http://www.carbontrust.co.uk/NR/rdonlyres/6A29EA3A-C9B1-4129-849A-554030DEA081/0/SmallscaleWindEnergyTechnicalReport.pdf

Small-scale wind energy
Technical Report
A report by the Met Office to accompany the Carbon Trust report,
Small-scale Wind Energy – Policy insights and practical guidance
July 2008
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Preface
This work was commissioned by the Carbon Trust as part of research into the potential for smallscale
wind energy to help reduce UK carbon emissions.
It is principally intended for engineers and scientists working in the field of small-scale wind
energy, and to be read alongside the Carbon Trust report “Small-scale Wind Energy – Policy
insights and practical guidance”, published in July 2008.
For more information about the work of the Carbon Trust, call 0800 085 2005 or visit
www.carbontrust.co.uk
For further information about the work of the Met Office call our 24-hour customer centre on
0870 900 0100, email consulting@metoffice.gov.uk or visit www.metoffice.gov.uk
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Small-scale Wind Energy – Technical Report
Urban Wind Energy Research Project
Part 1 – A Review of Existing Knowledge
Prepared for the Carbon Trust
by
Martin Best, Andy Brown, Pete Clark,
Dan Hollis, Doug Middleton, Gabriel Rooney,
Dave Thomson and Clive Wilson
Reviewed by: Brian Golding
Authorised for issue by: Ross Lothingland
July 2008
The information in this report is provided in good faith and is believed to be correct, but the Met. Office can
accept no responsibility for any consequential loss or damage arising from any use that is made of it.
Met Office FitzRoy Road Exeter Devon EX1 3PB
Tel: 0870 900 0100 consulting@metoffice.gov.uk www.metoffice.gov.uk
© Crown Copyright 2008
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Contents
1 Introduction.......................................................................................................... 5
2 Observations ....................................................................................................... 6
2.1 Met Office Anemometer Network ................................................................. 6
2.2 Summary Statistics..................................................................................... 11
2.2.1 Long-term Averages............................................................................ 11
2.2.2 Wind Speed Frequency Distributions .................................................. 13
3 Atmospheric Modelling ...................................................................................... 14
3.1 Large-scale spatial variations..................................................................... 14
3.1.1 The wind above the boundary layer and the geostrophic wind ........... 14
3.1.2 The effects of the boundary layer........................................................ 14
3.2 Numerical Weather Prediction (NWP) Models ........................................... 16
3.2.1 NWP and large–scale climatologies.................................................... 16
3.2.2 Downscaled climatologies from NWP data ......................................... 17
3.2.3 Dynamical downscaled climatologies.................................................. 19
4 Boundary Layer Modelling................................................................................. 21
4.1 Wind profile near the surface ..................................................................... 21
4.2 Internal Boundary Layers and Fetch Effects .............................................. 29
4.2.1 Overview ............................................................................................. 29
4.2.2 Canopy and roughness sublayers....................................................... 29
4.2.3 Inertial sublayer................................................................................... 30
4.2.4 Heterogeneity, blending methods and source areas ........................... 35
4.2.5 Boundary layer .................................................................................... 38
4.2.6 Mesoscale........................................................................................... 40
4.2.7 Implications for urban wind energy...................................................... 42
4.3 Urban Surface Energy Balance.................................................................. 43
4.3.1 The urban surface ............................................................................... 43
4.3.2 Radiation............................................................................................. 44
4.3.3 Turbulent heat flux. ............................................................................. 44
4.3.4 Turbulent moisture flux........................................................................ 45
4.3.5 Heat storage flux. ................................................................................ 45
4.3.6 Anthropogenic heat source ................................................................. 46
4.3.7 Impact of surface energy balance on urban wind................................ 46
4.4 Orographic Flow Models ............................................................................ 47
4.4.1 Introduction ......................................................................................... 47
4.4.2 Linear analytic models ........................................................................ 47
4.4.3 Linear numerical models ..................................................................... 48
4.4.4 Validity of linear models ...................................................................... 48
4.4.5 Non-linear models ............................................................................... 49
4.4.6 Mass-consistent models...................................................................... 49
5 Urban Wind Modelling ....................................................................................... 51
5.1 Effects of streets/buildings ......................................................................... 51
5.1.1 Average flow in the urban roughness sublayer ................................... 51
5.1.2 Street Canyons ................................................................................... 55
5.1.3 Individual buildings and other obstacles.............................................. 56
5.1.4 Flow at Particular Locations within Collections of Buildings ................ 58
5.1.5 Research in COST 715 ....................................................................... 60
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5.2 Field Experiments.......................................................................................
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