电力需求与定价(9)

to c, p3 becomes the optimal price corresponding to demand

0 3 and the SRMC line. Generally, the resulting large price

fluctuations over time will be unacceptable to consumers.

This practical problem may be avoided by adopting an LRMC

approach, and peak load pricing.

The basic static peak load pricing model shown in Fig. 3 has

two demand curves; for example, Dpk could represent the

peak demand during the x daylight and evening hours of the

day when electric loads are light. For simplicity, a single type

of plant is assumed with the SMC of fuel, operating, and maintenance

costs given by the constant a, and the LRMC of adding

to capacity (e.g., investment costs suitably annuitized and

distributed over the lifetime output of the plant) given by the

constant b. The diagram indicates that the pressure on capacity

arises due to peak demand Dpk, while the off-peak

demand Do, does not infringe on the capacity G. The optimal

pricing rule now has two parts corresponding to two distinct

rating periods (i.e., differentiated by the time of day); (i) peak

period price of ppk = a + b; and (ii) off-peak period price of

pop =a. The logic of this simple result is that peak period

users, who are the cause of capacity additions, should bear full

responsibility for the capacity costs as well as fuel, operating

and maintenance costs, while off-peak consumers only pay the

latter costs (see also Appendix).

C. Extensions of Simple Models

The simplified models presented so far must be extended to

analyze the economics of real-world power systems. First, the

usual procedure adopted in marginal cost pricing studies may

require some iteration as shown in Fig. 4. Typically, a deterministic

long-range demand forecast is made assuming some

given future evolution of prices. Then, using power system

models and data, several plans are proposed to meet this demand

at some fixed target reliability level (see below). The

cheapest or least cost system expansion plan is chosen from

these alternatives. Finally strict LRMC is computed on the

basis of this least cost plan and an adjusted LRMC tariff structure

is prepared. If the new tariff that is to be imposed on

consumers is significantly different from the original assumption

regarding the evolution of prices, however, then this firstround

tariff structure must be fed back into the model to

revise the demand forecast and repeat the LRMC calculation.

In theory, this iterative procedure could be repeated until

future demand, prices, and LRMC-based tariff estimates become

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