<Evaluation method>
When building a wind power plant in Japan, it is necessary to design wind turbines that can withstand wind disturbances caused by the terrain.
The "Wind Farm Certification - Onshore Wind Power Plants (NKRE-GL-WFC01, Edition: July 2021)" (hereinafter referred to as the "NK Guidelines") issued by Nippon Kaiji Kyokai, a general incorporated foundation, which summarizes the requirements for domestic wind farm certification (hereinafter referred to as WF certification), requires that a development site be properly evaluated to determine whether it is in a complex terrain with large wind disturbances. The indicator for this is the following, as shown in the international standard "IEC61400-1 Ed.4.0: 2019":TSI(Terrain Slope Index)TVI(Terrain Variation Index), and Cct (Turbulence structure correction parameter), which is obtained using these indices.
TSI and TVI is an index calculated based on the elevation values in all directions and for each 5° wind direction sector for each circle with a radius of 10, 20, and 30 times the assumed wind turbine hub height centered on the target point. Table 1 shows theTSIとTVIIt is a criterion for determining the complexity of terrain based on allTSIis less than 10°,TVIIf the Cct is less than 2%, it is judged to be "flat terrain", otherwise it is judged to be "complex terrain". Complex terrain is classified into three categories of terrain complexity: low, medium, and high according to the criteria. Cct ranges from 3 to 2 according to these categories, as shown in Table 1.00.
The NK guidelines indicate that the representative radius of the observation site, the type of airflow analysis model, and the number of wind direction sectors should be set according to the Cct value (Table 3).
Table 1: Criteria for determining terrain complexity based on TSI and TVI
Table 2: Relationship with terrain complexity
Table 3: Setting criteria for representative radius and airflow model based on Cct
<Our services>
We follow the NK guidelines and use Cct to evaluate the terrain complexity, select the wind model and determine the representative radius of the observation value. Furthermore, as shown below, we set objectives for each phase of wind development and support optimal decision-making.
Regarding the wind data required for terrain complexity assessment, in the phases from desk-top study to wind mast installation, nearby AMeDAS data and GPV (Grid Point Value) data distributed by meteorological agencies are used, while in the subsequent WF certification phase, wind observation data and simulation results that comply with the NK guidelines are used.
- Desk study
We perform a simple assessment of the risk of turbulence due to the terrain based on the complexity of the terrain at potential wind turbine sites. - Wind condition mast installation
We will calculate the topographical complexity of the proposed wind mast construction site, determine the representative radius, and evaluate the risk of reduced accuracy of the vertical Doppler LIDAR observations to be installed alongside it.
In recent years, the construction of wind masts in complex terrains where it is difficult to reproduce airflow in CFD models has been increasing, and there are many sites where it is difficult to demonstrate the validity and sufficient accuracy of airflow analysis. By evaluating the terrain complexity in this phase and installing wind masts in appropriate locations, it is expected that the calculation accuracy in power generation evaluation and design (WF certification) will be improved. - WF Certification
The evaluation of terrain complexity will be more rigorous in line with the requirements for WF certification and construction plan notification.
At any siteTSIとTVICalculation example
Cct calculation result example
References
- Nippon Kaiji Kyokai, Wind Farm Certification for Onshore Wind Power Plants
(NKRE-GL-WFC01, Edition: July 2021) - International electrotechnical commission, IEC61400-1:2019 Wind energy generation systems. Part 1: Design requirements., Edition 4.0