Technical and economic effects of charge controller operation and coulombic efficiency on stand-alone hybrid power systems

Abstract

This paper presents a study evaluating the effects of charge controller operation and coulombic efficiency on stand-alone hybrid power systems. The model used in the study makes it possible to consider the uncertainty related to renewable resources, fuel cost, the battery bank’s lifetime, energy demand, charge controller operation, and coulombic efficiency. As a case study, a hybrid system installed in Zaragoza, Spain, was analysed. The system includes photovoltaic panels, a wind turbine, a conventional diesel or gasoline generator, and a battery bank. First, the impact of charge controller operation and coulombic efficiency was studied through a comparative analysis of both the model presented in this paper and another that does not offer the ability to consider the charge controller operation or the relation between coulombic efficiency and the state of charge. The results show a difference between the models of approximately 33% in the number of hours of operation of a conventional generator, 31% in fuel consumption, and 31% in net present cost for hybrid power system configurations with low storage capacity. However, these differences were reduced when the capacity of the battery bank was increased because the charge currents were reduced, the acceptance of charge by the battery bank was improved, and the effect of the charge controller was minimised. Finally, a sensibility analysis was carried out for different sizes of battery banks, obtaining uncertainty in the net present cost, which depends on fuel cost and uncertainties about the battery bank’s lifetime.