Compact floating wave energy converter arrays: Inter-device mooring connectivity and performance

Achieving cost reduction in wave energy conversion is seen as essential to enabling the progress of the sector. At utility scale in a wave farm, multiple devices are likely to be deployed in array configurations. Closely spaced, compact wave energy converter (WEC) arrays are a promising option for cost reduction, realising synergies in operation and maintenance tasks and auxiliary installations, whilst achieving economies of scale. Mooring and anchorage systems are known to be a major component of the structural costs, and the use of interconnecting lines between neighbouring devices can reduce the number of anchors and minimise total line length. In this paper, we present the experimental study of different configurations of a five-device array of spar-buoy oscillating-water-column wave energy converters in a wave basin, focusing on the analysis of the power production performance. The study compares the performance of a single isolated device, an array with independently-moored devices and three arrays with inter-body connections, with different levels of connectivity in the mooring arrangement. Results show considerable performance implications linked to the interconnecting of devices, with the interconnected array configurations yielding a 75% increase in the annual energy extracted compared to the baseline (non-interconnected) arrangement. The performance enhancements are primarily attributed to the interconnecting moorings resulting in greater heave motion at higher frequencies for which the phase relationship between the water column and heave motion is more beneficial. Evidence is also presented that positive intra-array effects occur within interconnected arrays when the wavelength is equal to the array spacing.