In general, a generator set system may include a primary module including: an engine; a generator coupled to the engine and configured to convert mechanical energy of the engine to electrical energy; a primary frame configured to support the engine and the generator; and a first coupling. The generator set system also may include a secondary module including a secondary module including: at least one of a heat recovery module, an exhaust module, a cooling system module, a fuel system module, a solar power module, a battery module, an electrical system module, an air intake module, or an air outlet module; a secondary frame; and a second coupling. The first coupling and the second coupling are configured to automatically electrically or fluidically couple the primary module to the secondary module upon assembling the primary frame and the secondary frame.