Appendix F Noise Memorandum

Transcription

1 Appendix F Noise Memorandum Draft Environmental Impact Report Rosamond Solar by SGS Antelope Valley Development, LLC F 1 July 2010 ESA

2 Memorandum Date: To: Cc: From: Subject: Joan Heredia, Sempra Global; Marilyn Burke, Sempra Generation Andy Atiyeh, ICF Mike Greene, INCE Bd. Cert, ICF Noise Levels from Single Axis Tracking Motors, Rosamond Solar Project, Kern County, California This memorandum has been prepared to document the findings of a noise analysis conducted for the Rosamond Solar Project (Project) SPA No. 16, ZCC No. 33, CUP No.27, Map 232 Public Easement Vacation. Introduction SGS Antelope Valley Development, LLC (Applicant) submitted a Permit Application package to the Kern County Planning Department on January 15, Exhibit C of the Rosamond Solar Project Description included an initial study checklist that contained a noise assessment for construction activities. The Project Description indicates the solar field will consist of photovoltaic (PV) panels mounted on support structures that will be either fixed or pivoting, depending on the specific PV panel manufacturer(s) selected. Kern County subsequently requested an assessment of potential noise impacts for the pivoting, axis tracking system. This analysis estimates resultant noise levels from single axis tracking motors for the Project, in the event Applicant decides to incorporate tracking capabilities as part of the solar panel installation. Regulatory Setting and Local Initiatives Kern County General Plan The Kern County General Plan Noise Element (2007, page 149) sets a 65 dba L dn limit on exterior noise at sensitive receptors. Noise-sensitive receptors are generally considered to be human activities or land uses that may be subject to the stress of substantial interference from noise. Land uses associated with sensitive receptors include residential dwellings, hotels, motels, hospitals, nursing homes, education facilities, and libraries.

3 Page 2 of 8 Noise Impact Assessment Potential noise effects from the use of a single axis tracker system could result from the electricallypowered motors used to orient the solar panels for improved effectiveness as the sun s position in the sky changes throughout the day. The noise from the tracker motors was assessed using estimates provided by Applicant regarding motor locations / panel configuration, motor noise levels, tracker system operation data and project site plan. Following is a description of the data and assumptions used to arrive at the estimation of noise levels at the site boundary adjacent to the nearest residence. Input Data and Assumptions Motor Locations/Panel Configuration The PV panels would be organized into electrical groups referred to as blocks. In this example, each block would encompass about 9 acres of PV panels, producing two megawatts. This could be configured such that there would be ten motors per nine acres of solar panels. Motors would not be located at the edges of the blocks, but rather would be near the center. As shown in Figure 3 (Single Axis Solar Tracker, Typical Motor Locations for 2MW Block), the distance to the nearest row of motors would be 299 feet from the edge of the solar field, with a second parallel row located approximately 38 feet further away. The rows of motors would be spaced approximately 122 feet apart from one another. Based upon the proposed site plan sheet shown in Exhibit A of the Rosamond Solar project Description, the minimum distance from the site boundary to the edge of the solar field would be 109 feet, in the area where the nearest noise-sensitive use exists (the residence located at th Street West). Based upon the above information, the nearest motor would be located 408 feet from the site boundary; this analysis assumes an estimate of 400 feet minimum. Motor Noise Levels in terms of Sound Power and Sound Pressure Levels Sound power (L w ) is the total amount of acoustic energy produced by a given source and is therefore independent of reference distance. Based upon noise level specifications data provided by Applicant, the sound power level for a typical motor would not exceed 75 dba. For 60-Hertz operation, the listed sound power level would be increased by 4 db (per the data sheet); therefore, the adjusted sound power level per motor for this example would be 79 dba. In terms of sound pressure level (L p) - i.e., instantaneous noise level, this is equivalent to a noise level of 47.5 dba at a reference distance of 50 feet, assuming noise attenuation with distance from a point source in the free field above a reflecting plane (Diehl, page 80): L p (dba) = L w -20*Log(R)+2.5, Where R is the source-receiver distance in feet.

4 Page 3 of 8 As a conservative estimate, it was assumed that the nearest noise-sensitive receiver boundary location would be within earshot of six motors (two rows of three motors each) i.e., one pair of motors directly in front of the receiver and one pair each to either side of the first pair (see Figure 1, below). The corresponding L p from the motors at the site boundary were calculated using the equation deriving L p from L w, in the same manner as described above (Diehl, page 80). Table 1 summarizes the noise levels for each of the six motors analyzed and the combined noise levels. Note that this represents a conservative estimate, because it assumes that all six motors are operating simultaneously 1. As shown in Table 1, the total noise level from the six motors would be approximately 37 dba at the site boundary. As shown in Figure 2, a noise level of 37 dba would be quite low, corresponding to a considerably lower level than a typical home refrigerator or typical rural daytime noise levels. Therefore, the operation of the motors at the site boundary would likely be inaudible or otherwise audible as a very low noise level. Motor Noise Levels in terms of County of Kern Noise Standards The Kern County General Plan Noise Element sets a noise level for residential land use compatibility of 65 dba L dn. The L dn noise metric represents a 24-hour period and applies a time-weighted factor designed to penalize noise events that occur during nighttime hours when relaxation and sleep disturbance are primary concerns. Noise occurring during daytime hours, between 7:00 a.m. and 10:00 p.m., receives no penalty. Noise occurring between 10:00 p.m. and 7:00 a.m. is penalized by adding 10 db to the measured level. For this calculation, it was conservatively assumed that the total effective period of motor operation for all the adjustment periods for the sun s position would be 50 percent of the time during daytime hours. It was also conservatively assumed that the hours of daylight (and thus, motor operations) would occur from 5 AM to 8 PM (i.e., a very long day). Using these assumptions, the resultant noise level would be 35 dba L dn, which would be 30 decibels lower than the Kern County noise standard of 65 dba L dn. 1 The noise level presented above represents a conservative estimate because the motors would not operate on a continuous basis or in unison. Rather, each motor would be controlled by a sensor monitoring the sun s position in the sky (at intervals as frequent as once every 15 seconds), and minute, incremental adjustments would be made to the panel s position by means of the motor. Thus, periods of motor engagement would be frequent but very brief. Thus, it is unlikely that a large number of adjacent motors would be in operation simultaneously.

5 Page 4 of 8 Summary Noise level estimates were made of the noise levels likely to result from installation of single axis tracking motors for the Rosamond Solar Project. Using conservative assumptions, the noise levels from multiple, adjacent motors were calculated at the site boundary adjacent to the nearest noise-sensitive land use (a residence located to the east of the project site). Based upon example equipment data provided by Applicant, the proposed site plan and the potential motor locations, the noise level would be approximately 37 dba or lower. The 24-hour average weighted noise level would be 35 dba L dn or lower, which would be 30 decibels lower than the applicable Kern County General Plan Noise Element standard of 65 dba L dn. Therefore, no significant noise impact would result from the use of tracker motors as detailed in this memo. References Diehl, George M., ed Machinery Acoustics. John Wiley & Sons, Inc. New York, NY Kern County. March, Kern County General Plan, Noise Element. Bakersfield, CA

6 Page 5 of 8 Table 1 Noise Level Summary Individual and Combined Motor Noise Levels at Site Boundary Motor Sound Power (L w, dba) Distance (Feet) Sound Pressure Level (L p. dba) Total 36.6

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8 Page 7 of 8 Figure 2 - Sound Levels of Typical Noise Sources and Noise Environments (dba) Noise Level dba 120 Extremes Jet aircraft at 500 ft Home Appliances Speech at 3 Ft Motor Vehicles at 50 Ft General Type of Community Environment Chain saw Power lawn mower Shop tools Blender Dishwasher Air conditioner Refrigerator Shout Loud voice Normal voice Normal voice (back to listener) Diesel truck (not muffled) Diesel truck (muffled) Automobile at 70 mph Automobile at 40 mph Automobile at 20 mph Major metropolis Urban (daytime) Suburban (daytime) Rural (daytime) Threshold of hearing Source: Harris Miller Miller & Hanson, Inc Noise and Vibration Impact Assessment for the San Francisco Bay Area Rapid Transit District (BART) Warm Springs Extension Project. Draft report. February. (HMMH Report No ) Burlington, MA. Prepared for ICF Jones & Stokes.

9 Page 8 of 8 Figure 3 - Single Axis Solar Tracker, Typical Motor Locations for 2MW Block