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Sustainability 2016, 8, 1300 2 of 21

Studies on the assessment of wave energy potential in candidate sea sites for building pilot
plants and the performance estimation of WECs in those sites are still needed in order to support the
cost–benefit analysis of these technologies.
The siting of pilot plants for the exploitation of wave energy by means of WECs is a technical,
economic and strategic problem. The assessment of wave conditions is necessary to estimate the
wave energy resource available in the area of interest and to optimize the design of WECs for the
specific wave climate. Due to non-technical factors [3] such as cost of investments for building, control,
maintenance and energy transportation by submarine cables, nearshore areas are the candidate areas
due to their proximity to the coast and harbors. However, once waves propagate toward the shore,
part of their energy is dissipated due to frictional losses. At the same time, their interaction with the
sea bottom and coast features like shoals, headlands and bays, induce refraction mechanisms that may
lead the offshore wave energy to spread on a wider area or to focus on a smaller area. Considering the
characteristics of the waves of the Mediterranean Sea, once the water depth is greater than about 15 m,
the energy dissipation due to bottom friction or breaking is almost zero and the mentioned focusing
mechanisms may lead to coastal areas where the wave energy potentials are higher than the related
offshore values. Thus, the assessment of wave energy at coastal areas is pivotal in order to locate the
hotspots for the exploitation of the wave energy resource.
The purpose of this work is the assessment of the energy potentials on the offshore of the whole
Mediterranean Sea, the selection of the most promising Italian nearshore areas and the location of
their hotspots, the evaluation of performances of state of the art WECs and comparisons between their
energy productivity in Mediterranean hotspots and in EU oceanic hotspots.
The aims are to contribute to the present knowledge on energy assessment and selection of Italian
sea sites for the exploitation of wave energy and to select some of the proposed WEC technologies that
are most suited for the Mediterranean Sea climate. The content of this paper is of evident interest for
the EU and Italian communities that are investing in this field as well as companies worldwide that
are developing WEC technologies and thus need to optimize the device for specific wave climate in
order to reach the level of commercial maturity.
The results of this study discover the exact place of some hotspots where thanks to focusing
phenomena the wave energy potentials are higher than those in their surrounding areas. This finding
would have not been achieved if numerical models with appropriate spatial resolution were not
used; it suggests, to the research community, the need of such methodological approach. Moreover,
this work proves that, although the energy potentials of the ocean sites are higher than those in the
Mediterranean sites, this difference is drastically reduced in terms of the energy productivity potentials
of existing WECs even though none of the tested technologies were optimized for the moderate wave
climate. It suggests that, if the WEC technologies were optimized for moderate wave climate their
production of energy would approach the values that characterize the oceanic sites. This latter result
might contribute at the opening of a new market for WECs devices since, at present, they are under
development just for the most energetic oceanic climates.
The paper contents are structured as follows. Section 2 provides a review of current state
of research on each of the three topics, namely offshore assessment, nearshore assessment and
performance estimation of WECs. Section 3 describes the wave data used for the offshore assessment,
the methodology used for the nearshore wave propagation and a brief review of the state of the art
WECs considered in this study. The assessment of the offshore and nearshore wave energy potential is
presented in Section 4. Performance analyses of seven state of art WECs are discussed in Section 5.
Conclusions are drawn in Section 6.
2. Review of the Current State of the Research Field

2.1. Assessment of the Offshore Potential

Traditionally, the assessment of the wave energy has been carried out for offshore deep water
wave data [1,4–19], while, more recently, coastal areas have been investigated in order to locate