HVDC links are becoming an increasingly popular solution to interconnect previously isolated systems or to establish new corridors within highly meshed networks. As a matter of fact, HVDC links show outstanding advantages with respect to HVAC corridors such as full controllability of power flow avoiding the creation of parallel or, even, loop flows in meshed networks. Moreover, HVDC technology is the only feasible solution when crossing long marine distances. Particularly, in the case of the Mediterranean basin linking Europe to Africa requires the adoption of HVDC technology, with the only exception of the Spain-Morocco interconnection, given the short distance across the Strait of Gibraltar. Italy is especially interested in establishing new interconnections with the Maghreb countries, considering the shortfall of internal energy production and the heavy congestion across the trans-Alpine electricity corridors. Interconnecting Maghreb with Europe will offer mutual benefits in the technical, economical, environmental sectors, without forgetting the political dimension: indeed, a greater integration of North-Africa countries with the Europe has been recognised by the EU as a priority since the starting of the Barcelona process in 1995. On the wake of the mutual interests of the concerned countries, Italy and Maghrebian countries launched a series of feasibility studies aimed at identifying the most appealing solutions for trans-Mediterranean submarine electric interconnections. Since the investments are in the order of several hundreds of million of Euro for each interconnection, an appropriate methodology has been designed and tuned through the application to practical cases. The methodology is based on a two step-approach. In the first step, an accurate screening activity is carried out aiming at comparing the possible technical alternatives of the DC interconnector: location of the converter stations, sizing of the interconnector in relationship to the AC grid transfer capacities and the surplus/shortfall of power at both ends, selection of the DC technology, preliminary configuration of the DC schemes. At this stage, the possible DC voltage levels are also examined. At the end of the screening activity, a ranking of all the feasible alternatives is drawn through a “differential” approach consisting of comparing the alternatives on the basis of a series of indexes, the values of which are “different” in the various solutions. Then, the second step of the methodology is applied to the selected solutions to identify the DC schemes, the technical measures to be adopted for the connection of the converter stations to the AC grids, the preliminary routing through a desktop study and the economic and financial indexes.
The paper presents the main outcomes of the three feasibility studies of interconnection between Italy and Algeria, Tunisia and Libya. However, the proposed methodology is valid in general to decide the feasibility of DC links resorting to EHV or UHV for the transmission of large amount of power over long distances.