Weather Window Analysis of Irish and Portuguese Wave Data With Relevance to Operations and Maintenance of Marine Renewables

Abstract

This paper presents the results of a weather window analysis of wave data from the west coast of Ireland and the Atlantic coast of Portugal in order to quantify the levels of access to ocean energy renewables, which may be deployed there, for operation and maintenance activities. In order to operate and maintain offshore marine renewables, a device will have to be accessible for a certain period of time. This will require a weather window consisting of a consecutive period of wave heights low enough and long enough for the device to be accessed. It is important to quantify what the levels of access are off the Irish west coast and Portuguese Atlantic coast given their high wind and wave resource. Wave data from two wave buoys, the M3 buoy located 56km off the west coast of Ireland and the Leixoes buoy located 19km off the Portuguese coast, are analysed to quantify the levels of access that exist. The data is used to quantify the general regimes at both sites by presenting the wave energy resource, the mean annual exceedance and the wave height frequency at both sites. The levels of access are quantified at operations and maintenance (O/M) access limits of Hs 1.0, 1.5, 2.0 and 2.5m wave height, by presenting the number of windows and the percentage of the year that these windows make up as well as the total number of hours, monthly and annual, that the wave heights are below these limits. Also presented are the waiting periods between windows by showing both the longest individual waiting periods between windows in a year and also the total intervals between windows in a year. The levels of access observed off Ireland and Portugal are then compared to levels of access observed at other marine renewable locations, namely the North Sea, Irish East Coast and Pacific North-western US coast. The results indicate that the levels of access off Ireland and Portugal are far below those observed at other marine renewable locations, and at the lower wave height access limits, there are very few suitable weather windows and considerable winter waiting periods between these windows. The implications of these low levels of access suggest that maintaining wave energy converters, off the west coast, may not be feasible and devices will need to be brought ashore for O/M activities.