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Offshore forecast fears blow through European wind farms

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Via Financial Times

On the Holderness coast in the north-east of England, radar technology normally used to track hurricanes in the US has whipped up an unwelcome storm in Europe’s offshore wind industry.

Since 2016, Orsted, the world’s largest offshore wind developer, has been using the radar system to collect 3D images of the wind as it blew through its Westermost Rough project, in waters eight kilometres from the shore.

The 3D data collected from Westermost Rough, along with observations from Orsted’s other schemes, aroused suspicions within the Danish company that previous assumptions about how wind interacts with large offshore turbines — and how it affects their production levels — were possibly too simplistic.

Orsted went public with its findings on October 29 last year, describing the problems as “industry wide” and revising down offshore wind production forecasts made to the market a year earlier.

Shares in the company, previously known as Danish Oil and Natural Gas, fell 7 per cent on the day of the announcement as investors were caught off guard and wondered whether other developers would also follow suit.

The revision marked some rare negative news in an industry that has been declared a “major game changer” in meeting the world’s future electricity needs by the Paris-based International Energy Agency, and which has undergone rapid growth since the first offshore wind turbines were installed in Danish waters in 1991.

Concerns over production levels have been raised at a time when profit margins in the sector are already decreasing, as competition to build offshore wind schemes intensifies and governments also seek to reduce — or scrap altogether — subsidies for the industry. 

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Rival offshore wind developers rushed to check their own models.

“We have obviously gone round it [our models] again after they [Orsted] said something,” Alistair Phillips-Davies, chief executive of SSE, the UK power company, told the Financial Times.

“We believe that we are in a solid position and there’s nothing yet in what they’ve [Orsted] said that’s made us change our mind about our fleet and our portfolio.”

Spanish energy group Iberdrola said its own forecasts tended to be on the “conservative side” when it made a final investment decision to press ahead with an offshore wind scheme.

“Our operational offshore data [then] shows that performance is higher than the figures that we base the investment case on,” an Iberdrola spokesman said.

At the heart of Orsted’s findings are two wind effects known as “wake” and “blockage”. The wake effect describes how wind slows after hitting a turbine, affecting those situated further downstream. Blockage is where wind slows down as it approaches a turbine. 

Both effects have long been recognised by the renewables industry but Orsted believes their scope and complexity have been underestimated.

It has long been understood that there is an “individual” blockage effect for every single turbine but Orsted identified a “global” blockage effect that is greater than the sum of the individual effects. This arises from individual turbine losses also affecting neighbouring turbines.

Orsted also hypothesised that as more offshore wind farms are built, there could be higher wake effects from neighbouring wind farms.

Henrik Poulsen, Orsted’s chief executive, insisted it was not a case of the company’s previous forecasts having been too aggressive, as some competitors implied. “We have over the years benchmarked our internal production estimates against third-party views from industry experts and other developers,” Mr Poulsen told analysts.

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“In comparison, most production estimates from third parties have been trending towards a more positive view than ours,” he added.

Some independent consultants also believe long-held industry assumptions may be understating wind effects. Oslo-headquartered DNV GL published a report in 2018 challenging long-held assumptions about wake and blockage effects.

“It was assumed that a turbine could only affect other turbines located downstream. Any influence on turbines upstream or laterally was almost always ignored,” said James Bleeg, a principal researcher at DNV GL.

His company’s own research concluded that turbines located on the front row of a wind farm “will generally produce less than they would in isolation”. 

“This likely represents a material bias in energy prediction procedures used throughout the industry,” Mr Bleeg added.

Despite the pushback from many of Orsted’s major competitors, DNV GL believes some industry players are already taking note of the latest understanding of wind effects.

“What we see on projects in 2019 is an additional adjustment to the energy yield and the capacity factor of the projects to account for this [latest understanding],” said Simon Cox, DNV GL’s offshore wind business manager.

Wind turbine manufacturers have also been looking at how to minimise issues such as the wake effect. Every percentage point improvement in production will make a difference as profit margins tighten.

Siemens Gamesa said in November it was now able to direct the way wind flowed off a turbine to try to minimise the effect on those downstream. Wake effects are carefully modelled and turbines are adjusted remotely.

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Rather than being a negative, Per Egedal, chief product manager at Siemens Gamesa, believes work into phenomena such as wake effects is a sign the offshore wind industry is coming of age.

“It’s kind of a maturing process where we are going more and more into details and getting more and more accuracy on everything,” Mr Egedal said.

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