The wind’s variability is a fact of meteorology. It is essential that we understand and manage that variability if the industry is to achieve a significant proportion of wind energy generation. The challenge developers and operators face is the need to quickly and accurately assess wind resource over the lifecycle of the wind asset.

Weather patterns and accurate forecasting intelligence are critical in helping to optimise a site’s potential, manage and reduce risk and harness energy. The reliability of assessments has never been of greater importance.

Onshore or offshore, managing that risk is critical, as local wind speeds are one of the most uncertain factors driving revenue and profitability. Reductions in wind speeds of between 0.1 and 0.5m/s will result in unrealised power yields of between 4 and 20% respectively. Of greater concern is that higher potential under performances in wind speeds of 1.0m/s and more can result in unrealised power yields of up to 40%. As this outcome can destroy profitability, it is imperative to ensure long-term wind speeds are reliably defined for individual sites. That need becomes even greater with offshore wind projects, which can be significantly more costly than their onshore equivalents.

We are actively working to make the industry much more predictable, in order to help businesses and governments plan effectively. Our investment in science is increasing industry insight and understanding of climatology, wind risk management and the risk posed by climate variability. At the moment, we’re making assumptions based on the past, but everyone knows that’s not the best basis on which to plan for the next ten or 20 years.

Long-term variability risks

For the renewables industry, understanding that natural long-term variability of the weather – seasonally, annually and decadally – is critical for business planning and investment decisions. It’s also an opportunity to tackle the issue by drawing on what we know historically about the weather and wind, and to use scientific advances to help improve our long-range forecasting capability.

The offshore wind power industry is one of the fastest-growing areas in the renewable energy market. Yet when it comes to wind resource assessments, offshore has limited availability of suitable long-term wind reference data. As the UK’s marine energy industry plans wind power developments in deeper, more exposed waters, companies in the supply chain are presented with new challenges. Design and planning for these challenges can be difficult since quality-assured wind and weather observations are sparse in certain offshore areas, and observational campaigns are expensive to mount and cannot immediately provide a useful dataset.

The Met Office’s modelling technology is allowing wind farms, developers, investors and consultants to define how much wind can be relied upon at specific locations. For example, the Met Office’s Virtual Met Mast wind assessment tool uses 21 years’ data to analyse whether a proposed development would generate enough wind to make the investment worthwhile.

It uses a scientific model based on an advanced atmospheric weather forecast system, which analyses wind information to generate accurate, long-term wind climatology at a specific site and turbine hub height, anywhere across Europe. The output report contains a long-term mean wind speed with an associated level of certainty, turbulence intensity, wind shear and maximum gust information, as well as a wind map of the site and surrounding area.

Putting the past into context

The ability to map inter-annual and decadal wind variations shows that the last 50 years have seen wind resource differences of between 15 and 20% over the decades. We can now easily identify which areas within Europe have the greatest wind speeds and long-term resources. This helps the industry make more informed decisions about appropriate sites for wind farms.

Analysing wind patterns plays a vital role in painting a picture of what has happened historically. The Met Office’s modelling systems highlight changes in climate systems, enabling us to put today’s wind patterns and variability into context. For example, the 1990s in Europe can be described as windy decades, while the last three years have experienced low wind winter periods, compared with the long-term past. Although these are rare, we can’t rule in or out a new low-wind trend.

In the Met Office seasonal Wind Review, wind speeds are modelled across a number of European regions. In the latest edition, the North Sea had the highest average wind speed difference (6%) compared with the summer long-term average.

Looking at seasonal wind conditions across Europe enables owners and operators to put site performance into context and assess whether their farm’s under or over-performance is due to wind or other factors.

Short-term variability and long-range forecasting

Of course, the wind is also variable over much shorter periods, from days to hours, which can have a significant impact on operations. Our new Wind Production Forecast Plus is a local correction scheme based on Kalman filtering techniques, which are very efficient at removing systematic errors in the base forecast, and also help remove systematic errors or biases introduced by local terrain complexities.

"The Met Office’s modelling technology generates accurate, long-term wind climatology at a specific site and turbine hub height, anywhere across Europe."

We’re also starting to see the potential in long-range forecast systems, which enable us to map trends and put some certainty around climate variability. Current rates of advance in computational power have led to enormous improvements in the sophistication of atmospheric, ocean and wave models. For example, present capabilities enable decadal runs of mesoscale (order of 10km) atmospheric and wave models that can accurately represent local wind and wave fields in continental shelf seas, and how they impact on marine operations. Most modern offshore projects have been developed using 2-3MW machines.

Future projects are expected to use 3-7MW machines, to take advantage of higher wind speeds, resulting in an increase in energy production. We’re working on the science that will enable us to enhance forecasting with future modelling. Continued increases in supercomputing capability will allow more skilful forecasting and models with finer resolutions to show what drives large-scale climate processes and patterns.

Long-range forecasting, monthly to decadal, is a focus for the Met Office and the latest modelling results are encouraging. Although work so far has focused on winter resilience, these systems also have the potential to inform pressure patterns and wind conditions, which will provide even greater accuracy in wind forecasts.

New research published in the Journal of Environmental Research Letters in September 2012 suggests the Met Office has made steps forward in long-range guidance for winter resilience. The study compares the latest Met Office long-range forecast system with the one previously used and shows it can better warn the UK of extreme winter weather conditions.

"This is just one incremental step in our ongoing effort to improve long-range weather forecasts," said David Fereday, lead author of the study. "There is still much more research to be done in this developing area of meteorology."

The new model, dubbed the ‘high-top’ system, takes into account sudden stratospheric warmings (SSWs), which are responsible for cold conditions at ground level. SSWs happen when the usual westerly winds in the stratosphere, 10-50km above ground, break down and ultimately reverse.

Looking forward

It’s fundamental that we drive research into wind resource assessment so that the renewable energy industry can be informed about past wind patterns, future trends and how to manage wind variability risk. The continued research by the Met Office means that, in the future, investment and business decisions could be made by looking forward rather than back.