NOVELTY - A sulfur flow battery energy storage system (100) comprises: sulfur electrolyte containing dissolved electroactive sulfur species; and an electrochemical reactor containing first and a second electrodes (102, 104) configured in spaced apart relation defining an inter-electrode channel (101) through which the sulfur electrolyte is caused to flow. The first electrode comprises solid electroactive component containing a material having active metal ions of a particular metal. The second electrode comprises an electron transfer material having a surface in contact with the sulfur electrolyte.    USE - As a sulfur flow battery energy storage system (claimed), used as an energy storage solution for the electrical utility grid.    ADVANTAGE - The battery system is readily scalable and cost effective; minimizes the corrosion of battery electrode; and optimizes the service life of the battery. In the battery, a very high energy capacity can be achieved, even at low concentrations of sulfur in the electrolyte, since the overall system capacity is determined not by the open volume in or between the electrodes, but by the amount of electrolyte in the reservoir. The ability to achieve high-energy capacity using a low concentration sulfur electrolyte is a prominent advantage of the battery system, especially for certain applications, such as renewable grid storage, where exceptional service life is the key driving factor, and high rates of discharge and charge may be demanded. With decreasing sulfur concentration there is a concomitant lowering of the electrolyte viscosity, which is advantageous for electrolyte flow. The system is operated to maintain the electroactive species in a dissolved state, facilitated by microprocessor control, including electronics for counting coulombs of charge passed, and an algorithm for projecting the overall oxidation state of the electroactive species.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) operating a flow battery system involving providing the flow battery system; and activating the flow device to cause sulfur electrolyte present in the storage tank to flow through the inter-electrode channel; and    (2) conditioning a flow device system prior to operation involving: providing the flow device; inserting a conditioning electrode in the reactor between the first and second electrodes; electrically coupling the conditioning electrode to the first electrode; providing a second storage tank comprising a conditioning electrolyte which has a composition different than that of the sulfur electrolyte in the first storage tank; fluidly coupling the second storage tank to the reactor; activating a flow device to cause the conditioning electrolyte to flow through the inter-electrode channel; and providing electrical power between the first electrode and the conditioning electrode to electrochemically condition the first electrode.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the flow battery system.    Sulfur flow battery energy storage system (100)    Inter-electrode channel (101)    First and a second electrodes (102, 104)    Pipe (110)    Pump (115)    First external reservoir (120)    Second external reservoir (125)