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Over the last few years, a new type of noise source has come to light as a significant environmental noise issue. Battery Energy Storage Systems (BESS) are relatively new to the US, and communities are only just starting to become aware of the noise issues they can create. BESS’s are generally large power storage facilities, often comprised of hundreds of battery units the size of shipping containers spread over many acres of land. As Battery Energy Storage Systems are often located close to residential areas, they are becoming an increasing noise problem. Due to the high noise levels produced by BESS equipment, these facilities often require implementation of substantial noise control measures to comply with city noise ordinances.
This article examines the noise issues associated with BESS facilities and the noise control measures available to ensure they comply with local noise limits.
As of writing (in March 2024), we’ve worked on noise studies for 13 BESS facilities since 2022, mostly located in Southern California and Arizona. We’re fast becoming the experts in this specific area of noise control.
Our work has involved sound measurement of equipment, noise modeling and mapping of entire BESS facilities and design and testing of noise mitigation systems for BESS equipment. One particularly challenging project, requiring every noise control measure that could be thrown at it, is presented later in this article.
The function of a BESS facility is to store and release electrical energy as needed. These battery energy storage systems typically consist of rechargeable batteries, power conversion systems, cooling systems and control electronics.
BESS facilities tend to produce high noise levels generated mostly by the compressors and fans in the electrical equipment cooling systems.
The battery units at a BESS site make up the core of the facility
Our field measurements show a wide range of noise levels generated by the cooling systems of BESS equipment. Noise levels tend to range from 70 to 92 decibels when measured 1 meter from the component. Key components and noise sources of a BESS facility include:
- Batteries: Rechargeable battery units are the core of the Battery Energy Storage System. Battery units (often 20 ft. in length and 8 ft in width and height) include cooling systems to maintain optimal operating temperature. The cooling systems use fans and condensing units which can generate noise levels up to 92 dBA at 1 m from the equipment. Fan operations are controlled by an onboard temperature control system. During hot weather, it can be expected that all fans over the entire BESS facility could operate simultaneously as the batteries charge or discharge together. This may occur at any time of day or night and cause several hours of sustained noise at a constant level. This noise is often tonal, which can mean the facility noise levels are held to a more restrictive noise limit.
- Power Conversion System (PCS): The PCS is an essential component of the BESS as it converts electricity between direct and alternating currents. There is usually a lower quantity of PCS units than batteries (typically there is one PCS unit for each group of six or eight battery units). PCS units contain cooling systems with fans that can produce significant noise, in addition to some hum or electronic noise. Our field measurements show that PCS units can generate noise levels of about 85 decibels when measured 1 m from the equipment.
- Transformers: BESS facilities may have one or two large transformers that produce a constant hum. Typical noise levels for transformers are lower than the batteries and PCS units, producing a level of about 75 decibels at 1 m from the equipment. Again, this noise is generally tonal in nature.
With the noise levels outlined above, it’s not difficult to see why these facilities can be a nuisance when located near residences. A BESS facility comprising of several hundred battery units can easily produce noise levels over 70 decibels at residences located 100 ft from the site. With typical city noise ordinances requiring compliance with 45 dBA noise limits at night, mitigating these facilities can be a challenge! See below for a case study on one of the more challenging BESS facilities we’ve worked on.
Battery Energy Storage System Noise Case Study
In July, 2022, NMS was retained to conduct a detailed noise study for a new Battery Energy Storage Facility near Los Angeles (for confidentiality purposes, no identifying client or site information is included in this article). The facility consisted of over 300 batteries, over 60 PCS units and two transformers covering about 6 acres of land. Construction of the BESS facility had already started and it had become apparent that potential noise issues had been overlooked during the planning process. Our client, one of the leading renewable energy solutions suppliers in the US, had previously conducted a basic noise analysis for the site but needed help from a firm that could provide more expertise.
The site was adjacent to residences, some with back yards less than 30 feet from the nearest BESS battery units. The previous study had shown noise levels might be 75 dBA at the nearest residences but was considered unreliable as it had not taken into account some factors that could affect noise. The client needed a more detailed noise model and called us for help. With the client being held to a nighttime noise limit of 45 dBA at the residences, some very effective mitigation would be needed.
After discussions with the client, we agreed on a scope of work that would include:
- Specific noise measurements of the battery units and PCS units to obtain data that could be used in a detailed noise model of the BESS facility. The noise survey would need to measure the sound level, spectral characteristics and directivity of the noise sources.
- Ambient sound measurements at the project site to determine existing background noise levels and determine whether any ambient noise correction to the noise limit could be applied.
- Construction of a detailed 3D model of the site. The model was to include all equipment with the source spectrum and directivity characteristics determined as part of our measurements. We would also need to account for sound reflections within the site and existing noise barriers in the area.
- Design and testing of noise control measures for the battery and PCS units, and re-modelling of the site to account for various mitigation scenarios.
- Post-construction noise level measurements to verify compliance with the City’s noise limits.
Our detailed noise measurements of a battery unit included obtaining directivity and spectral data.
Since construction was already underway, we needed to start work immediately. The urgency was due to that fact that our client needed to immediately understand the noise issue they were going to have to deal with. Any required noise control measures would need to be designed, constructed and installed in time for the facility’s commissioning the following year.
After conducting noise measurements of the equipment and constructing the model, we confirmed that the noise levels would be above 70 dBA at the nearest residences if no environmental noise control measures were implemented. We also determined that the battery fan noise was tonal in character. This meant a tonal noise correction of 5 dBA would need to be applied to the City’s noise limit and therefore a noise limit of 40 dBA would apply at the residences if the tone could not be removed.
The BESS facility site was in a relatively noisy area, with two freeways and a rail yard located within a half mile of it. Unfortunately, even with these noise sources nearby, the ambient background noise level was still not high enough at night to permit an increase to the noise limit.
Our work resulted in 45 iterations of noise modelling for various equipment layouts and mitigation scenarios. We worked closely with our client to discuss potential solutions before performing each modelling iteration. The following images represent the modeling results of the initial unmitigated scenario, and the fully mitigated site.
Predicted noise levels of BESS facility (unmitigated scenario)
Predicted noise levels of BESS facility after incorporating sound control measures
One key noise control solution was the installation of custom-designed silencers on the battery fan discharge and PCS fan intakes. We brought in a local noise control application firm to work on the project, who constructed prototype silencers for the batteries and PCS units. We performed tests to verify their performance was consistent with our predictions before the same firm constructed silencers for all batteries and PCS units at the site.
The final noise control measures that were implemented were:
- Re-orientation of equipment to direct sound away from the residences. The original site layout had batteries oriented with fans facing some residences. With fans located only on one end of the battery enclosure, this equipment's noise was highly directional. Using noise modelling, we were able to quantify the noise reduction that would be achieved by rotating equipment 90 degrees and demonstrate the efficacy of this solution.
- Installation of a 20-foot-high sound wall between the BESS equipment and the nearest residences. The wall installed was a Sound Fighter Systems SonaGuard barrier, which is a high-performance acoustically absorptive wall.
- Reduction in battery fan speed. Working closely with the client and battery manufacturer, we performed multiple field noise tests to determine the optimal fan speed for achieving the City’s noise limit while maintaining appropriate airflow for cooling requirements. We determined that the battery fans would need to operate at 50% of the maximum speed to achieve the noise limit. This had the added benefit of making the battery fan tone less prominent.
- Custom silencers fitted on all battery fans and PCS intakes and vents. Battery fan silencers consisted of a duct lined with 2-inch acoustically absorptive foam and an acoustic louver mounted on the end. PCS units needed the same type of silencer on the fan intakes in addition to a long duct silencer around the top of the unit into which the vents discharged.
- Installation of acoustically absorbent foam lining the inside PCS air intake cavities. This material was installed to reduce the buildup of sound inside the cavity and further lower the noise escaping through the intake.
- Balancing noise emissions of equipment to mask the battery fan tone. Our noise measurements and modelling revealed that the tone produced by the battery fans could be effectively masked by the broadband PCS intake and vent noise so long as this source was not reduced in level too much. By effectively masking the tone, the 5 dB tonal correction to the City’s noise limit could be eliminated. This resulted in a noise limit of 45 dBA at the residences (a tonal noise limit of 40 dBA would probably have been impossible to achieve on this project).
Mitigation included a 20-foot-high sound wall and ducted acoustic louvers on the batteries
Silencers on the PCS units allowed enough broadband noise through them to mask the tone produced by battery unit fans
With the above measures installed, the noise levels at the site were reduced by nearly 30 dBA. During the commissioning of the facility in January 2024, we conducted week-long noise compliance monitoring at four residential locations. Verification of noise limit compliance was a challenge in itself. To determine compliance, we needed to analyze sound data obtained during a limited window between 2 am and 6 am, when background noise was lowest. We needed to demonstrate that any noise measured above 45 dBA was not caused by the BESS equipment. Using evidence from a week of data collected with advanced data-logging sound level meters, as well as some early morning site visits, it was possible to verify that the mitigation was performing as designed. We were able to demonstrate the facility complied with the City’s 45 dBA nighttime noise requirement.
If you want further advice on battery storage facility noise issues or have already decided to take action and need a noise output tested and analyzed, contact Noise Monitoring Services today on (323) 546-9902. As a company of engineers with advanced degrees in acoustical engineering, we can offer sound measurement and consulting for any noise issue.