A fuel cell power system has at least one fuel cell stack assembly having a clamp mechanism for holding plates of the fuel cell stack together, a fuel supply and exhausting stream, an oxidant supply and exhausting stream, and at least one of a fuel cell stack cooling loop and a cogeneration heat exchanger. The cooling loop or the cogeneration heat exchanger has a stack of heat exchange plates held together with the plates of said fuel cell stack by the clamp mechanism.