In Obergrafendorf, Lower Austria, a completely new type of hydropower unit has been in operation since October 2005. Apart from producing eco-electricity, it is said to have several other advantages. With the completion of this small “gravitation vortex hydropower unit” (as it is called by its inventor) on a minor Austrian watercourse, the theoretical concept previously nominated for the NEPTUN 2005 Water Prize has come one big step closer to reality.
The prototype, which has been partly financed by the local authorities and the Government of Lower Austria, produces enough power to provide about ten households with electricity. The energy produced is fed into the power grid of EVN AG, with VERBUND-Austrian Power Grid AG being the contractor.
Inventor of the new technology is the electrical engineer Franz Zotlöterer (aged 38) from Obergrafendorf, who now teaches at the St. Pölten University of Applied Sciences. He explains how this novel technique works: “At a first glance, the unit resembles a small aeration tank (diameter 5.5 m, water level 120 cm) like the ones used in a wastewater treatment plant.
At the centre of the tank is a water vortex into which a turbine (not yet built in when the picture was taken) is submersed. The turbine extracts rotational energy from the moving water, which it transfers to a generator. To achieve a maximum water vortex, very low falling heights in the range of 0.7 m to 5 m are needed.”
The water vortex fulfils yet another function in this new hydropower unit, which is the aeration of the water passing through. Zotlöterer explains that the hyperbolic funnel that is created enlarges the water surface as well as maximises the flow velocity of water on the surface.
“These two factors produce an optimum gas exchange between water and air,” he says. Conventional turbines tend to pose an ecological problem due to the big difference between turbine inlet and outlet pressure. The pressure difference makes it hard for many fish and other aquatic organisms to survive the passage and additionally destroys the microstructure of the water.
Thanks to the newly developed turbine wheel (with its four slightly curved blades) these negative side effects are avoided. According to the inventor, this is caused by the moderate acceleration of the water. The slow rotation of the turbine wheel (27 r.p.m. in the pilot unit) ensures that the water flow is not disrupted but gently deflected from the rotation axis, which is also important for maintaining the water structure.
In the larger of these hydropower units even lower rotation speeds are said to be possible. In any case, for the pilot unit authorities only require the installation of a coarse screen rake. Zotlöterer rates the efficiency of the new turbine wheel at 80 % for the Obergrafendorf hydropower unit, with a maximum 95 % efficiency to be expected in larger units yet to be developed. In the latter also two rotation tanks in parallel may be used.
Not only does this make the survival of fish alongside the flow direction of the water more likely; Franz Zotlöterer also expects that thanks to his technology even upstream fish migration aids will no longer be needed, and the water usually set aside for this purpose could instead be used for electricity generation. He believes that with a measured flow rate of 5 to 6 m/sec. the fish would in fact be in a position to overcome the vortex/turbine in the opposite direction to the water flow!
The idea to use a continuous, strong vortex flow actually occurred to Franz Zotlöterer while trying to solve the inherent problems with water quality of the natural swimming pond he had set up in his own garden. He finally decided to build a small rotation basin to aerate the water – and it worked. He then began to think about other potential fields of application for his aeration concept: drinking water supply, wastewater treatment, electricity generation.
Since water retention times of 20 seconds and more inside the pilot unit have been observed, this technology also seems to allow for a certain retention capacity with respect to floods. Especially so, if several of these units were set up alongside the tributaries of larger rivers.
After having been granted several Austrian patents, Franz Zotlöterer is currently focussing on further basic research and setting up his company Wasserwirbeltechnik. Moreover, he is already working on his next gravitation vortex hydropower unit to be erected in Mariazell, Styria, in 2006/07.
(Source: aqua press Int. 1/2006, Mag. Christof Hahn)
Contact & Information:
DI Franz Zotlöterer
Wildgansstraße 5, A-3200 Obergrafendorf
Tel. & Fax: +43/2747/3106