nonequilibrium case, such as in extreme urgency, the availability or the distance L is diminished. This effect is taken into account by rewriting L as where n is greater, but not too much greater, than 2. The total cost required for the development of SPS is an increasing function of time Ct as shown in Fig. 2. This is apparent if we estimate the cost in terms of the available energy. From Eqs. (2) and (3) and Ct, altogether, the cost per unit energy required for the SPS development is given by By differentiating Eq. (4) with respect to e/r, t for the minimum specific cost is obtained. The variation of Ct and e during t is ignored; regarded as slowly varying. In the case of n = 2, t0 = e is found. For other/? 2, the factor (//- I)1'" is close to unity, and t0 is approximated by e. The cost of SPS development is charged to energy users as an extra cost and should be reflected in the cost curve in Fig. 1. The curve is revised as shown in Fig. 3. Three curves are shown in this figure: (a) earlier start, (b) optimum start, and (c) delayed start. In the optimum case (b), the start time Tj is so selected that t, = t0 - t or t - e. The time averaged e should be taken for e in Eq. (5) if we approximate its time variation.
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