The Economical Capacity of a Combined Hydroelectric and Steam Power Plant

This paper develops a general method for determining the economical capacity of a combined steam and hydroelectric development. The method involves the use of two curves-one, the ''Percent-Deficiency,'' giving the stream regimen, the other, the ''Percent-Load,'' giving the characteristics of the load. The first curve gives the percent-deficiency of the water for any stream-flow, and hence fixes directly the deficiency in energy which must be made up by the steam plant. The second curve shows directly the proportion of the total energy of the load that is included above any proportional part of the maximum power, and fixes the capacity of the steam plant required to supply that part of the load which cannot be supplied by the stream. The use of these two curves differs for plants with pondage or without pondage. The capacity and output of the steam plant being thus determined, its total annual cost is determinable and with the annual cost of the hydroelectric plant, fixes the total annual cost of the combined plant. This is done for the range of stream-flow by means of numerical examples.