Estimating Unit Cost in a Cogeneration Plant Using Least Squares

A method for establishing unit costs of delivered steam and electrical energy is presented. This method employs the use of least squares, based on a linear model of electrical energy generation and delivered steam as functions of generated boiler steam. The model is based on a plant design that allows steam to be extracted from between stages of the generating turbines at a reduced pressure to be used to serve heating loads. Alternatively, the steam can be run through lower pressure stages in the turbine to generate additional electrical power, and be exhausted at a vacuum, as dictated by external steam and electrical demand. A discussion of the accuracy of the method is presented as well as an example of the use of the method using two years of actual plant production.