Reliability-Based Structural Optimization of Wave Energy Converters

More and more wave energy converter (WEC) concepts are reaching prototype level. Once the prototype level is reached, the next step in order to further decrease the levelized cost of energy (LCOE) is optimizing the overall system with a focus on structural and maintenance (inspection) costs, as well as on the harvested power from the waves. The target of a fully-developed WEC technology is not maximizing its power output, but minimizing the resulting LCOE. This paper presents a methodology to optimize the structural design of WECs based on a reliability-based optimization problem and the intent to maximize the investor's benefits by maximizing the difference between income (e.g., from selling electricity) and the expected expenses (e.g., structural building costs or failure costs). Furthermore, different development levels, like prototype or commercial devices, may have different main objectives and will be located at different locations, as well as receive various subsidies. These points should be accounted for when performing structural optimizations of WECs. An illustrative example on the gravity-based foundation of the Wavestar device is performed showing how structural design can be optimized taking target reliability levels and different structural failure modes due to extreme loads into account.