You’re stealing our energy: Accusations of offshore wind theft hurled across North Sea

A top executive at Swedish power company Vattenfall has said heavy wake losses sustained by German wind farms are pushing project power prices in Germany up well above those in other countries like Denmark. 

The comments, made last week, come amid a year of escalating disputes over so-called ‘wind theft’ that has embroiled almost all of the biggest companies in North Sea wind.

In early May, Equinor and SSE alleged that wake losses caused by a planned RWE offshore wind project, Dogger Bank South, would cost their neighbouring farms US$778 million (A$1,205 mil) over their lifetime. 

The energy giants asked for either mitigation or appropriate compensation for the potential losses sustained. 

Cumulatively, around 20GW of projects in UK waters are embroiled in these kinds of disputes, according to renewable consultancy Tamarindo Global, amounting to a discombobulating merry-go-round of wake loss accusations.

What are wake effects?

Much as a boat travelling through water leaves behind a wake, a turbine buffeted by a stream of wind also leaves a wake behind it, in the form of an area of lower windspeed, and therefore lower energy, as well as higher turbulence, which further dissipates wind energy.

The area of lower-energy wind behind it is also known as a “wind shadow”.

Wakes from wind turbines can extend for long distances, meaning the wind that reaches another turbine – or indeed another wind farm – is laden with less power, leading to less electricity produced and less profit for the project.

Estimates of these losses vary but generally wake effects between two wind farms can lead to a reduction in the downstream farm’s energy production by between five and 20 per cent.

And satellite imagery has shown that wake effects from wind farms can extend up to 70 kilometres.

The North Sea, at the centre of several western European countries, is a prime candidate, alongside the Baltic Sea, for housing a portion of the 300 GW of offshore wind the EU aims to build by 2050, not to mention the 50 GW the UK plans to have installed by 2030. 

But the North Sea is also a finite piece of ocean, meaning wind projects are inching closer together.

In a report published last month, Norwegian consultancy DNV predicted offshore wind farms will take up almost 9 per cent of the North Sea basin by 2050, or more than 60,000 square kilometres.

That means concerns around wake losses, as well as price cannibalization, will only become more acute, unless companies are able to mitigate these effects.

How can wake effects be improved/mitigated?

The University of Manchester, UK, is leading a national review of North Sea wake losses, funded by the UK’s Engineering and Phyiscal Sciences Research Council’s (EPSRC) Supergen Offshore Renewable Energy (ORE) Impact Hub.

The 12-month long project will assess how offshore wind farms affect each other’s energy production, the financial losses incurred, and how to best locate future offshore farms to minimise the effect.

Meanwhile, several of the key players involved in the disputes have either launched or been involved with other wake loss studies, including RWE’s collaboration on the C2-Wakes and X-Wakes projects, and Ørsted’s development of the TurbOPark wake model.

Addressing wake losses between separate farms requires either geographically distancing them, or adjusting the power derived from the wind by one farm to enable another to get its fair share. There’s also financial compensation, through a legal mechanism known as wake loss agreements.

Joel Manning, from engineering consultancy K2M, says widely touted claims that wake losses are underestimated are misleading.

“Despite decades of development in wind wake modelling, some voices argue that these models are still flawed and fail to fully capture the extent and impact of wind wakes,” he writes.

“Developers could still face unforeseen wake losses and legal disputes over “wind theft”, but accurate modelling to support decision-making is available. This already helps to minimise potential losses and provides clear information to resolve legal disputes.”

RWE, for its part, has stood firm, with the company’s UK chief arguing offshore wind developers should “live with the risks they’ve taken”, according to RechargeNews.

RWE’s position is that mitigation efforts around wake loss will result in a net loss of captured energy, ultimately meaning bad news for the UK and Europe’s renewable energy targets.