Comments on a Proposed Performance Standard for Small Wind Turbines

By Paul Gipe

A Memorandum to Colleagues in the U.S. Small Turbine Industry on the Draft Performance Standard AWEA 1.2.2000
May 25, 2000

    First, a note of appreciation to Mike Bergey for tackling the thankless job of bringing AWEA 1.1-1988 (the existing performance testing standard) into the 21st century. Mike’s been pushing AWEA and American small turbine manufacturers toward a performance standard for at least 21 years! Yes, you read that right, twenty-one years since the publication of his “Preliminary Performance Rating Document” in 1979. Mike should get a medal for persistence.
    I’ve supported Mike’s effort for more than 20 years. My first book, written in 1982, devoted several paragraphs to AWEA’s performance rating system. My second book, written in 1992, again encouraged consumers to look for AWEA’s performance ratings in product literature. I still support the use of AWEA’s performance rating standard. In fact, I encourage American manufacturers to comply with the existing standard today. There’s no need to wait for a new standard. U.S. manufacturers can show their good faith in developing a new standard by complying with the existing standard immediately.
    However, as of May 2000, not one manufacturer of wind turbines (large or small) in the USA complies with the existing AWEA standard published in 1988. This sad state of affairs has less to do with the standard than with AWEA, its structure, and its complete absence of an enforcement mechanism or any evidence of a willingness to use such a mechanism if it existed.
    Thus, the one page “Voluntary Agreement” that precedes revisions of the standard is far more significant than the revisions themselves because it suggests a modest mechanism for enforcement of the “voluntary” standards.
    In general, I am partial to the European system of independent testing laboratories. While manufacturers may perform their own measurements to international standards, the measurements that carry weight in product literature are those by Risø, DEWI (Deutches Windenergie Institut) or Windtest Kaiser-Wilhelm-koog.
    The requirement in both AWEA 1.1-1988 and AWEA 1.2-2000 for a publicly available test report was intended to obviate the need for an independent–and costly–testing laboratory. The standard allowed testing by manufacturers (self-certification) because competitors and consumers would police the results. It hasn’t worked that way. Manufacturers have simply ignored the standard. And AWEA has ignored the fact that manufacturers have ignored the standard. Most small turbine manufacturers have no “test reports” to release even if they chose to do so. That is, their turbines have not been tested to any accepted standard.
    Therefore, unless we want another exercise in futility, the manufacturers (Bergey Windpower, Southwest Windpower/World Power, Wind Turbine Industries, and Aeromag) must publicly accept, in writing to this list, the “Voluntary Agreement” before we go any further. Otherwise, we are just wasting our time.
    In hopes that we will proceed. Here are my specific comments.

Voluntary Agreement

    Section 1.2. Strike “subscribe to” insert, “abides by” AWEA’s Code of Ethics. Abide is used in 1.5 and should also be used in 1.2. One can subscribe but not abide to a standard of conduct. One U.S. manufacturer of medium-size wind turbines subscribes to AWEA’s code of ethics, but has consistently violated the same code without consequence. AWEA has no mechanism to enforce compliance with the code of ethics nor even a mechanism to render judgments on claims of violations brought to its board of directors. As a consequence, the current code of ethics is toothless and exists only to serve the political needs of AWEA, not that of wind turbine users which is the target of the standard. Therefore,
    Add Section 1.6. “Complaints of non-compliance with the code of ethics should be submitted to AWEA’s executive director or to any board member. The board of directors will sit as a body to determine the veracity of the claim and determine if the AWEA member has violated the code of ethics. If the board finds that a violation has occurred AWEA’s executive director will then issue a press release to AWEA’s full press distribution list to this effect and will post same on its www site.”
    Add Section 1.7. “Complaints of non-compliance with the ‘Voluntary Agreement’ should be submitted to AWEA’s executive director or to any board member. The complaint will then be forwarded to AWEA’s small turbine committee. The small turbine committee will sit as a body to determine the veracity of the claim and determine if the AWEA member has violated the ‘Voluntary Agreement’. If the committee finds that a violation has occurred AWEA’s executive director will then issue a press release to AWEA’s full press distribution list to this effect and will post same on its www site.”

Standard AWEA 1.2.2000

    1. Scope. Add “It is also the intent of this standard to provide consumers with a means to replicate the performance characteristics advertised by manufacturers when the wind turbine is installed to the manufacturer’s specifications.”
    Simply put, if small turbine manufacturers are to develop a reputation for honesty and integrity, their products must perform as advertised. Consumers can provide the policing necessary to insure that manufacturers comply with the standard if the testing procedures reflect what consumers can expect to see in the field. Testing the power curve at the top of the tower or even at the bottom of the tower does not reflect what a consumer will reasonably encounter.
    1.2. Limit the standard to turbines less than 10 meters in diameter. Remember that the initial work on international standards for medium-size turbines was begun at Risoe on turbines of the 10-15 meter size class. Anything larger than 10 meters in diameter should comply with the IEC standards.
    1.5. Power production should be measured at the perimeter of the tower fall zone. This is most representative of what consumers will encounter. Few consumers will live or install valuable loads within the tower fall zone. The tests should reflect what a consumer can reasonably expect to see. The stipulation that measurements be made at the base of the tower is arbitrary, as is stipulating the perimeter of the tower fall zone (one tower height from the base of the tower). However, stipulating the perimeter of the tower fall zone better reflects tests results in actual consumer use. Tests at the perimeter of the tower fall zone will include wire run losses from the turbine that a consumer is likely to see. Tests on one small turbine at the Wulf Test Field in the Tehachapi Pass reveals that consumers may be seeing as much as 18% power losses at certain wind speeds when installing small wind turbines to manufacturer’s specifications.
    2.1. Kudos. Great idea for a common reporting format of estimated annual energy generation.
    3.2. Leave unchanged. The tower, load, and wiring should be representative. That’s the point of the standard. By specifying measurements at the perimeter of the tower fall zone we have standardized a “representative” installation. Change accuracy to “1%”. 0.5% is excessive. The OSI power transducers that NREL and most of us use here in the USA has an accuracy of 1%. That’s sufficient. Most small wind turbines tested in the USA to date have not been tested to such a stringent requirement. Change accuracy to “1%”. Wire run losses from the turbine to the perimeter of the tower fall zone must be included. Additional losses from wire runs of greater length can be deducted as suggested.
    5.1 Summary. The use of 1-minute averages over the 10-minute averages of the IEC standard will greatly facilitate testing by small turbine manufacturers. This is the principal distinction between the small turbine standard and the “large” turbine standard and is fully justified.

III) Noise Test Method

    1. Summary; 2. Data Source; 3. Site; 4. Installation. Strike
    While the intent of including noise measurements in the standard rating system is laudatory, the test procedure outlined is flawed. Most significantly, wind turbine noise is greatest downwind of the turbine. The reference measurement position should be directly downwind of the tower, not upwind. Moreover, it is difficult enough to measure wind turbine noise with a sound level meter at ground level. It will be even more difficult to measure noise by placing the microphone at hub height. The microphone of a SLM is not an anemometer. It will be almost impossible to provide an adequate wind screen for a microphone at hub height.
    I suggest using the technique described in AWEA 2.1-1989 Procedure for Measurement of Acoustic Emissions from Wind Turbine Generator Systems Volume 1 with the exception noted in The proposed use of a Type 2 instrument will greatly facilitate noise measurements by a broader number of test sites, possibly even by consumers, because Type 2 (general use) instruments are significantly cheaper than Type 1 (precision) instruments. Strike “slow meter” and insert “fast meter” response. My sense is that international standards call for the fast meter response.
    7.3. I believe that Type 2 instruments are considered accurate to within 1.5 dB or about 2% for the typical range of wind turbine noise measurements.
    IV) Formulation of Parameters
    2.1.3. Kudos! Rounding to three significant figures is long overdue. This conveys the uncertainties in estimating annual energy.
    10. Noise Level
    The suggested reporting format for Average Noise Level and Peak Noise Level is not suited for wind turbine noise.
    At a minimum, the Leq should be reported as a discrete value at either 8 m/s or 10 m/s, or both. In addition, the source emission strength in Sound Power Level, Lw, at 8 m/s should also be included. This will allow consumers to compare European and U.S. products on an equal basis.
    The use of a noise curve for Leq at higher wind speeds may also be suggested. These curves are now found on most European wind turbine product literature.