A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Regional Field Verification — 

Operational Results from Four 

Small Wind Turbines in the 

Pacific Northwest 

Preprint 

K. Sinclair 

National Renewable Energy Laboratory 

J. Raker 

Northwest Sustainable Energy for 

Economic Development

Presented at the American Wind Energy Association 

WindPower 2006 

Pittsburgh, Pennsylvania 

June 4–7, 2006 

Conference Paper 

NREL/CP-500-38110 

August 2006 

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Regional Field Verification - 

Operational Results from Four Small Wind Turbines 

in the Pacific Northwest 

Karin Sinclair 

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401 

United States 

303-384-6946 

karin_sinclair@nrel.gov

Jessica Raker 

Northwest Sustainable Energy for Economic Development 

119 1st Avenue, South 

Suite 400 

Seattle, WA 98104 

United States 

206 - 267-2213 

jessica@nwseed.org

Abstract 

The purpose of the Department of Energy/National Renewable Energy Laboratory’s (DOE/NREL) 

Regional Field Verification (RFV) project is to support industry needs for gaining initial field 

operation experience with small wind turbines and to verify the performance, reliability, 

maintainability, and cost of small wind turbines in diverse applications. In addition, RFV aims to help 

expand opportunities for wind energy in new regions of the United States by tailoring projects to meet 

unique regional requirements, and document and communicate the experience from these projects for 

the benefit of others in the wind power development community and rural utilities. 

Under RFV, Bergey Excel S (10kW) wind turbines were installed at sites in the Pacific Northwest as 

part of Northwest Sustainable Energy for Economic Development's (NWSEED) Our Wind 

Cooperative. Each installation was instrumented with data acquisition systems to collect a minimum 

of two years of operating data. 

The four turbines highlighted in this paper were installed between 2003 and 2004. At least two years 

of operational data have been collected from each of these sites by Northwest SEED. This paper 

describes DOE/NREL's RFV project and summarizes operational data from these sites. 
Purpose 

The purpose of this paper is to describe the Department of Energy/National Renewable Energy 

Laboratory’s (DOE/NREL) Regional Field Verification (RFV) project and summarize the first two 

years of operation and performance data collected from four Bergey Excel S (10kW) turbines 

installed under this project. Data collection from a 5th turbine will be completed in Fall 2006. 

In 2000, DOE/NREL issued a RFV project Request for Proposal (RFP). The purpose of the RFP was 

to solicit projects that would support industry needs for gaining initial field operation experience with 

small wind turbines, and verify the performance, reliability, maintainability, and cost of small wind 

turbines in diverse applications. The RFV project was also intended to help expand opportunities for 

wind energy in new regions of the United States by tailoring projects to meet unique regional 

requirements, and document and communicate the experience from these projects for the benefit of 

others in the wind power development community and rural utilities. 

After reviewing proposals submitted in response to the RFP, NREL ultimately executed a subcontract 

with Northwest Cooperative Development Center (NWCDC). Under this subcontract, Bergey Excel S 

(10kW) wind turbines would be installed at a number of sites in the Pacific Northwest. Each 

installation was instrumented with data acquisition systems to collect a minimum of two years of 

operating data. 

Northwest Sustainable Energy for Economic Development (NWSEED), a lower-tiered subcontractor 

for NWCDC, is responsible for the actual project installations and data collection/analysis. 

NWSEED has expanded this project, known as Our Wind Cooperative (OWC), partnering with 

numerous other organizations, including Bonneville Environmental Foundation (BEF), Last Mile 

Electric Cooperative (LMEC), United States Department of Agriculture (USDA), Bullitt Foundation, 

Climate Solutions, Renewable Northwest Project, host utilities, and others to assist with lowering the 

project cost to hosts and supporting outreach activities. For information on OWC, go to 

http://ourwind.org/windcoop/. 

Host Sites 

Four of the systems installed under the RFV subcontract are described in this paper1

. They are all 

equipped with the same turbine system blades and connected to the utility grid. Three are located in 

Montana and one is located in Washington, as shown in Figure 1. The turbines were commissioned 

between December 2003 and October 2004 (Table 1). Because of the involvement of the Federal 

Government in this project, a National Environmental Policy Act (NEPA) determination from DOE 

was required. Ultimately, DOE determined a categorical exclusion B5.1 applied to each site. 

 

1 For a detailed discussion of each site, refer to a paper presented at last year’s Windpower conference: Regional 

Field Verification - Case Study of Small Wind Turbines in the Pacific Northwest, NREL/CP-500-38166. Presented at 

American Wind Energy Association Windpower 2005, Denver, CO, May 15-18, 2005.

http://www.nrel.gov/docs/fy05osti/38166.pdf 

2
Figure 1. Location of four RFV host sites 

3
Table 1. RFV Host Sites – Location and Commissioning Dates

Photo # Host Location Lat/Long Elevation 

Tower 

Type 

Assumed 

Wind Class2 Commission 

Date 

1 Alger, Jess Stanford, MT 47.265/ 

-110.234 

1219 m 30 m 

guyed 3 

 

10/2/2004 

2 Kennell, Ed Goldendale, WA 45.82/ 

-120.628 

670 m 24 m 

guyed 3 12/29/2003 

3 Liberty County Chester, MT 48.51/ 

-110.995 

969 m 24 m 

tilt up 3 2/24/2004 

4 Nelson, Doug Browning, MT 48.55/ 

-113.197 

1474 m 18 m 

guyed 5 2/24/2004 

Source: NWSEED 

Wind Speed Data 

Predicted and measured site-specific wind speeds, shown in Tables 2, 4, 6 & 8, have been normalized. 

Predicted wind speeds were taken from wind resource maps available for each state, modeled at sitespecific hub heights. Each site’s wind speed was measured at anemometer height (6 m below hub 

height) and adjusted to hub height. 

The average wind speed was calculated by figuring the 10-minute mean data collected over a 2-year 

period. At all sites, the annual average data recovery was 80% or better. In all cases, actual measured 

wind speed was lower than the predicted wind speed. However, in three of the four cases, the 

measured wind speed was reasonably close to the predicted wind speed. Wind speed distributions 

(Figures 2, 4, 6, & 8) have been developed for each site. 

Power Curves 

Predicted power curves were developed for each site using the manufacturer provided spreadsheet. 

Each site was adjusted for elevation. Measured power curves, reflecting two years of data, were 

developed for each site (Figures 3, 5, 7, & 9). 

Annual Energy Output 

Annual Energy Output (AEO), also known as annual energy production, is presented based on three 

different scenarios (Tables 3, 5, 7, & 9). In each of the first two scenarios, the predicted production 

was calculated utilizing the manufacturer’s power curve adjusted for the elevation at each site. The 

difference between these estimates is that the first one is calculated based on the predicted wind speed 

and the second one is calculated based on the measured wind speed. The third production figure 

reflects the actual measured annual energy production. 

Site-Specific Summaries 

For each host site, wind distribution graphs, power curves, average predicted and measured wind 

speeds, and performance data summaries are provided. The measured AEO is consistently lower than 

the estimated output, based on either the predicted or measured wind speed. Lower energy output 

attributable to differences between predicted and measured wind speeds have been identified. An 

analysis to identify the other factors contributing to the performance shortfall will be conducted at the 

completion of this project. These factors may include equipment, operator, or the environment. 

 

2

 Based on available wind resource maps for Montana and Washington. 

4
1. Alger (Stanford, MT) 

Photo 1: Turbine installed at Alger ranch 

Source: NWSEED 

Data from the Alger site (see Photo 1) are summarized in Tables 2 and 3 below for the period January 

2004 – December 2005. With 80% data recovery, the actual measured AEO is 37% lower than 

originally anticipated. Roughly 11% of this shortfall is attributable to the difference between the 

measured wind speed and the predicted wind speed. The remaining 26% of this underperformance is 

due to other factors, yet to be identified. 

As shown in Figure 3, the turbine underperformed but also exceeded the peak power production. 

Wind speeds found at this site were predominately 3 – 6m/s but rarely 15 – 20m/s (Figure 2). 

Table 2. Wind Speed 

Wind m/s 

Predicted wind speed 6.1 

Measured wind speed 5.8 

Table 3. Performance Data 

Wind kWh/y 

Based on predicted wind speed 18,034 

Based on measured wind speed 15,969 

Actual measured annual energy production 11,389 

Data recovery 80% 

5
Figure 2. Wind speed distribution

Figure 3. Estimated and actual power curves 

6
2. Kennell (Goldendale, WA) 

 Photo 2: Turbine installed on Kennell property 

 Source: NWSEED 

Wind speed and performance data from the Kennell site (Photo 2) for the period January 2004 – 

December 2005 are summarized in Tables 4 and 5 below. The wind distribution curve (Figure 4) 

does not follow a typical Rayleigh distribution, suggesting the anemometer may not have been 

working properly (perhaps due to icing or some other factors). 

The power curve (Figure 5) data have not been filtered, however the uncharacteristic scatter plots 

suggest a problem with the anemometer and/or manual furling. The actual measured production is 

32% lower than originally estimated, based on 87% data recovery. While approximately 6% of the 

lower production is a result of the difference between the predicted and measured wind speed, the 

majority is due to other factors. The specific causes have yet to be determined. 

Table 4. Wind Speed 

Wind m/s 

Predicted wind speed 5.9 

Measured wind speed 5.8 

Table 5. Performance Data 

Wind kWh/y 

Based on predicted wind speed 18, 485 

Based on measured wind speed 17,473 

Actual measured annual energy production 12,577 

Data recovery 87% 

7
Figure 4. Wind speed distribution 

Figure 5. Estimated and actual power curves 

8
3. Liberty County (Chester, MT) 

 Photo 3: Turbine installed at Liberty County Maintenance Facility 

 Source: NWSEED 

Tables 6 and 7 summarize wind speed and performance data from the Liberty County site (Photo 3) 

for the period February 2004 – February 2006. With almost 100% data recovery, AEO was 51% 

lower than the initial production estimate. Of the four sites covered in this paper, this is the only one 

where the wind map did not accurately predict the site-specific wind speeds. Almost 40% of the 

production shortfall was due to the difference between predicted and actual wind speeds. The 

remaining reduction in production is due to other factors. Figure 6 represents a reasonable Rayleigh 

distribution and there is no indication of manual furling in the power curve (Figure 7). 

Table 6. Wind Speed 

Wind m/s 

Predicted wind speed 5.7 

Measured wind speed 4.6 

Table 7. Performance data 

Wind kWh/y 

Based on predicted wind speed 16,242 

Based on measured wind speed 9,786 

Actual measured annual energy production 7,926 

Data recovery 98.5% 

9
Figure 6. Wind speed distribution 

Figure 7. Estimated and actual power curves 

10
4. Nelson (Browning, MT)

 Photo 4: Turbine installed at Nelson farm 

 Source: NWSEED 

For the period February 2004 – February 2006, wind speed and performance data was collected from 

the Nelson site (Photo 4). Tables 8 and 9 summarize these data. Figure 8 depicts a reasonable 

Rayleigh wind speed distribution. The data points on the power curve graph (Figure 9) reflect many 

points at zero, suggesting the inverter may have been off or the grid was down. The scatter plot also 

suggests the turbine may have been manually furled. 

Overall, measured AEO was 47% lower than originally estimated. Less than 2% of the production 

shortfall was due to the difference between the predicted and actual wind speed. 

Table 8. Wind Speed 

Wind m/s 

Predicted wind speed 5.7 

Measured wind speed 5.6 

Table 9. Performance Data 

Wind kWh/y 

Based on predicted wind speed 15,959 

Based on measured wind speed 15,679 

Actual measured annual energy production 8,424 

Data recovery 90% 

11
Figure 8. Wind speed distribution

Figure 9. Estimated and actual power curves 

12
Conclusion 

Under its RFV project, NREL has been monitoring 5 Bergey 10-kW turbines installed in the PNW. 

This paper summarized 2 years of data collected at 4 of the sites. Data collection for the 5th site will 

be completed in Fall 2006. At that time, a full analysis of the performance data for all 5 sites will be 

conducted. 

For the data presented in this paper, several observations can be made. Data recovery ranged from 

80% to 98.5%. In all cases, the annual energy output was lower than originally estimated. Actual 

performance was 32% to 51% lower than expected. A portion of this underestimation can be 

attributable to lower actual wind speeds than predicted. In three of the four cases, the difference 

between the estimated wind speeds (which were based on the state-specific wind resource maps) and 

the measured wind speeds accounted for a small portion of the shortfall. In one case (Liberty 

County), the lower measured wind speeds accounted for 40% of the 51% reduction in output. Thus, 

in 75% of the cases, the wind resource maps did a reasonable job of predicting the site-specific wind 

speeds. 

Numerous other factors contributed to performance shortfalls. These likely include operator decisions 

(such as manual furling), environmental factors (such as grid outages) or the equipment (including 

inverter outages). A detailed analysis of the performance will be conducted later this year. 

13
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Regional Field Verification — Operational Results from Four Small 

Wind Turbines in the Pacifc Northwest: Preprint 

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Golden, CO 80401-3393 

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This paper describes four Bergey Excel S (10 kW) wind turbines installed on sites in the Pacific Northwest under 

DOE/NREL's Regional Field Verification Program between 2003 and 2004 and summarizes operational data from 

each site. 

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small wind turbine; field tests; field verification program; Northwest Sustainable Energy for Economic Development 

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