ering the relatively high population density in Europe it is obvious that it would be very difficult to identify suitable areas for rectennas in the vicinity of most of these centres without a major relocation of people. A possible solution is seen in siting the rectennas offshore in European coastal waters (4). Based on a number of technical and economic requirements, location restricting aspects and boundary conditions, four areas in the North Sea between 51 degrees north and 57 degrees north latitude have been identified as potentially suitable (Fig. 4). Twenty-seven other places (marked with stars in Fig. 4) look promising as well. In the search for potentially suitable locations a preliminary inventory has indicated that most limitations are imposed by navigational interests, e.g., each year approximately 200,000 ships pass through the southern part of the North Sea. The natural and geotechnical boundary conditions encountered in the various areas result in many design criteria for the civil engineering works to be constructed there. In this respect they closely affect the construction and maintenance costs. Five basically different designs for a rectenna site are distinguished (Fig. 5): I. Artificial islands with sand beach and dunes/or hard sea defence construction; 2. Polder; 3. Atoll, with floating antenna; 4. Atoll, with rectenna supports founded on piles; 5. Exposed gravity or jacket structures. The artificial island and the polder are the only two solutions which permit installa-
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