4 Reasons Why Offshore Wind Farms Underperform

Louise Smyth

European offshore wind capacity has grown sevenfold since the end of 2010. This brings today’s total capacity to 22GW, of which 3GW was installed in 2019.

Recent figures from WindEurope indicate that offshore wind is now on course to supply 50GW of renewable energy to Europe by 2030 – the equivalent of more than 6% of the continent’s total energy supply. Crucially, the level of investment required to facilitate this boom in development depends on operational projects bringing in forecasted returns.

However, to date, the offshore wind industry has struggled to meet forecast energy production. This has a dramatic impact on revenue, as a drop in energy yield of as little as 2% could result in a shortfall of millions of dollars.

Although the causes of underperformance onshore are well understood and easily identified through in-depth, highly contextual data analysis techniques, the causes of underperformance offshore continue to remain something of an unknown.

Even the effects of known causes of underperformance, such as heavy rain or hail, cannot be gauged accurately for an offshore site due to a lack of data properly illustrating the effects of harsh offshore conditions on new turbine technology.

1.Are Longer Blades Better?

A key driver for offshore wind development has been the technology’s supersize potential – both the size of turbine technology itself and its resulting generating potential.

Larger rotors powered by blades that can reach in excess of 100m in length allow offshore turbines to produce twice as much energy as the average onshore turbine. Taller towers also enable the blades to interact with the stronger, more consistent winds typical of higher altitudes.

Long blades and tall towers that reach higher altitudes might have the advantage of access to greater wind speeds, but the increased blade length combined with lighter and lighter blade design and increased tip speed lead creates a higher risk profile.

Although heavy rain is known to cause leading edge erosion, there is not yet enough data available on how the constant interaction of water droplets at these high wind speeds with new leading edge protection may influence the lifespan of this new turbine technology and the propensity of the blade surface to wear-and-tear.

To ensure projects achieve maximum generation, owners must invest in comprehensive, in-depth analysis of both turbine performance data and environmental conditions. By monitoring when turbines are underperforming and charting this against environmental data, it is possible to develop a complete understanding of the impact of offshore conditions on their turbines and act on any faults as soon as possible.

2.Reliance On Power Curves

The annual energy production (AEP) forecasts that project owners and investors rely on are often calculated using the power curve for a given turbine out of the box. A power curve is based on a highly specific set of site conditions, with performance modelled against a given temperature range, air density, and turbulence.

However, if the site conditions fall outside of those modelled for in the power curve, the turbine may only produce a fraction of the power expected of it. As outlined above, with limited data available on the effect of the offshore environment on the longevity of turbine technology, performance forecasts continue to be based on impressive out of the box power curves, giving owners false confidence that a project will meet projected AEP. Building a complete picture of offshore site conditions is crucial if owners want to truly understand the potential energy yield of their projects.

3.Turbulent Balance Sheets

As there are no tall structures, mountains, or forestry to interrupt airflow, most offshore sites are considered to have a fairly consistent interaction with the wind resource.

However, the very existence of surrounding turbines can have a drastic effect on the flow of the wind downstream. As Ørsted found in 2019, if the effect of surrounding turbines on wind resource – otherwise known as the wake and blockage effect – is not taken into account in energy yield calculations, vast offshore wind farms can produce far less energy than initially forecast.

By monitoring energy yield and identifying the reasons for any shortfall early on – whether due to faults within the turbines themselves or the influence of their surroundings on wind resource– owners can address any discrepancy in performance and better inform the power curve.

4.Fear Of Embracing Digital Tools

Quantifying the impact of a site on performance – both in terms of the environmental conditions and the effect of surrounding turbines – is necessary to fully understand and solve sustained underperformance issues. To quickly find the actionable insights that will allow owners to optimise performance from the sheer quantity of data gathered from the turbine and site, they must embrace advanced digital tools.

To gain an accurate understanding of how site conditions affect turbine performance, the first step is always to fully digitise the turbine’s environment. SCADA data alone is simply not enough.

When Clir first onboards a wind farm to its platform, the company digitises all atmospheric and meteorological data relevant to the project site, as well as the geospatial data This contextual data is crucial to looking beyond wind resource and “turbine availability” to accurately identify the root causes of underperformance and advise the owner of what will rectify it.

Taking an in-depth, contextual data driven approach to quantifying the unknowns of harsh offshore environments is key to optimising the performance of the new, large scale turbines and wind farms that will take a defining role in the future of Europe’s renewable energy industry. Developing a bank of contextual, environmental, and turbine data from operational wind farms will support project financing, optimise generation, and back the financial decision making crucial to offshore wind’s continued success.

Gareth Brown is CEO of Clir Renewables

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