Optimization of an off-grid hybrid power supply system based on battery aging models for different battery technologies

This paper presents an advanced simulation tool for optimizing an off-grid hybrid PV-wind-diesel system to supply the required electricity to a telecommunication base station. The suggested system investigates a combination of three different battery technologies: Lead-acid, Lithium-ion and Vanadium Redox-Flow batteries. An adequate strategy has been developed to control the energy flow among the system components and to decide which battery has to be charged or discharged according to the actual system state (e.g. power generated from the renewables, states of charge of the different batteries). Additionally, it controls the operation of the diesel generator. The management strategy operates each battery under consideration of the respective aging characteristics in order to increase the overall economics of the system. For each battery technology an aging model has been developed to consider the calendric and cyclic aging. This has a big effect on the total system costs through the replacement costs of the batteries. It correspondingly affects the choice of the suitable combination of battery technologies made by the optimization algorithm (Genetic Algorithm) to find the best solution with the minimal costs. In this work a comparison between the optimization results in two different countries is done (Aachen-Germany and Quneitra-Syria with an annual solar radiation of 950 kWh/kWp and 1850 kWh/kWp respectively). Moreover, a sensitivity analysis for different battery prices is done and the results are demonstrated.