A Free-Market Energy Blog

Solar Power Noise and Dust: For the Record

By Robert Bradley Jr. -- March 8, 2022

“While quiet transformers and inverters exist [to reduce pure-tone transformer noise], due to premium cost, it is generally not a specification point the solar facility designers are willing to consider…. There is a real need for acoustic evaluation and noise control with respect to nighttime operations of solar energy components.”

“Clark County regulators have substantiated 37 of the 49 complaints they have received about the project from the public. ‘Can’t breathe from all the dust coming off the solar field!!!!!!,’ one person wrote to the county on Sept. 15. ‘Someone need to take care of this it happens way to often.’”

Anti-fossil-fuel environmentalists, when pressed, will state that all energy choices have environmental drawbacks and tradeoffs. But they do not take this seriously when it comes to wind and solar power, which have infrastructure requirements (including land and power lines) that are a multiple of other choices on a per kWh basis.

Solar “farms” cause a variety of problems, one project near where I now currently live involving flooding issues. Here are two more in the news: one concerning noise and the other with dust.

  1. Solar Noise

I recently came across an article from the acoustical company ACENTECH (June 2020), titled “Yes, Solar Farms Can Produce Noise!“. Excerpts follow:

At first look, one would think that a solar [Photovoltaic (PV)] facility generates NO sound. There are no large moving parts like the large blades of a wind turbine and no explosive processes like gas combustion.

The most visible part of the solar facility is the large solar panels and these indeed produce NO sound. However, there is noise-generating equipment at solar facilities and they are inconspicuously sited on small concrete pads.

Like any other energy-generating or industrial facility, the solar farm must be designed and operated to be compliant with state and municipal noise codes. Noise limits have various formulations, but those here in the Commonwealth of Massachusetts, are a good example of limits that at the same time, can be both routine and challenging to achieve by a solar facility.

The Mass noise code includes two elements. The first is that no source of sound shall be 10 dB greater than the existing background sound levels. The second is that no source of sound shall create a “Pure Tone”.

The first part of the Mass noise code referred to as the “broadband noise limit” will be easy to achieve by a properly designed solar energy facility. In other States or municipalities this limit may be relative (as Massachusetts) or absolute limit as it is for most municipalities.

The relative-type limit may be more restrictive if the solar facility components operate through the night. In this case, the noise limit will be based on background noise during the quietest period of the night, typically 3:00 am. For example, a solar farm operating in a quiet rural town can have a background sound level as low as 25 to 30 dBA. In Massachusetts, the sound level limit may then be 35 to 40 dBA. Achieving 35 dBA sound limit will have some challenges.

How is this tonal sound produced? Let’s start at the solar panels (also called PV modules). They produce direct current (DC) electrical power which is good when storing energy within a DC battery. However, in order to transfer this electrical power to the local grid, the DC power must be converted to alternating-current (AC) power. This conversion process is done by an “Inverter”.  The process of converting DC into AC power requires very fast switches which change the polarity (or direction of electrical flow). 

Since AC power cycles 60 times per second (or 60 hertz), the switches must activate twice per electrical cycle. This process produces tonal sound at twice electrical line frequency (120 hertz) and its harmonics (240, 360, 480 hertz and higher).The transformers in the solar facility are used to step-up the voltage for easier transmission into the local electrical grid. There are three sources of noise from within the transformer: (1) core noise, (2) coil noise, and (3) fan noise.

The core and coil noise are caused by electromagnetic forces which occur two times for every cycle of AC power. Like the inverters, this results in 120 hertz primary sound source, along with harmonics as noted above. The third source of sound is a cooling fan(s) mounted outside the transformer and usually directed across the fins of a heat sink. While the cooling fans can be the most significant source of overall broadband A-weighted sound, a warning from a 1977 BBN report is worth echoing here:

“…it is almost always the pure-tone transformer noise and not the broadband fan noise that is objectionable.  Therefore, fan noise is unimportant if human response to transformer noise is the only concern.  However, if the installation must meet objective noise limits at the property line, which may be stated in the form of maximum permissible octave band sound pressure level or maximum A-weighted values, fan noise must be considered.”

While quiet transformers and inverters exist, due to premium cost, it is generally not a specification point the solar facility designers are willing to consider. Therefore, the second line of noise control would be noise barriers.

One important matter to be aware of when using a noise barrier is that the primary sound from inverters and transformers is low frequency which results in sound with a longer wavelength. Noise barriers are less effective for longer wavelengths and then require a larger wall than might normally be expected.

The most aggressive sound control treatment for transformers and inverters is a full enclosure or even a building. Due to the heat generated by both devices, a forced-air ventilation system is almost always needed. The fans used in these cooling systems may be louder on an A-weighted basis than the electrical side of the hardware. This is something to keep in mind during concept design.

One thing in favor of solar facilities is that most of them only operate during the day. Some facilities with battery storage components could result in transformer and inverter operation during the night and that changes everything.

There is a real need for acoustic evaluation and noise control with respect to nighttime operations of solar energy components. However, even then, I am confident that a solar facility can be designed to be compliant with municipal and State noise codes. More importantly, taking siting and noise control together, I believe that solar energy facilities can be designed to be inaudible, but this will not happen by accident.

2. Solar Dust

I ran across this article in the Las Vegas Review-Journal (November 20, 2021), “Boulder City solar farm fined nearly $220k for air quality violations.” Blake Apgar tells the story:

A Boulder City solar farm construction site has racked up hundreds of thousands of dollars in fines this year for air quality violations, according to Clark County regulators.

Since April, the county has fined Rosendin Electric nearly $220,000 for failing to control dust during construction of a roughly 1,000-acre solar farm off of Interstate 11. In all but one of the eight instances, Rosendin has not contested the fines.

The county says the company is putting its business interests ahead of complying with air-quality standards.

“Well, from our perspective, they responded by continuing to be out of compliance and making business decisions that are based on how quickly they can get the project done, as opposed to implementing the best practices that are required in our air quality regulations,” said Marci Henson, director of Clark County’s department of environment and sustainability.

Those dust control efforts include keeping the ground wet to prevent dust from blowing away…. Henson said her department estimates anywhere from 40 tons to 70 tons of excess dust has blown from the Townsite Solar Garden project. Dust clouds can cause breathing issues and are particularly challenging for people with existing respiratory conditions, Henson said….

The company said it uses multiple approaches to control dust clouds in the area. To date, Rosendin has spent $3 million on dust control, including using six full-time employees to manage dust at the site, the company said….

Clark County regulators have substantiated 37 of the 49 complaints they have received about the project from the public.

“Can’t breathe from all the dust coming off the solar field!!!!!!,” one person wrote to the county on Sept. 15. “Someone need to take care of this it happens way to often.” … The most recent violations happened in September….

At the July hearing with the county, David Dean, a dust management program supervisor for the county, said the company has faced similar challenges with dust in the area, but the location of this project has garnered more attention.

He said the root of the problem is Rosendin’s construction plan and process. If the company wanted to correct the problem, it wouldn’t grade off more soil than it could control, he said.

“And that’s their business model. They have a set time limit to finish this in and they’re going to finish it,” Dean said. “And if it means get environmental issues or fines, then they’re going to do it, because it’s the cost of doing business.”

He said the company doesn’t want to change how it does business, so the problems will continue.

Rick Shaffer, division manager for Rosendin Renewable Energy Group, said at the hearing that it’s not the company’s business plan that has caused problems. It’s the rigid terms of the company’s contract, which could cost Rosendin nearly $150,000 per day if it were late, he said.

“We aren’t afforded, unfortunately, the luxury and the time to construct it in the manner that you are suggesting, which is the right way to do it, but we can’t because of our contract and our scheduling and our time,” he said.

A spokesman for the county’s department of environment and sustainability said officials are leaving all options on the table, including dust permit suspension if Rosendin continues to “neglect its duties” to control the dust and protect air quality.

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