Shadow Control of Wind Turbines

A shadow-control system of a wind turbine,

• the wind turbine having a rotor that, when rotating and when the sun is at a certain position, may cast an intermittent shadow onto an object in the vicinity of the turbine,
• the shadow-control system being arranged to cause the wind turbine to be stopped, based on a shadow-related shut-down condition, so that intermittent shadow is not cast onto the object,
• wherein the shut-down condition comprises a result of a comparison between a direct light intensity and an indirect-light intensity being beyond a direct-to-indirect light threshold,
• wherein the shadow-control system comprises a set of light sensors to provide measured direct- and indirect-light intensities for the comparison, the light sensors being able to measure the direct-light intensity when irradiated by the sun and the indirect-light intensity when not irradiated by the sun,
• wherein the set of light sensors to provide measured direct- and indirect-light intensities for the comparison has only two light sensors, an eastward-oriented light sensor and a westward-oriented light sensor.

A shadow-control system of a wind turbine,

• the wind turbine having a rotor that, when rotating and when the sun is at a certain position, may cast an intermittent shadow onto an object in the vicinity of the turbine,
• the shadow-control system being arranged to cause the wind turbine to be stopped, based on a shadow-related shut-down condition, so that intermittent shadow is not cast onto the object,
• the shadow-control system also being arranged to cause the operation of the wind turbine to be resumed, based on an shadow-related operation-resume condition,
• wherein the shut-down condition comprises a light-measurement result being beyond a first threshold, and wherein the operation-resume condition comprises a light-measurement result returning to a second threshold,
• wherein there is a hysteresis in the thresholds such that the light-measurement result causing shut-down is not sufficient to cause the operation to be resumed.