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DOE Develops ‘Self-Cleaning’ Coating

Monday, February 10, 2014

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A low-cost, transparent coating designed to combat soiling on solar panels is in development at the Department of Energy’s Oak Ridge National Laboratory.

Soiling—the accumulation of dust and sand—is one of the main efficiency drags for solar power plants, capable of reducing reflectivity by up to 50 percent in 14 days, according to an announcement on the research.

Oak Ridge National Laboratory

Oak Ridge National Laboratory / Flickr

Scientists at the DOE’s largest multi-program science and energy laboratory, Oak Ridge National Laboratory in Oak Ridge, TN, are developing a self-cleaning coating for solar panels.

The scientists say the coating will help solar reflectors and photovoltaic cells optimize energy efficiency, reduce operating and maintenance costs, and avert negative environmental impacts.

Currently, solar power plants must manually clean and brush panels with deionized water and detergent. This labor-intensive routine significantly raises operating and maintenance costs, which is then reflected in the cost of solar energy for consumers, the scientists note.

The research is sponsored by the DOE’s Energy Efficiency and Renewable Energy SunShot Concentrating Solar Power Program. The coating is being developed by members of the ORNL Energy and Transportation Science Division, including Scott Hunter, Bart Smith, George Polyzos, and Daniel Schaeffer.

Superhydrophobic Coating

The coating is based on a superhydrophobic technology developed at ORNL that has been shown to effectively repel viscous liquids, water, and most solid particles.

Unlike other superhydrophobic approaches that use high-cost vacuum deposition and chemical etching to nano-engineer desired surfaces, however, ORNL’s coatings are deposited by conventional painting and spraying methods using a mixture of organics and particles, the team says.

Superhydrophobic coating

Oak Ridge National Laboratory / Flickr

The coating is based on superhydrophobic technology developed at ORNL that has been shown to repel water, viscous liquids, and most solid particles.

In addition to being low cost, these methods are easily used in the field during repairs and retrofitting, the researchers say.

Hurdles in Development

The researchers admit to challenges in successfully developing a transparent, anti-soiling coating.

The coating must be extremely superhydrophobic to minimize the need for occasional cleaning. It must also have minimal (or even zero) effect on the transmission and scattering of solar radiation between the wavelengths of 250 to 3,000 nm.

"To meet these requirements, the coating must be no more than a few hundred nanometers thick, and the embedded particles must be considerably smaller," the team said.

The extremely thin coating must also be durable under environmental exposure, including UV radiation and sand erosion, and be compliant under the U.S. Environmental Protection Agency Clean Air Act emission standards—which limit the selection and combination of particles and organics that can be used effectively, the researchers add.

Process of Coating Design

The researchers say they have experimented with a variety of Clean Air Act–compliant organics and silica particles of different sizes.

They have discovered a particular formulation combining organic compounds with silica particles, which are dispersed in two sizes to enhance area coverage of particles within the coating.

Solar farm

U.S. Department of Agriculture / Flickr

The scientists say the coating will help solar reflectors and photovoltaic cells to optimize energy efficiency while lowering operating and maintenance costs associated with soiling.

The anti-soiling coating also exhibited "excellent superhydrophobic properties, losing less than 0.3 percent of transparency over the entire solar radiation wavelength range," according to the researchers.

When exposed to several hundred hours of accelerated UV radiation and 100 hours of salt fog exposure, the coating exhibited no degradation in superhydrophobic or optical transmission properties, the team reports.

Also, when glass slides with the coating were exposed to sand and dust in a custom-made wind tunnel, the particles did not adhere to the coated surface—showing great potential for its use in harsh environmental conditions, according to the researchers.

Future Applications

Throughout 2014, the team says it will be optimizing the coating and performing accelerated exposure tests. The researchers will also begin development on a scalable coating technique and perform small-scale field testing.

In addition to anti-soiling coating for solar applications, ORNL researchers note they are using their superhydrophobicity expertise to develop anti-soiling cool roof coatings, as well as anti-icing and anti-condensation coatings for air conditioning and evaporative cooling applications, respectively.

Oak Ridge National Laboratory in Oak Ridge, TN, is the DOE’s largest multi-program science and energy laboratory, with scientific and technical capabilities from basic to applied research. The lab’s mission is to “deliver scientific discoveries and technical breakthroughs that will accelerate the development and deployment of solutions in clean energy and global security, and in doing so create economic opportunity for the nation.”

   

Tagged categories: Coating chemistry; Oak Ridge National Laboratory; Photovoltaic coatings; Research; Self-cleaning coatings; Solar; Solar energy; U.S. Department of Energy

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