better performance data. On one hand, it can supply autonomous systems, e.g., measuring buoys, with energy and on the other hand it can work as a permanently installed system, e.g., for grid-connected energy generation

Prototype optimised in hydraulic engineering laboratory

All movements of StECon are cyclical and repeated in a circular orbit. Therefore, the machine belongs to the group of so-called cycloidal propellers. Comparable drivetrains have already been used in ships and airships. Up to five blades are moved using the planetary drive with triple tooth meshing. This type of gear with a freely movable sun wheel allows a very even and steady movement sequence through the full speed range and an optimum orientation in regard to the current. In previous years, the researchers at the University of Siegen investigated the fundamental performance characteristics and features of the machine. Subsequently, they optimised the design and built a prototype that was tested at laboratory scale. In doing so the design details of the gear and the optimum geometry of the blades were the focus of the investigations. Thanks to the optimised design, the prototype achieved a maximum efficiency of 44 percent, however, in the laboratory the amount of water was limited to 150 litres per second . However, efficiency of up to 26.8 percent is possible in free currents. The German Federal Ministry for Economic Affairs and Energy funded this forerunner research project that bore the name “Stiller energy converter compact water wheel” (Stiller Energiewandler Kompaktwasserrad, StEwaKorad) and ended in spring 2016.

The machine in field testing

In a currently ongoing follow-up project, the Siegen researchers are testing the StECon under real operating conditions. The European Regional Development Fund is sponsoring the work until the end of 2019. For this purpose, a further developed version of the existing laboratory prototype was converted for continuous operation and will be installed at the start of July 2017 in the outflow of a waste water treatment plant in Siegen. At the same time, a large pilot system on a jetty on the Rhine will be installed by the end of 2017. The aim is to compare the results from the two different locations and to generalise them as far as possible.

Parallel to the study of the two pilot systems, the Siegen researchers are working on a potential analysis for North Rhine-Westphalia. In this regard, they are identifying suitable locations and the necessary infrastructure facilities on various flowing waters in order to determine their hydropower potential. Subsequently, all data is incorporated in an economic assessment.



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