Anti-soiling coating results on a 330 MW solar plant in Vietnam

BIM AC Renewables owns and maintains the BIM 1, 2 and 3 solar plants in Ninh Thuan, Vietnam: 330 MW in all. The soiling is fine dirt and dust, seasonal pollen, and now and then beeswax and bird droppings. A SolarCleano F1 robot cleans the plant about four times in the dry season, and not at all in the rainy season. The question was whether an anti-soiling coating would make those cleans easier and keep more energy between them.

• Coated strings: three complete strings of 285 panels, treated with Chemitek D-Solar Defendor (DSD), a hydrophobic anti-soiling coating.
• Control strings: three complete strings of 285 panels, cleaned with water only.
• Application: DSD was mixed into the robot’s cleaning water and injected over its brushes during a normal clean. Water beading on the glass afterwards showed the coating was on. The strings were then cleaned three more times without reapplying it.
• Period: one year. The energy tables run from May 2020 to April 2021; the report doesn’t give the date the coating went on.
• Measure: energy at the inverter, summed for each group of three strings, with both groups under the same irradiation and ambient temperature. The O&M team also tracked water use and how easily the panels cleaned.

1. Rainy season, May–Oct 20200.99%
2. Dry season, Nov 2020–Apr 20212.64%

D-Solar Defendor applied by the cleaning robot (Chemitek case).

Each figure is the sum of three strings of 285 panels. Chemitek labels both tables “before cleaning” and doesn’t say which days they cover.

The O&M team also reported:

• Faster cleaning. Soiling came off more easily, and crews no longer had to go back over stubborn spots such as bird droppings.
• Softer brushes. The robot could run softer brushes, which lowers the risk of scratching the glass.
• Less water: 15–25% less, in line with the time saved. The range depended mainly on how dirty the panels were, and partly on the skill of the robot’s operator.
• No grip problems. The coating didn’t affect the robot’s grip on the panels.

BIM AC Renewables judged the test a success and decided to apply DSD across all three plants in the next dry season.

How to read it. The energy comparison is the strongest part: three strings against three, a full year, both seasons. Three cautions. The plant has no soiling sensors, so the soiling side rests on what the crew saw. There’s no comparison of the two groups before the coating went on, which would show how closely they matched to begin with. And Chemitek reports that in laboratory tests by ÉMI-TÜV SÜD the coating raised light transmission by 1.8%, an effect the report says can’t be separated from the field result. Read +0.99% and +2.64% as the combined effect of everything the coating changed.

• Dry spells are where soiling builds. The Vietnam gain, too, was largest in the dry season. South African dry-season rates are in soiling losses in South Africa.
• Hydrophobic coatings are site-specific. In a published Northern Cape trial, a hydrophobic coating increased dust soiling, opening a performance-ratio gap of up to 5.5% against uncoated modules (du Plessis et al., 2020). DSD is hydrophobic too, so Vietnam is a reason to test it on your dust, not proof that it will work there.
• Soft water. DSD is diluted in soft water: reverse osmosis, distilled, or water treated with Water Softening Agent (Chemitek). Check yours with our cleaning-water testing.
• Robots and tractors. Here DSD went on through a robot’s brushes. Chemitek’s coatings also go on with tractor-mounted and rotary brushes. See brushes and equipment.
• Measure the soiling. A soiling station beside test and control strings shows what the coating does between cleans, which this plant couldn’t. See soiling monitoring.

Want to know whether a coating pays on your plant? Our pilots put coated strings beside matched water-cleaned strings, with a baseline before treatment, and are free for utility-scale and large C&I plants. If your crews already clean and you only need the product, order just D-Solar Defendor.