A method for controlling a wind power installation, wherein - the wind power installation has a rotor with rotor blades with an adjustable blade angle (θ), and the rotor can be operated with a variable rotational speed (n), and wherein - the wind power installation is operated in a partial load range in which sufficient wind is not present to operate the wind power installation with rated power, - the wind power installation can be operated as an operating point (302, 308, 310) which can be specified in a changing fashion, and - the operating point (302, 308, 310) is characterized by the blade angle (Θ) and a tip speed ratio (λ), and wherein - the operating point (302, 308, 310) can be represented in a λθ diagram, wherein - in the λθ diagram the tip speed ratio is plotted against the blade angle (θ), and - the operating point (302, 308, 310) can be represented in the λθ diagram as a value pair composed of a blade angle (θ) and tip speed ratio (λ), wherein - each operating point (302, 308, 310) is assigned a power coefficient (Cp value), and - a plurality of operating points (302, 308, 310) with the same Cp value can be represented as an iso-characteristic curve in the λθ diagram, comprising the steps: - operating the wind power installation at a normal operating point at which the wind power installation is not operated in a throttled fashion if there is no request for throttling, - operating the wind power installation at a throttled operating point at which, in response to a throttle request, the wind power installation is operated with output power (P A) which is throttled in comparison with the normal operating point, and - changing over the operation of the wind power installation from the throttled operating point to a reserve operating point at which the wind power installation is operated with higher output power in comparison with the throttled operating point, in reaction to a power increase request wherein - the throttled operating point has an increased tip speed ratio in comparison with the reserve operating point, and - the throttled operating point lies on an associated iso-characteristic curve in the λθ diagram, and the associated iso-characteristic curve has, at the throttled operating point, a negative characteristic curve gradient at which the tip speed ratio decreases as the blade angle increases, characterized in that the characteristic curve gradient at the throttled operating point decreases with a value which is at least 0.5/1° in terms of absolute value. - the wind power installation has a rotor with rotor blades with an adjustable blade angle (θ), and the rotor can be operated with a variable rotational speed (n), and wherein - the wind power installation is operated in a partial load range in which sufficient wind is not present to operate the wind power installation with rated power, - the wind power installation can be operated as an operating point (302, 308, 310) which can be specified in a changing fashion, and - the operating point (302, 308, 310) is characterized by the blade angle (Θ) and a tip speed ratio (λ), and wherein - the operating point (302, 308, 310) can be represented in a λθ diagram, wherein - in the λθ diagram the tip speed ratio is plotted against the blade angle (θ), and - the operating point (302, 308, 310) can be represented in the λθ diagram as a value pair composed of a blade angle (θ) and tip speed ratio (λ), wherein - each operating point (302, 308, 310) is assigned a power coefficient (Cp value), and - a plurality of operating points (302, 308, 310) with the same Cp value can be represented as an iso-characteristic curve in the λθ diagram, - in the λθ diagram the tip speed ratio is plotted against the blade angle (θ), and - the operating point (302, 308, 310) can be represented in the λθ diagram as a value pair composed of a blade angle (θ) and tip speed ratio (λ), wherein - each operating point (302, 308, 310) is assigned a power coefficient (Cp value), and - a plurality of operating points (302, 308, 310) with the same Cp value can be represented as an iso-characteristic curve in the λθ diagram, - operating the wind power installation at a normal operating point at which the wind power installation is not operated in a throttled fashion if there is no request for throttling, - operating the wind power installation at a throttled operating point at which, in response to a throttle request, the wind power installation is operated with output power (P A) which is throttled in comparison with the normal operating point, and - changing over the operation of the wind power installation from the throttled operating point to a reserve operating point at which the wind power installation is operated with higher output power in comparison with the throttled operating point, in reaction to a power increase request wherein - the throttled operating point has an increased tip speed ratio in comparison with the reserve operating point, and - the throttled operating point lies on an associated iso-characteristic curve in the λθ diagram, and the associated iso-characteristic curve has, at the throttled operating point, a negative characteristic curve gradient at which the tip speed ratio decreases as the blade angle increases, characterized in that