A hybrid energy system is provided in a vehicle including an autonomous power supply and being connectable to an external power supply infrastructure along the route of the vehicle, and which vehicle is arranged to operate in an autonomous power supply mode and/or in an external power supply mode. The system includes a first high voltage circuit including a first traction motor connected to an energy storage system by a first power converter for propelling the vehicle; a second high voltage circuit including a second traction motor connectable to an external power supply by a second power converter for propelling the vehicle; and where the first high voltage circuit and the second high voltage circuit are connectable by a third power converter between the first and the second power converters. A method for operating the hybrid energy system is also provided.