not considered in the collector cost estimates in section 3.1.2 are the operation and maintenance (0 + M) costs and external plumbing hook-up charges. Due to the unavailability of reliable 0 + M data, these costs have not been included in this study. Effort is underway to independently estimate these costs. If the 0 + M costs are not negligible (which is highly likely), the cost optimum size of the collector will be shifted so that a smaller total number of collectors are used for a given power level. Fewer collectors should have more favorable 0 + M costs with numerically fewer tracking devices, motors, controls, etc. This effect would influence the optimum size selection and make it somewhat larger than the upper limit of the squared cost relationship. External plumbing hook-up costs, which are part of the energy transport subsystem, have a similar impact on optimum dish size as does 0 + M cost. That is, a smaller total number of dishes is more desirable. For this preliminary evaluation, the optimum size dish collector was chosen as 36 feet. The cost was estimated at $11.50/ft2 (1974 dollars), which is greater than $10/ft2 at 15 ft diameter, but fewer dishes are required. To generate 150 MWe rated power with an overall system efficiency of 25%, 46,500 15-ft.-diameter dishes are needed. This is nearly 6 times the number of 36 ft diameter dishes required. Although this is not a rigorous costing exercise, it is suitable considering the current status of dish collector cost information. The major remaining trade-off is between the performance and cost of the energy transport and Rankine heat engine subsystems. As described in Section 3.3.2, the temperature rise in the collector ( ) is the independent parameter that is yet to be resolved. A low has higher energy transport costs due to higher flowrates, while the Rankine plant efficiency is higher leading to lower
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