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'Met towers belong in a museum, not at modern wind projects'

OPINION | A quiet but decisive shift is underway from wind measurement systems that have been overtaken by advanced sensor technology, argues Pascal Storck

Despite its critical importance for developing and operating a profitable wind farm, wind measurement – and the technology that enables it – has rarely been a headline concern for the industry.

As the sector looks to bring down levellised cost of energy (LCOE) and increase production, while simultaneously raising standards and expanding in scale, most focus has been on the performance of wind turbines themselves. Longer blades, taller hub heights, condition monitoring; a plethora of technological innovations have been introduced to ensure maximum output and operational efficiency over the long-term.

In this context, it seems somewhat strange that the industry still relies on 30-year-old wind measurement technology. Fixed met towers continue to be constructed during site prospecting and left up, should the site prove suitable, for the life of the wind farm. If issues are suspected with turbine performance, the reference weather measurement is, yet again, another met tower installed especially for the purposes of a power performance test.

As turbine hub heights increase, those met towers are becoming harder – and more costly – to permit, construct and move. They pose a hazard to aircraft and personnel, send a clear signal of your development plans, and, what’s more, the data they collect can’t be applied to the full area of the project site, without a series of complex extrapolations, and associated loss of accuracy.

Wind choosing remote sensors over met towers: Vaisala

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A better option is available – and has been for some time now. Versatile remote sensing devices – SoDAR and LiDAR – offer a more flexible, cost-effective and mobile means of resource measurement. They are easy to set up, regardless of terrain, and capable of being used – and reused – across multiple sites, or moved around a single site to monitor wind performance. They offer an array of commercial, logistical and data advantages that met towers simply can’t.

These advantages are by no means an industry secret. So why the ongoing reliance on the met tower?

Uncertainty of acceptance, leading to a fear that data will be rejected, is definitely a factor. While the recent IEC 61400-1 ed. 2 guidelines have provided formal rules for the use of remote sensing for the purposes of power performance testing, no such formal guidelines currently exist for wind resource assessment – which has also created confusion about whether remote sensing data can be used in project financing.

And while independent validation and R&D efforts continue to demonstrate the reliability and accuracy of remote sensing devices, some may still be awaiting that official ‘nod of approval’ from a higher authority before they take the plunge and start using SoDAR and LiDAR as standalone measurement tools.

To some degree, this confusion about acceptance is also limiting those who have started to standardise remote sensing in place of met towers across their portfolios – and there are more than you might think – from revealing the full scope of their adoption.

"It’s understandable some early adopters of the technology are wary of alarming investors"

It’s understandable that some of these early adopters of the technology are wary of alarming risk-averse investors by announcing a comprehensive shift in measurement technology. It’s also entirely understandable that some would seek to maintain a competitive edge by keeping quiet about the benefits of remote sensing.

Nevertheless, the word is getting out as the industry shares its collective experience. Vaisala’s Triton SoDAR units have recently passed the milestone of 20 million hours – that’s 2,300 years – of data collected around the globe, and we’re poised to ship our 1,000th unit. LiDAR has been adopted on a comparable scale.

The fact is that the market is reaching a tipping point, and, while published international standards may still lag behind the reality of what is being undertaken on the ground by developers and operators globally, it is clear that those who fail to take advantage of state-of-the-art remote sensing technology and expertise will soon find themselves at a significant disadvantage.

Where the industry leads, standards and financial acceptance will inevitably follow. As contributors to our Remote Sensing Revolution report attest, the revolution is already well underway.

Our message to those who are still reliant on met towers is to think now about how they can reshape their measurement practices. Perhaps, in a few years, the only place that fans of met towers will be able to appreciate them is in their rightful home – a museum dedicated to the history of wind energy.

Pascal Storck is director of renewable energy for Vaisala

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