temperature versions might reach 46% even in these small sizes (10 kW to 50 kW) at similar costs. Nearer term (1 to 3 year) Brayton engines would have reduced performance. Performance-cost data are discussed in Section 3.3. 2.1.3 Electric Power Collection The distributed generation power plant produces electric power throughout the field of solar collectors. The collection of this electric power to a central site for external distribution is a problem of detailed design tradeoffs using commercially available equipment without need of advanced R&D. The major assumptions used in the study of this subsystem are 1) no energy storage (sun following operation), 2) automated controls, 3) fail-safe characteristics for the system, 4) extremely high reliability and 5) local repairs possible while the rest of the system is operating. The major questions to be resolved concern the type of generator such as ac synchronous, ac induction or de shunt wound machine; the use of ac or de in the collection network; and the techniques used for power conditioning and control. The use of a de shunt wound generator is ideally suited to parallel operation. Startup is relatively easy, and constant voltage operation is possible with variable speed on the shaft. The output voltage depends upon the shaft speed (n) and the level of excitation (0), i.e., E = kn0. Thus, variations in speed due to varying solar input can be compensated by controlling the excitation to maintain constant voltage output. Controls can easily be automated. Synchronization is not a problem at all, but the generator is about 150% as costly as equivalent ac synchronous machines. Maintenance may be high unless brushless versions are used at even higher initial cost. Inversion from de to ac is required even if de external transmission is used. The generator currently used almost universally is the synchronous ac machine. It is more efficient than other types of generation. Startup is difficult since
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