This paper presents a complementarity assessment of the four renewable resources, i.e. wave, tidal, wind and solar, around the Island of Ireland (including Northern Ireland). A particular focus is given to the potential benefits of combining relatively unexploited but significant marine renewable energy resources (wave and tidal) in Ireland, with more established renewable technologies, such as wind and solar. New complementarity metrics, based on the mathematical principle of total variations, variance and standard deviation, are utilised here, since they can be used to assess the complementarity of more than two resources. The results show clear benefits of diversifying the resource mix with the highest complementarity achieved for combining all four resources.