Value of Flexibility Following this approach, it can be seen that significant economic benefits would arise if SPS systems were designed: 1. to allow a satellite to switch some or all of its transmitted power between two or more "rectennas" according to the pattern of demand on the rectennas, and 2. to allow rectennas to receive microwave power from one or more satellites simultaneously. The combination of these enhancements would permit the achievement of a high load factor on the satellite (which represents some 80% of the total cost) while utilising the rectennas to which it delivered power at lower load factors for the provision of daytime and peak load power, for which the cost to utilities is substantially more than for base-load power. That is, since the capital costs of both satellite and rectenna dominate their operating costs, the contribution of both segments to the cost of SPS power is dependent on the load factors at which they are operated, the space segment being substantially more important. Thus, provided that the load factor on the space segment can be kept high by delivering power to more than one rectenna in succession during the day rectennas could be operated profitably even at relatively low load factors. Figure 1 illustrates the additional flexibility of rectenna operation that this permits: A particular system might not be competitive as a baseload power source even if both satellite and rectenna were operated at the maximum load factor of 0.9, and it might not be economic if operated with a load factor of only 0.67 (typical for daytime demand) on both satellite and rectenna. The system could nevertheless provide daytime power profitability with a load factor on the rectenna as low as 0.6 if the satellite load factor was 0.9. The shaded area illustrates the range of load factors over which the system could be both profitable and competitive for supplying daytime power. Thus in a given case, an SPS might be uncompetitive as a base-load power source, but be attractive as a source of daytime and peak power. In order to exploit
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