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An Update on NREL’s 

Small Wind Site Assessor

Guidance Document

2014 Small Wind Conference 

Stevens Point, Wisconsin

Karin Sinclair

June 18, 2014

NREL/PR-5000-61881
2

Background

The purpose of the Small Wind Site Assessor manual 

is to provide:

• A resource on how to conduct a small wind site 

assessment, in lieu of a small wind site assessor 

certification which may be available in the future

• A resource for state incentive managers (i.e., 

Interstate Turbine Advisory Council, or others)

• A resource for consumers.

The intent is to serve as a:

• Resource for small wind site assessment, 

highlighting the impacts on installation and 

productivity and the guiding principles using 

currently available tools and experience

• Guide for small wind turbine selection and siting 

decisions based on costs, benefits, and risks. 

What the manual is NOT:

• Training for site assessment (although it could be 

a resource for a training program)

Bergey Excel 10, 10-kW turbine, 

Klickitat County, Washington

Photo by Gwen Bassetti, NREL 26429
3

Document Development Process

Completed

o Workshop held at end of SWC 2013

– 20+ attendees

– Reviewed/modified draft outline

– Solicited volunteers

– Identified experts team

o Contractor developed 1st draft

o Experts team reviewed 1st draft

o Contractor developed 2nd draft

In progress

o Complete peer review of 2nd draft

o Develop final document

o Post on OpenEI Entegrity EW50, 50-kW turbine, 

Kittery, Maine 

Photo by Donald Doval, NREL 28427
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Document Content

A. Executive Summary

B. Introduction

C. Site Description

D. Wind Characteristics

E. Micrositing and Analysis

F. Other Considerations

G. Site Assessment Report

H. Conclusions

I. Glossary

J. References

K. Sample Checklist

L. Sample Report Outline

M. Case Studies and Lessons Learned

Endurance E3120 turbine; 50-kW turbine, 

Appleton, Wisconsin

Photo by Kettle View Renewable Energy, LLC, NREL 28428 
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Primary Resources

o Small Wind Site Assessor Job Task Analysis developed for the 

North American Board of Certified Energy Practitioners (2011)

o A Siting Handbook for Small Wind Energy Conversion Systems 

(PNNL, 1980)

o Wind Power Basics (Chiras, D., 2010)

o Expert team

Northwind 100, 100-kW wind turbine; Hempstead, New York

Photo courtesy of the Town of Hempstead, NREL 28963
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Site Description

• Land use considerations

• Site information and administrative data

• Safety and environmental concerns

• Topography

• Vertical wind shear

• Obstacles

Airflow near a shelterbelt1

1. Harry Wegley, James Ramsdell, Montie Orgill, Ron Drake. A Siting Handbook for Small Wind Energy Conversion Systems, US 

DOE/Pacific Northwest Laboratory/Battelle Memorial Institute, Contract DC-AE06-76 RLO 1830, 1980
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Wind Characteristics

• Wind characteristics and 

analysis

• Wind maps

• Wind data

• Wind measurement 

instruments

Example of wind rose
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Micrositing and Analysis

• Micrositing (site selection)

• Wind resource data and analysis (example: remote and/or low resolution wind 

information)

o Source Wind Data: Use map estimates or actual wind data sets as described 

above.

o Topography Adjustment: Derive a factor and rationale to adjust wind speeds 

from source data.

o Wind Direction Adjustment: Derive an angle in degrees and rationale to adjust 

wind rose from source data.

o Roughness Adjustment: Derive a factor and rationale to adjust wind speeds.

o Wind Shear Adjustment: Apply displacement height, vertical wind shear 

exponent, data height, and hub height to adjust wind speeds.

o Wind Shade Adjustment: Set up a wind direction sector analysis to derive the 

effects of each nearby obstacle by applying its shade factor with a weighting 

for the amount of wind in that direction from the obstacle to the turbine.
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Micrositing and Analysis (continued)

o Adjusted Wind Speeds: Summarize the composite results of the steps above to 

produce new estimates for average wind speed, range, distribution, Weibull

parameters, turbulence intensity, and other parameters at the selected site.

o Gross Annual Energy Production Estimate (GAEP): Apply this estimated wind 

distribution to the wind turbine power curve (and possibly multiple options) to 

estimate monthly and annual energy production. 

o Loss Estimation: Determine or estimate other factors that could further reduce 

the actual energy produced, including downtime for faults and servicing, blade 

soiling, turbulence intensity causing control error/hysteresis and yaw error 

losses, icing losses, grid outages, wire losses, inverter losses, and possibly 

several others.

o Net Annual Energy Production Estimate (NAEP): Reduce the gross annual 

energy production by the estimated losses to estimate the net annual energy 

production.

o Uncertainty Analysis: Apply composite uncertainty estimates. Because each 

step of this process introduces uncertainty to the estimated results, these 

uncertainties also need to be estimated so that a composite uncertainty can be 

calculated and applied to the final results for winds peed and energy 

production.
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Wind Speed Estimates

~22 miles

~14 miles

NW100 turbine 

at Hempstead

MERRA data 40.5N 73.33W

LT mean WS @ 50m: 7.05 m/s

LT mean WS @ 37m: 6.84 m/s

MERRA data 40.5N 74.0W

LT mean WS @ 50m: 5.96m/s

LT mean WS @ 37m: 5.74m/s

The graphic shows the synthesized mean 

monthly averaged wind speed from two 

nearby MERRA1 sites at 37 m for the period 

1999-2013 (green) and for the period since 

the NW100 was installed (blue). The yellowdotted area is the 12-month period used for 

the Wind Analysis Summary Report 

prepared for the Town of Hempstead.

Wind data was both 

measured and estimated 

for the project site 

(Hempstead). These data 

were validated using 

historical long term average 

and one-year average data 

from two MERRA sites.

1 MERRA: Modern-Era Retrospective Analysis for Research and Applications – a NASA reanalysis (http://gmao.gsfc.nasa.gov/research/merra/)
11

Terrain Influence on Wind Flow

Acceleration of wind over a ridge

Vertical profiles of air flowing over a ridge

Source: A Siting Handbook for Small Wind Energy Conversion Systems, US DOE/Pacific Northwest Laboratory/Battelle Memorial 

Institute, Contract DC-AE06-76 RLO 1830, 1980
12

Obstructions – Case Study Example

Aerial photo of the Hempstead NW100 turbine site. Pre-installation (left) with obstructions. Postinstallation (right) with obstructions removed and turbine installed.

Photo courtesy of Northern Power Photo source: Google Maps
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Obstructions – Case Study Example

Bergey Excel 10, 10-kW turbine; Peshastin, Washington, 

Photo by Abigail Krich, NREL 13495

Bergey Excel 10, 10-kW turbine;

Ellensburg, Washington

Photo by Randy Brooks, NREL 29553 

• Same turbine; different locations.

• Performance differences:

o Left: 500 kWh actual annual compared to 8,000 

kWh estimated

o Right: Averaging 17 MWh annually compared to 

16 MWh estimate

• No on-site anemometry data was collected at either 

site
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Next Steps

• Revisit need/timing/options for small wind 

site assessor credential

• Monitor manual on OpenEI – update as 

appropriate

Associated activity:

• Revisit need/timing/options for small wind 

installer credential

o North American Board of Certified Energy 

Practitioners suspended program
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Contributors

Lead author

• Tim Olsen (Advanced Energy Systems and AnemErgonics)

Experts Team

• Lisa DiFrancisco (REVision Consulting, LLC)

• Rich Hasselman (Tetra Tech)

• Ken Kotalik (Primus)

• Mark Mayhew (New York State Energy Research and Development Authority)

• Charles Newcomb (Endurance Wind Power)

• Mick Sagrillo (Sagrillo Power and Light)

Peer Reviewers

• Experts Team (above)

• Bret Barker (New West Technologies/DOE)

• Roy Butler (Four Winds Renewable Energy)

• Roger Dixon (Skylands Renewable Energy)

• Patrick Gilman (U.S Department of Energy)

• Steve Woll (Smallwind.com)

Other contributors

• Karin Sinclair, Frank Oteri, Robert Preus, Jim Leyshon, Robi Robichaud (NREL)
Contacts:

Karin Sinclair – NREL

Karin.sinclair@nrel.gov

(303) 384-6946

Tim Olsen – Advanced Energy Systems, 

LLC and AnemErgonics

tolsen@windtechnology.com

(303) 777-3341

Frank Oteri – NREL

Frank.oteri@nrel.gov

(303) 384-6952