In this work, an extended overview of the marine renewable energy in the Mediterranean Sea is provided as regards current status, potential problems, challenges, and perspectives of development. An integrated and holistic approach is necessary for the economic viability and sustainability of marine renewable energy projects; this approach comprises three different frameworks, not always aligned, i.e., geotechnical/engineering, socio-economic, and environmental/ecological frameworks. In this context, the geomorphological, climatological, socio-economic, and environmental/ecological particularities of the Mediterranean basin are discussed, as they constitute key issues of the spatial context in which marine renewable energy projects are to be implemented. General guidelines for the sustainable development of marine renewable energy in the Mediterranean are also provided.

In this work, 20 years (2000–2019) of ERA5 wave and wind data are analyzed and evaluated for the Greek Seas by means of in-situ measurements derived from the POSEIDON marine monitoring system. Four different statistical measures were used at six locations, where in-situ wind and wave measurements are available from oceanographic buoys. Furthermore, the ERA5 wind and wave datasets were utilized for the estimation of the available wind and wave energy potential for the Greek Seas, as well as for the assessment of complementarity and synergy between the two resources. In this respect, an event-based approach was adopted. The spatial distribution of the available wind and wave energy potential resembles qualitatively and quantitatively the distributions derived from other reanalysis datasets. Locations with high synergy and complementarity indices were identified taking into account water depth. Finally, taking into consideration a particular offshore wind turbine power curve and the power matrix of the PELAMIS wave energy converter, the estimation of the combined energy potential on a mean annual basis is performed.

Identification of prominent sea areas for the efficient exploitation of offshore wind energy potential requires primarily the assessment and modeling of several aspects of the long-term wind climate. In this work, the offshore wind speed and wind direction climate of the Mediterranean Sea is analytically described, the corresponding offshore wind energy potential is estimated on an annual and seasonal basis, and candidate areas for potential offshore wind farm development are identified. The analysis is based on ocean surface wind fields obtained from the Blended Sea Winds product, provided by the U.S. National Oceanic and Atmospheric Administration (NOAA), from 1995 to 2014. The satellite data are evaluated with reference to buoy wind measurements in the Spanish and Greek Seas. Wind data analysis reveals areas in the western and eastern Mediterranean Sea with high mean annual wind speed combined with rather low temporal variability. The obtained results suggest that offshore wind power potential in the Mediterranean Sea is fairly exploitable at specific suitable locations, such as the Gulf of Lions (with mean annual wind power density up to ~1600 W/m ² ) and the Aegean Sea (with mean annual wind power density up to ~1150 W/m ² ), that are certainly worth further in-depth assessment for exploiting offshore wind energy. Finally, based on the available offshore wind resource potential and the water depth suitability, three specific sites (in the Gulf of Valencia and the Adriatic and Ionian Seas) are selected and the average wind power output for a specific wind turbine type is estimated.