Investigation for a more reliable yaw system design for the deltastream tidal turbine

Abstract

Tidal power is a growing industry in the world but particularly in the United Kingdom. Many companies have started the race to achieve a cheap and efficient tidal turbine design. For instance, Tidal Energy Limited has opted for an innovative design by incorporating three horizontal axis turbines in a triangular frame that will be lying on the seabed. This project is called “DeltaStream” and a test device will be placed in Ramsey Sound, in the Welsh coast. The design of the project includes a yawing mechanism capable to turn the nacelle around the vertical axis in order for the turbines to face the tidal flow. This mechanism maximizes the power production as the tidal speed changes in direction every 6 hours. But it has another function. Due to the tidal speeds and the water density, the torque created in the rotor is very large. As Tidal Energy Ltd. has opted for an optimized blade design with no blade pitching mechanism, the only way to decrease the huge rotor torque in order to stop it is by the yawing of the nacelle away from the flow. However, it is believed by the author of this thesis that the yawing mechanism can be improved in system redundancy terms, in relation with the important role that accomplishes in the overall turbine design. The present thesis is an analysis of the weakest points of the current yaw system design and an investigation in an alternative to be cheaper, simpler and improved in reliability terms. The proposed design uses motors with reduction planetary gearboxes attached to the nacelle to drive the gear ring fixed on the tower structure. The new design is believed to be more reliable than the original due to the high level of redundancy. Nevertheless, it is not as cheap as expected due to a very expensive yaw brake system. In that point, the author recommends further investigation in the price reduction of that component without decreasing the level of brake fixation.