The site and the test
Santiago Solar is a 115 MWp plant on single-axis trackers near Santiago, Chile, owned and operated by EDF Energies Nouvelles and Marubeni. The soiling is fine dirt and sand dust. The plant was cleaned four to six times a year with a tractor-mounted articulated brush, alternating one wet clean with two dry ones, and frequent sandstorms decided how many cleans a year needed. The question was whether an anti-soiling coating would make those cleans easier and keep more energy between them.
- Coated strings: three complete strings treated with Chemitek D-Solar Defendor (DSD), a hydrophobic anti-soiling coating.
- Control strings: three complete strings cleaned with water only.
- Application: during a normal wet clean. DSD was mixed into the cleaning water and injected over the brush, and water beading on the glass afterwards confirmed the coating was on.
- Period: six months, October 2020 to March 2021.
- Measure: energy at the inverter, summed for each group of three strings, with both groups under the same sun and temperature. The cleaning team also reported how fast and how well the dry cleans went. The plant has no soiling sensors, so the soiling itself was judged by eye.
Results
| Measure | Result |
|---|---|
| Energy, three water-cleaned strings, Oct 2020 – Mar 2021 | 108,170 kWh |
| Energy, three coated strings, same period | 110,777 kWh |
| Difference | +2,607 kWh (+2.41%) |
| Average tractor speed on the two dry cleans after coating | 1.35 km/h, up from 1.1 km/h |
Chemitek labels the energy table “before cleaning”; the heading above it gives the six-month period. The report doesn’t say whether the faster tractor speed applied to the coated strings only.
After coating, the plant ran two dry cleans. The team reported removing more soiling with more ease, so it could drive the brush faster, and the coated panels showed no visible encrusted dust afterwards. Between cleans, the coated strings looked less soiled. EDF Energies Nouvelles and Marubeni judged the test a success and decided to apply DSD at their plants from the next clean.
How to read it. The energy comparison is sound as far as it goes: three strings against three, six months, same conditions. Three cautions. There is no comparison of the two groups before the coating went on. Without soiling sensors, the soiling side rests on what the crew saw. And Chemitek reports that in ÉMI-TÜV SÜD laboratory tests DSD raised light transmission by 1.8%, which the report says can’t be separated from the field result. Read +2.41% as everything the coating changed, combined.
What this means for a South African plant
- Trackers and tractor brushes are common here. Tractor-mounted rigs are the usual kit on South African plants that clean; see soiling losses in South Africa. A coating that lets the tractor drive faster saves time on every pass. See brushes and equipment.
- Dry cleans benefit too. Two of every three cleans here were dry, and the coating still helped. That matters where water is scarce; see water-scarce cleaning.
- Pick the coating for the climate. Hydrophobic coatings are site-specific: in a published Northern Cape trial, one increased dust soiling (du Plessis et al., 2020). Chemitek now positions D-Solar Defendor for very rainy sites, steep tilts, snow and ice, and recommends Solar Wash Protect or Antistatic Solar Armor for most plants. See our anti-soiling coatings.
- 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 untreated strings, with a baseline before treatment, and are free for utility-scale and large C&I plants.
