Micro Hydroelectricity

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onderslag waterrad

An undershot water wheel is characterized by a low head (generally maximum 2 meters) and a large flow rate (usually more than 400 l/s). The water flows into the mill at high speed through a sluice just in front of the mill. Then the blades are driven, which are enclosed between 2 walls. The water flows freely behind the mill. The reel can run in the water, but only when it is turning slowly. High speed undershot wheels should run clear of the tail water as much as possible.

Due to the combination of head and flow rate, the electrical power is usually between 5 and 25 kW. In all cases, an industrial gearbox must be installed to increase the speed for the generator. The rotational speed and torque are high, so that such a gearbox can be large. Sometimes the existing gears can be used. Then a simple belt transmission will suffice.

An undershot water wheel has an average efficiency since water is always lost between the blades and the guidance. In addition, there are inflow and outflow losses due to turbulence. The higher the speed of the water and the wheel, the higher these losses. That in itself is not a problem as long as there is enough water to compensate for these losses. The power will then remain high.

In the case of new construction or restoration, the existing situation is connected as much as possible. However, the blade shape often proves to be inefficient. Choices have often been made in the past based on manufacturing possibilities. In the current era of laser cutting, much more can be optimized. Gratia Hydro has developed optimized models based on classic designs such as Zuppinger, Sagebien or Poncelet. Each of these old designs has its own starting points, but also its limitations. Precisely by taking a critical look and also taking into account the local situation, we can often make a better design than there has ever been.

The projects below have been carried out by Gratia Hydro. The considerations for the choices are described for each project.