Accessibility for operation and maintenance tasks in co-located wind and wave energy farms with non-uniformly distributed arrays

Operation and maintenance is a particularly challenging aspect of offshore wind energy. First, the harsh marine environment requires more frequent tasks relative to onshore wind turbines; and second, these labours can be delayed by difficult sea conditions - in particular, large wave heights - leading to down time and, consequently, increased costs. This can be offset in part by combining offshore wind and wave energy systems: wave energy converters adequately deployed extract part of the incoming wave energy, resulting in a milder wave climate within the wind park, and hence better accessibility for maintenance tasks and reduced down time. The actual results depend on the layout of the co-located wave-wind energy farm. Previous works showed that peripherally distributed arrays, i.e., co-located wave energy converters deployed along the periphery of the wind farm to act as a barrier, bring about good results in terms of wave height reduction and average accessibility. However, important differences between the accessibility to the wind turbines located directly behind the barrier and the other turbines in the farm were found. On this basis, the objective of this paper is to analyse whether non-uniformly distributed arrays can lead to a more uniform wave height reduction throughout the farm. The analysis is based on 4 offshore wind farms currently in operation: Alpha Ventus, Bard 1, Horns Rev 1 and Lincs. It was found that non-uniformly distributed arrays lead to a more significant average wave height reduction (by over 4.7%) and more uniformly distributed throughout the farm, as well as a greater power output from the co-located devices (by up to 16.5%).