Abstract: A power generation system with flat fuel cells of solid electrolyte construction permits the building up of a large capacity system. There are a train of pile units of flat fuel cells of solid electrolyte disposed in a horizontally extending fuel gas duct. The gas fuel duct supplies to the train of pile units of flat fuel cells fuel gas. Each of said pile units of flat fuel cells has a horizontal flat flow path for the fuel gas disposed above each fuel-side porous electrode sheet of the fuel cell opening freely at two path ends on the opposing side faces of the pile unit. There is a horizontal flat flow path for the oxidant gas disposed beneath each oxygen-side porous electrode sheet separated from the fuel gas flow paths and each connected at two path ends to either a supply line or to an exhaust line for the oxidant gas.