Undertaking accurate wind resource assessments in the Benelux onshore wind market
Getting the wind resource assessment right is crucial for the development of any wind energy project. Wind studies ultimately rely on the available data for any region in the world. Within the Benelux (Belgium, Netherlands and Luxembourg) onshore market, wind resource assessments and energy predictions have mainly been performed based on available wind maps covering the region and the extrapolation of energy output from neighbouring wind farms. Although this is an accepted approach in the region, it is believed to carry a fair amount of uncertainty in the energy assessment.
Recently, financial lenders to large wind farm projects have requested studies to be based on project-specific onsite measurements, something which follows state-of-art methods to estimate wind energy potential. The use of onsite measurements would typically reduce the uncertainties in the final production estimate. To adopt these new requirements, developers in Benelux are mainly deploying onsite remote sensing devices, in this case LiDARs (Light Detection And Ranging technique), while also utilizing production information from existing neighbouring wind farms.
The deployment of LiDAR devices has many practical advantages. They provide great wind speed and wind direction measurements accuracy across a large range of heights when all requirements are met and in benign terrain. In addition, the process of applying for permits required to install LiDARs are relatively straightforward. When LiDARs are used in an energy production assessment, it is important that the device is of a proven technology, and that the unit has passed independent pre- and possibly post-verifications. It is also important to ensure that it has been installed following the standards of a wind measurement campaign. Some technical parameters also need to be assessed, such as the verifications and deployment criteria, power supply and traceability of documentation covering the whole measurement campaign, to name a few critical ones.
Noticeably, even if these milestones are successfully reached, turbulence intensity and maximum wind speed values recorded by LiDARs are hard to compare against required standards. LiDAR devices are known to yield different results in comparison with cup anemometry, mainly due to the differences of volume versus point measurements. Meteorological mast data might then be required for a project, but this will be at the discretion of the turbine manufacturer.
Production data from existing wind farms is also a significant source of information. Wind turbines SCADA (supervisory control and data acquisition) data and information from adjacent operational wind farms can be used to predict the long-term energy output of a proposed wind farm. This analysis provides an opportunity to further validate onsite wind resource data, or if none is available, validate a high-resolution modelled time series. It also helps owners/operators to investigate the under- or over-performance of existing wind farms.
Actual site measurements should always be the preferred method undertaken. This follows the standards set out in a detailed wind resource and energy production assessment, thereby reducing the uncertainties of a final energy production estimate. Trusted independent advisors should be consulted at an early stage in wind measurement campaign planning, to ensure a high-quality wind data set. Whether a wind project is in the early stages or even if it’s operational, independent experts can help with site identification, measurement campaign monitoring, pre-construction assessments, balancing analysis, turbine data post-construction assessments, extension analysis, performance monitoring and short-term forecasting.
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