PSC REF#:186233
Public Service Commission of Wisconsin RECEIVED: 06/14/13, 11:46:09 AM OFFICIAL FILING BEFORE THE PUBLIC SERVICE COMMISSION OF WISCONSIN
Application of Highland Wind Farm, LLC for a Certificate of Public Convenience and Necessity Docket No. 2535-CE-100 To Construct a 102.5 MW Electric Generation Facility and Associated Electric Facilities, to be Located in the Towns of Forest and Cylon, St. Croix County, Wisconsin
REHEARING DIRECT TESTIMONY OF JESSE STOWELL
1 Q. Please state your full name and business address.
2 A. My name is Jesse Stowell, and my business address is 463 New Karner Road, Albany,
3 New York 12205.
4 Q. By whom are you employed and in what capacity?
5 A. I am employed by AWS Truepower (“AWS”) as a Senior Business Development
6 Manager. Established in 1983, AWS is an international leader and innovator in
7 renewable energy consulting and information services. Our team of meteorologists,
8 engineers, and environmental specialists are field-oriented and fully conversant with the
9 latest turbine technologies, large commercial projects, utility electrical systems, remote
10 field measurements, and distributed applications. AWS uses the best science and
11 technology to deliver accurate results for our clients. From resource and energy
12 assessment, project consulting, due diligence/independent engineering, performance
13 assessment and power production forecasting, we use science to help our clients’ projects
14 succeed.
Direct-HWF-Stowell-1p Jesse Stowell, Direct Testimony Docket No. 2535-CE-100
1 Q. Would you briefly state the duties of your present position?
2 A. My role is twofold. I consult on topics concerning turbine technology and I work as a
3 business development manager. In the role of turbine technology expert, I consult on a wide
4 range of topics having to do with the features and performance of modern wind turbines.
5 Often my focus is how a particular turbine technology will affect the performance (energy,
6 environmental impact, reliability, etc) of the project that is utilizing that turbine. In my role
7 as a business development manager, I function primarily in the commercial capacity. My
8 job there is to work directly with clients seeking to understand how AWS can provide
9 services and expertise that will best address their project needs.
10 Q. What is your educational and professional background?
11 A. I’ve been working in the wind energy business since 1999. Prior to working for AWS, I led
12 the development of on-site and community-scale wind energy projects for the Energy
13 Solutions business unit of Johnson Controls. I was responsible for specification of turbine
14 technology (from a variety of different turbine OEM’s, including Siemens and Nordex) and
15 management of the wind project development process. Before joining Johnson Controls, I
16 was an Engineering Program Manager at Northern Power Systems where I was responsible
17 for the commercialization of a 100kW direct-drive, permanent-magnet wind turbine that was
18 originally developed for community-scale applications in cold climates. I have a Bachelor's
19 degree in Mechanical Engineering and Materials Science from Duke University and am a
20 licensed Professional Engineer in the State of Vermont.
21 Q. What is the purpose of your testimony?
22 A. The purpose of my testimony is threefold. First, I will present the results of two
23 curtailment production models prepared for the developers of the Highland Wind Farm
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Jesse Stowell, Direct Testimony Docket No. 2535-CE-100
1 (“Project”). Second, I will describe, in detail, the technical capabilities of the Nordex
2 N117 and Siemens SWT-2.3 turbines with regard to their ability to meet the 45 dBA
3 nighttime sound limit contained in Wis. Admin. Code § PSC 128.14. Finally, I will
4 provide testimony regarding the prevalence of using these types of wind turbine sound
5 reduction capabilities in wind projects today.
6 Q. Are you sponsoring any exhibits in connection with your direct testimony?
7 A. I am sponsoring Ex.-HWF-Stowell-1 which is a set of production models for the turbines
8 being considered for the Project. In my testimony I also rely on Exs.-HWF-Osterberg-2c,
9 3c and 4c.
10 Q. Please describe Ex.-HWF-Stowell-1 and how it was modeled.
11 A. Ex.-HWF-Stowell-1 is the Energy Production Estimate (“EPE”) for the Project that was
12 modeled by AWS. It reflects the long term average (and first year) annual energy output
13 for the turbine layouts utilizing the Nordex and Siemens turbines and a sound-based
14 curtailment strategy. It was modeled using the openWind Enterprise software to
15 calculate the energy output (gross and net of wake losses) both for the entire plant and for
16 each turbine. Other plant losses were subtracted to yield the net energy production.
17 Q. Please describe the results of the curtailment production modeling.
18 A. The net capacity factor for the Nordex N117 and the Siemens SWT-2.3-113 came to
19 percent and percent respectively. The reduction in output due to the noise
20 curtailment strategy is percent for the Nordex turbine and percent for the Siemens
21 turbine.
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Jesse Stowell, Direct Testimony Docket No. 2535-CE-100
1 Q. Do you consider these results conservative?
2 A. Yes. The results are conservative because the sound curtailment strategy that was used in
3 the energy production model assumes that the sound emissions from the turbine are
4 always propagating in the worst case wind direction during all nighttime hours (10PM –
5 6AM). Mr. Hankard describes this modeling characteristic in more detail. In reality
6 there will be many periods of time during nighttime hours when the wind is blowing from
7 other directions, and noise reduced operation will not be necessary to keep sound levels
8 at neighboring receptors below the prescribed limits. This is due to the directional nature
9 of sound propagation in the presence of wind. Mr. Hankard’s analysis also demonstrates
10 that when the directionality of wind turbine noise emissions is taken into account when
11 programming the turbines the reduction in energy output is less than when relying solely
12 on nighttime curtailment that does not account for actual wind conditions. Finally, the
13 Nordex EPE’s are even further conservative because turbine 39 was modeled to cut out
14 (i.e. shutdown) at wind speeds higher than 8m/s during nighttime hours (10PM – 6AM).
15 In reality, this turbine will likely be able to operate at all wind speeds when the wind is
16 blowing from certain directions (for the same reasons previously stated above).
17 Q. Can you describe, generally, the abilities of modern utility scale wind turbines to
18 change or control the level of sound emitted by a turbine or set of turbines?
19 A. Since the majority of sound emissions from a wind turbine come from the tip of the blade
20 moving though the air, reducing the rotor rotational speed (and therefore the speed of the
21 blade tips) effectively reduces the level of sound emissions from the turbine. Modern
22 wind turbines utilize blade pitch control to regulate the rotational speed of the rotor, so
23 implementing changes in blade pitch control to slow down the rotor results in quieter
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Jesse Stowell, Direct Testimony Docket No. 2535-CE-100
1 operation of the turbine. When the rotor speed is reduced so is the power output level for
2 a given wind speed. The result is a series of noise reduced power curves. Each power
3 curve has a maximum sound level and an associated (reduced) power rating.
4 Q. Please describe in detail the technical capabilities of the Siemens SWT-2.3 wind
5 turbine to meet the nighttime 45 dBA sound requirement in PSC 128.14?
6 A. Utilizing rotor speed control via changing the blade pitch as described above, the
7 Siemens SWT-2.3 wind turbine can be programmed to automatically change from normal
8 operation mode to reduced noise operation mode as a function of any combination of the
9 following parameters: day of the week, time of day, wind direction and wind speed. For
10 example, a given turbine could automatically change to reduced noise operation mode on
11 Monday - Thursday, during nighttime hours, when the wind is above 8m/s from any of
12 the directional sectors defined to be sensitive. These capabilities provide a great amount
13 of flexibility in specifying the conditions that require curtailment. As can be seen in Ex-
14 HWF-Osterberg-4c, the literature for the Siemens turbine does not state any limitations
15 with respect to how many directional sectors can be defined.
16 Within the reduced noise operation mode, there are six different reduced noise
17 operating curves (i.e. power curves) as shown in Ex-HWF-Osterberg-4c, Figure 2.2 (PSC
18 Ref. # 181229). See also Ex.-HWF-Hankard-8. Each power curve results in a lower
19 maximum power level, and a correspondingly greater reduction in sound emissions. The
20 user settings for the parameter setpoints and for the operating curve can be accessed via
21 the wind farm SCADA (Supervisory Controls and Data Acquisition System) and at the
22 individual turbine controller level. In addition, the Siemens SWT-2.3 turbine can be
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Jesse Stowell, Direct Testimony Docket No. 2535-CE-100
1 manually changed “on the fly” to reduced noise operation mode at any time (independent
2 from any existing set points).
3 Q. Please describe in detail the technical capabilities of the Nordex N117 wind turbine
4 to meet the nighttime 45 dBA sound requirement in PSC 128.14?
5 A. The noise reduction capabilities of the Nordex N117 are quite similar to that of the
6 Siemens SWT-2.3 described previously. Like the Siemens turbine, the Nordex N117 can
7 also be programmed to automatically convert to reduced noise operation mode as a
8 function of any combination of day of the week, time of day, wind direction and wind
9 speed. Unlike the Siemens turbine, the Nordex control system has enabled only two
10 noise-reduced sectors to be defined based on wind directionality for all turbines produced
11 since 2010. In speaking with the Nordex technical team, they are working to expand this
12 capability to include the specification of more sectors and reduced noise operating curves
13 and hope to have this new capability available in the first quarter of 2014. Because this
14 technology is implemented purely via software (no hardware changes needed), all Nordex
15 N117 turbines can be enabled to use this capability once it is updated, even those N117
16 turbines that are already installed.
17 Q. As noted above and on page 4 of Ex.-HWF-Osterberg-4 (PSC Ref. # 181229) unlike
18 the Siemens turbine the Nordex N117 can only be programmed for two wind
19 sectors. Does this mean the Nordex turbines cannot be programmed to meet the
20 variety of wind direction parameters calculated by Mr. Hankard?
21 A. No. The Nordex turbines can be programmed to be responsive to Mr. Hankard’s
22 parameters as follows. The Nordex NC2 control system currently enables two wind
23 sectors to be specified in addition to the base turbine performance. Mr. Hankard’s wind
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Jesse Stowell, Direct Testimony Docket No. 2535-CE-100
1 direction parameters would be used to select the best combination of sectors to include in
2 the reduced-noise operation sector definitions for each turbine. For example, three of the
3 eight total sectors may be placed in one of the turbine program sectors and three of the
4 eight may be placed in the other control sector leaving two sectors available to operate at
5 full power. The noise reduced mode required to be used in the sector would be specified
6 to meet the lowest sound level requirements of any of the directions contained in the
7 noise reduced sectors. This programming would be completed on a turbine by turbine
8 basis guided by Mr. Hankard’s work for each turbine site so the operation of the Project
9 would automatically adjust into the required modes to meet the sound level requirements.
10 Q. In multiple places in Exs.-HWF-Osterberg-2 and 3 it indicates there is a ten minute
11 delay before the Nordex turbine goes into reduced power mode once the applicable
12 wind speed and direction parameters occur. Does this mean the Nordex turbines
13 will be non-compliant with sound requirements for 10 minutes each time the turbine
14 is supposed to go into reduced power mode?
15 A. No. The Nordex control strategy uses a transition zone referred to as “hysteresis” when
16 moving into a noise reduced directional sector. The use of the hysteresis parameter
17 allows the turbines to be programmed to transition into a noise reduced mode prior to
18 entering the sector that requires noise reduced operation. This same hysteresis control
19 concept is applied relative to any time based mode changes such that a transition time
20 period is specified to allow the turbine to transition to reduced power mode before a
21 required reduced operation mode time period begins.
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Jesse Stowell, Direct Testimony Docket No. 2535-CE-100
1 Q. Do you concur with Mr. Hankard’s methodology for determining the wind direction
2 and speed parameters to be programmed into the Project turbines to ensure
3 compliance the 45 dBA nighttime sound requirement?
4 A. Yes. This is the intended use of the reduced noise features described above for the
5 Nordex N117 and Siemens SWT-2.3 wind turbines.
6 Q. In your professional opinion will the Nordex N117 and Siemens SWT-2.3 turbines
7 utilizing the parameters calculated by Mr. Hankard, meet the nighttime 45 dBA
8 nighttime sound requirement and the 40 dBA requirement for the sensitive
9 receptors?
10 A. Yes. Based on the turbines’ capabilities and the results of Ms. Blank’s and Mr.
11 Hankard’s sound modeling and programming assumptions, the turbines will meet the
12 noise limits imposed in PSC 128.14 and the 40 dBA standard for the sensitive receptors.
13 To the extent subsequent sound measurements show an exceedence of the regulatory
14 sound limit, simply adjusting the programming of the applicable turbine is all that will be
15 necessary to bring it back into compliance with the requirement.
16 Q. Do you have any comments on the prevalence today of using wind turbine noise
17 reduction capabilities to lower the sound signature of a turbine or turbines whether
18 to meet a regulatory or other requirement?
19 A. While I cannot speak to particular projects due to client confidentiality, AWS routinely
20 implements client-specified sound-based curtailment strategies when modeling the pre-
21 construction energy production of wind farms and the requests for this type of modeling
22 are increasing at a rapid pace. Further, every major wind turbine OEM offers some type
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Jesse Stowell, Direct Testimony Docket No. 2535-CE-100
1 of noised reduced operation mode. The OEM’s would not offer such a feature unless it
2 was needed by the market.
3 Q. Does that conclude your pre-filed direct testimony?
4 A. Yes.
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