Generating electricity from waves at a breakwater in a moderate wave climate

The purpose of this thesis was to develop a preliminary concept design of a wave energy converter. The type of device designed was limited by several starting points which stipulated, among other criteria, a robust structure which can be constructed within a breakwater and can generate electricity from a fairly mild (in the order of Hs=0.5-1.5m) and regularly occurring wave climate. Integration with a caisson breakwater was selected to ensure survivability. Three concepts using the theories of wave overtopping, wave run-up, and wave pressure were evaluated. A multi-criteria analysis was performed on the three concepts. Concepts were scored based on power output, functionality in wide range of conditions, ease of construction, and theory reliability. Theory reliability was scored based on the three aforementioned criteria. The concept analysis concluded the most promising device to further investigate was the concept based on the theory of wave pressure. This device excelled in (theoretical) output having the highest peak power and wider power curves. In the concept, wave pressure is exerted on an underwater opening. This opening leads water into a pipe with a gradual constriction. This constriction increases the pressure allowing the water to be brought to an optimal level above MWL. Through a turbine the water is returned to MWL. A model was built with three different opening ratios and three separate basins open to the wave flume at the bottom. A series of tests were performed of varying wave climates and crest freeboards. During the tests the head difference was measured between the internal basins and the water elevation at the rear of the model. The holes in the bottom of the basins allowed for constant flow of water out of the basins and a calculation of flow rate based on the hydraulic head was required. This allowed for the calculation of the theoretical power generated during the tests. Additionally, the input wave power was known so the device efficiency could be calculated for each test allowing for the identification of the optimal geometry and the generation of a full-scale efficiency curve. The device was evaluated at two design locations in Panama and Japan. The wave climate, tidal influence, system headloss, and sea level rise were calculated in order to discover the power generation at each location. Revenue associated with the generation of electricity was calculated to give an indication of the device’s cost effectiveness. It was found that sea level rise has a negligible impact on efficiency if sea level rise is appropriately accounted for. The impact is in the order of 1.5% over 50 years if the rise is assumed to be 80cm over 100 years. Including sea level rise, the device has been calculated to generate an average of 16,413 and 5,766 kWh/m/yr at Panama and Japan, respectively. The report concludes that the proposed design can be constructed using existing techniques for caisson construction. However, the design must be further optimised and tested in order to become a fully feasible wave energy converter.Hydraulic EngineeringCivil Engineering and Geoscience