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Turbine loads

A key element of the layout design is the minimum turbine spacing used.  In order to ensure that the turbines are not being used outside their design conditions, the minimum acceptable turbine spacing should be obtained from the turbine supplier and adhered to.  

The appropriate spacing for turbines is strongly dependent on the nature of the terrain and the wind rose for a site.  If turbines are spaced closer than 5 rotor diameters (5D) in a frequent wind direction, it is likely that unacceptably high wake losses will result.  For areas with predominantly uni-directional wind roses, such as the San Gorgonio Pass in California, or bi-directional wind roses, such as Galiciain Spain, greater distances between turbines in the prevailing wind direction and tighter spacing perpendicular to the prevailing wind direction will prove to be more productive.  

Tight spacing means that turbines are more affected by turbulence from the wakes of upstream turbines.  This will create high mechanical loads and requires approval by the turbine supplier if warranty arrangements are not to be affected.  

Separately from the issue of turbine spacing, turbine loads are also affected by:

• ‘Natural’ turbulence caused by obstructions, topography, surface roughness and thermal effects
• Extreme winds

Defining reliable values for these parameters, for all turbine locations on the site, may be difficult.  Lack of knowledge is likely to lead to conservative assumptions and conservative design.

Within the wind industry there is an expectation that all commercial wind turbines will be subject to independent certification in accordance with established standards or rules.  A project-specific verification of the suitability of the certification for the proposed site should be carried out, taking into account the turbine design specifications and the expected climatic conditions of the site.