The environmental impact of an HVDC interconnection system
HVDC technology is the only feasible solution when crossing long marine distances. This is the case of some electric interconnection projects in the Mediterranean Sea area. In fact, for long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses and underwater power cables avoids the heavy currents required to charge and discharge the cable capacitance each cycle .
Only in the last few years the connections between Italy and Greece and between the Italian mainland and the island of Sardinia have been completed, and different studies have been carried-out for connections between Spain and Balearic Islands, Spain-Algeria, Italy-Algeria, Italy-Tunisia, Italy-Libya, Italy-Montenegro. On this matter the European Community has funded a project (MEDRING – Mediterranean Power Ring) whose goal is to develop a coherent approach for interconnections between countries of the Mediterranean sea basin thus linking the European network with North Africa and Middle East one.
All of these projects, besides the engineering studies of the electric distribution network, focus on an attentive analysis of the environmental and territorial context, thus spotting the optimal positioning for the converter stations, positioning of the marine cable hubs together with siting analysis of the complete connection so as to minimize all possible environmental impacts.
An HVDC transmission system can produce effects on environment through several potential impacts occurring during both its construction and working phase.
Some main recurring impacts during the construction phase are related to cable landing, that could generate interferences to marine flora and fauna, due for example to sediment suspension, use of sonar, noise emission and possible collision with operation vessels.
During the working phase the generation of electric and magnetic fields are predictable; this can annoy the marine fauna and  navigation system based on magnetic compasses.
Additional impacts are related to other elements composing HVDC transmission system (converter stations, land connection, electrodes or return cable), having consequences on different environmental components.
Usually, the main environmental components that could be interfered by an HVDC project are:Water (sea bottoms, water streams, quality water)Biosphere (marine and land flora, fauna and habitat)Population (interferences with fishing and navigation, traffic)Landscape (landscape degradation)Soil (occupation and consume of valuable soils)Electric and Magnetic fieldsMicro clime (heat generation)Noise (annoyance to marine fauna and population)
The experience achieved through the years by CESI in environmental feasibility siting and analysis, allows to define practical methodologies or, in some case, a Decision Support System (DSS) for the identification and assessment of the environmental impacts of an HVDC project in the preliminary phases of analysis so that it can help to better locate the positioning of the stations and terrestrial / marine paths helping to discard areas that are environmentally unsuited among a group of alternatives.