This thesis is devoted to the topic of energy storage system modelling, and to the integration of such systems to increase the utilisation of renewable energy. In particular, the use of a nickel-metal hydride battery storage system is considered in combination with energy produced by solar and wind to power an electric vehicle fast-charging station situated in Norway. The thesis aims to develop a flexible model for the battery energy storage system that can accurately describe battery performance and performance-reducing effects. The motivation of which is to be able to evaluate the feasibility of the charging topology in mention. A semi-empirical, battery model based on real data is designed and implemented in the Simulink modelling environment. Further, a system model is developed in the same modelling environment which uses actual data from Norwegian renewable energy producers and charging station operators. We report on the influence of renewable energy mixture, capacity sizing, production sizing and vehicle charging behaviour on the feasibility of the topology. The thesis is written as a contribution of the now finished project INTEGRARE (Intelligent prediction and integration of renewable energy sources into the Norwegian electricity grid, headed by the Department of Technology Systems). The topic is in line with an ongoing effort in the energy storage system research group to promote, design, model and validate the feasibility of energy systems powered by renewable energy sources.