A energy supply system with at least a renewable energy generator and a standard generator driven by fossil energy and a dump load system, which could be a battery. The renewable generator may be limited in it's energy production when the load is to low. The generator may be feed with energy, i.e. driven in motor load to take over short term surplus energy. The system may contribute to stabilization of grid fluctuations with its mechanical inertia from the rotating alternator in the engine stopped mode and with the engine in other modes.