Study supports use of CFD/lidar system on complex terrain

Companies developing wind farms in sites featuring complex terrain often encounter difficulties deploying older measurement technologies such as met masts due to siting restrictions, access and ground conditions. Remote sensing technologies, such as finance-grade lidars, overcome this issue. However, the ‘volume-based’ measurements obtained are currently required to be converted to match met mast point data for presentation in Energy Yield Assessments. Any such conversion must be well-documented, publicly available and easily scrutinised by 3^rd parties during due diligence and financing stages of wind farm project development.

The study, undertaken by Natural Power to support this acceptance, was founded on data from more than three years of commercial and research-based deployments and initially included a total of 21 site campaigns with stringent considerations taken as to the location and quality of anemometry used. The CFD model used, VENTOS, was assessed with respect to all parameters that may cause sensitivities within the model.

The conclusions of the study demonstrate that no additional uncertainty is caused by the conversion, known as Dynamics, in any of the sample sites when using VENTOS CFD and ZephIR 300 wind lidar. The resulting conversion in all cases showed an equivalent level of accuracy from ZephIR 300 could be achieved when compared to a met mast operating in complex terrain.

Natural Power considers ZephIR 300 wind speed data, when converted with CFD-based tool Dynamics, to be at DNV GL Stage 3 (finance-grade) in complex terrain / complex wind flow and can be used with little or no additional on-site met data, subject to such lidars having transparent and well-understood wind vector processing. It is central to a robust anemometry campaign that representative and suitable measurement locations are selected and appropriate levels of data coverage are attained.

“The announcement unlocks the potential of many wind energy sites located in challenging, complex topographies or where complex wind flows are present,” noted Lauren Wheatley, Technical Director, Natural Power. “In Natural Power’s opinion as bank’s engineer, ZephIR 300 can now be deployed to conduct finance-grade wind studies removing or reducing the requirement for siting tall traditional met masts which is often challenging in these types of site due to access and installation constraints.”

Ian Locker, MD, ZephIR Lidar, welcomed the announcement, stating: “Natural Power is a leading authority in the field of wind engineering in complex terrain, where an increasing number of potential sites are found. The Dynamics tool is the perfect partner to ZephIR 300 for clients operating within these more challenging environments. The CFD-based conversion provides a very transparent audit trail to both the pre- and post-converted data giving the necessary confidence when conducting finance-grade wind resource assessments and energy reports. ZephIR 300 has demonstrated itself as a truly versatile wind lidar capable of not only operating across all onshore and offshore applications, but being accepted by technical advisors such as Natural Power, and the lending communities investing in project finance.”