EXHIBIT O Noise Study
APPLICATION TO THE OHIO POWER SITING BOARD FOR A
CERTIFICATE OF ENVIRONMENTAL COMPATIBILITY AND PUBLIC NEED FOR THE
GRANGE SOLAR GRAZING CENTER
Case No. 24-0801-EL -BGN
TECHNICAL REPORT
Engineering Offices: 5096 N Silver Cloud Drive St. George, UT 84770 USA
703-303-0341
www.hesslernoise.com
Title: Existing Conditions Background Sound Survey and Noise Impact Assessment
Project: Grange Solar Grazing Center
Location: Logan County, OH
Prepared For: Grange Solar, LLC
Prepared By: David M. Hessler, P.E.
Issue Date: September 24, 2024
Reference No: TR-2281-091024-B
Attachments: Graphic A Overall Site Map and Ambient Survey Measurement Positions
Table T-2281-091224-A Transformer and Inverter Sound Power Level Derivations
Plot 1-1
Project Sound Emissions Contour Map – Daytime – Western Section
Plot 1-2 Project Sound Emissions Contour Map – Daytime – Central Section
Plot 1-3 Project Sound Emissions Contour Map – Daytime – Eastern Section
Plot 2 Project Sound Emissions Contour Map – Nighttime – Substation Area
1.0 Introduction
A study has been carried out to evaluate the sound emissions from the proposed Grange Solar Grazing Center (the Project) located just south of Russells Point in Logan County, Ohio in order quantitatively evaluate any potential community noise issues. Compared to other types of power generation facilities, possible noise impacts from a photovoltaic solar energy project are relatively few, relatively mild and, moreover, have the unusual characteristic of essentially occurring only during the daylight hours when noise is much less likely to be an issue in the first place. In this case, any possible concerns about noise are largely confined to the step-up transformers in the proposed substation, the 129 electrical inverters within the various solar panel fields and some short-livedactivitiesduringconstruction. Inanefforttomethodicallyevaluatethepotentialimpact of theProject onthe surrounding community,afieldsurveywasconducted to establishthe existing levels of background sound within the site area so that projections of future Project sound could be evaluated within an appropriate context. This report summarizes the findings from that field survey and discusses the potential noise impacts associated with the Project.
1.1 Executive Summary
A field survey of the existing ambient sound levels within and near the Grange Solar Grazing Center project area was carried out in April of 2024 to quantify the baseline environmental conditions. Seven monitoring stations distributed throughout the Project area, as it was conceived at the time, recorded continuously day and night for seven days. All statistical measures were remarkably consistent and followed the same trends at all positions despite the relatively large site area stretching about 10 miles from end to end. This indicates that the average measured level from all seven test points would be reasonably representative of any specific location within the Project area. Nevertheless, the sound levels at one relatively remote test location, Position 4 in a quiet field in the southwestern corner of the Project area, were consistently lower than the levels at the remaining monitoring station so the daytime design background sound level was taken exclusively from that location.
Current regulations state that the sound emissions from a renewable energy project cannot exceed the existing L50 background level by more than 5 dBA or an absolute level of 40 dBA, whichever is greater. The site-wide average daytime L50 from all seven test points was 40 dBA, but the average daytime L50 at Position 4 was 37 dBA; consequently, a conservative design goal of 42 dBA for Project sound at any residence has been assumed, versus the nominal regulatory limit of 40 dBA + 5, or 45 dBA. At night the Project is essentially idle and silent, but some sound is possible from the substation transformers. The average nighttime L50 of 39 dBA measured at Position 3, representing the substation area, was used to derive a nighttime regulatory limit of 44 dBA for that local area.
A noise model of the site was subsequently developed to evaluate how the Project sound levels will compare to the daytime and nighttime ambient-based design goals. The model inputs are the sound power levels of the main step-up transformers in the proposed substation and the inverters, which are distributed throughout the panel arrays. In order to quantify the maximum operational sound emissions from the Project on a sunny day, the sound power level of the substation transformers was conservatively calculated at 98 dBA re 1 pW from its maximum expected rating of 90 MVA ONAF2, which represents a hot summer day operating scenario where the radiator fans are on in high speed mode. This is most likely a rare operating configuration occurring only during unusually hot conditions. The inverter make and model for this project will be finalized at a later stage, but a likely/representative candidate is the Power Electronics Model HEM FS4200 MU. The sound power level spectrum of this inverter model was derived from detailed field measurements of a similar Model HEM FS3430 MU unit in actual operation with a scale-up factor added to account for the size differential. An effective sound power level of 94 dBA re 1 pW was used for each unit.
The maximum daytime sound level due to Project operation is expected to be below the 42 dBA design goal at all residences. The maximum level at any house is 40 dBA and all others are lower.
These predicted Project sound levels, mostly in the 30’s dBA or lower, are generally comparable to the existing daytime ambient sound level suggesting that any sound emissions from the Project will likely be inconsequential, if not inaudible, at all residences in the Project area.
Although solar energy projects are, for all intents and purposes, operational only during the day, the substation transformers remain energized at night and may potentially be used in reactive compensation mode that assists with grid stability. Using a conservative operating level of 11 MVA to derive the transformer sound emissions, extremely low sound levels in the 20’s dBA, well below the nominal design target of 44 dBA, are calculated at the nearest homes to the substation at night. Such levels are so quiet in absolute terms that no disturbance is anticipated, if the substation is even audible at all. While the inverters are minimally active during reactive compensation, the level of operation is a tiny fraction of that during normal operation; consequently, the sound emissions are expected to be negligible.
In contrast to other forms of power generation, the sound emissions from construction activities on a solar project are expected to be dramatically lower in both magnitude and duration. Some unavoidable disturbance is possible when the mounting posts are driven in, but this activity will be fairly short-lived in any particular location. Other sounds from trenching, road building and material delivery will also be brief in duration and will progress from place to place avoiding prolonged exposure at any specific location. Exposure to construction noise is also limited by regulation to the daytime hours and to an even shorter time window for piling and the possible use of hoe rams.
In general, the potential noise impacts from all aspects of the Project are expected to be minimal.
2.0 Existing Conditions Sound Survey
In order to quantitatively evaluate the potential noise impact of the Project, sound monitoring equipment was set up at seven locations distributed throughout the Project area to measure the existing baseline ambient sound level for later comparison to the predicted sound levels from the substation and other equipment. Unless very low in absolute terms, generally at or below 40 dBA, the potential noise impact from any project is normally a function of how much its sound exceeds the background level that would otherwise exist. The survey was carried out over a 7 day period from April 8th through the 15th, 2024 using continuously recording sound monitors in general accordancewith ANSI S12.9-R2013 Quantities and Procedures for Description and Measurement of Environmental Sound. Part 2: Measurement of Long-term, Wide-Area Sound.
The site area is almost entirely rural in character consisting of isolated farms and residences with open fields and small patches of woods in between; however, the towns of Russells Point and Lakeview are located a short distance north of some land parcels where panel installations are planned. These areas are relatively densely populated and contain a mixture of commercial and residential development, as well as other noise sensitive uses such as churches, schools, etc. There
is about 1500 to 1700 ft. of buffer distance between the edges of the northernmost panel arrays and the nearest residences in these communities.
2.1 Measurement Locations
Seven measurement locations, illustrated in Graphic A, were selected as being representative of the various Project areas, which are spread out intermittently over a fairly large geographical area extending about 10 miles from end to end.
Figure 2.1.1 is an aerial view of Position 1 and its surroundings in the northwestern corner of the site. Figures 2.1.2 and 2.1.3 show the instrumentation set up on the edge of a large field
Figure 2.1.4 shows test Position 2 and Figures 2.1.5 and 2.1.6 show the meter and microphone. This location was in a quiet corner of Emil Davis Park and was intended to represent the southern edge of the town of Lakeview, which begins in earnest on the north side of SR 720.
Sound monitor Position 3 was selected to represent the immediate vicinity of the Project substation,whichisshowninFigure2.1.7. Figures2.1.8and2.1.9showthemonitoringequipment at the edge of an open field near a wooded area.
Substation Location
Position 4 is illustrated in Figures 2.1.10 through 2.1.12.
2.1.12 Test Instrumentation at Position 4 Looking NW
Position 5, illustrated in Figures 2.1.13 through 2.1.15, is representative of a group of nonparticipating residences along Township Road 94 in the center of the Project area.
2.1.15 Position 5 Looking S
Position 6, illustrated in Figures 2.1.16 through 2.1.19, was set up on land that was being explored as a possible part of the Project at the time of the survey. This position may now be considered supplemental to the other locations within the final Project footprint but still helpful in characterizing the environmental sound level in and around the general Project area. The monitor was placed in a large open field remote from any trees or roads.
Figure 2.1.18 Position 6 Looking N
Finally, Position 7, illustrated in Figures 2.1.19 through 2.1.21, is generally representative of a grouping of leased parcels in the northeast corner of the site north of Huntsville.
2.1.21 Position 7 Looking SW
2.2 Survey Equipment and Measurement Parameters
Norsonic N-140, ANSI S1.4-1983(R2006) Type 1 precision, 1/3 octave band frequency analyzers were used at all positions. The meters were field calibrated with a Rion NC-74, ANSI S1.401984(R1990) Class 1 calibrator at the beginning and end of the survey and exhibited only a small amount of drift within the 0 to +/- 0.2 dB range. Weather-treated 7 in. diameter windscreens were used to minimize self-generated distortion from wind The microphones were fixed to metal posts at a standard height of about 1.2 m above local grade.
A variety of statistical sound levels were measured in 10-minute increments over the seven day survey period; however, the parameter of primary relevance was the L50 statistical level, or the soundlevelexceeded50%ofthetimeduringeach10minutemeasurementinterval. Newlyrevised Ohio Power Siting Board (OPSB) noise standards, contained in Section 4906-4-09(E)(2) of the Ohio Administrative Code, use the L50 ambient as the baseline for determining the permissible project sound level. Additional measures, such as the L90 and Leq were also recorded. The L90 statistical measures the level exceeded 90% of the time during the measurement period, or the quietest 1 minute in every 10 minute period. The Leq sound level is the actual average sound level over each measurement period.
2.3 Survey Conditions
The weather conditions over the survey period were mixed in the sense that five separate periods of rain and/or elevated wind speeds (>12 mph) occurred during the survey, but suitable conditions for valid data collection existed for about half of the total period. All data collected during times of precipitation or wind speeds above 12 mph have been omitted from all averaging calculations.
3.0 Regulatory Noise Limits
As alluded to in Section 2.2, the Ohio Administrative Code has recently been revised with respect to permissible sound levels from renewable energy projects. The new key provisions in Section 4906-4-09(E) for both construction and operational sound emissions are quoted below.
(1) General construction activities shall be limited to the hours of seven a.m. to seven p.m., or until dusk when sunset occurs after seven p.m. Impact pile driving, hoe ram, and blasting operations, if required, shall be limited to the hours between ten a.m. to five p.m., Monday through Friday. Construction activities that do not involve noise increases above ambient levels at sensitive receptors are permitted outside of daylight hours when necessary. Sensitive receptor, for purposes of this rule, refers to any occupied building. The applicant shall notify property owners or affected tenants within the meaning of paragraph (B)(2) of rule 4906-3-03 of the Administrative Code of upcoming construction activities including potential for nighttime construction activities.
(2) The facility shall be operated so that its daytime and nighttime noise contributions do not result in noise levels at any non-participating sensitive receptor within one mile of the project boundary that exceed the greater of 40 dBA or the project area ambient daytime and nighttime average sound level (L50) by five A-weighted decibels (dBA).
4.0 Survey Results and Ambient-Based Design Goals
The overall survey results from all seven positions are plotted in Figure 3.0.1 in terms of the L50 statistical sound level.
L50(10min)AmbientSoundLevelsatAllPositions
3.0.1
This plot shows that the sound levels at all positions were generally similar in magnitude and followed the same large-scale trends on a site-wide basis, despite the fact that the monitor stations were spread out over a gross area of roughly 30 square miles. This remarkable consistency suggests that the overall average of all locations would serve as a reasonably good indicator of the sound level at any given location within the site area. For daytime (7 a.m. to 10 p.m.) conditions, when this solar project would be active, the overall average L50, excluding all periods of rain and wind,is40dBA. ThiswouldputtheostensibleregulatoryProjectnoiselimitat45dBApercurrent rules. However, there is a fairly wide range of variation between the various positions, approximately 10 dBA on average, and Position 4 is generally lower than the rest most of the time This suggests that it might be prudent to use a lower baseline value than the simple average of 40 dBA to calculate the +5 dBA allowable Project noise limit. At the risk of being overly conservative, the minimum average daytime L50 measured at Position 4 of 37 dBA is recommended as a safer choice, leading to a Project design goal of 42 dBA at any neighboring residences during normal daytime operations. This value is 3 dBA below the nominal regulatory limit of 45 dBA and is considered a unilaterally adopted design goal.
At night the project is generally idle but there is a possibility that some sound at a diminished level relative to normal daytime operation could be generated by the substation transformers. The only area that might be potentially affected would be the immediate vicinity of the substation represented by ambient monitoring Position 3. The average nighttime (and daytime) L50 at Position 3 was 39 dBA. This implies a regulatory limit of 44 dBA at night at any residences in the general vicinity of the substation.
For informational purposes, the L90 sound levels measured at all positions are plotted below.
L90(10min)AmbientSoundLevelsatAllPositions
Figure 3.0.2
The residual (L90) background levels are generally about 3 dBA lower than the L50 levels shown in Figure 3.0.1. The overall daytime average L90, after all periods of rain or wind have been removed, was 37 dBA. Coincidentally, this is the same value (based on the Position 4 L50) used to calculate the 42 dBA project design target for daytime operations. In other words, had the design goal been based on the average daytime L90 sound level, the same target of 42 dBA would have resulted.
Finally, the average, or Leq, sound level recorded during the survey are plotted below.
Leq(10min)AmbientSoundLevelsatAllPositions
The overall average daytime Leq was 43 dBA. This suggests that a Project sound level of 42 dBA, were such a level to actually occur at any potentially sensitive receptor, would be comparable to the existing average daytime sound level, and therefore unobtrusive. Lower Project sound levels would even be less perceptible, if audible at all.
4.0 Sound Emissions from the Project
4.1 Substation Sound Emissions
The input sound power level for the two step-up transformers in the Project substation during daytime operation has been conservatively estimated in octave bands in Table T-2281-091224-A based on each unit’s maximum expected MegaVolt Ampere (MVA) rating of 90 during ONAF2 (oil natural air forced, fans on high speed) operation using empirically derived algorithms from the “Electric Power Plant Environmental Noise Guide1” published by the Edison Electric Institute (EEI). Numerous transformers over a wide range of sizes and manufacturers were measured in the EEI study to develop a formulaic relationship between the MVA rating and sound power. For this size transformer, the EEI methodology nominally predicts a near field sound pressure level of 79 dBA and an associated sound power level (Lw) of 98 dBA re 1 pW2 Experience suggests,
1 “ElectricPowerPlantEnvironmentalNoiseGuide”,PreparedbyBoltBeranekandNewmanfortheEdison Electric Institute, 2nd Ed., 1984.
2 Soundpowerlevelisanessentiallyintangiblequantity,usedonlyformodelingpurposes,thatiscalculated from the measured sound pressure level and the radiating wave front area at the point of (cont. next page)
however, that this prediction methodology is conservative for modern transformers (the EEI study was carried out over 40 years ago) and a lower sound power level from the actual transformers is likely. In cases where the measured performance has been determined, a sound level about 6 dB lower than the calculated EEI value has been observed, as shown in Section 2 of Table T-2281091224-A. Nevertheless, to be conservative, the as-calculated sound power level without modification, tabulated below, has been used in the modeling analysis.
Table 4.1.1
Estimated 250 MVA ONAF2 Transformer Sound Power Level (Lw) Spectrum - Daytime
500 1k 2k 4k 8k dBA
It is important to note that this sound level conservatively represents operation at maximum capacity with the radiator fans on high speed, as might rarely occur on an especially hot summer day. It will be much more common for the unit to operate without any fans on, or with the fans at low speed at significantly lower sound levels.
At night, the Project is essentially inactive, but the substation transformers remain energized and may produce some sound, although nothing close to the daytime sound power level of 98 dBA re 1 pW assumed above with all the radiator fans on high speed. At this time, the exact operational state of the transformers at night is not definitively known. They could be largely idle supplying only a minor amount of back feed, house load power to the Project with no significant noise, or they may intermittently interact with the grid by supplying some reactive compensation when needed. It is estimated by electrical specialists involved with the Project that if reactive compensation were to occur the transformers might be active at an MVA rating that is roughly 20% of the base 54 MVA ONAN (oil natural air natural, fans off) operating mode, or 11 MVA. Consequently, for design purposes, the nighttime sound emissions from the transformer have been calculated from this 11 MVA value per the EEI algorithm (Table 4.1.2).
Table 4.1.2
Estimated 11 MVA ONAN Transformer Sound Power Level (Lw) Spectrum - Nighttime
measurement. It is expressed in units of Watts and the designation “re 1 pW”, or ‘with reference to one picoWatt’, is used by convention to distinguish power levels from pressure levels, which are measured in units of pressure, Pascals.
4.2 Inverter Sound Level
At the present time the specific inverter model for the project has not yet been completely finalized but the Power Electronics (PE) Model HEM FS4200 MU is currently anticipated. Adequate sound emissions information on this particular model is not available from the manufacturer; however, a thorough field sound survey of a slightly smaller, but otherwise similar, PE Model HEM FS3430 MU unit has been carried out at an operating solar project to quantify the unit’s sound power level.
All the significant noise emerges from the cooling air intakes on both sides of the package (three louvers in Fig. 4.2.1) and is broadband in nature (i.e. with a smooth, bland spectrum) and free from any tonal content, even when measured a few inches out. The plot below shows the A-weighted 1/3 octave band spectra measured incrementally from the vent face out to 100 m.
A-Weighted 1/3 Octave Band Frequency Spectra at Incremental Distances from Power Electronics HEM -FS3430 MU Inverter
Face of Transformer Vent
Octave Band Center Frequency, Hz
Figure 4.2.2
This figure shows the absence of any tonal character and that the overall sound level beyond about 30 m becomes obscured and dominated by minor high frequency insect and bird sounds. In Figure 4.2.3 this contamination has been mathematically removed and the overall A-weighted sound recalculated based on the spectrum below 4000 Hz.
A-Weighted 1/3 Octave Band Frequency Spectra at Incremental Distances from Power Electronics HEM -FS3430 MU Inverter At Face of Transformer Vent
Insect/Bird Sounds Deleted
1/3 Octave Band Center Frequency, Hz
4.2.3
In this case, a steadier regression in the A-weighted sound level (dashes down the right side of the chart) is evident at the further distances and the level becomes essentially insignificant (<40 dBA) at about 65 m (213 ft.).
The un-weighted spectra at progressive distances are plotted below to evaluate the potential for tones in more detail.
Unweighted 1/3 Octave Band Frequency Spectra at Incremental Distances from Power Electronics HEM -FS3430 MU Inverter
Sounds Deleted
Figure 4.2.4
Prominent tones are defined in Annex B of ANSI/ASA S12.9-2005/Part 4 as an exceedance of one 1/3 octave band above its neighboring bands by 15 dB for center frequencies between 25 and 125 Hz, inclusive, by 8 dB for center frequencies between 160 and 400 Hz, inclusive and by 5 dB for all bands above 400 Hz. In the chart above it can be seen that no tones, per this definition, are present in the measurement right at the face of the unit (top blue line) nor do any appear at 100 m away (bottom blue line), or generally anywhere in between. The measurements at 5 and 10 m do exhibit a minor prominence at 500 Hz where the differential from the neighboring bands is just over the 5 dB threshold, but this sound immediately disappears at the next test point 20 m out.
The survey measurements were obtained under ideal sunny day, calm wind conditions at a remote solar site with virtually no man-made, interfering ambient noise. The measurements were made of an isolated inverter adjacent to an access road where unobstructed visual contact could be maintainedoutto100m. Beyondabout20mbirdandinsectsounds,allabove4000Hz,dominated the audible sound level. This interference has been removed in some of the graphics above. The measurements were made using an ANSI Type 1 precision Norsonic N-140 1/3 octave band analyzer that was field calibrated before and after the survey and exhibited no drift.
The 1/1 octave band sound power level for each side of the unit (i.e. each cooling air vent) is derived in Section 3 of Table T-2281-091224-A from pressure level measurements 5, 10 and 20 m out. The overall measured sound pressure levels at these distances of 71,65 and 58 dBA display an essentially ideal 6 dB loss per doubling of distance demonstrating that the measurements are
uncontaminated by other noises. The conversion from pressure to power uses a ¼ sphere surface area because the sole sound source is a vent on the vertical side face of the package, which can only radiate in one direction. The package shell, as a whole, emits no noticeable noise. The measurements at each distance have been normalized to reverse propagation losses due to ground and air absorption per ISO 9613-23 and give the true sound power level. The maximum sound power level in each octave band of the three nominally equivalent results has been taken as the effective sound power level. Lastly, a scaling factor was added to account for the difference in electrical rating from the measured prototype (3430 kV) to the planned Grange units (4200 kV) to form the effective design sound power level spectrum shown in Table 4.2.1 below.
Table 4.2.1
Design Inverter Sound Power Level (Lw) Spectrum, Each Side
This sound power level radiates with a quarter-sphere wave front from each side of the package. For modeling purposes, a single point source with this magnitude is assumed to radiate over a hemispherical surface area, representing the sound emissions from both sides of the unit. This simplification is conservative in the sense that the sound is assumed to radiate equally in all directions, whereas, in reality, the sound emissions off the ends of the package are somewhat lower.
At night the inverters shut down as soon as the sun sets. However, if the Project interacts with the grid at night to provide reactive compensation the inverters do play a role in that along with the transformers in the substation. It is our understanding that the estimated 20% transformer MVA load that might occur in connection with reactive compensation is supplied cumulatively by all 129 inverters, such that each inverter might be operating at roughly 1% of its normal capacity. This suggests that any sound emissions from the inverters during this mode of operation will be insignificant and may be neglected.
4.3 Tracking Motors
The only other sound of any kind that may emanate from the Project is from the tracking system that could be used in some areas to intermittently tilt each panel row individually a few degrees to optimize its angle towards the sun. A mixture of static (fixed) and dynamic tilt arrays are being considered for this Project. The motors that drive this function via a worm gear are extremely
3 Acoustics – Attenuation of Sound during Propagation Outdoors, Part 2, “A General Method of Calculation,” ISO 9613-2, International Organization for Standardization, Geneva, Switzerland, 2017.
small, as shown in Figure 4.3.1, and, based on firsthand observations, make no perceptible noise when operating.
Theonlysoundisaslightcreaking/flexinginthepanelframesandarmatureslasting1or2seconds, which is only faintly audible when standing within the panel array itself. Consequently, this sound source is not significant with respect to off-site receptor locations.
4.4 Modeling Assumptions
Based on the input sound power level spectra above, the normal, sunny day sound emissions from the Project as well as its estimated nighttime sound levels have been modeled using Cadna/A® modeling software, which is essentially an automated version of ISO 9613-2 Acoustics –Attenuation of Sound during Propagation Outdoors4 .
In this instance, a mid-range, somewhat conservative ground absorption coefficient (Ag from ISO 9613-2) of 0.5 (on a scale of 0 to 1) has been used to represent the site vicinity, which mainly consists of open fields and intermittent wooded areas Normally, farm fields would be considered more acoustically absorptive and would warrant a higher coefficient than 0.5. No propagation losses have been taken for wooded areas or vegetation. There are only minor undulations in the
4 Ibid.
area topography, so flat terrain is assumed along with ISO “standard day” conditions (10 deg. C/70% RH).
4.5 Model Results
The anticipated overall A-weighted sound emissions from the Project during normal daytime operations are shown in Plots 1-1, 1-2 and 1-3 illustrating the western, central and eastern parts of the Project area, respectively. The contours are mathematically plotted out to an extremely low sound level of 35 dBA for informational purposes; however, the key result is that all residences lie outside the yellow 42 dBA contour line representing the design goal for the Project. Generally speaking, the 42 dBA contour frequently occurs within the leased land parcels and always well short of any homes. The expected Project sound level at any particular property line of interest may be determined from the plots.
The maximum predicted daytime sound level at any residence is 40 dBA at a house on the east side of CR 35 visible in the left center of Plot 1-1. All other residences and all potentially sensitive receptors within the towns of Lakeview and Russells Point are outside the 40 dBA sound contour, which is often regarded as a design threshold below which no significant disturbance can generally be expected even in extremely quiet environments. The expected sound levels in the 30’s dBA at nearly all surrounding sensitive receptors are comparable to the existing background level, meaning that any sound from the Project is likely to be inconsequential, if audible at all above the normal environmental sound level. These low levels are not accidental and generally result from a self-imposed design setback distance of at least 500 ft. between any inverter and any nonparticipating residence. This design approach essentially mitigates any noise issues proactively.
At sundown, the photovoltaic panels stop producing power and the inverters shut down. While the Project is essentially inert and out of service at night, the substation transformers remain energized and may back feed a small amount of house load to the Project and may possibly also interact with the grid to provide some reactive compensation. This function is not comparable to normal daytime operation and there would never be a need for any radiator fans. Plot 2 illustrates the potential nighttime sound emissions from the Project in the vicinity of the substation if the transformers were to supply a conservatively estimated 11 MVA of reactive compensation each to the grid This plot shows that extremely low sound levels well below a negligible level of 35 dBA are predicted at the nearest houses, meaning that the proposed substation should be largely imperceptible, if not completely inaudible, at the nearest residences at night.
5.0 Sound Emissions during Construction
In contrast to other forms of power generation, the construction phase of a solar energy facility is relatively short in duration and the activities that generate any significant noise are few. Where a fossil or wind project would require extensive earthworks and the pouring of massive concrete foundations over a period of many months, a solar energy project generally involves, from a noise
generation perspective, the installation of the mounting posts for the panel racks along with some trenching, grading and road building activities.
As illustrated in Graphic A, the Project is generally located in existing open fields some distance from the nearest residences. Consequently, much of the time construction will be occurring at locations that are hundreds or thousands of feet from any residences.
In general, it is very difficult to quantify or evaluate construction noise in a meaningful way because the noise itself is highly variable with time as individual pieces of equipment start and stop, move forward and backward and, in this case, operate in different parts of the Project area, which extends approximately 10 miles from east to west. Nevertheless, Table 5.0.1 gives representative sound levels from construction equipment associated with the different phases of construction relevant to this Project. Figures are given at the standard test distance of 50 feet5 and at 500 and 2000 feet. The 500 foot distance very generally represents the sound from construction activities as perceived at some of the closer neighboring homes. The 2000 foot distance gives the sound levels that are more representative of what might be heard in the less densely populated areas of the Project area where homes are much further from the actual construction sites.
Table 5.0.1
Typical Construction Equipment Sound Levels per the FHWA by Phase
5 U. S. Dept. of Transportation, Federal Highway Administration, Roadway Construction Noise Model User’s Guide, Table 1, Jan. 2006.
1 Not all vehicles are likely to be in simultaneous operation. Maximum level represents the highest level realistically likely at any given time. 2 Based on manufacturer’s information.
While the sound levels 50 feet from the equipment are significant, as might be expected, the sound levels at hundreds or thousands of feet away are fairly moderate and would only occur temporarily and intermittently during the construction period.
Minimal grading will be required, since the local terrain is flat enough that the panel arrays can follow the existing ground contours, but access roads will need to be constructed throughout the Project area. There is no need for concrete pouring beyond the substation area. The inverters and other electrical equipment will typically sit on gravel pads, metal skids or drop-in prefabricated concrete slabs. Concrete pouring is only likely for the transformer basins in the substation. A concrete pump truck and its servicing mixers typically generate a sound level of about 82 dBA at 50 feet6, or roughly at the boundary of the substation. At the nearest residence approximately 1,100 ft. away, this sound level would decrease to 51 dBA or less and occur only intermittently during the day: probably only for a day or two.
No significant structures are needed for the Project beyond one or two small electrical enclosures in the substation.
In addition to roads, electrical lines will need to be installed underground to connect all the various and separated sections of the project to the substation. It is likely that mobile chain-type ditch diggers will be used for trenching possibly supplemented by a hoe ram to break up any large rocks or bedrock encountered, if needed. Horizontal directional drilling (HDD) rigs will be needed to cross under roads and will likely be used extensively. The projected sound levels for the trenching phase in Table 5.0.1 would be considerably lower if HDD were assumed as the predominant trenching method, which it may be, rather than basing the sound estimate on the possible and occasional use of hoe rams. No blasting is expected to be needed for this Project.
The most common method of installing the support posts is to drive them into the ground with a small mobile driver, such as a Vermeer PD-10, that has been largely designed for this specific task. This procedure produces a rapidly repetitive, metallic impact noise, which will be unavoidably audible for some distance and may well result in some annoyance. On the other hand, this activity is reasonably short-lived and would proceed fairly quickly, only occurring for a period of days in
6 Ibid.
any one area of the site. In accordance with OAC 4906-4-09(E)(1), the noise impact from pile driving will be mitigated to some extent by limiting the time period when this activity can occur to between 10 a.m. and 5 p.m. Monday through Friday.
Once the supports are in place thousands of panels will need to be transported to the site and installed. It is currently estimated that 8500 to 9000 truck deliveries will be needed over an 18 month period, or 25 a day on average. Of course, these material deliveries will be spread out over the site area so the trucks will be using different roads in different areas at different times as construction progresses. The actual installation of the panels, i.e. attaching them to the armatures and frames is not an inherently noisy activity.
Per current regulations, construction activities in general, unless they “do not involve increases above ambient”, will be limited to “7 a.m. to 7 p.m., or until dusk when sunset occurs after 7 p.m.”
6.0 Conclusions
A field survey of the existing ambient sound levels within and near the Project area was carried out in April of 2024 to quantify the baseline environmental conditions. Seven monitoring stations distributed throughout the Project area, as it was conceived at the time, recorded continuously day and night for seven days. All statistical measures were remarkably consistent and followed the same trends at all positions despite the relatively large site area stretching about 10 miles from end to end. This indicates that the average measured level from all seven test points would be reasonably representative of any specific location within the Project area. Nevertheless, the sound levels at one relatively remote test location, Position 4 in a quiet field in the southwestern corner of the Project area, were consistently lower than the levels at the remaining monitoring station so the daytime design background sound level was taken exclusively from that location.
Current regulations state that the sound emissions from a renewable energy project cannot exceed the existing L50 background level by more than 5 dBA or an absolute level of 40 dBA, whichever is greater. The site-wide average daytime L50 from all seven test points was 40 dBA, but the average daytime L50 at Position 4 was 37 dBA; consequently, a conservative design goal of 42 dBA for Project sound at any residence has been assumed, versus the nominal regulatory limit of 40 dBA + 5, or 45 dBA. At night the Project is essentially idle and silent, but some sound is possible from the substation transformers. The average nighttime L50 of 39 dBA measured at Position 3, representing the substation area, was used to derive a nighttime regulatory limit of 44 dBA for that local area.
A noise model of the site was subsequently developed to evaluate how the Project sound levels will compare to the daytime and nighttime ambient-based design goals. The model inputs are the sound power levels of the main step-up transformers in the proposed substation and the inverters, which are distributed throughout the panel arrays. In order to quantify the maximum operational sound emissions from the Project on a sunny day, the sound power level of the substation
transformers was conservatively calculated at 98 dBA re 1 pW from its maximum expected rating of 90 MVA ONAF2, which represents a hot summer day operating scenario where the radiator fans are on in high speed mode. This is most likely a rare operating configuration occurring only during unusually hot conditions. The inverter make and model for this project will be finalized at a later stage, but a likely/representative candidate is the Power Electronics Model HEM FS4200 MU. The sound power level spectrum of this inverter model was derived from detailed field measurements of a similar Model HEM FS3430 MU unit in actual operation with a scale-up factor added to account for the size differential. An effective sound power level of 94 dBA re 1 pW was used for each unit.
The maximum daytime sound level due to Project operation is expected to be below the 42 dBA design goal at all residences. The maximum level at any house is 40 dBA and all others are lower. These predicted Project sound levels, mostly in the 30’s dBA or lower, are generally comparable to the existing daytime ambient sound level suggesting that any sound emissions from the Project will likely be inconsequential, if not inaudible, at all residences in the Project area.
Although solar energy projects are, for all intents and purposes, operational only during the day, the substation transformers remain energized at night and may potentially be used in reactive compensation mode that assists with grid stability. Using a conservative operating level of 11 MVA to derive the transformer sound emissions, extremely low sound levels in the 20’s dBA, well below the nominal design target of 44 dBA, are calculated at the nearest homes to the substation at night. Such levels are so quiet in absolute terms that no disturbance is anticipated, if the substation is even audible at all. While the inverters are minimally active during reactive compensation, the level of operation is a tiny fraction of that during normal operation; consequently, the sound emissions are expected to be negligible.
In contrast to other forms of power generation, the sound emissions from construction activities on a solar project are expected to be dramatically lower in both magnitude and duration. Some unavoidable disturbance is possible when the mounting posts are driven in, but this activity will be fairly short-lived in any particular location. Other sounds from trenching, road building and material delivery will also be brief in duration and will progress from place to place avoiding prolonged exposure at any specific location. Exposure to construction noise is also limited by regulation to the daytime hours and to an even shorter time window for piling and the possible use of hoe rams.
In general, the potential noise impacts from all aspects of the Project are expected to be minimal.
End of Report Text
Table: T-2281-091224-B
Title: Substation Transformer and Inverter Sound Power Level Deriviations
Project: Grange Solar Grazing Center
Revision: B
Date: 9/24/24 Octave Band Center Frequency, Hz
1. Main Step Up Transformers in Collector Substation, 2 Plcs.
A. Daytime - Sound Power Level Estimate Based on Max. MegaVolt Ampere (MVA) Rating - ONAF2
(1) 90
m) Based on NEMA
= NEMA Rating + Size Factor + Freq. Adj. Factors
B. Nighttime - Sound Power Level Estimate Based on Min. MegaVolt Ampere (MVA) Rating - ONAN x 20%
(1) Oil Natural Air Forced (ONAF2), All radiator fans on high speed. (2) Edison Electric Institute, "Electric Power Plant Environmental Noise Guide", 2nd Ed., BBN, 1984. (3) Oil Natural Air Natural (ONAN), All radiator fans off. Reactive compensation
at 20% of ONAN 54 MVA.
2. Evaluate Validity of Transformer Sound Power Level Algorithm
Check Calculated vs. Measured Level for Typical Solar Project Substation Transformer MVA Rating of Observed Unit at ONAF 108 MVA
Near Field Lp(1 m) Based on NEMA Rating
= NEMA Rating + Size Factor + Freq. Adj. Factors
Attenuation to Measurement Point:
Table: T-2281-091224-B
Title: Substation Transformer and Inverter Sound Power Level Deriviations
Project: Grange Solar Grazing Center
Revision: B
Date: 9/24/24
Descriptor
Octave Band Center Frequency, Hz
Measured Sound Pressure Level of Operating 108 MVA ONAF Solar Project Substation Transformer Compared to EEI Calculation
Octave Band Center Frequency, Hz
Calculated Lp at 45 m Measured Lp at 45 m
3. Power Electronics Model HEM FS4200 MU Inverter
Derive from Field Test of Power Electronics
Model HEM FS3430 MU Inverter
Sound power level derived from field measurements at operating 120 MW site
All significant noise from transformer ventilation air discharge each side of unit.
Test Conditions: Clear, Sunny, 90 deg. F, Calm Winds. Facility at Full Production
No significant background noise present except high frequency noise from birds and insects
ANSI Type 1 precision N-140 1/3 OB Frequency Analyzer, Cal. 94.0 dB at 1 kHz before and after test.
A. Measured Lp at 5 m
Remove and Normalize Propagation Losses per ISO 9613-2
Table: T-2281-091224-B
Title: Substation Transformer and Inverter Sound Power Level Deriviations
Project: Grange Solar Grazing Center
Revision: B
Date: 9/24/24
Band Center Frequency, Hz Descriptor
3. Power Electronics Model HEM FS4200 MU Inverter (Cont.)
1/4 Sphere Wavefront Area at Test Pt
Remove and Normalize Propagation Losses per ISO 9613-2
Absorption, Hs=Hr=1.5
Remove and Normalize Propagation Losses per ISO 9613-2
Scale up from 3430 to 4200 kV
Delta Lw = 10 log (4200/3430)
