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Improve and expand offshore and onshore wind turbine performance evaluation with nacelle-mounted lidar

DNV is leading the way in the use of nacelle-mounted lidar (NML) for wind turbine power performance testing. Well-designed IEC-compliant wind measurements form the crux of warranty performance assessments, mitigating risk for wind farm developers and operators. NML-based performance testing requires unique design and analytical expertise, but the technical complexity of testing is easily justified by advantages such as cost, scalability, bias-correction, and overcoming layout constraints.

Deployment of NML has several advantages over meteorological masts owing to the significant reduction in hardware, permitting, and installation costs. The relative cost savings are growing as modern turbine hub heights (and associated hub-height met mast costs) continue to increase. Further, NMLs are easily transferable from turbine to turbine and wind farm to wind farm.

Unlike ground-based lidar deployments, where the IEC requires the use of monitoring masts, there is no mast requirement for NML deployments. On-nacelle NML installations allow for straightforward co-installation of hub-height air density measurements. NML measurements characterize directly incoming wind fields, unlike stationary wind measurement approaches (e.g. met masts and ground-based lidar) that limit wind characterization to a single point that may be misaligned with the wind direction and turbine yaw. The horizontal orientation of NMLs also allows for the characterization of wind farm blockage effects by measuring at several distances in front turbines, enabling evaluation of potential sources of bias in performance results.

Finally, NML enables performance testing in otherwise limiting settings. At wind farms with constrained boundaries, NMLs can measure at IEC-prescribed distances that may extend beyond the buildable area for met masts. This characteristic is similarly valuable at “repower” sites where, due to larger turbine rotor sizes, existing mast locations may no longer be properly positioned for IEC-compliant wind measurements. In offshore environments, where mast construction is unfeasible, NML continues to be the established norm for performance testing.

Capitalizing on the advantages of NML for turbine performance testing requires expert measurement design. Careful mounting design enables unobstructed measurements at contractually required heights. Optimizing beam configurations for a given positioning, and for a given NML type, is essential to minimizing measurement uncertainties in the face of dynamic turbine tilt and, in onshore cases, variable terrain conditions under the NML measurement arc.

Poor NML configuration design can lead to elevated measurement uncertainties and violations of contractual testing terms. Without careful consideration of turbine tilt dynamics under wind load, measurement height-related uncertainties can decrease the precision of test results. Minimizing measurement height-related uncertainty also requires consideration of the weight of wind speed bin-specific uncertainties (a function of site-specific wind speed distributions and power curves) in final annual energy production estimates. Ill-conceived NML mounting approaches may limit measurable heights and introduce contractual deviations regarding the characterization of veer and shear in performance tests.

DNV was busy surmounting these challenges ahead of the release of the 61400-50-3 IEC standard (50-3) for NML-based power performance testing, establishing best practices, analytical tools, and an industry-leading NML calibration facility. Since the release of 50-3, DNV has designed and led NML power performance campaigns for both onshore and offshore projects around the globe. In multiple instances, the cost and logistical efficiencies of NML deployments have enabled clients to easily expand the quantity of tested turbines, constraining the uncertainty of aggregate performance estimates.

We are proud to be leading the application of cutting-edge technology that is advancing turbine performance testing and re-risking investment in the global energy transition. Contact us to learn more.

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Derek Roberts

Derek Roberts

Senior Technical Project Manager Measurements

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