‘GLOBAL BLOCKAGE EFFECT’

UNPARALLELED ‘GLOBAL BLOCKAGE EFFECT’ RESEARCH APPROVED

GBE, as defined by the Carbon Trust, is a phenomenon that occurs as a complex interaction between the wind farm and the atmosphere as the wind flows through, over and around large offshore wind farms. The effect is subtle, difficult to measure and hard to extract from legacy campaign data, therefore assumptions incorporated into performance calculations are impacted by existing magnitude and model uncertainties.

There have been several controversial theories regarding the impact of GBE on the wider scope of offshore wind farms but there is a broad industry consensus that the GBE causes decelerations in front of offshore wind farms which reduce the energy yield. Different opinions exist on how to consider its downstream impacts and how to account for redistribution of energy. This information is commercially relevant as uncertainty in wind turbine and wind farm performance drives a high cost of capital for offshore sites. Any over estimation of the GBE leads to the de-valuation of offshore wind projects. Consequently, efforts to increase understanding of the GBE are a key focus for the offshore wind industry.

The 'OWA GloBE' project focuses on planning, realisation and evaluation of a measurement campaign to be conducted by the end of 2021, which is designed to assess several aspects of the GBE at full scale and observe the atmospheric phenomena that drive it. The aim is to produce a comprehensive dataset that can be used as the industry benchmark for assessing and gauging the impact of the GBE on energy production. This project is designed to test multiple hypotheses and theories on how to reflect the GBE in models and in wind energy assessments. 

The project will monitor the Heligoland windfarm cluster in the German Bight, at the Nordsee Ost and Amrumbank West wind farms which are both owned by RWE. The two wind farms are separated by a strip of empty seascape measuring approximately 4km wide. This section of shoreline is known as the ‘Kaskasi gap,’ in which RWE will construct the Kaskasi wind farm. This new wind farm is expected to be operational by 2022. This provides an opportunity to create a unique experimental setup for GBE using multiple remote sensing techniques, including dual doppler scanning light detection and ranging (LiDAR) measurements in combination with turbine production data. The combination of Nordsee Ost, Amrumbank West and the ‘Kaskasi gap’ is expected to concentrate the flow features that the project aims to observe.

Richard Sandford, Director Offshore Wind Development Europe at RWE Renewables, commented: “The offshore wind industry will benefit immensely from the data collected in this project as it will help us gain a better understanding of Global Blockage Effect. By appraising and testing various industry hypotheses under live conditions, we will be able to close existing knowledge gaps and reach an industry-wide consensus on the effect. OWA GloBE can increase certainty in offshore wind energy yield estimates and thereby help lower the Levelized Cost of Energy.”

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