The proportion of renewable energy has risen in a global effort to fight climate change over the past few decades. Due to the intermittent and varying nature of power outputs from renewable energy generation units, a temporal and spatial mismatch between demand and supply can result inevitably. Energy storage system (ESS) which typically comprises batteries and supercapacitors is used to help manage the temporal imbalance in renewable energy supply [1-2]. However, ESS alone is not sufficient for resolving this problem because of its high investment cost and unsuitability for long-term energy storage.