In addition, the electric power collection subsystem (Section 3.2.2) has an efficiency of 93.4% when sized for a 1000 MWe plant. A smaller plant with shorter distances from the average dish to the external transmission point would have somewhat greater efficiency. The overall system efficiency is the product of collector, heat engine and electric power collection with a correction factor for some loss of peak power and off-load heat engine operation. This overall system efficiency is A 5% heat leak is included in the collector efficiency for the heat transport from the cavity to the heat engine. The above efficiency value does not include any significant blockage factor since with distributed generation the ground cover ratio (GCR) can be quite low (~0.2) and not have a significant effect on the energy transport subsystem. If there is concern for using less land, a GCR of 0.4 is near optimum for central generation systems and is appropriate for a tighter field layout. The penalty loss for this spacing is approximately 5% and is due to increased blockage and shadowing. The overall efficiency becomes 21.4% at a GCR = 0.4. Based on the GCR = 0.2, the total overnight direct costs are displayed in O 9 Table 10. The $11.50/ft collector cost becomes $12.76/ft in 1975 dollars. 2 The 36 foot diameter dish has an aperture of 1018 ft and generates 17 kWe rated output at an overall system efficiency of 22.5%. The cost is 764$/kWe for the dish collector. The cavity receiver cost was found to be 33$/kWt (see Section 3.3.1); this would correspond to $102/kWe. The cost of the heat engine was developed in Section 3.3.1 and shown to be 345$/kWe based on 25.1% system efficiency. This was noted to be 1974 dollars and included the cost of the cavity receiver. Correcting for 1975 dollars, 22.5% efficiency, oversizing the engine by 20% and removing a cost of 102$/kWe for the receiver results in an engine cost of 390$/kWe.
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