A method for operating a wind farm having a plurality of wind power installations or a wind power installation for feeding electrical power into an electrical supply grid, comprising the steps of: - feeding electrical power into the electrical supply grid, - identifying a forecast power (P W,P), which describes a power that can be fed in in a predetermined, future forecast period by the wind farm or the wind power installation, - determining a reduction forecast power (P nR), which denotes, for the forecast period, a power by which the power (P M) fed in in the forecast period can be reduced, and - supplying the reduction forecast power (P nR) as negative control power, wherein - the reduction forecast power (P nR) is determined - depending on the forecast power (P M) and - depending on a controllable consumption power, wherein the controllable consumption power describes a power that can be consumed on demand in the forecast period by controllable consumers present in the wind farm or in the wind power installation, characterized in that the infed power (P M) is reduced by a value up to the level of the reduction forecast power (P nR) in response to a demand for grid support in the forecast period and the reduction forecast power (P nR) is determined so that it is additively at least made up of - the production power (P W,P) or a value thereof, in particular a minimum value thereof, multiplied by a prescribable quality value, and - the controllable consumption power, wherein in each case a forecast availability of the respective controllable consumer is taken into account to determine the controllable consumption power. - feeding electrical power into the electrical supply grid, - identifying a forecast power (P W,P), which describes a power that can be fed in in a predetermined, future forecast period by the wind farm or the wind power installation, - determining a reduction forecast power (P nR), which denotes, for the forecast period, a power by which the power (P M) fed in in the forecast period can be reduced, and - supplying the reduction forecast power (P nR) as negative control power, - the reduction forecast power (P nR) is determined - depending on the forecast power (P M) and - depending on a controllable consumption power, wherein the controllable consumption power describes a power that can be consumed on demand in the forecast period by controllable consumers present in the wind farm or in the wind power installation, the infed power (P M) is reduced by a value up to the level of the reduction forecast power (P nR) in response to a demand for grid support in the forecast period and the reduction forecast power (P nR) is determined so that it is additively at least made up of - the production power (P W,P) or a value thereof, in particular a minimum value thereof, multiplied by a prescribable quality value, and - the controllable consumption power, wherein in each case a forecast availability of the respective controllable consumer is taken into account to determine the controllable consumption power. - the production power (P W,P) or a value thereof, in particular a minimum value thereof, multiplied by a prescribable quality value, and - the controllable consumption power, wherein in each case a forecast availability of the respective controllable consumer is taken into account to determine the controllable consumption power.