Fig. 4. Cost of power transmission system. This is partly a measure of the simplifications made above. However, the slope of the curve is fairly shallow near the minimum (the more than 70% increase in area between the minimum cost configuration and the Reference Design is accompanied by an increase of less than 8% in cost), and in fact several studies recommend the use of a larger antenna (23,24). Second, it is clear that a marine rectenna should be substantially smaller than one on land. These figures give an optimum land rectenna of 7.5 km diameter with an antenna of 1.3 km diameter; but a marine rectenna of 6.2 km diameter with antenna of 1.6 km diameter — representing a decrease of 30% in rectenna area, and an increase of 50% in antenna area. In round figures this result suggests that for a North West European marine rectenna we should be considering a structure in the region of half the beam area of the NASA Reference Design, or about 7 km by 14 km, with an antenna at the satellite about twice the area of the Reference Design, some 1.5 km in diameter. It should be noted in particular that to the extent that the cost estimates for marine structures used above are optimistic, the minimum cost configuration will be even further from the Reference System configuration.
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