Operation of disconnected wind turbine

A method of operating a wind turbine is provided, wherein the wind turbine is not connected to or has become disconnected from an electrical power grid (200) capable of supplying electrical power to the wind turbine (100). The method comprises: operating the wind turbine (100) in a first operating mode (71) in which an auxiliary system (10) of the wind turbine is supplied with electrical power from an energy storage system (50) of the wind turbine, a first group (11) of auxiliary power consumables (12, 13, 14) of the auxiliary system (10) and a second group (21) of auxiliary power consumables (22, 23, 24) of the auxiliary system (10) are supplied with electrical power from an energy storage system (50). When predefined conditions are met, the wind turbine (100) is operated in a second operating mode (72) in which power supply from the energy storage system (50) to the first group (11) of auxiliary power consumables (12, 13, 14) is stopped. When the state of charge of the energy storage system (50) reaches or