电力需求与定价(7)

developments.

A. Basic Marginal Cost Theory

The rationale for setting price equal to marginal cost may be

clarified using Fig. 1. Let EFGDo be the demand curve (which

determines the kilowatt-hours of electricity demanded per

year, at any given average price level), while AGS is the supply

curve (represented by the marginal cost (MC) of supplying

additional units of output).

At the price p, and demand Q, the total benefit of consumption

is represented by the consumers willingness to pay, i.e.,

the area under the demand curve OEFJ, and the cost of supply

is the area under supply curve OAHJ. Therefore, the net benefit,

or total benefit minus supply costs, is given by the area

AEFH. Clearly, the maximum net benefit AEG is achieved

when price is set equal to marginal cost at the optimum market

clearing point G, i.e., ( po, Po). In mathematical terms, the

net benefit (NB) is given by

Q

NB =I m ) d e -

JQ m e ) d e

where p(Q) and MC(Q) are the equations of the demand and

supply curves, respectively. Maximizing NB yields:

d(NB)ldQ = P(Q) - MC(Q) = 0

which is the point of intersection of the demand and marginal

cost curves (PO, Qo). Next, we add to this static analysis, the

dynamic effect. of growth of demand from year 0 to year 1,

which leads to an outward shift in the demand curve from Do

to D l . Assuming that the correct market clearing price po

exists in year 0, excess demand GK will occur in year 1. Ideally,

the supply should be increased to Ql and the new optimal

market clearing price established at p1. But data concerning

the demand curve Dl may be incomplete, making it difficult

to locate the poinLt .

Fortunately, system data permit the marginal cost curve to

be determined more accurately. Therefore, as a first step, the

\

E \

I I I l l .b

0 0 Qo Q’ Q1 kwh

Fig. 1. Supply and demand diagram for electricity consumption.

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