OWA GloBE measurement campaign extended to bolster data and analysis on Global Blockage Effect in offshore wind farms

The measurement campaign for the Global Blockage Effect in Offshore Wind project (OWA GloBE), a joint industry project organised within the Carbon Trust’s Offshore Wind Accelerator (OWA), has been extended by four months. This will allow data to be gathered during the spring period, when atmospheric boundary layer heights are low and Global Blockage Effects (GBE) are expected to be more pronounced. Since its launch in early 2021, the project has continued to attract interest from industry, with four new partners joining the consortium, Ocean Winds, Ørsted, The Crown Estate and TotalEnergies, increasing the total budget to €5.9 M, including in-kind contributions. Following the completion of the measurement campaign, the primary data will be used by a specialist group of experts to validate and improve various computational models. Some of these models are already used to inform investment decisions; others represent the next generation of models. 

An increasingly important phenomenon due to its potential impact on energy yields, GBE refers to the slow-down of the wind as it approaches a wind farm, and the corresponding speed-up of the wind elsewhere. Historically, wind farm designers considered only wake effects, i.e. the reduction of wind speed downstream of a turbine or wind farm. However, as wind farms get bigger, the impact of GBE grows, creating an increased need for the industry to understand this phenomenon to minimise financial uncertainty.  

The OWA GloBE project aims to reduce such uncertainty by creating a comprehensive primary dataset, comprising of several terabytes of measurements, that can be used as the industry benchmark for assessing and quantifying the impact of GBE on energy production.?The project aims to build industry consensus regarding how offshore wind farms interact with the atmosphere by answering three key questions: 

• Does this slow-down lead to a loss in energy yield, or can this energy be recaptured elsewhere in the wind farm? 
• What factors determine the strength of GBE? 
• How does GBE scale to interactions between wind farms? 

The measurement campaign started at RWE’s offshore wind farms Amrumbank West and Nordsee Ost in the German Bight in September 2021. The two wind farms are separated by a strip of empty sea approximately 4?km wide, in which RWE is currently constructing its Kaskasi wind farm. Until the first turbines are placed, the Kaskasi site provides an opportunity to create a unique experimental setup to detect and quantify GBE both within a wind farm and between wind farms. 

Seven scanning Light Detection and Ranging systems (LiDARs) have been deployed and commissioned on turbine transition pieces. Six devices scan the wind upstream, between and behind the two existing wind farms, and one measures the atmospheric boundary layer above the site. All devices have been equipped with bespoke sensors, so that the motion of the turbines can be accounted for. 

In addition, a floating LiDAR has been deployed in the sea west of the wind farms to measure the undisturbed wind. An existing RWE on-site met mast has been refurbished with a profiling LiDAR and new instrumentation to measure turbulence and atmospheric stability parameters. 

OWA GloBE is partnering with two publicly funded projects. The floating LiDAR buoy and the LiDAR measuring the atmospheric boundary layer are provided by Fraunhofer IWES as part of an extension of the X-Wakes project, funded by the German Federal Ministry for Economic Affairs and Climate Action. Data processing, including the application of machine learning processes to create more value from Lidar measurements, is performed by TNO within project AFFABLE, partially funded through TKI-Energy from the Allowance for Top consortia for Knowledge and Innovation (TKI’s) from the Ministry of Economic Affairs and Climate.  

The pointing accuracy of the scanning LiDARs has been calibrated using a high-precision GPS-controlled drone, which enables very low measurement uncertainties to be achieved. It is believed that OWA GloBE is the first ever campaign to have used drones for calibrating LiDARs offshore.  

In parallel, the project has assembled an Independent Technical Review Group (ITRG), comprising of six leading consultancies (Deutsche Windguard, DNV, EMD International, UL, Whiffle and Wood Group) working in close collaboration with DTU, Fraunhofer IWES and TNO. The ITRG reviewed the campaign design prior to installation and will have access to selected measured data to validate and refine a wide spectrum of models. This should allow the project to build cross-industry consensus on how blockage should be described, modelled and measured in the future. Frazer-Nash Consultancy has also been contracted to tune, validate and deliver coupled engineering models (building on previous work from the OWA) to predict the combined blockage and wake effect.  

The RWE led project kicked off in early 2021 with support from the other OWA members: EnBW, Equinor, Shell, Vattenfall, ScottishPower Renewables, plus EDF Renewables, Leosphere and DTU as external partners. The measurement campaign will finish in May and will be followed by analysis, modelling, validation and reporting, to conclude the overall project by the end of 2022.  

Renske Ytsma, Head of Offshore Development Continental Europe at RWE Renewables, explains: 

“The whole offshore wind industry will benefit immensely from this project as it will help us gain a better understanding of the Global Blockage Effect. We very much appreciate the support of the new project partners which will allow the extension of the offshore measurement campaign. OWA GloBE will allow us to close existing knowledge gaps and reach an industry-wide consensus on an effect that has a high impact on the planning and operation of offshore wind farms.” 

Jan Matthiesen, Director of Offshore Wind at the Carbon Trust, commented: 

“OWA GloBE’s collaborative approach aims to foster a common understanding across the industry and is another great example of effective joint industry projects accelerating the scale-up of offshore wind. The GloBE project is undertaking a significant measurement campaign, both in terms of its scale and its unique set up, to increase primary data on how the Global Blockage Effect impacts yield in operational wind farms. The decisive phase will be how this data can then be used to help improve existing computational models which are used to inform the cost of finance for future wind farms. The level of interest in the OWA GloBE project  has exceeded our expectations, reinforcing  the importance of improving the understanding of this phenomenon and its impact on yield at a time when offshore wind farms are expanding in size.” 

Jonny Boston, Business Development Manager, Offshore Wind at The Crown Estate commented: 

“Ensuring that decisions on future offshore wind farm development are based on the best possible data and evidence is vital if we are to rise to the challenge of achieving Net Zero emissions. That’s why we’re supporting this pioneering initiative to better understand the impacts of the global blockage effect, working in collaboration with industry and some of the sharpest minds in the research community. The improved modelling techniques that are developed by this project will enable improved co-ordination, certainty and efficiency for UK offshore wind."