Wind Shear and Turbulence Profiles at Elevated Heights: 

Great Lakes and Midwest Sites

Dennis Elliott, Marc Schwartz, George Scott

WINDPOWER 2009 • May 4-7, 2009 • Chicago, IL

Background

• Considerable uncertainty exists in extrapolating wind resource data available from Considerable uncertainty exists in extrapolating wind resource data available from

typical measurement heights (50 m – 60 m) to turbine hub-heights of 80 m –

100+m

• Numerical model data and available wind maps for heights of 80 m – 100 m are 

largely unvalidated

• Tall-tower and remote sensing (sodar & lidar) wind data are needed to evaluate 

wind shear and turbulence profiles over turbine rotor heights that can extend well 

above 100 m

Objectives

• Analyze wind resource characteristics at elevated heights (50 m – 200+m) 

including shear and turbulence profiles for some areas of the Great Lakes and 

Midwest 

• Show case studies and comparisons for

Goodland IN Low

Carthage, IN – Low/moderate 

roughness, prevailing strong 

winds from S-SW

— Indiana towers located in areas of different surface roughness

— Iowa towers with heights up to 200+m and different surface roughness

Variation in Average Wind Shear

• Measurement data indicate that average wind shear exponents at elevated heights, 

such as 50 m – 100 m, can vary considerably among sites

• Considerable uncertainty can exist in estimates of wind speed at 80 m – 100 m 

heights from extrapolation of data at 50 m 

• Even in areas of similar wind climate, such as northern Indiana, variations in surface 

roughness and terrain among sites can cause average shear exponents to vary from 

about 0.2 to 0.35 between 50 m – 100 m

Goodland, IN – Low

roughness, prevailing 

strong winds from S-SW

Iowa Analysis Results

• Profiles of average shear exponents differ among the 3 sites 

—Low layer (50 m –100 m) shear exponents varied by site’s surface roughness 

type

—Mid layer (100 m – 150 m) shear exponents can be similar or exceed those at 

heights of 50 m –100 m

—Upper layer (150 m – 200 m) shear exponent less than lower layers

• Average TI profiles differ among sites

—Lowest TI at low roughness site, at all heights

—TI decreases with height, but there is less decrease at the low roughness site 

than other sites

Iowa Iowa Analysis Results – Homestead Diurnal Variations

• Diurnal variations in average wind speed increase with height, from <1 m/s at 50 m 

to >3 m/s at 200 m

• Average shear exponent is highest in 100 m – 150 m layer, especially during April –

June

• Nocturnal shear exponent decreases above 150 m

• Average turbulence intensity is very low at night, especially at heights above 100 m

Indiana Analysis

• Four tall towers located in 

different types of surface 

roughness

• Highest anemometers 

90 m – 100 m

• Approximately one year of data 

collected from each site collected from each site

• Wind shear and turbulence 

profiles evaluated by roughness 

type and height

• Wind speeds of at least 3 m/s 

required for the analysis

• Data excluded from directions 

with tower shadow effects

Indiana Analysis Results

• Notable variations in the annual wind shear exponents at elevated heights

(50 m – 100 m) among the 4 sites 

—Highest shear exponent (0.35) at site with highest surface roughness

—Lowest shear exponent (0.21) at site with lowest surface roughness

• Notable variations in the turbulence intensity (TI) profiles among the 4 sites

—Considerable TI difference at 50 m (16% vs 11%) between high and low 

roughness sites

—Significant TI difference at 100 m (11% vs 9%) between high and low 

roughness sites

• Analysis of shear and TI by wind direction highlight the effects of surface 

roughness, especially in the prevailing wind directions

Conclusions

• Analysis of tall-tower data proved beneficial to evaluate and better understand the 

variability of wind shear and turbulence profiles at elevated heights

• Surface roughness effects on wind shear and turbulence profiles can be significant at

LaGrange, IN – High 

roughness, prevailing 

strong winds from S-SW

• Wind shear and turbulence 

profiles evaluated by 

height, roughtness and 

time of day

• Wind speeds of at least 3 

m/s required for the 

analysis

Iowa Analysis

• Three very tall towers with measurements at several heights from about 50 m – 200 m

• Approximately one year of data collected at each site

• Terrain and surface roughness conditions varied among the sites

—Mason City, exposed hilltop site in rolling terrain, low roughness

—Homestead, exposed site in rolling terrain, low/moderate roughness

—Altoona, exposed site in rolling terrain, moderate/high roughness near town

Surface roughness effects on wind shear and turbulence profiles can be significant at

heights up to 100 m

• Wind shear exponents at heights of 100 m –150 m can exceed those at heights of 50 

m –100 m

• Large differences in shear exponents at elevated heights can exist among sites, even 

in local areas of similar wind climate 

Recommendations

• Measurement data at elevated heights are needed to validate model-derived wind 

resource estimates and shear extrapolations

• Use of tall towers and remote sensing equipment (sodar and lidar) provide 

opportunities to evaluate wind resource characteristics at elevated heights

The information contained in this poster is subject to a government license | WINDPOWER 2009 | Chicago, IL | May 4 – 7, 2009 | PO-500-45455

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Geetinsville, IN –

Moderate/high roughness, 

prevailing strong winds 

from S-SW

analysis

• Data excluded from 

directions with tower 

shadow effects

• Data excluded for heights 

with insufficient data

—Excluded 157 m at 

Mason City and 213 m 

at Altoona