ABSTRACT
Minimizing the costs of meeting a given growth in load obviously involves thousands of design and construction problems. Decisions to build gas turbine plant or to scrap old conventional plant can, however, be reconsidered during this period in the light of changing circumstances. Costs depend on the programme and help to determine tariffs, which in turn affect the growth of the load. For any given hour, the merit order can be represented as a rising marginal cost curve. The marginal optimality conditions first stated related to the plant mix at a single node, given the future loads to be met. These marginal conditions all take the location of capacity as one of the givens. To deal with this an additional set of marginal conditions is required, relating to the allocation of capacity between nodes given the transmission capacity linking them.
