Application of combined power and thrust capping to tidal turbine farms

As an important form of renewable energy, tidal energy is challenged by many factors including its high cost and potential environmental concerns. This thesis is aimed to contribute to the development of tidal energy by introducing an operation strategy that is able to reduce the capital cost and environmental impacts of extracting tidal energy. This thesis considers the optimal strategy for the design and operation of tidal stream turbine farms. Such operation strategy aims to reduce the capital cost of tidal turbine farms by reducing the maximum power and thrust loading. In addition, this strategy can potentially reduce the environmental impacts with the cost of reducing a certain amount of overall power production. Because of the advantages in computation time and ease in interpreting results, an idealised 0D model is used first to explore the effectiveness of implicating power and thrust capping (i.e. limiting the peak power and peak thrust of the turbines) to a tidal turbine farms. In addition, the impact brought by tidal turbine support structures to the tidal energy farm and the local flow field is considered by this idealised 0D model. The power and thrust capping strategy is further explored by using a 2D Shallow Water Equations (SWEs) model based on one real candidate tidal energy site locating at North Scotland, the Pentland Firth. The impact of power and thrust capping on power production and on the environmental impacts are further evaluated in detail. Different combination of power capping and thrust capping are also evaluated. The effects of combined power and thrust capping are believed to be representative. However, the detailed setting (i.e. choice of capping ratio) are very likely to be site specific and thus more specific analysis would be required for the capping strategy to be applied to other potential tidal energy sites. The results suggest that a combined power and thrust capping strategy is beneficial to a tidal turbine farms in terms of optimising power production, reducing capital cost and reducing environmental impacts, and therefore should be adopted in the design of tidal stream turbine farms.