A Study of Energy Production Change according to Atmospheric Stability and Equivalent Wind Speed in the Offshore Wind Farm using CFD Program

Atmospheric Stability Effects on Offshore and Coastal Wind Resource Characteristics in South Korea for Developing Offshore Wind Farms

“…In general, it is difficult to accurately calculate wind resources because the wind in the lower part of the atmospheric boundary layer is generated by the simultaneous action of mechanical forcing due to surface friction and thermal forcing involving the heat balance due to surface heating [11,12]. In particular, in the case of coastal areas, a large amount of water vapor is distributed in the atmosphere and the change in atmospheric stability is relatively larger than that of land due to the difference in heat balance between the ocean and inland [13].…”

“…However, the atmosphere is still assumed to be in a neutral state on several reports and software. Therefore, in order to reduce the prediction error in the AEP calculation process, an accurate power curve of the wind turbine according to external environmental conditions, especially atmospheric conditions, is required [12,19]. Atmospheric conditions include turbulence intensity, wind shear, and heat flux, all of which depend largely on atmospheric stability.…”

Analysis of Vertical Wind Shear Effects on Offshore Wind Energy Prediction Accuracy Applying Rotor Equivalent Wind Speed and the Relationship with Atmospheric Stability

“…As the capacity and scale of wind turbines increase, accurate measurement of power curves, and the calculation of expected power generation are required, and conflicting interests arise in that regard [19,20]. Traditionally, to calculate the expected power generation of a wind turbine, only the wind speed at a single height corresponding to the hub height is considered, under the assumption that atmospheric stability is in a near-neutral state [21][22][23]. This was proper in the past to apply to small wind turbines with short blade lengths, and in calm offshore or flat land without obstacles, the difference in wind speed by height is small.…”

“…This was proper in the past to apply to small wind turbines with short blade lengths, and in calm offshore or flat land without obstacles, the difference in wind speed by height is small. So even if the expected power generation was calculated by selecting the hub height wind speed as the representative wind speed within the rotor disk, the error compared with the actual power generation was not large [21,22]. However, in recent years, as the diameter of the rotor area of the wind turbine has exceeded 200 m, the hub height wind speed cannot be the representative value in complex terrain, such as mountains, or even in flat terrain, where wind speed fluctuations by height occur in short time, due to the meteorological characteristics within the local atmospheric boundary layer.…”

“…The IEC Technical Committee 88 (TC88) recognizes that if the wind shear coefficient is kept constant, the difference between the rotor equivalent wind speed and the hub height wind speed is generally small [24]. However, in special cases, the vertical wind speed profile cannot be sufficiently explained by a constant wind shear coefficient, and such cases may be influenced by local meteorological characteristics or atmospheric stability distribution [12,21,22]. In this case, it is necessary to recognize that the difference between the rotor equivalent wind speed and the hub height wind speed may be considerable.…”