How to evaluate the complex terrain of the wind development site? ~ Quantification of terrain complexity using CCT-

When building a wind power plant in Japan, it is necessary to design a windmill that can withstand the disturbance of the wind due to the terrain.

The "Wind Farm Certification and Ground Wind Power Plant Edition (NKRE-GL-WFC01, Edition: JULY 2021)" (hereinafter, "NKRE-GL-WFC01, Edition: JULY 2021) of the Japan Maritime Association, which summarizes the requirements for domestic wind firm certification (hereinafter, WF authentication). NK guidelines are required to properly evaluate whether the development site corresponds to a complex terrain with a large wind disturbance. The indicators are shown in the international standard "IEC61400-1 Ed.4.0: 2019",TSI(Terrain Slope Index; terrain gradient index)TVi(Terrain Variation Index; terrain fluctuation index) and CCT (Turbulence Structure Corraction Parameter) obtained using these indexes).

TSIWhenTViIs calculated based on the altitude values ​​for each direction and 30 ° width of each circle of 5, 10, and 20 times the assumed wind hub height centered on the target point. Index. Table 1 isTSIWhenTViThis is a criterion for terrain complexity based on. AllTSIIs less than 10 °,TViIf it is less than 2%, it will be "flat terrain", and the rest will be "complex terrain". Of these, complex terrain is classified into three categories: low terrain complexity, medium and high, according to the reference value. As shown in Table 2, CCT takes a value from 1.00 to 1.15 according to these categories.

The NK Guideline shows that the representative radius of the observation site, the type of airflow analysis model, and the number of wind direction sectors of the observation site according to the value of the CCT (Table 3).

Table 1: Diability for terrain complexity based on TSI and TVi

Table 2: Relationship with terrain complexity

Table 3: Setting standards for representative radius and airflow models based on CCT


In accordance with the NK guidelines, we will select airflow models and determine the radius of observation values ​​based on topographic complexity evaluation using CCT. In addition, as shown below, we will set a purpose for each phase of wind development and support optimal decisions.

Regarding the wind -fashioned data required for terrain complexity evaluation, the phase from desk study to the installation of the breeze mast is the GPV (Grid Point Value) data distributed by nearby Amedas data and meteorological agencies, and later. The WF authentication phase uses the wind -fashioned observation data and simulation results compliant with the NK guidelines.

  1. Desk study
    We simply evaluate the risk of turbulence due to terrain due to the terrain complexity of windmill candidates.

  2. Winding mast installation
    Calculate the terrain complexity of the planned mast mast construction site, evaluate the risk of deterioration of the representative radius and the accuracy of accuracy of the vertical doppler rider observation.

    In recent years, the construction of the airflow in complex terrain, which is difficult to reproduce airflow in CFD models, has increased, and some sites have been seen that it is difficult to show the validity and sufficient accuracy of airflow analysis. By evaluating terrain complexity in this phase and installing a breeze mast in an appropriate place, it is possible to improve the calculation accuracy in the amount of power generation and the design (WF authentication).

  3. WF certification
    Based on the requirements for WF authentication and construction plan notification, we will evaluate terrain complexity more strictly.

On optional sitesTSIWhenTViCalculation example


CCT calculation result example


  1. The Japan Maritime Association, Wind Farm Certificate and Athletics Power Station edition
    (NKRE-GL-WFC01, Edition: JULY 2021)
  2. International Electrotechnical Commission, IEC61400-1: 2019 Wind Energy Generation Systems. Part 1: Design Requirements., Edition 4.0