Worldwide, ecological aspects are an issue of growing attention in the ­authorization process of hydro power plants. In the area of the power plants downstream migrating fish need to find a safe way of passing the turbine chamber.

Fish-friendly rake and bypass systems are the main component to guide the fish around the turbine chamber. Moreover, fish friendly turbines also enable a safe passage of the turbine itself for fish that can pass through the fine rake. By combining a fish friendly rake system with a fish friendly turbine an overall ecological power plant can be realized.
DIVE Turbinen GmbH & Co. KG has developed the DIVE-Turbine, a turbine that is highly efficient in terms of power generation and in the same time a very fish friendly system. The first emprirical studies on the DIVE- Turbine have been realized in 2016.

The DIVE-Turbine is a double regulated propeller turbine for capacities of 50kW – 2 000kW. The development and manufacturing of the DIVE Turbine are located in Amorbach, a small town in the North of Bavaria about one hour from Frankfurt (Main).
The DIVE-Turbine is regulated by the guide vanes and the runner speed, which is adapted for high efficiencies at any operation point. The runner blades are fixed to the runner hub. Hydraulically, the ­adaption of the runner speed of the DIVE-Turbine has the same effect as the adaption of angle of the runner blades for a standard ­Kaplan-Turbine with fixed runner speed: the blades of a Kaplan-­Turbine are closing when the flow is reduced. At a DIVE-Turbine, the runner speed is lowered. Due to the fixed runner blades of the ­DIVE-Turbine there is no gap between the runner blades and the runner hub. The gap between the runner blades and the outer vessel is very tiny, because the blades don’t need space to be turned. Moreover, the fixed connection between runner blades and runner hub doesn’t require an inside mechanism of the hub to move the blades. Therefore the number of runner blades of a DIVE-Turbine is not restrained by mechanics of joint.

FISH FRIENDLINESS ON HYDRO POWER TURBINES
The subject of fish friendly turbines is to minimize the risk to get stuck in gaps, the collision probability and collision velocity for a fish that would eventually pass the fine rake and make it to the turbine chamber. In most cases diadromous fish species like eel and salmon smolt are subject to fish friendliness examinations, as they are facing many hydro power plants on their way downstream to the sea. Empirical studies about the effect of Kaplan-Turbines on salmon smolts and eels have been carried out ever since the invention of Kaplan-­Turbines. Based on these experiments, guidelines and calculation ­methods were developed to estimate the turbine mortality. In many aspects, the guidelines for fish friendly turbines are met by the ­DIVE-Turbine:

• runner blades remain constantly open: low collision risk, low collision speed.
• no gap between runner blades and runner hub: no risk to get stuck.
• very small gap between runner hub and runner blades: no risk to get stuck.
• reduced speed due to large-scale dimensioning of the turbine.

EMPIRICAL RESEARCH ON THE DIVE-TURBINE
DIVE Turbinen GmbH & Co. KG has started empirical studies on turbine mortality in 2016. The first tests took place at a
DIVE-hydropower plant near Toulouse, southern France, at the river Ariége. Rainbow trouts in the size of salmon smolt (TL=18cm…25cm) were introduced directly into a turbine and recaught and examined behind the draft tube. The turbine had a runner diameter of 1,600 mm and 5 runner blades. The mortality rates after 48h were 15% at full load (Q=11m³/s), 2% at 80% part load and 1% at 60% part load. The size of trouts tested corresponds to a fine rake with max. 25mm rake bar distance. If the efficiency of the rake system itself is considered 75%, the overall mortality rate of the power plant (fish-friendly rake-and-bypass-system & DIVE-Turbine) can be considered max. 1,5%. This mortality rate can still be lowered by reduction of number of runner blades (3 instead of 5 to reduce collision probability).
It is also possible to reduce the runner speed and therefore the collision risk for fish by amplifying the runner diameter.

EFFICIENT RAKE SYSTEMS
Still, the design of the fine rake  is the most important criterion for a fish friendly power plant, as the rake is both a physical and a hydraulic barrier for any downstream migrating animal. A fish friendly designed rake hydraulically guides the fish towards a bypass or any other safe downstream passage without the need of being also a physical barrier. Vertically very inclined rakes or horizontal rake-and-bypass-systems (EBEL, GLUCH & KEHL) are of very high efficiency considering safe downstream migration. Moreover and most important, those rake systems also minimize the rake-induced hydraulic losses and operation cost compared to conventional inclined rakes.
In cooperation with fish biologists all over the world DIVE Turbinen GmbH & Co. KG has developed the turbine technology to realize fish friendly power plants in accordance with local demands. In the same time the DIVE-Turbine has proven to be an economic turbine solution of high efficiency.
One of the most fish friendly hydro power plants in Europe is currently under construction in Germany. It has a horizontal rake-and-bypass-system, a fish ladder and three DIVE-Turbines with 3 runner blades each. The combination of the downstream and upstream migrating system and the DIVE-­Turbine will set an example in terms of ecological hydro power worldwide. The power plant will be set into operation in 2017.