The spinner anemometer measures wind in front of and at the centre of the rotor where the wind flow is undisturbed. The spinner itself influence the flow around it, but in this case it is this influence that is actually part of the principle of the spinner anemometer. Until now the spinner on wind turbines has had an aestetic and protective role, but with the spinner anemometer it gets a new role with utilization of the aerodynamic properties.
The key spinner anemometer technology is however not the wind measurements themselves on the spinner, but how these measurements can be converted to ordinary free wind components like wind speed, yaw error and flow inclination angle. Fortunately this conversion can be made very easily with only two unknown constants that needs to be calibrated for each type of spinner anemometer.
The spinner anemometer has further features which eliminates the need for very precise mounting and adjustments of instruments and which makes the system both redundant and very robust.
Read the article in the danish engineering newspaper "Ingeniøren" about the spinner anemometer
here.