Supply of Daytime Power by a Satellite to more than one Rectenna A satellite supplying daytime power to a rectenna would be unloaded between the hours of approximately 10 p.m. and 6 a.m. local time at the rectenna. It would therefore be free to transmit power to other rectennas during this period each day. Transmission to other rectennas sited in different time zones from the primary rectenna would permit the transmission of daytime power to these rectennas during the night-time load period of the primary rectenna. Time zones are typically 15 degrees of longitude in East-West extent, and consequently, assuming similar daily load curves, rectennas separated by more than 15 degrees of longitude could differ by one or two hours in the timing of their load curves, while rectennas separated by more than 30 degrees could differ by two or three hours. Thus a satellite at the same longitude as its primary rectenna might deliver three hours of daytime power to a rectenna some 30 degrees West of primary rectenna from 7 p.m. to 10 p.m. at the rectenna (i.e. 10 p.m. to 1 a.m. local time at the satellite) plus three hours daytime power to a rectenna some 30 degrees East of the primary rectenna from 6 a.m. to 9 a.m. local time at the rectenna (ie 3 a.m. to 6 a.m. local time at the satellite) in addition to supplying full daytime power to the primary rectenna 6 a.m. to 10 p.m. as illustrated in Figure 2. When power is transmitted from a satellite to a rectenna with a longitude offset from the satellite, the area over which the microwave beam is spread at the ground increases. For a longitude offset of 30 degrees the area of the rectenna increases by some 50% (depending on the latitude of the rectenna) over the area of a rectenna delivering equal power with zero longitude offset. This would increase the cost of the rectenna by some 25% [5]. Following this schedule, the satellite would thus save both plant capacity and fuel costs for the full daytime load period of the utility operating the primary rectenna, as well as providing three hours’ daytime fuel saving for each of the other two utilities. The load factor on the satellite would of the order of 0.9, which is the target for the SPS space segment [6], while that on the rectennas would be 0.67, 0.125 and 0.125 respectively. In order to be economic for the utilities operating the secondary rectennas, these would each have to receive power from some other satellite for some part of the day in order to increase their overall load factors. If, for instance, each of the secondary rectennas had similar arrangements with two other satellites, the load factors could reach 0.37, which might be economic for a rectenna uprated to receive power from multiple satellites [5], Back-up Supplies and Grid Interlinking The antenna design that has to date been considered most appropriate for the SPS is a phased-array antenna. Such systems have the technical capability to alter the direction of the transmitted microwave beam in a very short time: Radar transmitters with power outputs of the order of 100 kW currently switch their beam direction in time periods of less than 1 millisecond. Consequently, even allowing
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