A modular fuel cell stack assembly comprising a plurality of fuel cell stacks, each of the stacks having a plurality of stack faces and a plurality of stack corners formed between the stack faces, wherein the plurality of stack faces include a cathode inlet face adapted to receive oxidant gas for use in a cathode side of the fuel cell stack, a cathode outlet face adapted to output cathode exhaust from the cathode side, an anode inlet face adapted to receive fuel for use in an anode side of the fuel cell stack and an anode outlet face adapted to output anode exhaust from the anode side, and wherein at least one of the cathode inlet face, cathode outlet face, anode inlet face and anode outlet face is an open face without a manifold, and a containment structure for housing the plurality of fuel cell stacks and for providing fuel and oxidant gas to said fuel cell stacks, the containment structure including at least one sealed chamber for sealingly enclosing and isolating at least one open face. Also provided is a modular fuel cell assembly comprising a plurality of fuel cell stacks, an oxidizer disposed centrally of the fuel cell stacks and adapted to receive anode exhaust from the fuel cell stacks, to generate oxidant gas using the anode exhaust and to distribute the oxidant gas to the fuel cell stacks, and a containment structure for housing the plurality of fuel cell stacks and the oxidizer and adapted to receive fuel and distribute the fuel to the fuel cell stacks.