To clarify the wind veer characteristics with height and their effect on the wind turbine power outputs, an investigation was carried out at the wind farms with complex and simple terrains. A 2 MW and a 1.5 MW wind turbine were tested, each having an 80 m tall met mast and a ground lidar to capture wind veering. Wind veer conditions were divided into four types based on wind direction changes with height. The power deviation coefficient (PDC) and the revenue differences for the four types were derived from the estimated electric productions. As a result, the wind veer angle across turbine rotors were more significant at the complex site than at the simple site. For the two sites, the PDC values ranged from − 3.90 to 4.21% depending on the four types, which led to a 20-year revenue variation of − 274,750–423,670 USD/MW.

An investigation was performed to identify the wind veer impact on wind turbine power performance at a wind farm located on Jeju Island, South Korea. A 2 MW wind turbine was used as a test turbine. An 80 m-tall met mast was located 220 m away from the test wind turbine and a ground lidar was installed close to the met mast. The wind veer conditions were divided into four types: veering in upper and lower rotor (VV), veering in upper and backing in lower rotor (VB), backing in upper and lower rotor (BB) and backing in upper and veering in lower rotor (BV). The frequency of the four types was identified at the wind farm. The characteristics of wind veer was analysed in terms of diurnal variation and wind speed. In addition, the power curves of the four types were compared with that under no veer condition. Also, the power deviation coefficient (PDC) derived from the power outputs was calculated to identify the effect of the four types on the turbine power performance. As a result, the frequencies of the types, VV, VB, BB and BV were 62.7 %, 4.9 %, 9.2 % and 23.1 %, respectively. The PDCs for the types VV and BV were 3.0 % and 4.2 %, respectively, meaning a power gain while those for the types VB and BB were -2.9 % and -3.9 %, respectively, meaning a power loss.

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