In Germany, researchers at Technische Universitaet Muenchen (TUM) have developed a small-scale hydroelectric power plant that is simple and cheap enough to work even with modestly high dams. Moreover, the whole system resides in a shaft, minimizing the impact on the landscape and waterways.
Until now, the use of hydroelectric power in connection with a relatively low dams meant that part of the water had to be guided past the dam by way of a so-called bay-type power plant. This design has inherent disadvantages that include high costs associated with concrete construction for the diversion of water and a power house. And each such plant is usually a custom-designed, one-off project. There is usually an allowance for fish-passage facilities to help fish bypass the power station. Quite often, these facilities don't work well and the result is a lot of injured fish.
Prof. Peter Rutschmann and Dipl.-Ing. Albert Sepp at the Oskar von Miller-Institut at TUM came up with a hydroelectric approach that addresses these problems. Only a small transformer station is visible on the banks of the river. In place of a large power station building on the riverside, a shaft dug into the riverbed in front of the dam conceals most of the power generation system. The water flows into a box-shaped construction, drives the turbine, and is guided back into the river underneath the dam.
TUM researchers say this solution has become practical because several manufacturers have developed generators capable of underwater operation so there's no need for a riverbank power house.
The TUM researchers also considered how to prevent undesirable vortexes where water suddenly flows downward, and how to best protect the fish. Rutschmann and Sepp solved two problems with a single solution – by providing a gate in the dam above the power plant shaft. In this way, enough water flows through to let fish pass. At the same time, the flow inhibits vortex formation that would reduce the plant's efficiency and make the turbine wear out.
The shaft power plant is capable of operating economically given a low "head" of water of only one to two meters, while a bay-type power plant requires at least twice this head of water. In the case of wider bodies of water, several shafts could be dug next to each other – also at different points in time, as determined by demand and available financing.
The TUM work has special significance in Europe because of an EU Water Framework Directive. The directive stipulates that fish obstacles are to be removed even in smaller rivers. Researchers say construction of thousands of fish ladders would not only cost billions but would also load the atmosphere with tons of climate-altering greenhouse gas emissions. In contrast, installation of shaft power plants with fish gates and additional upstream fish ladders were would let investors shoulder the costs and ensure the generation of climate-friendly energy over the long term.