UK Wind Speed Index

The UK Wind Speed Index provides an indication of the mean wind speed of a historical period relative to that of a designated long-term period, averaged over the entire UK.

GH has visited and assessed a large number of UK Meteorological Office reference stations for consistency, accuracy and exposure. Of these stations, a relatively small number are considered to accurately represent conditions over the last 10 years or more.

These selected stations have been used to assess the windiness of the UK as a whole, over a 10 year long-term period. This windiness is expressed as a percentage of the long-term mean.

The index is updated at the start of each year, using the previous 10 years' data. Stations that have recorded consistently for the entire 10 year period are used. In order to improve the number of stations eligible for inclusion year on year, the long-term remains a 10 year "rolling" period. Below is the annual index for the period 1999 to 2008 inclusive.

There are significant benefits to developing indices on a monthly, regional and bespoke basis. Such an approach provides more geographically representative results and is therefore more applicable to individual wind projects.

GH offers a service whereby a monthly wind index is set up for an individual wind farm project, followed by the ongoing provision of monthly index updates. This provides the wind farm owner or other interested parties with an immediate indication of the windiness of each month in the context of long-term mean conditions. This bespoke monthly index service offers a means of minimising local effects and gradual exposure changes that can affect the reliability and accuracy of raw meteorological station feeds.

In addition to this monthly index service, both the Energy and Development Services group and Asset Management and Operational Services group employ bespoke wind speed indices when producing energy production estimates for pre-construction and operational wind farms.

Bespoke indices can be generated anywhere in the UK and in many of the other areas of the world where the necessary data sources are available.

Please contact us for further information.

Year	GH UK 2009 Index
1999	105.2%
2000	102.7%
2001	95.6%
2002	100.8%
2003	95.0%
2004	98.3%
2005	99.5%
2006	98.8%
2007	100.1%
2008	103.9%

The GH UK Wind Index uses a rolling 10 year long-term period. This table shows the index in previous years for comparison.

Also shown in the table is the number of stations used in the index each year. Historically this has increased each year as more confidence was gained in the reference stations around the UK. However, in 2008 the UK Meteorological Office commenced a nationwide programme of upgrades to the wind monitoring equipment at its meteorological stations. The upgrades have affected the consistency of wind data from at least 50 % of the reference stations in the UK. GH therefore considers that only 17 stations are appropriate for inclusion in the 2009 index.

The choice of a 10 year rolling long-term period is a compromise between wanting the longest index duration possible, while needing a sensible spread of stations around the UK that have recorded consistently for this period.

These historical index figures are provided for reference; the most recent index should be used in preference to others due to the increased number of reference stations.

Year	GH UK 2005 Index 9 Stations	GH UK 2006 Index 14 Stations	GH UK 2007 Index 20 Stations	GH UK 2008 Index 22 Stations	GH UK 2009 Index 17 Stations
1995	103.3%
1996	101.5%	101.4%
1997	97.5%	97.5%	97.9%
1998	106.3%	106.3%	107.2%	106.6%
1999	103.3%	104.7%	105.5%	104.9%	105.2%
2000	101.7%	101.0%	101.7%	101.2%	102.7%
2001	94.5%	94.6%	94.7%	94.5%	95.6%
2002	98.2%	99.9%	100.6%	99.4%	100.8%
2003	95.0%	94.9%	94.9%	94.5%	95.0%
2004	98.2%	98.3%	98.8%	98.8%	98.3%
2005		101.4%	100.5%	101.4%	99.5%
2006			98.0%	98.4%	98.8%
2007				100.2%	100.1%
2008					103.9%

DISCLAIMER

The information presented here is freely provided by Garrad Hassan and Partners Limited for non-commercial use. No warranty implied or otherwise is made and Garrad Hassan and Partners Limited are not in any way to be held responsible for the application or use made of this information. Such responsibility remains with the user.