Optimization of the lay-out of a farm of wave energy converters in the North Sea: analysis of wave power resources, wake effects, production and cost

Wave energy holds a lot of possibilities, as oceans contain an infinite amount of energy. In the past many concepts for wave power conversion were invented and tested. A Wave Energy Converter (WEC) converts the kinetic and/or potential energy of waves into electricity. Thus far, none of the concepts for wave power conversion has reached a maturity that makes it economic exploitable due to several technological and non-technological barriers. As the rated power of a single WEC is rather small, several WECs need to be arranged in a geometric configuration or in a `farm'. WECs in a farm are partly absorbing and partly redistributing the incident wave power. The power produced by each individual WEC in the farm is affected by the presence of its neighbouring WECs. The current knowledge about the redistribution of energy inside and behind a farm of WECs is rather limited. Both the power production and cost of a farm are dependent on the lay-out of the farm. So far, most studies concentrate on the optimization of a single WEC, rather than optimizing a complete farm. To develop a commercial technology, the impact of arranging WECs in a farm has to be investigated as well. The optimization of the lay-out of a farm of WECs in the North Sea is the focus of this PhD research. The wave power resources and possible locations for the deployment of a farm of WECs in the North Sea are quantified in a first part of this PhD research. In this PhD work an optimal balance between power production and cost of a farm of WECs is aimed at. Therefore in a second part the wake effects behind a farm of WECs are studied in a time-dependent mild-slope wave propagation model MILDwave, developed at Ghent University. Finally the cost of a farm is discussed in a third part of this PhD work. Moreover an investment analysis of the deployment of a farm of WECs in the southern North Sea is presented

Power absorption by closely spaced point absorbers in constrained conditions

The performance of an array of closely spaced point absorbers is numerically assessed in a frequency domain model Each point absorber is restricted to the heave mode and is assumed to have its own linear power take-off (PTO) system Unidirectional irregular incident waves are considered, representing the wave climate at Westhinder on the Belgian Continental Shelf The impact of slamming, stroke and force restrictions on the power absorption is evaluated and optimal PTO parameters are determined For multiple bodies optimal control parameters (CP) are not only dependent on the incoming waves, but also on the position and behaviour of the other buoys Applying the optimal control values for a single buoy to multiple closely spaced buoys results in a suboptimal solution for the array Other ways to determine the PTO parameters are diagonal optimisation (DO) and individual optimisation These methods are applied to two array layouts consisting of 12 buoys in a staggered grid and 21 buoys in an aligned grid Compared to DO, it was found that individually optimising the CP increased the energy absorption at Westhinder with about 16-18% for the two layouts, respectivel