The optimization of hybrid energy conversion systems using the dynamic programming model—Rapsody

Abstract

The paper describes a stochastic, dynamic programming model, RAPSODY, which is designed to analyse and determine optimal operating strategies for a hybrid electricity generating system comprising up to three diesel sets with optional battery storage and augmented by variable wind or photo-voltaic power. The model takes capital, operating and maintenance, and fuel costs into account to assess the optimal operating strategy for the auxiliary and to calculate the average daily cost of satisfying an electrical load profile which may also contain a stochastic element. In doing so, the decreased fuel efficiency and lifetime of the diesel set as it is operated below full capacity is explicitly taken into consideration as is a further important cost component attributable to switching on. The model is provided with an efficient optimizing routine which allows the user to obtain optimal component sizes for a particular load profile and wind or solar resource. An example is given in which a hybrid wind power system incorporating battery storage and an auxiliary diesel generator is optimized. For the case studied, the auxiliary switching cost and the shape of its operating cost function were important in defining the optimal operating strategy which was a significant factor in minimizing generating costs.