Marine renewable energies in the Mediterranean. Towards a new landscape

In his “Mediterranean Breviary” (1987), Predrag Matvejevic reports on characteristic traits of the landscape through a realistic writing. He just shows a simple taxonomy of Mediterranean identity factors and elements, including ports, piers, docks, bollards, wharfs, winches, buoys, lighthouses, warehouses and markets. Even smells and materials, such as hemp and coal tar, are mentioned in the list. The book reveals an authentic picture that, far from looking like a postcard, shows contrasts between natural and human elements, both included in the anthropic coastal and maritime landscape.

The exploitation of marine energy sources opens a discussion on Mediterranean landscape, more than other renewable energies. The research on blue energy is not limited to technological issues but calls for a wider approach. Nowadays, the barriers to the deployment of these solutions in the Mediterranean sea, besides the technology readiness level and economic profitability, concern regulations, approvals, overlay with other marine activities, environmental sustainability, social acceptance and landscape compatibility. Can blue energy properly become part of the Mediterranean landscape? 

The Blue Deal partnership aims at transferring knowledge on blue energies and prompting their deployment in the Mediterranean, starting from a simple classification.  

On-shore Wave Energy Converters are systems embedded in docks and piers. The vertical motion of waves within caissons compresses and decompresses air that, flowing throughout pipes, makes wind mills generate electricity; similarly, the wave motion lets floating buoys fixed on piers oscillate and compress hydraulic pistons or, otherwise, it pulls seawater up to reservoirs and then fall down through micro-hydro turbines. These technologies are profitable in combination with the construction of new piers, such as for the extension of existing harbours, although production yields are still uncertain (almost 500 MWh/year per 100 m pier).

Among onshore solutions, systems exploiting thermal gradients between seawater and air through heat pumps have been successfully tested. These can supply heating and cooling energy for buildings along the seacoast, such as housing, hotels and other services, achieving good levels of performance (CoP > 4). Other innovative technologies exploiting salinity gradients, such as based on inverted electrolyses, are under study in combination with desalinating plants.

Near-shore Wave Energy Converters can have interesting applications in the Mediterranean. Buoys fixed on seabed and connected to underwater generators would require manageable maintenance processes and have good production yields, especially considering their installations in clusters or in line, such as by replacing boundary marker buoys of protected marine areas (a 25 buoys cluster can generate from 1000 to 1500 MWh/year). 

Macro-algae are a potential source of energy, such as for the production of bio-gas or bio-fuel through bio-refinery. These processes are used in Northern Europe but are not easily transferable in the Mediterranean since marine biomass growth is not enough for efficient productions. Nevertheless, the combination with aquaculture can represent an opportunity, especially considering the additional function of algae to absorb nutrients.

Off-shore Wave Energy Converters include bigger buoys embedding an electric generator within the floating body. These can be installed in open sea areas with high wave energy potentials even if production yields are still variable. Other technologies exploiting marine currents have not many chances to be used in the Mediterranean, except for locations in the straits of Messina and Gibraltar with current speed over the minimum threshold of 2.5 m/s (generally, in the Mediterranean, currents achieve at least 0.1-0.2 m/s). These devises do not have visual impacts but need deep analyses concerning their possible interference with marine animals.

Finally, off-shore wind farms can represent a good opportunity, considering for example the minor frequency and intensity of adverse weather events in the Mediterranean compared to the North Sea. Anyhow, given a deep and variable bathymetry, most profitable solutions concern floating wind turbines. The high maturity of wind  technology makes it economically sustainable but the main problem is still its landscape impact. To this regards, the floating wind farms can be easily disassembled or delocalised. Moreover, their visual impact is reduced by the long perspective of seascapes with respect to their localisation in terrestrial landscapes. 

Therefore Blue Deal does not deal with technological issues of blue energy but, starting from existing technologies, investigates sustainability of its deployment in the Mediterranean. One important observation must be done regarding the European and national objectives of greenhouse gas emission reduction: Europe aims to be the first carbon neutral continent by 2050. It is crucial to understand that this massive energy transition to renewables will have social and environmental impacts. How can we expect the Mediterranean landscape to change accordingly? What shall we take into consideration to manage this transition in terms of landscape impact?

Integrated energy systems from different renewable sources connected to smart grids would potentially become a reality and contribute to increase the complexity of the Mediterranean landscape. Social acceptability will be crucial to accomplish this transition that, first of all, is a cultural transition. Blue Deal focuses on this cultural transition. It develops participative processes of stakeholders engagement, including administrations, enterprises and citizens, in order to build capacity and achieve agreements. Just like the devices described by Matvejevic in his Breviary, blue energies can be likely mentioned in the next future among the identity elements of the Mediterranean landscape. 

Riccardo M Pulselli and Elena Neri (Indaco2)