a method of operating a wind power installation selectively in a first or second operating mode is disclosed . in the first operating mode , the installation generates as much electrical power as possible based on the prevailing wind and design of the wind power installation , and in the second operating mode generates less electrical power than in the first operating mode . the wind power installation is controlled in the first and second operating modes with first and second adjustment parameter sets , respectively . when the installation is operated in the second operating mode the maximum power which can be generated with the first adjustment parameter set or a differential power between the maximum power and a power currently generated in the second operating mode may be ascertained . the second adjustment parameter set may be selected based on a desired power reduction and the maximum power .