The wake effect – inside the Offshore Wind Accelerator programme

In March 2014, the Westermost Rough wind farm off the coast of Yorkshire and the Gwynt y Môr wind farm off the coast of North Wales received a combined total of £461 million from the UK Green Investment Bank (GIB), making them the first offshore wind projects in the UK to receive significant debt financing in the construction phase. However, researchers behind a £2-million wake-effects measurement campaign - collecting data since 6 May 2013 and completed in May this year - hope, and may soon have reason to believe, that they won't be the last.

Part of the Carbon Trust's Offshore Wind Accelerator (OWA), a joint industry project working towards reducing the cost of offshore wind by at least 10% by 2015, the wake-effects measurement campaign is specifically designed to address the requirement for more and better validation of data for wake-effects models.

Through the publication of these validation studies, the researchers behind the campaign hope to reduce the uncertainties associated with offshore wind, providing detailed measurement data to the wind industry about how the wind behaves in complex situations offshore and how this ultimately impacts wind farm yield.

The idea is that this will reduce the cost of financing these projects, in turn increasing their likelihood of receiving debt financing, particularly during construction, and, therefore, helping the UK to meet its 2020 renewable energy targets, as well as delivering significant benefits to the country in the form of additional jobs and increased revenue. Indeed, PwC has estimated that, for every one percentage point reduction in the cost of capital for offshore wind, the levelised cost of energy (LCOE) reduces by 6%.

With a little understanding

European Union (EU) countries have tough renewable energy targets to meet in the coming years. While the EU has made a legally binding commitment to generate 20% of its energy from renewable sources by 2020, in the UK specifically, the expectation is that meeting this target means 30% of electricity will have to come from renewable sources. Looking further to the future, the UK then has a target of reducing its greenhouse gas emissions to 80% below 1990 levels by 2050.

Offshore renewable power will make a major contribution to the 2020 and 2050 targets. "Precisely how much will depend on many factors, but particularly on the funding cap from the Levy Control Framework of the government's new contract-for-difference (CfD) and anticipated cost reductions in offshore renewables," says Breanne Gellatly, the OWA's associate director of innovations.

The government has modelled offshore wind deployment scenarios for total capacity to reach 8.1-15.0GW by 2020. Currently, the 4C Global Offshore Wind Farm Database lists approximately 3.7GW of offshore wind capacity that has already been fully commissioned, with a further 1.4GW already under construction and 3.0GW with consent authorised.

As Gellatly explains: "If we assume the wind farms under construction already have finance secured, then, under the 8.1GW deployment scenario, an additional 3.0GW of projects remain to secure finance, while, under the 15.0GW scenario, an additional 10.9GW of projects remain to secure finance."

Enter the wake effects group of the OWA's research development and demonstration programme, which, from May 2013, measured the wakes passing through the Rodsand 2 wind farm in Denmark in an effort to improve the understanding of this crucial area of offshore wind.

"The data currently available in the public domain for validation of offshore wind farm wake models is limited to met-mast and turbine-power data for a small number of wind farms," says Gellatly. "Better understanding of wake effects over a wider range of spatial and temporal scales is essential to understanding the phenomena that affect wake generation and transport within and between wind farms."

By using a combination of high-frequency met-mast anemometry, long-range scanning lidar and nacelle-mounted lidar, the group hopes to get, for the first time, a comprehensive characterisation of wake effects at short and long distances.

In specific terms, this involves the measurement of three separate elements: unsteady inflow characterisation, bulk-flow characterisation and turbulence. By measuring and validating data relating to all three, the group should be able to increase its - and the industry's - understanding of the links between atmospheric stability, turbulence and wake losses; farm-on-farm interactions; and how wakes develop, merge and dissipate.

In layman's terms, they will improve their understanding of how wind behaves within and between wind farms and, crucially, how this affects energy outputs.

This should then lead to the validation of wake effects models, such as DTU's Fuga and ANSYS's WindModeller, that OWA has worked closely with in recent years. More validation will, in turn, help de-risk projects, reassuring investors that they know what they're getting into, and, more importantly, what their potential return on investment will be, before injecting significant amounts of capital into offshore wind.

"We need to provide evidence to financiers that we know how to model and design wind farms before they can reduce the uncertainties that drive the cost of finance," Gellatly says.

Different future wind farm layouts may also result from the wake measurement campaign - again, as a result of improved understanding of the wind's behaviour in complex situations. "An improved understanding of these phenomena will allow more informed decisions to be made on turbine and wind farm siting," explains Gellatly.

The increased energy yields that would result from optimised wind farm layouts could then open up debt financing for the construction of many more Round 3 projects in the UK by further improving the upside for investors.

Results from the wake-effects measurement campaign have not yet been released, Gellatly says, as the team involved - which includes DONG Energy and E.ON - are seeking to get as much value as possible from the programme.

"The feedback we have been given by financiers is 'the more studies and publications the better'. Construction financing in offshore wind can be about 12.0% of the cost of energy, vs 3.8% for onshore, so even a small reduction in cost of financing can make a huge difference," she says.

She is also keen to emphasise that the Carbon Trust is not the only organisation seeking to improve the industry's understanding of the physics of wind flow through offshore wind farms. "There are other measurement campaigns that will also have important results to reduce uncertainties and improve modelling techniques," she says. At Alpha Ventus offshore wind farm in Germany, for example, various wake-effects evaluations have been undertaken to the same end.

Root of the ripple

Looking at OWA's overall goal - to reduce the cost of offshore wind by at least 10% by 2015 - wake effects data alone will by no means be enough. The programme is also focusing on five other key areas, all of which, along with wake effects, were chosen as they were thought to have the greatest potential for reducing the total cost of constructing, operating and financing large offshore wind farms.

These areas are: foundations (developing new turbine foundation designs for 30-60m water depths that are cheaper to fabricate and install); access systems (improving access systems to transfer technicians and equipment onto turbines for operations and maintenance in heavier seas); electrical systems (developing new electrical systems to reduce transmission losses and increase reliability); cable installation (improving cable installation methods); and environmental impact (consenting risks).

When taken together, the cost reductions afforded by developments in these areas could more than meet the Carbon Trust's target, and, moreover, analysis from the company suggests that, if deployed correctly, offshore wind has the potential to deliver other benefits to the UK, including a 7% reduction over 1990 in UK carbon emissions, a quarter of a million new jobs by 2050 and annual revenues of £19 billion by the same year.

But this simply will not happen if investment is not made in the sector, which is why the wake-effects measurement campaign is of such critical importance. By helping to open up debt financing for groundbreaking offshore wind projects, the data collected through the programme could have a dramatic impact on the UK's offshore wind sector.

Indeed, investment in the industry, as is set to be demonstrated by GIB with its recent investments in the Westermost Rough and Gwynt y Môr offshore projects, should cause something of a ripple effect.

The bank is committing £241 million to Westermost Rough and £220 million to Gwynt y Môr, with the proceeds of the sales expected to be reinvested back into renewable energy projects in the UK.

Not only is GIB contributing to the creation of thousands of new skilled jobs - and helping players in the offshore wind industry deliver the next round of new offshore wind projects - but, by investing on fully commercial terms, the institution is also seeking to set an example that will spur investors to follow. More reliable data on the potential energy outputs of offshore wind farms can only have a positive effect on this cycle.