NOVELTY - The APU has array (214) of fuel cells that comprises sets (210) of series-connected fuel cells. A switch (222,224) has first state condition related to electrical coupling of two of sets in parallel and second state condition related to electrical uncoupling of two of sets in parallel. A controller (12) is operably coupled to the switch and controlling the change of state of the first switch between the state conditions. The two of the sets are interconnected in parallel when the switch is in first state condition to increase the current provided by the APU.    USE - Fuel cell-based auxiliary power unit for providing electrical power to load e.g. aircraft.    ADVANTAGE - The controller can direct the operation of the APU and monitor the overall system and its individual components, by communicably coupling to other elements of the APU. The controller receives additional instructions and report system faults to the flight deck controls through the aircraft data-bus or is in communication with the bus power control unit (BPCU) to enable start up in an emergency situation. The need for a large on-board storage tank of hydrogen is mitigated, by producing hydrogen from a fuel such as diesel or avtur through a process of reforming of hydrocarbons. The network of parallel-connected sets of series connected fuel cells delivers a desired power output without raising the output voltage to undesirable levels. The fuel cell APU includes a minimal number of moving elements including the fuel cell array, which contains no moving elements. Desirable operating characteristics of a fuel cell APU include a low operating temperature, low audible noise level and no appreciable pollution beyond the water, heat and depleted oxygen air outputs are obtained. The associated maintenance costs are relatively low, because fuel cells runs indefinitely provided clean fuel and air are available unlike batteries whose performance degrades over time. The fuel cell APUs has a lower maintenance burden than that of conventional gas turbine APUs and approaches 20,000 operating hours whereas conventional gas turbine APUs average 12,000 hours between overhauls. The fuel cell APU acts as an emergency power system thus replacing the ram air turbine (RAT) because the fuel source is independent from that of the main engines. The fuel cell APU designed is quickly adapted for use between different aircraft types with different power requirements and modes of operation. The number of fuel cells in series can be used to control the voltage provided by the set of series-connected fuel cells. The ability is provided to sub-divide the fuel cell array as desired to provide different power sources for different loads with each power source having a predetermined voltage and current which can be selected for the expected load.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the electrical power network configuration of the fuel cell array of the fuel cell APU.    Controller (12)    Direct current load (124)    Set of series-connected fuel cells (210)    Array of fuel cells (214)    Switch (222,224)