Stack-based technologies for energy storage: a comparative assessment

Mobile and stationary energy storage systems will grow worldwide in the next future due to the evolution toward carbon-free renewable energy sources. On one side energy storage is the most challenging hurdle to the success of electric mobility. On the other side, stationary storage is expected to face not only the intermittency of renewable sources, but also to offer advanced services in the framework of the smart-grid concept. Electrochemical storage systems are the solution of choice to face most of these services. Among them Fuel Cells and Redox Flow Batteries exhibit high potentials because of their power/energy independent sizing, that makes them extremely attractive when longer discharge times are needed. Both are made of several cells connected together to form stacks, which are fed with fuel delivered from external tanks. Nevertheless, they present major differences, which make the one or the other more suitable for specific services.