电力需求与定价(11)

outages; SC is supply costs (i.e., system costs); OC is outage

costs (i.e., costs to consumers of supply shortages); D is demand;

and R is reliability.

In the traditional approach tosy stem planning both D and R

are exogenously fixed, and therefore NB is maximized, when

SC is minimized, i.e., least cost system expansion planning.

However, if R is treated as a variable:

d(NB)

dR

- ( S C + O C ) + - ( T B - S C - O C ) - - - = O

aR aD aR

-=- a a aD

is the necessary first-order maximization condition. Assuming

Therefore, as described earlier, reliability should be increased

by adding to capacity until the above condition is satisfied.

An alternative way of expressing this result is that since TB is

independent of R , N B is maximized when total costs: TC =

(SC + OC) are minimized. The above criterion effectively subsumes

the traditional system planning rule of minimizing only

system costs, but it raises new problems stemming from the

need to accurately estimate outage costs [ 271, [ 291.

Third, consider again the choice between SRMC and LRMC

for pricing. The SRMC may be defined as the cost of meeting

additional electricity consumption, (including the costs of

shortages) with capacity fixed. The LRMC is the cost of providing

an increase in consumption (sustained indefinitely into

the future) in a situation where optimal capacity adjustments

aD/aR = 0, yields: a(sc)/aR = - a(oc)/aR.

are possible. When the system is optimally planned and operated

(i.e., capacity and reliability are optimal), SRMC and

LRMC coincide. However, if the system plan is temporarily

suboptimal, significant deviations between SRMC and LRMC

will have to be carefully resolved. For example, in the post

1973 period many utilities are replacing oil fired plant with

coal fired units to realize fuel cost savings. This may result in

significant excess capacity, and low marginal capacity costs

in the short run, thus justifyinga reduction in demand charges

below the LRMC level. However, as peak demand grows and

the system approaches optimality again, the capacity charges

should rise smoothly towards LRMC. This transition could

become undesirably abrupt if the initial reduction in demand

charges was too large and demand growth was overstimulated.

Finally, if there are substantial outage costs outside thpee ak

百度搜索“77cn”或“免费范文网”即可找到本站免费阅读全部范文。收藏本站方便下次阅读，免费范文网，提供经典小说教育文库电力需求与定价(11)在线全文阅读。