Composite Representation of a Multireservoir Hydroelectric Power System

A composite model for multireservoir hydroelectric power systems is constructed for studying the monthly decision conceming total hydrogeneration. This is an important decision when the inflows are uncertain and when hydro, with zero marginal cost, can be used not only to satisfy firm load commitments but also to displace other firm resources or to serve secondary loads. In such a case, the tradeoff between savings at the present and expected benefits in the future is determined mainly by the total hydrogeneration. The construction of a composite representation for the multireservoir hydroelectric power system in the Pacific Northwest is described. The composite model is based on a single measure "potential energy" which is indicative of the system's generating capability. This results in a one-dam representation of the multireservoir system which, in effect, receives, stores, and releases potential energy, in a statistical model for the potential energy inflow and in a generation function which relates potential energy released to actual electric power generated. It has applications in the study of different operating policies, market structures, and investment programs through simulation or optimization. As an example, it is used to obtain the net operating revenues as a function of the excess thermal in the system.