RWE leads Global Blockage Effect research initiative

4th February 2021

By: Marleny Arnoldi

Deputy Editor Online

     

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Renewable energy company RWE Renewables has announced a new project to reduce the commercial uncertainty around the modelling of the Global Blockage Effect (GBE).

The GBE in offshore wind is the latest joint industry initiative under the Offshore Wind Accelerator (Owa) programme and is designed to improve understanding of the true impact of GBE by undertaking the first of its kind measurement campaign under real offshore conditions.

The Owa is the Carbon Trust's flagship collaborative research, development and deployment programme. The joint initiative was set up between the Carbon Trust and nine offshore wind developers in 2008, with the aim to reduce the cost of offshore wind to be competitive with conventional energy generation, as well as provide insights regarding industry standard (and best practice) health and safety requirements.

The current phase involves participation and funding from eight international energy companies: EnBW, Equinor, Ørsted, RWE Renewables, ScottishPower Renewables, Shell, SSE Renewables, and Vattenfall, who collectively represent 75% of Europe’s installed offshore wind capacity.

RWE explains that GBE 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.

A number of competing classes of models and approaches to the evaluation have emerged. While 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, for example.

This 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 GBE project budget, including in-kind contributions, is €3.9-million. Over the course of the project, leading consultancies and expert organisations dealing with GBE modelling will also be engaged to help build a broad industry consensus around the treatment of the GBE.

The project centres around the planning, realisation and evaluation of a measurement campaign to be conducted in the second half of this year and which is designed to assess the multiple 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 quantifying the impact of the GBE on energy production.

Moreover, it is also designed to consider and agnostically test multiple existing hypotheses on how to reflect the GBE in models and in wind energy assessments. In addition, it will test the emerging hypothesis that calculations done with rapid fully coupled methods might represent physics fundamentals associated with the GBE better than current tools.

Since the rapid coupled approach combines wake and blockage models, the GBE on annual energy production would be combined into an overall turbine interaction effect – removing the need to apply any further blockage treatment.

Pre-investigations suggest the impact of the GBE could be less than currently assumed by the industry.

The project will be conducted at the Heligoland wind farm cluster in the German Bight, at the Nordsee Ost and Amrumbank West wind farm, which are both wholly-owned by RWE.

The two wind farms are separated by a strip of empty seascape about 4 km wide, known as the “Kaskasi gap”, in which RWE will build the Kaskasi wind farm, anticipated to go on line in 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 measurements in combination with turbine production data.

RWE offshore wind development director for Europe Richard Sandford says the offshore wind industry will benefit immensely from the data collected in this project as it will help gain a better understanding of GBE.

“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 can then increase certainty in offshore wind energy yield estimates and thereby help lower the levelised cost of energy.”

Edited by Chanel de Bruyn
Creamer Media Senior Deputy Editor Online

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