The power flow and the wave energy flux at an operational wave farm: Findings from Mutriku, Bay of Biscay

Abstract

Mutriku is a wave farm on the Spanish coast of the Bay of Biscay that has now been continuously supplying electricity for more than nine years. Since 1979, there has been a growing trend in wave energy flux for the whole Bay of Biscay. ERA5 data at the grid point nearest to Mutriku indicate an increase of 0.146 kW/m per decade for the 1979–2019 period. In this paper, a Self-Organizing Map (SOM) with a 2X5 architecture has been fitted to identify ten major sea-state types, each with a distinctive electricity generation pattern at a daily scale. This rendered it possible to reconstruct the daily electric power that would have been generated if the Mutriku wave farm had been operational over the entire 1979–2019 period and, accordingly, evaluate the impact that the observed changes in the wave climate and associated wave energy flux would have had on the electricity production. The results indicate that the electricity production or power flow would have remained constant during that period despite the increasing trend in wave energy flux. This is due to the regulation procedures and mechanisms used in the operation of Mutriku's Oscillating Water Column (OWC) wave energy converters, which dampen the effect of the increasing trend observed. The main conclusion is that the power flow levels off above a given threshold, making it more stable than the wave energy flux.