2003-04 Anemometer Loan Program Final Report

The North Carolina Anemometer Loan Program was designed to provide North Carolina land owners with equipment, labor, and expertise to assess their wind resource. Another goal was to provide ASU students and the public with the opportunity to gain experience in wind resource measurement. The program has reached these goals in the following ways:

Literature and Advertising

Starting in the Fall of 2002 the Program developed literature describing the North Carolina Anemometer Loan Program and application materials for interested land owners (see appendix). Also, the Program advertised itself through local news agencies in western North Carolina (samples in appendix). As a result of the response from such advertising, over fifty information packets were mailed out to interested land owners. Of the over fifty information packets mailed, over twenty loan applications were returned to the NCALP office. Based on the information provided in the loan application the Project Coordinator made over fifteen site visits to more accurately determine the viability of the interested party's site. These site visits were the basis for the assignment of the wind monitoring towers.


With NCALP grant funds the Program purchased four 20m NRG NOW tower kits that included NRG Wind Explorer data loggers. The program also purchased a telephone, office supplies, a 12,000 lb winch and materials for a portable winch base, and associated tower tools and equipment. The program was given an office in the Department of Technology at Appalachian State University to house equipment and to serve as a base for Program activities including data analysis, phone and e-mail correspondence, and Program literature generation. The Program purchased a computer for Program activities through the ASU computer "Bone Yard" program (from which retired but very usable computers can be purchased at a low cost). Also, the Program was given access to all software on the ASU server, which proved invaluable for completing Program tasks.

Equipment Installation

During the grant period the program has installed wind measurement equipment at 9 sites. The Program began in 2003 by installing 4 - 20 meter wind monitoring towers. Data has been collected at these sites for the 2003-2004 year. This data has been analyzed and is reported and discussed in the following pages. The program also began collecting data on a fifth site using an existing tower on Beech Mountain starting in October of 2003. The initial four towers have been taken down and have been reinstalled at four new wind sites for the 2004-2005 collection period. Each one of the tower raising events has involved five or more ASU students and faculty, as well as the Project Coordinator and the land owners. Over 30 students have participated in the tower raising activities with many of them being regular participants. Due to their involvement students have gained skills that have allowed them to work on several 50m tower raising projects with the TVA. Skills that students and landowners gain from Program activities include site selection, tower design and mechanics, tower maintenance, sensor design, data logger capabilities and logger operation, as well as data logger and sensor interfacing.

Wind Site Assessment

From the collected data the Program is issuing end of year reports to the owners of the first four data collection sites. These reports include maps, data analysis conclusions, wind turbine modeling, suggestions for site usage, and information on wind turbine manufacturers and installers. The goal of these reports is to give the land owner a guide for utilizing the wind potential on his or her land. To accomplish these report goals the Program Coordinator has learned and used several software packages. Through other funding the NCALP is able to use WindPro software to help in data analysis. The Program has also developed its own data analysis and data visualization program using the program language Perl and MS Excel. Some wind turbine modeling software was provided by Bergey Wind Power and turbine modeling spreadsheets from Paul Gipe. Approximately 225,000 lines of wind data have been processed to date in several different ways using the above software.

Another goal of the NCALP is to make a comparison between the collected data and the information that is given in the computer modeled wind resource map by Truewinds for North Carolina. This comparison will be given in the individual site data summary.

Click here for Map of WNC Anemometer Loan Program Site Locations for 2003 - 2005

Summary of Wind Site Data:

  Elevation Prevailing Wind Direction Average Speed      Average Power Density Wind Power Class
Site 0001 3854 Ft
1174 m
2.8 m/s
44.3 W/m2 -1
Site 0002 4250 Ft.
1295 m
WNW 11.4 MPH
5.1 m/s
165.7 W/m2 2
Site 0003 4990 Ft.
1520 m
WNW 15.6 MPH
6.9 m/s
413.8 W/m2 6
Site 0004 3480 Ft.
1060 m
NW 6.59 MPH
2.94 m/s
45.6 W/m2 -1
Beech Mt.
Site 1001
5180 Ft.
1579 m
NW and SW 13.2 MPH
5.9 m/s
236.8 W/m2 3/4

Estimated Annual Energy Production

As a means of demonstrating possible energy production and site comparison a Bergey Excel 10kw is modeled for annual energy production. The following is a table of the wind sites and modeling outcomes.

  Average Wind Speed     Average Annual Production with 10KW Bergen Excel (KWH) Average Monthly Production (KWH)
Site 0001 6.3 MPH
2.8 m/s
2,306 192
Site 0002 11.4 MPH
5.1 m/s
13,080 1,090
Site 0003 15.6 MPH
6.9 m/s
24,253 2,021
Site 0004 6.59 MPH
2.94 m/s
2,819 235
Beech Mt.
Site 1001
13.2 MPH
5.9 m/s
19,705 1,642

True Winds vs. Collected Data

The following table shows the actual site and TrueWinds wind speed averages as well as the difference in the two values.

  Collected Average      Collected Average adjusted to 30m with wind shear exponent of .2 TrueWinds Average    Difference in 
Site 0001 6.3 MPH
2.8 m/s
6.8 MPH
3.4 m/s
9.90 MPH
4.42 m/s
3.1 MPH
1.4 m/s
Site 0002 11.4 MPH
5.1 m/s
12.3 MPH
5.5 m/s
11.40 MPH
5.09 m/s
-0.9 MPH
-0.4 m/s
Site 0003 15.6 MPH
6.9 m/s
16.8 MPH
7.5 m/s
17.85 MPH
7.97 m/s
1.1 MPH
0.5 m/s
Site 0004 6.6 MPH
2.94 m/s
7.1 MPH
3.2 m/s
10.39 MPH
4.64 m/s
3.3 MPH
1.5 m/s
Beech Mt.
Site 1001
13.2 MPH
5.9 m/s
14.3 MPH
6.4 m/s
16.13 MPH
7.20 m/s
1.8 MPH
0.8 m/s

TrueWinds data is for wind speed at 30m and NCALP data is from 20m. To account for this discrepancy the collected data was adjusted to 30m with the wind shear equation S/So = (H/Ho)0.2. Based on collected data, on average, TrueWinds overestimated the average wind speed of the tested sites by 1.7 MPH.


Project Results:

It is readily apparent from the above tables that some sites in this study are significantly better than others. The best sites would be at higher elevations. Sites 2, 3 & 1001 had the highest elevations (4250', 4990', & 5180') and the highest average wind velocities (11.4, 15.6, & 13.2 mph). However, the data collected also shows that if the site is not right on top of the mountain then a good exposure to the prevailing winds would be desirable. Based on our data (see wind roses) the prevailing winds are from the NW and to a lesser extend the south. Previous work has documented a site with a lower elevation than site 1 (3600' vs 3854') but with a significantly higher average wind velocity (12 mph vs 6.3 mph). A big difference between the sites was that site 1 was sheltered all around by higher mountains (see illustration) while the previously studied site had a great western exposure or long range view to the west. We have also previously measured the wind at an even higher site close to 5,000, but with a long range view to the east and sheltered from the west. Average wind speeds were much lower at this site than the elevation would suggest. Another potential factor affecting wind velocity is the orientation of the mountain ridge. The literature suggests that ridges running north/south would be perpendicular to the prevailing winds and as a result would have higher average wind velocities. Site 0003 was running in a north south orientation and had higher average wind speeds than site 1001 which had an east/west orientation, despite the fact that site 0003 had a slightly lower elevation than 1001.

Site 1 with higher ridges surrounding the site Site 1 with higher ridges surrounding the site

The trends found in the data are as follows:

Higher average wind speeds are found at higher elevations and the predominant wind direction and wind energy potential for all sites was from the North West. This corresponds with the conclusions of the DOE and NASA from their wind measurements in the late 70's and early 80's and from the Truewinds map of North Carolina. A good northwestern exposure would seem to be essential for a good wind site, with a wide western exposure preferable. Obstructions to the northeast and east may not be very significant. However, the very best sites would have a 360° exposure and a high elevation.

The times of the year when the most wind occurred at all sites was late fall, winter, and early spring. This is in agreement with the common perception that winter is the windiest time of year, and the fact that the low level jet stream dips down further into the US during winter.

Sites 0001, 0002, and 0003 had their highest winds in the early morning hours and lowest in the late afternoon, but site 0004 showed an opposite trend. Site 0004 had its highest winds at 3pm and lowest at 9am. These trends need to be taken into consideration for peak loading in grid inter-tie production situations. Future work will look at this more closely.

Since the average American uses 9,000 KWH of electricity a year, the two lowest wind average wind speed sites (sites 1 & 4) simply would not meet the needs of an average individual with the 10 KW Bergey modeled for this report with wind production alone and the cost of energy would be extremely high. However if a Bergey Excel were placed on the best site (site 3), our analysis suggests that it could supply almost 3 average American homes with electricity and the cost of energy would be less than $.10/KWH. The features of the high power density sites in this study have been high altitude, bald earth, and significant height above the surrounding land forms especially to the North and West (a great view to the west/northwest). Beech Mountain and the ridge that site 0003 was on are dramatic examples of these characteristics. The sites with lesser wind potential were characterized by having trees close by and by being below or adjacent to taller land forms, especially to the west and northwest. Because an investment in wind energy on one of our sites with lower wind potential could take ten times longer to make a simple payback than the best sites, we would encourage these land owners to investigate other options for electricity production which would include hybrid electric systems.

This map is a good illustration of the differences between site 0001 and 0003. Site 0001 is shielded to the west and northwest by the very mountain that site 0003 is on.

Differences between Site 0001 and 0003

Continued Interest in the Program:

As described earlier there has been a great deal of interest in the Program relative to the material resources that the Program possesses. There continues to be constant interest in the services that the NCALP offers and as word spreads we are being contacted by people from all over western North Carolina. As of now there are appropriate sites to put up our anemometers for two years after the completion of the current year loans. We constantly get calls and e-mail asking for advice ranging from simple to in-depth practical issues. We hope to expand further from our home base in Boone in the coming years.


During the two years of the North Carolina Anemometer Loan Program two main problems have arisen. First, as is apparent with the raw data files and the Wind Pro reports, there has been some data lost and some data has contained erroneous time labeling. We believe that all of these problems can be attributed to improper data plug application and logger setup. A strong understanding of the importance of working with the data plugs must be impressed on the land owner. Data plugs must be put in a regular place in the owner's house and at the end of the collection period the correct data plug must be put back into the logger. To rectify the time labeling problem the logger must be programmed with complete and accurate information before a data plug is installed. The latter sites have had no such problems and we feel that they have been overcome.

Secondly, the tower at site 0003 had a failure that caused the upper third of the tower to break and fall. After examining the site carefully and getting input from the land owner we feel that the tower failure was caused by a combination of dramatic ice build up on the guy wires and guy wire failure due to abrasion. Icing can certainly be a problem in Western North Carolina, and the towers can experience icing for substantial portions of the winter. The land owner of site 0003 reports several times seeing ice build up of several inches on the tower and guy wires. This drastic increase in guy wire stress due to weight and wind resistance no doubt contributed to the tower failure. The point of guy wire failure was at the point of attachment between the guy anchor and the guy wire. It was observed that the loop of the guy wire through the anchor eye was abraded and frayed. We believe the most significant way to prevent this from occurring is to increase the radius of the guy wire loop. This lessens the stress on the guy wire by avoiding drastic bending. A cable thimble or properly designed anchor will provide for a more gentle bend in the guy wire.

Initially a deposit and service fee were written into the NCALP agreement with the intent of increasing the land owner's interest in keeping the tower in good order and to raise money for possible equipment replacement or repair. We found that the fee and deposit were presenting a barrier for some land owners with promising sites and decided to do away with that portion of the agreement.

Pic of Guy Wire Failure due to ice stress and tight bending radius
Example of Guy Wire Failure due to ice stress and tight bending radius

Site 0003 after tower failure
Site 0003 after tower failure


We believe that the program is a valuable resource for the people of North Carolina and should be continued. Being able to loan out equipment and provide analysis and advice can be a great advantage to a land owner as they try to justify the investment of wind turbine equipment. By taking away this significant hurdle we help people avoid spending money on systems that will not work well and we can foster the increase in capacity of wind electricity production in North Carolina and beyond. This increase in capacity has had and will continue to have significant environmental and social impact for the good of our state and nation. We feel that continuing to promote these types of impacts is certainly in the interest of our governing bodies.

The NCALP could be improved by increasing advertising throughout the region. We purposely decided to focus our energies to within about an hour drive from Boone during the initial years of the project while we learned about the processes involved and because of limited labor and travel resources. There seems to be a significant interest in the program throughout the region and we plan in the coming years to accommodate interested property owners all throughout the 24 western counties. Additional monitoring equipment and funds for travel and labor would allow us to provide these valuable services to more landowners and larger areas. The Program could also be improved by purchasing taller monitoring towers and better data loggers so that wind shear and other data can be studied. The improved data loggers could be used to make more confident recommendations about tower height, energy output and system economics. Sites with trees or other low obstructions near by could also be more accurately assessed with the taller towers.