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Wake modelling: Improving prediction accuracy, reducing finance costs and optimising windfarm layouts

In 10 years, the Offshore Wind Accelerator (OWA) has run over 150 projects supporting innovations that have led to both a significant reduction in the cost of energy and risk, whilst making offshore operations safer. To mark this milestone in R&D collaboration, we have selected 10 high impact innovations to showcase the breadth and depth of the programme.

wake-modelling

The more certainty offshore wind can offer investors, the more investment it can attract.

As a result, every little tweak which refines our predictions of how wind farms will perform has the potential to have a big difference to the cost of wind energy.

Improvements in our ability to estimate ‘wake loss’ is an example of a tweak which made a big difference.

Picture wind blowing towards a single turbine. It hits the blades of the turbine in a relatively fast and concentrated way. As it flows past the blades, its speed, direction, and concentration changes. The wind is moved and muddled, and the flow which emerges behind the turbine is much more turbulent and less concentrated. This wind – the wind behind the turbine – is known as the wake.

Now picture a wind turbine behind that first one. The wind which rushes towards this one is the wake from the one in front. It is, of course, much less concentrated than the flow which rushed towards the front turbine. It moves with less force as well. This reduces the second turbine’s production capacity.

This reduction is known as ‘wake loss.’

Investors considering wind farms need an estimate of wake loss in order to assess the productive capacity of their investment.

But they don’t just need to know what the wake loss will be. They also need to know how confident they can be in that figure. In other words, they need an estimate of how accurate the wake loss figures are likely to be. The more certainty they have, the easier it is to invest.

Traditionally, they assumed that the wake loss uncertainty was 50 per cent. In other words, if wakes are expected to reduce energy production by 12 per cent, the uncertainty around that figure is plus or minus 6 per cent. That’s a lot of uncertainty.

But this estimate of 50 per cent wake loss uncertainty wasn’t really based on evidence; it was just an assumption investors used to be safe.

One of the unsung heroes of the story of the falling cost of offshore wind is the improvement in the certainty of our estimates of wake loss. Just a decade ago, there was very little information on which to base these estimates, so there was limited confidence in the wake loss predictions.

The OWA partners decided to add to the bank of data available. As data came in about wake loss from more offshore wind farms, we became more certain about how correct our models were. In July 2015 the OWA published a journal article which showed that the default wake loss uncertainty of 50 per cent was unnecessarily high. In fact, it is more appropriate to apply an uncertainty of 25 per cent or less.

In July 2015 the OWA published a journal article which showed that the default wake loss uncertainty of 50 per cent was unnecessarily high. In fact, it is more appropriate to apply an uncertainty of 25 per cent or less.

This made a massive difference. Halving the estimate for uncertainty makes investing in offshore wind look significantly less risky, attracting both equity and debt to the project.

For some projects, this increase will have a significant impact on the levelised cost of energy – the cost of building and operating a new wind farm today measured over the whole period it will be used – due to better financing terms.

This is another example of how the offshore wind sector has reduced cost by improving the data used for estimates, reducing uncertainty.

To make sure that predictions for new projects are generated according to the OWA’s benchmarking work, we wrote a detailed guide for those using models from lenders to advisers, and wind farm developers.

This article is part of 10 years, 10 innovations: A summary of the impact of the Offshore Wind Accelerator

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