Compact floating wave energy converter arrays: Mooring loads and survivability through scale physical modelling

Abstract

The current cost of electricity has been preventing the technological progress of wave energy converters. The use of compact wave energy converters arrays is seen as a technological breakthrough for reducing these costs. These array configurations aim to maximize the energy extracted per unit area of marine space and to promote the sharing of components and installation, operation and maintenance tasks. Mooring lines are fundamental components in these systems and represent a considerable portion of the project cost. Reducing the number of mooring lines through the application of arrays with inter-body connections has a high potential for cost reduction. 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 devices motion and the mooring line loads. 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. Tests were carried out for moderate and extreme wave conditions. Results show good performance for all configurations when subjected to moderate sea conditions. Under extreme sea conditions, high peak tensions were observed in the lines of all array configurations. Particularly large values were detected in the inter-body lines, caused by their full extension. Based on these results, guidelines for the design of mooring systems for compact wave energy converter arrays are presented.