Hybrid energy storage: Features, applications, and ancillary benefits

Energy storage devices (ESDs) provide solutions for uninterrupted supply in remote areas, autonomy in electric vehicles, and generation and demand flexibility in grid-connected systems; however, each ESD has technical limitations to meet high-specific energy and power simultaneously. The complement of the supercapacitors (SC) and the batteries (Li-ion or Lead-acid) features in a hybrid energy storage system (HESS) allows the combination of energy-power-based storage, improving the technical features and getting additional benefits. The value of HESS increases with its capacity to enhance the quality of power (PQ), maximize battery performance, sizing optimization, and non-technical profits related to efficiency, cost reduction, and environmental impact. This review proposes a HESS-main classification with an ancillary services sub-classification into (i) power quality support and power systems protection, (ii) energy management, and (iii) non-technical benefits. The services-oriented review considers the scope and goals achieved by each application, and it discusses the ancillary services covered directly and collaterally as a reference to evaluate and provide insight into the HESS implementation value and open the panorama to a potential reduction in investment costs to help this storage technology more profitable. Finally, it summarizes the current status of HESS, analyzing the storage needs of future electronic devices, large-scale power systems, and the growth outlook of isolated renewable energy (RE) systems for the research and development of new HESS.