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UK windiness 2018: How does the quiet first half of the year impact your project?

Monitoring, recording and interpreting wind speed trends can be extremely valuable to wind farm investors, owners and operators, enabling project performance to be assessed and evaluated. But what do the 2018 first half of the year results mean for you?

2018 first half wind speed trends

In our last blog, we presented the 2017 UK wind speed results. Although most months were less or equally windy than the reference period, June and October 2017 were notably windier than the long-term mean due to the presence of Atlantic storms, such as the Ex-Hurricane Ophelia, which influenced the weather across the entire UK.

According to the data from the first semester in 2018, it has been approximately 4% less windy than the long-term average across the entire UK and 5% less windy when the seasonality is removed. Although January 2018 positively contributed to the wind generation in the UK, being 4% windier than the average of previous Januarys, May and June presented exceptionally low wind speeds with seasonal indices of 19% and 13% below average for these months.

As a result, while the first quarter of 2018 was in line with the long-term expectations, the second quarter was 11% below the expected long-term wind speed index.

But why was the second quarter of 2018 so low? 2018 will be remembered as England’s hottest summer on record (beating 1976), while across the UK the title of hottest summer is shared between 2018, 2006, 2003. A six-week spell from the end of June to early August brought about a sustained heatwave across the UK, which saw temperatures consistently exceed 30°C in many parts of the country. This was largely caused by the jet stream moving north of the UK, which blocked out more windy, wet and cloudy conditions from the Atlantic Ocean and sucked in more warm, settled air from southern Europe. This meant that the UK missed the higher winds from the west which provide stronger and stable winds.

A full breakdown of the monthly and quarterly wind indices for the first semester of 2018 is given in the following tables, along with the wind speed index since 1996.

Interpreting the data to establish an answer

What does the drop-in wind speed during the first half of 2018 represent for owners, investors and developers?

Wind farm owners would have seen lower production for UK projects during the first half of 2018, compared to the long-term, because of the reduced windiness. Using typical project wind speed to energy sensitivity ratios, it is noted that nearly a 4% reduction in wind speed corresponds to a reduction of approximately 7% to 8% in terms of energy production. This should be taken into consideration during reviews of project performance.

Wind farm developers who conducted wind measurements during the first semester of 2018 would have seen that the average wind speed was lower than the long-term average and this should be taken into consideration when adjusting measurements to be representative of a long-term period.

However, as in 2017, the observed deviation from the long-term mean wind speed is noted to fall within the expected range of wind speed inter-annual variability. This event is expected to be covered by “industry standard” assumptions for future wind speed uncertainty, as modelled in energy production assessments.

Will the wind speeds continue to fall below average for the rest of the year? Find out in our next blog article.

The UK Wind Index           

DNV GL maintains a UK Wind Index, which enables investors and owners to assess the performance of potential or operating projects. Likewise, the UK Wind Index is a robust tool for wind farm developers, empowering them to understand the ‘windiness’ of their wind monitoring campaigns compared to a long-term period.

The UK Wind Index is continually maintained with a wealth of monthly average wind speed data using over 60 Met Office stations geographically spread across the UK mainland and Reanalysis data from different and independent sources geographically spread across the UK mainland. Our tool covers the long-term period, from January 1996 to the present day.

The UK Wind Index is normalized so that the average wind speed over the period January 1996 to the present day is 100%, for a period representing all complete years in the index. The windiness of any given period is expressed as a percentage of the long-term average wind speed. Therefore, a value exceeding 100% indicates that a period was windier than the long-term average, whilst a value below 100% suggests that a period was less windy.

Seasonal effects

Wind speeds in the UK exhibit strong seasonality, with a tendency for higher wind speeds during the winter months and lower wind speeds during the summer months. As a result, we in DNV GL also derive a seasonally adjusted UK Wind Index, which has been corrected for seasonal bias.

To be more precise, the windiness of any given period is expressed as a percentage of the long-term average wind speed for that specific period. For example, the long-term windiness of the month of January is 120%. If a specific (individual) January has an index value of 124%, the seasonally adjusted value for that January would be 124%/120% = 104%.

About DNV GL

DNV GL offers a new service for your Portfolio generating bespoken Windiness Reports on a monthly basis delivered to you on the 1st day of each month. This includes an average of your entire portfolio and a breakdown of each one of your assets. For more information please contact Ioannis Agiol.

Learn more about our full range of services and products.

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