The Energy Collective, Oct. 28, 2016, by Xavier Moreau.
http://www.theenergycollective.com/xmoreau/2391089/9-subtleties-of-grid-storage-revealed

"Storing MWh of electricity in a battery at grid scale is not trivial because it requires a set of connected equipment and software that operate together: battery cells, power electronics, sensors, fire protection, telecommunication, relays, switchgears, controlling computer and software to name a few. Furthermore this system must be optimized along four dimensions: energy (quantity of electricity to be stored, i.e. MWh), power (flow of electricity, i.e. MW), chemistry (how electrons will actually be withheld, e.g. LiOn), and usage (charging/discharging cycles and ageing patterns over system life time)."