电力需求与定价(14)

curve (LDC) ABEF for the starting year 0, divided into

two rating periods: peak and off-peak. As demand grows over

time, the LDC increases in magnitude, and the resultant forecast

of peak demand is given by the curve D in Fig. 5(b), starting

from the initial value MW. The LRMC of capacity may be

determined by asking the following question: what is the

change in system capacity costs AC associated with a sustained

338 PROCEEDINGS OF THE IEEE, VOL. 69, NO. 3, MARCH 1981

increment AD in the long run peak demand (as shown by the

shaded area of Fig. 5(a) and the broken line D +AD in Fig.

5(b)). Consequently, the LRMC of generation would be

(AC/AD), where the increment of demand AD is marginal

both in time, and in terms of MW. In theory, AD can be either

positive or negative, and generally the ratio (AC/AD) will vary

with the sign as well as the magnitude of AD. If many such

values of (AC/AD) are computed, it is possible to average

them to obtain LRMC.

In an optimally planned system, the new incremental load

would normally be met by advancing future plant or inserting

new units such as gas turbines or peaking hydro plant (see

Fig. 5(b)). Using a computerized generation planning model,

it is easy to determine the change in capacity costs AC by

simulating the expansion path and system operation, with and

without the demand increment AD. If a more sophisticated

tariff structure having many rating periods is used, then the

LRMC in any rating period may be estimated by running the

computerized system expansion model with a sustained load

increment added to the LDC during that particular period.

This method that simulates the optimal system planning process

is based on the dynamic LRMC concept.

When constraints due to time, data and facilities preclude

this ideal approach, more approximate methods may be used.

Several practical methods of estimating LRMC are analyzed in

[35] and [36]. Simple considerations based on a more static

interpretation of LRMC often yield very good results. Suppose

that gas turbines are used for peaking; then the required

LRMC of generating capacity (LRMCG,,. cap.) may be approximated

by the cost per kW installed, annuitized over the expected

lifetime. This figure must be adjusted for the reserve

margin (M%a)nd losses due to station use (tu%)T.h us a

typical expression would be:

LRMC-. cap. = (Annuitized Cost per kW)

'(1 +RM%)/(l - L,%).

In our basic model, all capacity costs are to be charged to

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