Jessica Standen, Clive Wilson

A New Wind Atlas for Ireland
Jessica Standen, Clive Wilson
The Met Office has been awarded a contract by the Sustainable Energy Authority of Ireland (SEAI), following a competitive tender process, to produce an
updated wind atlas for Ireland. The current wind atlas of Ireland was produced in 2003 [1]. Wind atlases are becoming an industry standard tool and can be
used to give an indication of the potential wind energy resource in an area, by displaying average information of the climatological winds on maps at different
heights above orography. The wind atlas being generated is based on 10-years of forecast data, with downscaling corrections applied to produce a wind atlas on
a 100m grid.
Initial Data
Sample Results
The approach used to generate the updated Irish wind atlas is based on the method’s used in
the Met Office’s Virtual Met Mast™ Tool (VMM), a site screening tool designed to assess the
feasibility of potential wind farm sites. This approach relies on the use of past high resolution
(4km) data from the Met Office numerical weather prediction (NWP) models.
This project is still in the process of being completed and all results shown are provisional.
When the atlas is complete a number of outputs will be available, including the mean wind
speed for each of the months and over the full 10-years on a 100m grid, the frequency of
twelve wind direction bins and the corresponding mean wind speeds for each of these,
Weibull parameters and information to produce wind roses.
The Met Office Unified Model (MetUM) is an atmospheric model that was designed to be
‘seamless’ from its inception. This means that different configurations of the same model are
used across all time and space scales, being used operationally for both global and limited
area NWP as well as for climate research [2]. The atmospheric model is non-hydrostatic, fully
compressible, with semi-lagrangian advection and semi-implicit time stepping [3].
Mean wind speed (m/s) over SW Ireland
2001-2010 at 50m agl on 100m grid
(a)
(b)
The MetUM was used to rerun 10-years of forecasts (2001-2010). This was run as a nested
configuration, where ERA-Interim [4] was used to initialise an N216 global model, nested
inside this was a 12km Western European model, which in turn contained three 4km domains,
centred over the UK, Poland and Turkey. The Western European (green) and UK (red)
domains are shown below:
(a) Fully Corrected
(b) No Corrections
Sample wind roses for (a) a valley and (b) a hill in SW Ireland at 50m agl
The 4km hourly model level wind components from the UK model forecasts are used as the
base data for the wind atlas. The model set up was designed to be as close to the operational
NWP models as possible in order to replicate past forecasts as closely as possible.
(a)
(b)
Outline Approach
• Apply a scaled roughness correction to adjust the 4km winds over significant orography
• Adjust for local height difference on the 1km grid using a wind direction dependent Mason
and King linear model (4 wind directions)
• Produce the mean and standard deviation of wind speed for each month, as well as the
frequency of twelve 30°wind direction bins on the 1km grid
• Use the Mason and King linear flow model [5] to further downscale the monthly mean wind
speeds from a 1km grid to a 100m grid producing the fully corrected fields
The frequencies of wind speeds shown for each wind direction were calculated by fitting a
Weibull distribution to the mean and standard deviation (1km grid) for each bin over the full
10 years worth of corrected data based on Method 3 in [7].
Land use data
Sample Weibull distribution for
a valley in SW Ireland at 50m
agl
The 100m resolution Corine land use data set [6], which comprises of 44 different land use
classes, was used to provide land cover information over Ireland. Each of the classes had a
roughness length and displacement height assigned to them, which were then used in both
the corrections applied to the data.
The Weibull parameters are
calculated on the 1km grid over the
full 10 years based on the mean and
standard deviation using Method 3 in
[7].
References
[1] Brower M, Ewing G, McCullen P, 2003. Republic of Ireland – Wind Atlas 2003. Project Report, No.
4Y103A-1-R1, Sustainable Energy Ireland
[2] Cullen MJP, 1993. The unified forecast/climate model. Meteorol. Mag., 122:81-93
[3] Davies T, Cullen MJP, Malcolm AJ, Mawson MH, Staniforth A, White AA, Wood N, 2005. A new
dynamical core for the Met Office’s global and regional modelling of the atmosphere. Q.J.R.
Meteorol. Soc. 131:1759-1782
[4] Dee DP, Uppala SM, Simmons AJ, Berrisford P, Poli P, Kobayashi S, Andrae U, Balmaseda MA,
Balsamo G, Bauer P, Bechtold P, Beljaars ACM, van de Berg L, Bidlot J, Bormann N, Delsol C,
Dragani R, Fuentes M, Geer AJ, Haimberger L, Healy SB, Hersbach H, Hólm EV, Isaksen L, Kållberg
P, Köhler M, Matricardi M, McNally AP, Monge-Sanz BM, Morcrette J-J, Park B-K, Peubey C, de
Rosnay P, Tavolato C, Thépaut J-N, Vitart F, 2011. The ERA-Interim reanalysis: configuration and
performance of the data assimilation system. Q.J.R. Meteorol. Soc. 137:553-597
[5] Mason PJ, King JC, 1985. Measurements and predictions of flow and turbulence over an isolated hill
of moderate slope. Q.J.R. Meteorol. Soc. 111:617-640
[6] European Environment Agency, 2007. CLC2006 technical guidelines. Technical Report 17/2007
[7] Justus CG, Hargraves WR, Mikhail A, Graber D, 1978. Methods for estimating wind speed frequency
distributions. J. Appl. Meteor. 17:350-353
Met Office FitzRoy Road, Exeter, Devon, EX1 3PB United Kingdom
Tel: 01392 885680 Fax: 01392 885681
Email: [email protected]
Conclusion
This method uses 10 years worth of hourly wind data from a consistent data set, which is
made up of rerun forecasts initialised from ERA-Interim data. Through taking a
comprehensive wind atlas technique such as this it is possible to provide more useful
information than just the traditional map of mean wind speed. Outputs will include Weibull
distribution parameters, frequency of twelve 30°wind direction bins and mean wind speed for
each hour of the day, giving details of how the mean wind speeds vary diurnally.
Once observations have been made available, this approach will be verified over Ireland and
estimates of uncertainty will be produced.
© Crown copyright 2012 12/0559 Met Office and the Met Office logo are registered trademarks