NOVELTY - A flow battery system (450) comprises first battery stack including first half-cell utilizing liquid electrolyte, first gravity feed system, including first storage tank and first standpipe, designed to generate a first hydrostatic pressure in the first standpipe for the liquid electrolyte in the first standpipe sufficient to force the liquid electrolyte to be fed from first gravity feed system through first half-cell; and a return system to return the liquid electrolyte from the first half-cell to the first gravity feed system.    USE - As flow battery system (claimed).    ADVANTAGE - The flow battery system avoid the need of high-pressure storage tanks and allows all the storage tanks to reside at ground level, or near ground level; produces a smooth continuous nearly-laminar flow of electrolyte through the battery stack that minimizes stress on the membranes and seals. Such advantages can be obtained at a comparatively low cost of an added standpipe and associated standpipe pumping system, e.g. storage tank.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for flow battery control method of flow battery system including a first battery stack including first half-cell utilizing a liquid electrolyte, involving controlling a height of the liquid electrolyte in the first standpipe to match a predetermined height above a height of the battery stack to generate a sufficient first hydrostatic pressure to force the liquid electrolyte to be fed from the first gravity feed system through the first half-cell when charging or discharging battery cells of the first battery stack, and controlling a variable feeding of the liquid electrolyte from the first gravity feed system to the first battery stack, to control a flow rate of the liquid electrolyte through the first battery stack when charging or discharging through battery cells of the first battery stack.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of gravity feed system.    Storage tanks (401)    Bottom pipe (402)    Variable opening valve (403)    Battery stack (404)    Return pump (405)    One-way valve (406)    Pipe (407)    Trapped gas (414)    Electrolyte (415)    Controller (420)    Processing devices/microcontroller (421)    Electrolyte height sensors (432)    Pressure sensors (434)    Flow battery system (450)