A system for generating electricity which includes an internal manifold fuel cell stack having an anode fuel gas duct, an anode exhaust gas duct, a cathode air duct and a cathode exhaust duct and a plenum having a fuel gas inlet, an anode exhaust gas outlet, an air inlet and a cathode exhaust gas outlet, which plenum is adapted to deliver a fuel gas and air to the internal manifold fuel cell stack. At least one air preheat panel is provided having two parallel planar surfaces disposed proximate and parallel to the internal manifold fuel cell stack and forming at least one air duct between the two parallel planar surfaces, which at least one air duct extends parallel to the two planar surfaces and has at least one cold air inlet and at least one preheated air outlet. The preheated air outlet is in fluid communication with the cathode air duct. In accordance with one embodiment, the internal manifold fuel cell stack, plenum and the at least one air preheat panel are all disposed within a housing.