The collector efficiency is considered to be constant at a value of 79% based on a constant exit steam temperature of 510°C (950°F). Due to the heat leak in the transport system, some of the superheat is lost as indicated above. This reduces the turbine efficiency as indicated in Section 3.3.2.1. When these results were corrected for 1975 dollars and the total heat delivered scaled so that it corresponded to a 150 MWe system, the transport system direct cost became 42, 48.6, 49.4 and 53.5$/kWt for FTR = 0, 0.4, 0.6 and 0.8, respectively. The cavity heat exchanger for the steam system is made of low alloy steel, and is designed to preheat, boil and superheat the water. The cavity heat exchanger was assumed to cost 14$/kWt. The 36 ft. dish delivers 54.4 kWt to the fluid so that the cavity receiver cost is $762. The total collector and receiver cost is thus $13500. Table 13 shows the results of evaluating the system costs at each FTR. The FTR equal to 0.8 seems to produce the lowest system cost (1016$/kWe). The return water is heated to 250°C. This case was selected as the system design point. A summary of system temperature and efficiency characteristics are shown in Table 12 for the steam transport system. The overall system efficiency is 25.5, and the efficiency of the "rest" is 81.2%. This factor is lower than for the water transport case since pumping power and heat leak are greater. Nevertheless, the overall system efficiency is higher due to the higher Rankine
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