What do the 2020 results mean for you?
Monitoring and recording wind speed trends can provide valuable insights to assess project performance. But interpreting, understanding and acting on those trends is where the real value lies. So, what do the 2020 results mean to you?
2020 wind speed trends
The windiness index followed a rather normal trend across 2020 based on the seasonality of wind resource in the UK, except for some extremes which shaped the annual mean. Most months would be considered normal although there were certain periods where indices peaked at +40% or reached a low of -6%.
Overall, DNV’s UK Wind Index demonstrates that 2020 was 6% windier on average than the 1996-2019 long-term reference (106.1%). A full breakdown of the monthly and quarterly wind indices for 2020 is given in the tables below, along with the ‘windiness’ for each complete year in the index. For ease of referencing, the monthly index for 2019 is also shown.
The year started very strongly with January exhibiting wind speeds 4% higher than the long-term. February was a record month (seasonally adjusted +40%) while wind in March was also exceptionally high (+12%). This was largely due to the higher than normal wind speeds caused by storms Brendan (13-14 January), Ciara (8-9 February), Dennis (15-16 February) and Jorge (28 February – 1 March) during the first quarter of the year.
The index for quarter two of the year was calculated at 99% which indicated a slight drop in wind speeds mainly due to the low wind resource of March and April. However, the June to November period continued with a steady positive anomaly (+3% to +15%) with winds stronger that their seasonal long-term references. Seasonally adjusted quarter three and quarter four indices have been calculated at 106.3% and 99.7% respectively, resulting in an Annual Index of 106%. This means that 2020 was one of the top four windiest years recorded between 1996-2020.
It is also important to consider the spatial distribution of the wind regime across the country during last year. Looking at the windiness maps below, we can observe that although the entire country observed positive trends, there was an increasing trend of recording higher than usual wind speeds while moving southwards. Offshore was exceptionally windier in the Irish and Celtic Seas, as well as in the English Channel and the Southwest parts of the North Sea near the Strait of Dover (>6%), while the rest of the UK offshore areas also recorded positive anomalies (1-5%).
Interpreting the data to establish an answer
But what does the increase in mean wind speed during 2020 represent for wind farm owners, investors and developers?
All other things being equal, wind farm owners can expect to have seen higher production at UK projects during 2020, compared to the long-term, because of the increased windiness. Using typical project wind speed to energy sensitivity ratios, it is noted that a 2% increase in wind speed corresponds to an increase of approximately 3-4% in terms of energy production. This should be taken into consideration during reviews of project performance. Investors will have seen higher energy productions in their wind projects when compared to 2019. This is mainly due to increased wind resources particularly during the traditionally windy quarter one and four.
Wind farm developers who have been conducting wind measurements during 2020 can also expect the average wind speed to be higher than the same period in 2019 and higher than in the long-term. This trend should be taken into consideration when adjusting measurements to be representative of a long-term period.
However, the observed 2020 deviation from the long-term mean wind speed is noted to fall on a positive extreme but still within the expected range of wind speed inter-annual variability. Therefore, whilst 2020 has had an above-average wind speed, this event is expected to be covered by “industry standard” assumptions for future wind speed uncertainty, as modelled in energy production assessments.
The UK Wind Index
DNV maintains a UK Wind Index, which enables owners and investors 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 long-term reference period represents all years between 1996 and the year prior to the analysis. The UK Wind Index is normalized so that the average wind speed over the long-term period is 100%. The windiness of any given period is expressed as a percentage of the long-term average wind speed. Thus, 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, DNV also derives 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 118%. If a specific (individual) January has an index value of 123%, the seasonally adjusted value for that January would be 123%/118% = 104% (+4%).
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