The performance of the three-float M4 wave energy converter off Albany, on the south coast of western Australia, compared to Orkney (EMEC) in the U.K.

Abstract

In this study we compare wave climates and their potential for wave energy conversion for the two energetic but quite different sites of Albany and Orkney. Energy capture is based on the M4 machine with well defined characteristics. The M4 machine is a self reacting system with 3 floats, each float with a circular cross-section when viewed from above. The smaller two floats are rigidly connected by a beam, and the largest float is connected to the mid float by a beam with a hinge. The machine generates power through the relative angular motion of this hinge above the middle float. The machine performance was previously assessed for various locations in the eastern North Atlantic including the European Marine Energy Centre (EMEC) site west of the Orkney Islands, Scotland, for wave power output (Santo et al., 2016a) and extreme response (Santo et al., 2017). In this study, we apply the analysis to a location off Albany on the south coast of western Australia, an area well-known for almost continuous exposure to long period swells. We use Australian Department of Transport (DOT) wave buoy data measured in 60 m of water over the period 2009−2017. The hourly data is close to continuous but contains some gaps corresponding to ∼ 13% of the total duration, these are patched to form a continuous wave record.Having sized the machine based on mean wave period, extreme wave height statistical analysis is performed using storm-based identification and a peaks-over-threshold technique, following Santo et al. (2016b), providing information relevant for any wave energy converter at the location. From operability and power scheme economics, we then compare the optimal size of machine, practical power output and the associated variability in power produced by an M4 machine at Albany to the open North Atlantic location off the Orkneys. This is performed with the methodology outlined in Santo et al. (2016a). For survivability, it is important to identify extremes of machine motion. Hence, extreme responses are also compared for the central hinge angle of the machine in survival mode with the power take-off turned off. We find that a much larger machine is required at Albany, because of the longer waves compared to Orkney. However, at the two very different locations the power/cost ratios are similar.