Offshore wind energy system

The wind energy system (2) has wind-power plants (6) that are electrically connected by a power cable (8). A monitoring device (18) is provided for monitoring the wind energy system. A control device (20) is provided for setting electricity generation reference value for wind-power plant. The control device is established upon detection of a power failure by monitoring device, such that the electricity generation reference value for wind power plant is adapted as a function of power cable parameter. An independent claim is included for a method for operating wind energy system.