ceramic insulators was used to determine the height of the rectenna elements. The elevation view given in Figure IV-D-2-3 shows the maximum height the structure has to be above the ground as well as the relative height of all rectenna elements to insure adequate fault protection to ground. Ten of these feeders are required to produce the total rectenna output of 5000 MWe. The feeders are then routed to ten 500 megawatt inverters located at the edge of the rectenna. The inverters are made up of solid-state thyristors that operate at 250 KV, at an efficiency of 96 percent. These units use reactive power from the grid to gate the thyristors, which maintains synchronous operation with the grid. The output voltage may range between 66 KV and 500 KV. The costs for materials involved in the above option is given in Table IV-D-1. If the structure is to be used as the collection buss, the large costs associated with having many parallel conductors carrying high current (2500 amperes) is eliminated. In the LVDC configuration, the power is collected at inverters located along the major axis of the rectenna. The inverters change this power to high voltage AC. With the proper grid controls the inverter outputs are summed and transmitted along a high voltage transmission line also located along the major axis. In the high voltage DC collection system, the 1000 VDC terminals are in series requiring much less conductor material. However, there is a requirement to insulate each 1000 VDC terminal from ground by the amount of voltage it exists above ground. This requires a support structure like the one shown in Figure IV-D-2-3. At present, there are no existing large-scale application for insulators that posses the structural characteristics required of this design. This is viewed as a new technology issue. The 250 KVDC terminals are then routed to ten 500 megawatt inverters located at the edges of the rectenna through a radial network. If the inverters were required to be located remotely from the rectenna site, the HVDC could be transmitted more efficiently and at less cost than LVDC or high voltage AC. Cryogenic LVDC transmission may also be a viable option, in a case where the load density if unusually high. In comparing the two options, the principal consideration is cost. The high voltage DC inverters are somewhat cheaper ($30/KW HVDC; $45/KW LVDC) than low voltage inverters. However, the efficiency of both is identical. The major cost uncertainty is in the insulators required by the high voltage system. In order to be competitive, the cost of these insulators must be on the order of $15/KW for the entire rectenna, increasing the structural cost.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==