It is easy to understand the cases of (a) and (b) in Fig. 3. The earlier start in (a) requires longer lead time e to attain the transition from oil cost curve to SPS curve. The optimum start (b) represents the smoother transition. The delayed start (c) involves three problems. First, the work of construction is supported by using much more expensive energy than in cases (a) and (b). This is reflected in the variation of Ch and the shaded area in Fig. 3(c) is larger than in Fig. 3(b). Second, the basic social activity is supported by more expensive oil energy than SPS energy during /0 tf- This fact imposes an extra charge represented by the hatched triangle region abc in Fig. 3(c). Third, it is very hard to consider the occurrence of a sharp decrease of cost from the point b to c. The natural trend may be a gradual merging from the point b to the SPS curve as represented by the dashed line. If the hatched region in t tf is regarded as extra charge, an enormous long lasting burden is imposed on the energy users. The discussion above relies totally upon well-established cost curves. The inaccuracy of the predicted cost may obscure the transition time to and, hence, the time of initiation. However, since the economic impact is so great in the case of delayed start as demonstrated above, the philosophy of the foregoing discussions will never be blurred by the uncertainties in the prediction. It is apparent in Fig. 3. that the earlier start is much safer than the delayed start. CONCLUSION It is strongly advised that the start time of the SPS development be the earliest possible time of energy resource transition minus the technological relaxation time, REFERENCES I. R.U. Ayers and I. Nair, Thermodynamics and Economics, Phys. Today, 62-71, November, 1984. 2. B. Andresen, P. Salamon, and R.S. Berry, Thermodynamics in Finite Time, Phys. Today, 62-70, * September, 1984. 3. P. Salamon and R.S. Berry, Thermodynamic Length and Dissipated Availability, Phys. Rev. Lett. 51, 1127-1130, 1983.
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