DNV GL will assess the climatic conditions, other environmental factors and the ground conditions at a site in order to assess the suitability of the WTGs chosen. This condition data may also be used for a detailed load calculation or an estimate of turbine lifetime. A comprehensive assessment of a site will also include a review of the electrical conditions at the interface between the wind farm and the local grid.
A site suitability assessment will typically include the following four services:
- Assessment of climatic conditions: On-site wind measurements – annual average wind speed, wind speed and direction distribution, reference wind speed, wind shear, flow inclination and characteristic turbulence intensity – are almost always required to assess climate conditions at a site. Ground and seismic, electrical and other environmental conditions are also assessed.
- Pre-assessment of load assumptions: All climatic conditions are assessed with respect to their influence on the site suitability of the WTGs. Where site conditions are within the turbine’s design conditions, no further action is required. Where a marginal situation exists, an assessment of the design equivalent turbulence for assumed generic turbine conditions normally allows firm conclusions to be made about the turbines’ site suitability.
- Load calculation: If the design conditions for a turbine are exceeded at a site, a more detailed evaluation of the site-specific fatigue loads is performed. The load duration distribution of the rotor torque is evaluated and compared to the design values of the gearbox. In some cases, e.g. where extremely gusts of wind occur, a site-specific extreme load calculation is required. Where appropriate, seismic loads will also be assessed on the bass of assumed input earthquake conditions.
- Lifetime estimate: If required, DNV GL can estimate the expected lifetime of relevant turbine components on the basis of the fatigue loads calculated for the relevant site conditions.