电力需求与定价(8)

Price

I t Unit

I

I I -I +

0 Qo 5 5 kwh

Fig. 2. The effect of capital indivisibilities on price.

supply may be increased to an intermediate level Q’, at the

price p’. Observation of the excess demand MN indicates that

both the supply and the marginal cost price should be further

increased. Conversely, if we overshoot L and end up in a situation

of excess supply, then it may be necessary to wait until

the growth of demand catches up with the over capacity. In

this iterative manner, it is possible to move along the marginal

cost curve towards the optimal market clearing point. Note

that, as we approach the optimum, it is also shifting with demand

growth, and therefore we may never hit this moving

target. However, the basic rule of setting price equal to the

marginal cost and expanding supply until the market clears, is

still valid.

B. Capital Indivisibilities and Peak Load Pricing

Owing to economies of scale, capacity additions to power

systems (especially generation) tend to be large and long-lived,

resulting in lumpy investments. Suppose that in year 0, the

maximum supply capacity is Q, as shown in Fig. 2, while the

optimal price and output combination (PO, Qo) prevails, corresponding

to the demand curve DO and the short-run marginal

cost (SRMC) curve (e.g., fuel, operating, and maintenance

costs). As demand grows from DO to D1 over time, with capacity

fixed, the price must be increased to p1 to clear the

MUNASINGHE: MODERN ELECTRICITY PRICING 335

0 h av. kwh pr hour

Fig. 3. Basic peak load pricing model.

Fixed Targer

Reilabillry

Lerei. R

Econornjc

EffKlanCy

Obpctir Fairnm. and

F8nincm Viabiiiry,

Sccial-Subsidy,

Other Objectives

Fig. 4. The use of price feedback in estimating LRMC based tariffs.

market. When the demand curve has shifted to D2 and the

price is pz , new plant is added on. Once the capacity increases

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