The announcement last week by Danish developer Orsted that it was downgrading its power production forecasts across its global offshore wind portfolio after misjudging the impact of “blockage” and “wind wake” in its modelling sent shockwaves through the industry – even reaching the pages of The Times where the spectre of an “industry-wide” problem of “entire wind farms being a greater brake [on output] than expected” was raised.
Energy consultancy DNV GL had warned last year that the impacts of blockage, where wind slows suddenly in front of a turbine — and wake effect, where winds are slower and more turbulent as it passes through ranks of turbines — though well-known to industry, could have a “pronounced influence” on total power production.
And Orsted, which had been studying the phenomena since 2014, admitted the modelling used until now “had not been sophisticated enough”, as it shaved 2% off lifetime load factor forecasts for its European offshore wind plant.
But industry experts tell Recharge that the Orsted revelations are likely to be looked back on as an “offshore storm in a teacup”, as advances in turbine technology, finer granularity of power production modelling and new techniques such as “wake steering” combine to boost wind farm output — and crediting the developer with lifting the lid on “long-recognised” issues to the benefit of the wider sector.
“The cat is out of the bag now,” says Henrik Stiesdal, who was been a leading figure in the global wind industry since developing one of the so-called “Danish model” turbines that became a go-to design as the sector modernised in the 1970s and 1980s. “But it is nothing new.
“We had interesting cases back in the 1980s in the Altamont Pass wind farms in California, where there are surprisingly very smooth wind conditions, and wakes behave sometimes much as they do offshore, even though the landscape is undulating.
“And even there we had some disappointing results [in terms of production output] because there were upwind projects that unexpectedly disrupted other wind farms — you simply didn’t get the mixing and reinjection of wind energy downwind.
“We also saw this at Vindeby [the world’s first offshore wind farm, built off Denmark in 1991, where Stiedal oversaw the turbine design], where wind wake would ‘persist’ many kilometres behind the wind farm and energy levels would not pick up.”
But while Stiesdal acknowledges that the downward drag on production caused by blockage and wind-wake would “undeniably” impact the wider industry, he feels the focus should be placed on the fact that “Orsted has been doing the best homework on this [area of research] and so is surely ideally positioned to develop the answers to the issues”.
“We now have the [modelling] tools — and so much higher computing power than when then earlier models were made — to really understand how big the effect [of blockage and wind-wake] is and so will be better able to predict the impact it will have, and how to develop the technologies and techniques we need to improve performance and production in these conditions,” he says, pointing to the US Department of Energy’s A2e (Atmosphere-to-electrons) project as an example of the “new philosophy” being applied to wind energy R&D.
Those technologies and techniques range from the more obvious, such as longer blades to increase energy capture; to the innovative, like “wake steering” where the rotor is directed into the richest part of the wind stream; and the transformative — smart wind farm layout and fleets of machines “working synergistically” within the electricity grid, as Katherine Dykes, a wind researcher at the Danish Technology University, tells Recharge.
Dykes, who is member of a 28-academic international team that recently produced a paper on the “grand challenges” of wind energy, puts the “physics of atmospheric flow” — including blockage and wind-wake — top of a list, on which “engineering the largest dynamic rotating machines in the world” comes a close second.
Ever larger machines, ever-deeper waters, we are constantly going beyond where wind power has been and uncovering uncertainties we didn’t know existed
“The Orsted announcement reaffirmed so much of we have been saying — that we still have a lot of challenges in wind energy science. As ‘mature’ as the wind sector seems, we are constantly pushing the envelope with technology and the environmental conditions in which they are deployed,” she says.
“Going to ever larger machines, going into ever-deeper waters, we are constantly going beyond where wind [power] has been before, and uncovering uncertainties we didn’t know existed.
“Ten years ago, we were saying land-based turbines would top out at 2MW, now we are looking at 5MW and bigger machines. And offshore, we are already at 10MW-plus and we were at 3MW only a few years ago; 20MW machines will soon be feasible. When you make those leaps in scale you get more challenges, but also so much more capacity [out of a turbine].”
But it is not just about upscaling turbines and exponential growth in computing power, Dykes tells Recharge.
“Some of the terminology used among [the research group] considering the wind farm of the future was, for instance, how an offshore plant would ‘dance’ with the energy system — much more interactive, how this resource would serve and support the grid.”
It is in the area of grid integration — “making wind an integral part of a [decentralised] energy system” — that Dykes feels there is untold potential. “Smart turbines, smart plants, operated and controlled with higher reliability, working synergistically within the electricity grid is the future,” she states.
Though sanguine about the long view when it comes to greater accuracy in power production modeling, Philip Totaro, chief executive of industry consultancy IntelStor, sees potential short-term blowback around the capital loans made to existing offshore wind projects that may now have lengthier pay-back periods than anticipated due to blockage and wind wake — and the knock-on effect on investor sentiment toward the sector.
“The implications of this are that power production will be a bit lower than predicted, so having a more sophisticated model will be helpful,” he tells Recharge. “The real problem is that project-finance levels, including the term and tenor of project [capital expenditure] loans, were fixed using the old power production methodology, and this will have a potential impact on the payback period and could diminish subsequent investor interest in existing projects.”
But Totaro points to 19 wind-wake research projects under way globally — “most of which are collaborative between universities and industry” — as evidence of the march of progress in the long term. “The reality of all this is that technology improves over time, and the industry will implement better solutions for how to accurately predict power output.”
The inconvenient truth remains that the explosive growth of the offshore wind industry now under way — the International Energy Agency’s first standalone report on the sector broadcast a 15-fold expansion to 360GW by 2040 — could turn out to be a somewhat double-edged sword, as Stiesdal notes, as the sprawl of multi-gigawatt-scale projects begins to ‘reduce’ the global wind resource.
“Offshore there are no [natural] obstacles [as on onshore terrain]. We are the ones who are putting the obstacles in. The relative changes to the offshore environment compared to onshore is greater [because of the number of utility-scale wind farms being built offshore],” he says.
“The next question, of course, is ‘Will the day come when we have so many offshore wind farms operating that we quantitatively reduce the wind resource around the world?’. ‘Yes, it will’. Is that a problem? Yes and no.
“If we do business as usual there will be future disappointments. However, one thing our industrial history has taught us is that you can keep on increasing the capacity factor tremendously even though you have a diminishing resource."
Stiesdal notes the ascending curve of turbine power production capacity since the first units were set turning almost 50 years ago. The pioneering Danish onshore designs had lifetime capacity factors of only 18%, a figure that rose to 23% for those installed between 1980-2000, and again to 33% for machines switched on from 2000-2017, all due mainly to the use of upscaled rotors and taller towers.
Offshore turbines are already operating with capacity factors of 50% and the world’s floating wind array, Hywind Scotland in the UK North Sea, saw a 65% capacity factor during its first months at sea.
“We thought we knew everything about onshore turbines and yet we have been able to get 50% more out of them. That is a huge improvement. What we can achieve offshore? We can’t yet have any idea really — but the Orsted drama is useful [as a wake-up call] to remind us about how much more [improvement] offshore [there is ahead] for us.”