7. The UK NOABL Wind Speed Database Program.
(includes Northern Ireland)
For the UK, there is a national wind speed database available from the Department of Energy and Climate Change (known as NOABL)
that gives estimates of wind
speeds at heights above the ground of 10, 20 and 45 metres. It is based on the Ordnance Survey grid system and
gives speed estimates at grid points 1 kilometre apart. However, it is not a very convenient means
of accessing wind speed data and a program is available from
our download page that is far
more flexible to use. This program gives much better access to the database by being able to scroll your
position to anywhere within the UK.
It also gives an interpolated wind speed for any height above the ground up to 80 metres. The position input
can be either an Ordnance Survey grid position or latitude and longitude. A postcode can also be converted
to the nearest Ordnance Survey grid code using the conversion tool below. The resulting OS grid code can be
used directly as the position input to the program.
PROGRAM DESCRIPTION.
The wind speeds at the location at 10m, 25m and 45m above the ground are shown in the table along with the values at the adjacent grid points. The graph shows the speed variation above the ground fitted by a simple power law
where U is the speed in metres/second at the height y (in metres). U10 is the reference wind speed at 10 metres above the ground and the exponent N is often known as the Hellman coefficient. The Hellman coefficient is shown on the graph. For a turbulent boundary layer on a flat surface, the Hellman coefficient is typically around 1/7 = 0.143. When the wind is accelerating over high ground, the Hellman coefficient will drop below this value and, by contrast, it will tend to be larger than 1/7 in decelerating flow at the bottom of hills or in valleys. For speed estimates at other heights, there is a scroll bar that enables a user to obtain speed estimates at any height up to 80 metres.
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| Click forward and back buttons to show different map displays. |
It is important to stress that the calculations on which the database is constructed makes use of the large scale geographical topography of the area but not the detailed topography - particularly the man-made contribution to the topography. In particular, it is difficult to get reliable estimates of wind speeds in urban areas because there is such variability in wind speed depending on the local building layout. Speed estimates from the database are likely to greatly over-estimate the wind speeds in urban areas which are generally so low (i.e. typically 3 to 4 metres/second) that they entirely unsuitable for wind turbine installations.
It is interesting to note a comparison between the wind speeds obtained from the database and the measured wind speeds from Meteorological Office weather stations. The figure below is obtained from the report Small-scale wind energy Technical Report. July 2008. (UK Met Office Report). It shows that there is tendency for the database to underestimate wind speeds in the range from 5 to 10 knots (i.e. 2 to 5 metres/second) but possibly to overestimate them above this speed range. However, the scatter in the results is such that not too much emphasis should be put on this comparison.
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As a final example of a screen capture of the program, the figure below shows the database windspeed results for a location in Cumbria called Great Dun Fell at an elevation of 857 metres. It can be seen that the speed profile is nearly uniform because of the rapid acceleration of the flow over the top of this fell - see the discussion on the previous web page 6. In this example, the latitude and longitude was used for the position input which is shown by the blue dot on the zoomed-in map.
The picture below shows the top of Great Dun Fell with a radar station on the top. It would be a very good site for a wind turbine too!
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It should be noted that this program uses a very large road map file and it works best in the zoomed mode with a reasonably fast processor of around 2GHz.
The next page gives links to turbine manufacturers.
