We have shown that the only rational optimization for a solar energy collection and conversion system is that for which the relative incremental efficiency gains are precisely balanced by the associated relative incremental cost increases—that is, when the logarithmic derivatives of the performance and cost functions are equal. Very generally, we conclude that the optimum for any system is likely to lie in a range of parameters in which both the costs and performance are varying significantly.
All cited data serve to emphasize the importance of understanding performance cost trade-offs in trying to choose among alternative paths toward the ultimate goal of low-cost solar energy.
In general, an approach such as that developed here can be particularly useful in defining both cost and performance goals. It emphasizes that accurate knowledge of the cost structure associated with all design trade-offs is essential both for choosing an optimized cost-effective design and for fully appreciating the relative merit of two-stage designs. Probably no single approach can provide the dramatic cost breakthrough still necessary for solar to compete favorably with conventional high-temperature thermal sources. However, perhaps a number of innovative technologies can be combined synergistically to deliver acceptable performance at greatly reduced cost.