Bornish Wind Power Project Shadow Flicker … Wind Power Project Shadow Flicker Assessment GENIVAR...

Bornish Wind Power Project Shadow

Flicker Assessment

GENIVAR #103, 2710 – 3 Ave. NE Calgary, Alberta, Canada T2A 2L5

Phone: (403) 248-9463 Fax: (403) 250-7811 www.genivar.com www.windserver.ca

Procedures and Calculation Results

Prepared by: GENIVAR Submitted to: NextEra Energy Canada ULC October 7, 2009

Bornish Wind Power Project Shadow Flicker Assessment

GENIVAR i October 7, 2009

DISCLAIMER

The following report was generated for NextEra Energy Canada ULC with the purpose of assessing and documenting the shadow flicker at the Bornish Wind Power Project. The distribution, modification or publication of this report is only permitted with the written agreement from GENIVAR.

While this document is believed to contain correct information, neither GENIVAR nor any of its employees makes any warranty, either expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any results or any information disclosed. The interpretation of this and any other data or report related to this project is solely the responsibility of the client.

APPROVALS

Written by: Breanne Gellatly Date: October 7, 2009

Reviewed by: Mathew Breakey Date: October 7, 2009

DOCUMENT INFORMATION

Client: NextEra Energy Canada ULC

Issue Date: October 7, 2009

Document Version: 01


GENIVAR ii October 7, 2009

Table of Contents

Executive Summary .............................................................................................................1

Objective ..............................................................................................................................2

Overview of Shadow Flicker ...............................................................................................2

Shadow Flicker Algorithm & Assumptions .........................................................................3

Conclusions & Recommendations .......................................................................................5

Appendix 1: WindPRO Algorithm ....................................................................................10

Introduction to SHADOW .................................................................................................................. 10

The SHADOW calculation method .................................................................................................... 11

The SHADOW calculation model ...................................................................................................... 12

Appendix 2: WindPRO Results for the Bornish Wind Power Project...............................14


GENIVAR 1 October 7, 2009

EXECUTIVE SUMMARY

The Bornish Wind Power Project is located in southern Ontario. The purpose of this analysis was to quantify the impact of shadow flicker in terms of modelled shadow hours per year and minutes per day. The SHADOW module of WindPRO was used to model ‘worst-case’ and ‘real-case’ shadow flicker at 94 receptors (17 participating receptors and 77 non-participating receptors) located within the proposed 75 mega-watt wind farm. The layout considered in the calculation consisted of 50 GE 1.5xle wind turbines and 3 turbines at alternate locations. In both cases receptors were modelled using the green house mode. This assumes that the receptor does not face any particular direction, but instead faces all directions. Additional conservatism was taken by excluding any possible sheltering from nearby vegetation. Modelling is based on terrain data, turbine specifications, location of the sun and on-site meteorological data. Worst-case shadow flicker assumes maximum bright sunshine hours according to geographical location and operation hours; whereas, real-case shadow flicker incorporates Canadian Climate Normals1 and on-site meteorological data into the model.

Non-participating receptors experiencing the most shadow flicker are mentioned below:

- The worst-case maximum shadow flicker (minutes per day) is 30 minutes at R76. - The real-case maximum shadow flicker (hours per year) is 8.18 hours at receptor R27. - The worst-case maximum shadow flicker (hours per year) is 33.98 hours at receptor R76.

In the event that shadow flicker is a concern, placing shutters on windows, planting trees and turbine curtailment for specific wind directions and time of day are all effective mitigation techniques. As the level of annoyance caused by flickering is dependent on time of day and time spent near effected windows, additional information from the affected residents with respect to their level of concern may help to quantify the impact of the results.

1 Agriculture and Agri-Food Canada, A National Ecological Framework for Canada Canadian Ecodistrict Climate Normals 1961-

1990, 8 December 1999, <http://sis.agr.gc.ca/cansis/nsdb/ecostrat/climate_normals_1961-90.html> (23 October 2008).



OBJECTIVE

The purpose of this report is to quantify the impact of shadow flicker in terms of modelled shadow hours per year and minutes per day for the Bornish Wind Power Project. This report presents the algorithm, assumptions and results of the shadow flicker calculation at the Bornish Wind Power Project.

OVERVIEW OF SHADOW FLICKER

Wind turbines cast a shadow of their rotating blades during periods of bright sunshine. If these shadows are cast on the windows of nearby dwellings, residents may experience a strobe or shadow flicker effect inside the house. Shadow flicker can be calculated using the worst-case scenario or the real-case scenario. The worst-case or ‘astronomical maximum’ shadow considers only relative geographical location between turbines and receptors, assuming the sun is shining during all possible daylight hours. The real-case or ‘meteorologically probable’ shadow uses on-site wind data and expected sunshine probability statistics to account for turbine availability as well as variation in sunlight based on cloud cover and wind directions.

The actual amount of shadow flicker measured inside the receptor requires a direct line-of-sight between a window and a turbine. Obstructions and orientation of the turbine and window may result in reduced actual shadow flicker at a receptor. In the event that shadow flicker is a concern, placing shutters on windows, planting trees and turbine curtailment for specific wind directions and time of day are all effective mitigation techniques. There are no proven health impacts caused by shadow flicker; however, a study in Sweden has shown that the flickering effect is annoying to residents, particularly during summer evenings2.

Most Canadian jurisdictions do not have established shadow flicker regulations; however, international standards have been followed to produce a best practice facility design. Denmark recommends a maximum real-case shadow flicker of 10 hours per year3 and German guidelines specify a limit of 30 hours per year of worst-case shadow flicker. The County of Bruce in Ontario has followed the German guidelines and limits shadow flicker to 30 hours per year and 30 minutes per day (worst-case) at non-participating receptors4.

2 Wind Power Environmental Impact of Wind Power Station Siting, (VINDKRAFTENS MILJÖPÅVERKAN FALLSTUDIE AV VINDKRAFTVERK I BOENDEMILJÖ), A. Widing et al, Centrum för Vindkraftsinformation Institutionen för naturvetenskap och teknik, Gotland University, Sweden, 2004.

3 Emmanuel et al. Spatial Planning of Wind Turbines, European Action of Renewable Energies. Retrieved March 24, 2009 from www.cler.org/info/IMG/pdf/WP8_ANG_guide.pdf.

4 County of Bruce (2008). Planning & Economic Development Department. Retrieved on March 24, 2009 from http://www.brucecounty.on.ca/downloads/planning/2008-Wind-Farm-Submission-Requirements.pdf.



SHADOW FLICKER ALGORITHM & ASSUMPTIONS

The WindPRO SHADOW module was used to model the shadow flicker at the Bornish Wind Power Project. The SHADOW module calculates how often and in what interval each receptor could be affected by the shadow of nearby turbines. A distance of 2000 metres and a minimum angle of 3º above the horizon were used for calculating the visible range of shadow flicker caused by the turbines. The modelling software executes a site specific simulation of the solar trajectory relative to the wind project for an entire year. The complete description and shadow flicker calculation algorithm of WindPRO is provided in Appendix 1: WindPRO Algorithm. Both modelling scenarios assume that houses within the project have windows oriented in every direction and are susceptible to flicker effect from every direction. This is known as the “green house mode,” and represents a conservative estimate of the impact of shadow flicker. Further conservatism was taken by not including sheltering from nearby vegetation, which could screen some potential flicker. Topography was included in the modelling; however, elevation changes smaller than the resolution of the contour data may not have been captured.

The calculation of real-case shadow flicker incorporated probability of sunshine (% of daylight hours with expected sunshine) as reported by Environment Canada1 and on-site meteorological tower data into the modelling. The monthly probability of sunshine used in the modelling is presented in Table 1. On-site wind data were measured for nearly two years at Site 9008. These wind data were provided to GENIVAR in raw wind data files and did not undergo any internal quality control as this was outside the scope of this analysis. Wind speed data were averaged for the 50-metre and the 40-metre monitoring heights since there were redundant anemometers. Detailed shear binning was not available to extrapolate the 50-metre dataset; however, since record-by-record wind speed data were available at the 50-metre and the 40-metre heights, the 50-metre wind speed data was extrapolated using the power law on a record-by-record basis. A record-by-record shear value was calculated rather than a constant shear since shear values vary with time of day, season and wind direction. Wind speed data from Site 9008 were loaded into WindPRO to predict operational hours. As a conservative measure, the WindPRO calculation does not account for turbine down time due to maintenance and other atypical circumstances that may curtail turbine production. The GE 1.5xle turbine has a rotor diameter of 82.5 metres and hub height of 80 metres (the power curve used was at an air density of 1.24 kg/m3 for normal turbulence intensity5).

5 Technical details were contained in the document 01.1 1.5XLE Technical Description and Data r0.pdf. and 05.2 XLE Calculated

Power Curve r5.pdf.



Table 1: Probabilities of Bright Sunshine for the Bornish Wind Power Project

Month Probability January 28%

February 34% March 35% April 45% May 53% June 58% July 62%

August 58% September 48%

October 42% November 28% December 22%

The yaw system of the wind turbine changes the orientation of the rotor according to the wind direction, thus the shadow of the rotating blades changes according to the wind direction. The wind rose representing the wind direction distribution at the Bornish Wind Power Project is presented in Figure 1. It was assumed that the wind directions from the 50-metre monitoring height were representative of hub height conditions of the entire project.

Figure 1: Wind Direction Distributions (frequency %) at Site 9008

(August 26, 2007 to June 2, 2009)



CONCLUSIONS & RECOMMENDATIONS

The Bornish Wind Power Project consisted of 94 receptors and 53 GE 1.5xle wind turbines. Worst-case and real-case shadow flicker results for each receptor are presented in Table 2. Time is presented in decimal hours (e.g. 2.5 = 2 hours 30 min). Figure 2 shows the real-case shadow hours per year as a contour line and identifies the maximum shadow flicker minutes per day at each non-participating receptor. Non-participating receptors experiencing the most shadow flicker are mentioned below:

- The worst-case maximum shadow flicker (minutes per day) is 30 minutes at R76. - The real-case maximum shadow flicker (hours per year) is 8.18 hours at receptor R27. - The worst-case maximum shadow flicker (hours per year) is 33.98 hours at receptor R76.

Potential mitigations techniques to reduce shadow flicker exposure include placing shutters on windows and strategic placement of vegetation



Figure 2: Shadow Flicker Contour Map – Bornish Wind Power Project



Table 2: Shadow Flicker Results for the Bornish Wind Power Project

Receptor

UTM Zone 17

Elevation

(m)

Worst-Case Real-Case NAD 83

Easting Northing days/year mins/day hours/year hours/year

R1 447,615 4,773,387 241 60 11 6.98 0.93 R2 447,074 4,773,519 238 0 0 0.00 0.00 R3 446,563 4,773,650 235 0 0 0.00 0.00 R4 446,511 4,773,750 232 0 0 0.00 0.00 R5 445,664 4,773,957 226 0 0 0.00 0.00 R6 444,493 4,773,978 222 106 16 13.85 2.13 R7 444,543 4,774,133 222 70 9 5.35 0.93 R8 444,496 4,774,220 222 79 9 7.40 1.13 R9 444,124 4,774,335 220 71 13 9.72 1.72

R10 442,089 4,774,807 212 42 16 6.87 1.12 R11 441,521 4,774,943 212 138 16 17.92 5.17 R15 438,086 4,775,744 210 9 5 0.52 0.12 R16 437,989 4,775,657 211 32 10 3.63 0.52 R17 437,496 4,775,876 212 26 5 2.05 0.27 R18 437,435 4,775,794 213 52 9 5.80 0.83 R19 439,351 4,777,038 201 0 0 0.00 0.00 R20 439,421 4,777,027 203 0 0 0.00 0.00 R21 439,911 4,776,901 204 0 0 0.00 0.00 R22 440,538 4,776,745 203 0 0 0.00 0.00 R23 440,666 4,776,840 201 0 0 0.00 0.00 R24 440,782 4,776,706 201 0 0 0.00 0.00 R25 441,091 4,776,727 205 0 0 0.00 0.00 R26 447,191 4,771,732 230 26 17 5.10 1.15 R27 447,320 4,771,865 231 90 23 25.23 8.18 R28 447,456 4,771,732 232 62 15 10.43 3.32 R29 447,683 4,771,839 232 110 16 15.78 5.18 R30 447,805 4,771,673 232 79 13 7.77 2.58 R33 444,909 4,772,422 244 177 14 19.13 4.38 R34 444,657 4,772,426 242 200 16 25.88 6.25 R41 436,989 4,774,194 240 161 25 29.28 5.75 R42 437,210 4,772,352 246 35 4 1.58 0.48 R43 437,540 4,772,183 246 0 0 0.00 0.00 R44 438,244 4,771,973 241 0 0 0.00 0.00 R45 438,688 4,772,081 241 9 2 0.30 0.08 R46 438,788 4,771,895 236 0 0 0.00 0.00



Receptor

UTM Zone 17

Elevation

(m)



R47 439,071 4,771,955 242 12 6 0.83 0.22 R48 439,307 4,771,775 237 20 10 2.13 0.63 R49 439,363 4,771,853 236 20 11 2.45 0.72 R50 439,422 4,771,758 233 25 12 3.37 1.02 R51 439,532 4,771,702 237 39 13 5.75 1.80 R52 439,562 4,771,796 237 29 14 4.62 1.40 R53 439,361 4,771,770 236 22 11 2.53 0.75 R54 439,966 4,771,712 241 25 4 1.40 0.45 R55 440,033 4,771,602 241 0 0 0.00 0.00 R56 440,418 4,771,606 246 12 3 0.47 0.13 R57 440,492 4,771,514 246 21 3 0.88 0.28 R59 441,150 4,771,457 245 23 4 1.10 0.32 R60 441,310 4,771,389 246 33 5 2.12 0.63 R61 441,490 4,771,253 242 25 8 1.85 0.55 R62 441,977 4,771,297 243 72 13 9.42 2.87 R63 442,335 4,771,021 238 33 16 4.70 1.10 R64 442,469 4,770,950 238 38 20 6.87 1.75 R66 445,577 4,770,404 240 0 0 0.00 0.00 R67 445,950 4,770,504 240 0 0 0.00 0.00 R69 441,576 4,776,282 205 69 14 10.00 1.35 R71 444,977 4,773,035 236 95 16 10.13 2.05 R72 444,945 4,773,179 235 69 15 8.03 1.60 R73 445,193 4,773,159 236 80 22 13.48 2.37 R74 445,068 4,773,388 231 99 18 14.78 2.45 R75 445,333 4,773,628 230 17 5 0.90 0.17 R76 444,972 4,771,983 248 184 30 33.98 7.68 R77 444,918 4,771,559 244 134 28 29.17 7.43 R79 444,425 4,770,964 239 87 20 12.45 3.48 R80 444,442 4,770,061 239 0 0 0.00 0.00 R81 444,358 4,770,042 238 0 0 0.00 0.00 R82 446,627 4,770,918 236 0 0 0.00 0.00 R83 439,354 4,765,081 232 0 0 0.00 0.00 R84 439,462 4,765,855 231 0 0 0.00 0.00 R85 439,466 4,766,106 229 0 0 0.00 0.00 R86 439,458 4,766,286 228 0 0 0.00 0.00 R87 439,445 4,764,425 234 0 0 0.00 0.00



Receptor

UTM Zone 17

Elevation

(m)



R88 438,920 4,764,270 237 0 0 0.00 0.00 R89 438,791 4,764,389 235 0 0 0.00 0.00 R91 439,771 4,764,338 232 0 0 0.00 0.00 R92 440,054 4,764,339 230 0 0 0.00 0.00 R93 440,171 4,764,358 229 0 0 0.00 0.00 R99 440,684 4,771,333 247 0 0 0.00 0.00

Participating Receptors

R12 440,556 4,775,164 212 103 12 11.95 2.20 R13 439,974 4,775,313 210 153 38 50.12 13.80 R14 438,543 4,775,543 210 32 12 3.40 0.82 R31 446,689 4,772,024 237 68 25 19.30 3.33 R32 446,141 4,772,012 244 86 37 46.25 6.55 R35 443,326 4,772,729 240 103 25 20.67 3.73 R36 443,253 4,772,892 236 251 57 92.12 23.73 R37 442,080 4,773,157 232 261 66 103.97 28.83 R38 441,208 4,773,238 237 290 36 73.05 17.38 R39 440,110 4,773,577 236 182 30 49.27 9.37 R40 439,608 4,773,718 236 246 112 198.47 58.63 R58 440,754 4,771,654 246 37 7 3.18 1.02 R65 442,804 4,771,133 244 55 28 15.62 3.62 R68 441,090 4,774,106 218 162 33 32.98 6.37 R70 443,131 4,773,964 223 145 70 74.50 14.78 R78 444,591 4,771,289 242 143 53 71.85 23.30 R98 441,116 4,773,272 233 301 52 126.87 30.07



APPENDIX 1: WINDPRO ALGORITHM

The following appendix has been taken from the WindPRO help files.

Introduction to SHADOW

SHADOW is the WindPRO calculation module that calculates how often and in which intervals a specific area will be affected by shadows generated by one or more wind turbines. These calculations are expected case scenarios (i.e. calculations which are solely based on the probability of sunshine as calculated from the monthly maximum total duration of bright sunshine and the position of the turbine relative to the sun or the astronomical maximum shadow). Shadow flicker impact may occur when the blades of a wind turbine pass through the sun’s rays seen from a specific spot (e.g. a window in an adjacent settlement). If the weather is overcast or calm, or if the wind direction forces the rotor plane of the wind turbine to stand parallel with the line between the sun and the neighbour, the wind turbine will not produce shadow flicker impacts.

Apart from calculating the potential shadow flicker impact at a given neighbour, a map rendering the iso-lines of the shadow flicker impact can be printed. This printout will render the amount of shadow flicker impact for any spot within the project area.

The time of the day for which shadow flicker impact is critical and the definition of a receptor for which shadow flicker impact is calculated are less rigidly defined by the guidelines and is often something which should be evaluated in each individual case.

As an example, a factory or office building would not be affected if all the shadow flicker impact occurred after business hours, whereas it would be more acceptable for private homes to experience shadow flicker impact during working hours, when the family members are at work/school.

Finally, the actual amount of shadow flicker impact as a fraction of the calculated potential risk will depend heavily on the geographic location in question. In areas with high rates of overcast weather the problem would obviously decrease, and during potential hours of shadow flicker impact in the summer the wind turbine may often be stationary due to lack of wind.

Statistics regarding the wind conditions and number of hours with clear sky can also be taken into account.

As in the other WindPRO modules, input of data can be based solely on entering coordinates and characteristics for the individual wind turbine and shadow flicker receptors manually.

A significant strength in the WindPRO system is the option of direct graphic on-screen input of wind turbines and receptors on a map.



The SHADOW calculation method

The calculation of the potential shadow flicker impact at a given receptor is carried out simulating the situation. The position of the sun relative to the wind turbine rotor disk and the resulting shadow flicker is calculated in steps of 1 minute throughout a complete year. If the shadow flicker of the rotor disk (which in the calculation is assumed solid) at any time casts a shadow flicker reflection on the window, which has been defined as a receptor object, then this step will be registered as 1 minute of potential shadow flicker impact. The following information is required:

- The position of the wind turbines (x, y, z coordinates) - The hub height and rotor diameter of the wind turbines - The position of the receptor object (x, y, z coordinates) - The size of the window and its orientation, both directional (relative to south) and tilt

(angle of window plane to the horizontal). - The geographic position (latitude and longitude) together with time zone and daylight

saving time information. - A simulation model, which holds information about the earth’s orbit and rotation relative

to the sun.



The SHADOW calculation model

In the shadow flicker calculation model used by WindPRO the following parameters defines the shadow flicker propagation angle behind the rotor disk

• The diameter of the sun, D: 1,390,000 km • The distance to the sun, d: 150,000,000 km • Angle of attack: 0.531 degrees

Theoretically, this would lead to shadow flicker impacts in up to 4.8 km behind a 45 m diameter rotor disk. In reality, however, the shadows never reach the theoretical maximum due to the optic conditions of the atmosphere. When the sun gets too low on the horizon and the distance becomes too long the shadow dissipates before it reaches the ground (or the receptor). How far away from the wind turbine the shadow will be visible is not well documented and so far only the German guidelines set up limits for this (see section 4.2.0). The default distance of WindPRO is 2 km. and the default minimum angle is 3 degrees above the horizon. If the German guidelines are used, the maximum distance from each wind turbine can be calculated using the formula

Max. distance = (5*w*d) / 1,097,780

where w is the average width of the blade. The value of 1,097,780 is derived from the diameter of the sun, reduced by a compensation factor for the fact that the sun disk is a circle and not a square.



APPENDIX 2: WINDPRO RESULTS FOR THE BORNISH WIND POWER PROJECT

Bornish Wind Power Project Shadow Flicker … Wind Power Project Shadow Flicker Assessment GENIVAR...

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