Battery energy storage system, where to start controlling "noise"?

Ethan Brush, a technical expert at noise and acoustic services company Acentech, recently released a research report. In his report, he pointed out that as land becomes increasingly scarce, more and more battery energy storage systems are deployed in densely populated residential areas, which has led to increasing attention to the noise problem of battery energy storage systems.

As battery energy storage systems become more popular and begin to be deployed in densely populated areas, the scarcity of land resources makes this trend inevitable. Therefore, the noise problem of battery energy storage systems and corresponding control measures have become increasingly important.

In densely populated areas such as Europe, the noise problem of battery energy storage systems is particularly prominent, and it is also gradually intensifying in countries and regions such as the United States and Australia. In order to meet this challenge, battery energy storage system manufacturers need to pay more attention to acoustic design to provide battery energy storage systems that meet the living needs of residents.

Source of noise

Ø Cooling system

Battery energy storage systems, like other electronic devices, operate best and safer at suitable temperatures and humidity. To this end, various air or liquid cooling systems are required. These systems often generate noise, which originates from vents, fans, and pumps, and this noise is usually constant.

Ø Energy Storage PCS

Energy storage PCS is responsible for converting the DC power provided by the battery to AC power for power supply. During the charging process, the inverter rectifies the AC power to DC power. During this power conversion process, a certain degree of energy is converted into heat, so cooling is required to prevent overheating, usually through fans, which inevitably generates noise.

The process of converting DC power to AC power involves high-speed switching to change the polarity (or direction of current flow). In the United States, the frequency of AC power is 60Hz, so the high-speed switching is operated twice in one second. This process produces a sound that is twice the power supply frequency (120Hz), and also produces other harmonics (such as 240Hz, 360Hz, 480Hz or higher frequencies).

Many countries and regions have an AC frequency of 50Hz, so the harmonics it produces are slightly different (100Hz, 200Hz, 300Hz, 400Hz). These sounds usually have a buzzing characteristic. These noises are often more noticeable in environments with high background noise, causing annoyance to people around them.

There are three sources of noise inside the transformer: core noise, coil noise, and fan noise. Core and coil noise are caused by magnetic forces, and similar to inverters, transformers also produce 120Hz or 100Hz sounds and their harmonics. The third type of noise comes from the cooling fan outside the transformer, although some transformers use heat sinks instead of fans, which is a quieter option.

Mitigation measures

Ø Learn more about noise standards

Globally, countries and regions generally follow clear noise regulations aimed at limiting noise disturbances from industrial facilities to residential areas. These regulations vary in detail and clarity, with some specifying specific noise emission standards and conditions, while others only specify decibel limits.

In some regions, noise regulations related to battery energy storage systems may not yet be established. Nevertheless, developers of battery energy storage systems should also fully consider the impact on the surrounding environment and the possible negative reactions of residents, even if the law does not explicitly require noise reduction.

For example, the standards of the National Electrical Manufacturers Association (NEMA) in the United States clearly define the noise levels of electrical equipment when they meet the NEMA rating.

In addition, the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE) have also developed standards for the sound output of various types of electrical equipment. Similarly, the Air Conditioning, Heating and Refrigeration Institute (AHRI), the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the American National Standards Institute (ANSI), and the International Standards Organization (ISO) have also published standards for refrigeration systems.

These standards not only provide specifications for the energy storage industry, but can also be combined with actual sound measurement data of battery energy storage systems to more comprehensively evaluate and manage the noise of battery energy storage systems.

Ø Sound modeling of battery energy storage systems

During the design phase of battery energy storage systems, acoustic consultants and technical experts need to accurately identify and determine the main sound sources in various equipment. Equipment suppliers may provide detailed data on product noise emissions. By using this data to build an acoustic model, the sound level generated by the battery energy storage system in its surrounding environment (such as a residential area) can be simulated.

The acoustic model not only includes the sound sources of each device of the battery energy storage system, but also takes into account the surrounding terrain characteristics. The final modeling evaluation results will be compared with the noise limit standards applicable to the engineering project.

Not all battery energy storage system equipment manufacturers provide noise data for their products. In a battery energy storage system, various equipment may come from multiple different suppliers, and the lack of certain information undoubtedly increases the difficulty of accurately modeling the noise level of the energy storage system.

Ø Measure ambient sound levels

Many noise regulations (such as those of the Massachusetts Department of Environmental Protection) stipulate that the sound levels of industrial facilities must not exceed certain thresholds of environmental conditions. These ambient sound levels need to be determined before the industrial facility is installed or when the facility is completely shut down.

Usually, ambient sound is measured for a week or more in relatively quiet weather conditions to obtain a comprehensive characterization of the on-site sound environment. Because noise limits are related to on-site environmental conditions, quiet areas require lower limits than noisy areas.

Noise regulations in other areas often stipulate that there is a fixed upper limit on the noise generated by battery energy storage systems. This may not require verification on site, but it is usually recommended to use ambient noise measurement methods to help combine the results of modeling work with existing environmental scenarios.

Control noise

Noise control of battery energy storage systems is a continuous improvement process. If the design and layout of noise-generating equipment exceeds the noise limits associated with the engineering project, the acoustic consultant needs to design new solutions to reduce noise levels. By considering the source/path/receiver model, effective solutions to noise problems can be found.

System operators can integrate various mitigation measures into the acoustic model of the facility and the surrounding area. Noise can only be effectively controlled if the predicted sound levels meet the noise standards associated with the battery energy storage system.

Once the battery energy storage system is installed, the sound levels need to be measured to verify compliance with the noise standards for the site. This is usually done at night when the noise level is lowest in the environment. It may be necessary to start and shut down all the equipment of the battery energy storage system for a period of time to fully evaluate its overall noise characteristics.

For the equipment used to measure environmental sound, it needs to comply with international standard regulations on the accuracy of the measurement equipment. These devices are classified according to aspects such as their accuracy and performance.