NOVELTY - The fuel cell system (100) has an accumulator (106) that receives and supplies water from/to fuel cell. The accumulator comprises an upper region (R1) to store predefined volume of water during steady state operation of the fuel cell and a lower region (R2) to fill with water at a rate greater than the water filling rate of the upper region. The accumulator includes a drain (121) arranged in the lower region, for allowing water from the lower region to the drain during shutdown of the fuel cell, to prevent freezing of water in the lower region.    USE - Fuel cell system for propulsion system of electric vehicle.    ADVANTAGE - The fuel cell system with porous water transport plates can be started under freezing conditions, when a small amount of water can be made available to the fuel cells from the accumulator, so that water consumption can be reduced and the need for a supplemental thawing unit can be prevented. The need for dump water from the accumulator to suppress freezing of water in the lower region can be prevented, since the lower region of the accumulator becomes dry and receives water quickly during start-up, by draining water from the lower region. The lower region of the accumulator can be maintained dry, since water is actively or passively drained from the lower region for rapid refilling with water during start-up of the fuel cell. The amount of water returned to the upper region can be increased, by increasing the speed of the condenser fan. The fuel cell can be driven for a long period of time under cold condition, for collecting water in the lower region and returning to the fuel cells. The efficient draining of the accumulators can be enabled using the sloped sidewalls. The condensing rate of moisture from the air exiting from the fuel cell stack can be improved, by controlling the variable-speed fans associated with the condenser. The need for discharging liquid water overboard during non-frozen/warm start-up condition of the fuel cell can be prevented.    DETAILED DESCRIPTION - The fuel cell system has an accumulator comprising a lower region positioned below the upper region, such that the upper region and lower region comprise sidewalls that define respective cross-sectional areas along the vertical extents. The cross-sectional area of the lower region is less than the cross-sectional area of the upper region. The sidewalls of the upper region and lower region are inclined inwards along the downward direction. The volume of the upper region is greater than the volume of the lower region. A valve (121) is provided in the drain of the accumulator, to permit selective drainage of the accumulator. The valve of the drain is automatically controlled by a controller (119). A water conduit (126) is operatively connected from the lower region to the fuel cell, to return water to the fuel cell. A variable speed condenser fan (117) is operated at a maximum fan speed in response to the start-up condition of the fuel cell. A stack (102) of multiple proton exchange membrane fuel cells is provided in the fuel cell. The water from the fuel cell is directed to the accumulator, to direct most of water from the fuel cell to the lower region and upper region of the accumulator. A passive device comprising a porous plug is provided in the drain, for allowing continuous restricted flow of water to the upper region of the accumulator. An overflow arrangement is provided in the lower region, to discharge water from the lower region to the upper region at a rate greater than the continuous restricted flow through the passive device, when water contained in the lower region exceeds a predetermined level. The water conduits are extended from the upper region and the lower region, to return water to the fuel cell. An INDEPENDENT CLAIM is included for operating method of fuel cell system, which involves draining water from a region of the accumulator, for maintaining the region in ice-free state, during shutdown state of fuel cell. One of the regions of the accumulator is filled with water at a rate rapidly than the water filling rate of other region, so that water is drained from the rapid water filling region. The rapid water filling region is positioned relatively above the other region, so that draining of rapid water filling region is performed continuously through a passive drain discharging into the other region.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the fuel cell system.    Fuel cell system (100)    Stack (102)    Accumulator (106)    Variable speed condenser fan (117)    Controller (119)    Drain (121)    Water conduit (126)    Upper region (R1)    Lower region (R2)