Solutions for Tidal- and continous current power plants


Typically subsea rotors have considerably smaller rotor diameters than wind turbines of the same nominal power. This is based on the fact that, in connection with the roughly 850fold higher density of water compared to air, high forces are applied on the complete system even at low flow velocities. A straightforward and very robust way of transforming the rotor input power into power to drive a fast turning generator is based on the application of a continuous variable hydrostatic transmission as a hydraulic converter. In this case the rotor rotation is transferred to a low speed high volume displacement device which generates a hydraulic flow. This flow is driving with high efficiency a variable high speed axial piston motor coupled with a generator.

Thereby it is possible without costly and comparably fault-prone power electronics and mechanical gearbox to optimally adapt the rotor speed to the current water flow velocity. Additionally, due to a low moment of inertia and good damping properties of a hydrostatic transmission, this allows to filter load peaks close to their origin.

A particular advantage: By use of the distributed design of the hydraulics it is possible to reduce the number of components under water. Merely the robust rotor pump for generating hydraulic flow is placed in direct proximity of the rotor, whereas the hydro motor generator set can be installed in a machine house easier to access. Also here the goal is to reduce the maintenance effort and to increase the availability.

Above all this solution simplifies the complete design, since, in the case of fixed turbines, the variable displacement motors directly capture the changing rotational directions between low and high tide. In addition the distributed design of the hydraulics is reducing the number of components under water: Only the robust rotor pump for producing the hydraulic flow is placed directly in the device. The device operator can install the hydro motor-generator set above the water surface. This reduces maintenance efforts and increases availability considerably.