The test and how it was set up
Green Energy Park, a solar research platform in Benguerir, Morocco, ran this test with Chemitek, and the results were published in the peer-reviewed journal Heliyon in 2023. The authors are Abderrazzak Elamim, Said Elhamaoui, Khalil Tijani, Aboubakr Benazzouz and Abdellatif Ghennioui of Green Energy Park, with Cesar Martins, Bruno Queiroz and Clara Faria of Chemitek. Chemitek developed and applied the products.
Five identical strings of seven monocrystalline PERC modules (2.345 kWp each, 11.725 kWp in total) were fixed at 32°, facing south, each on its own inverter.
| String | Treatment | Cumulative energy vs the water-cleaned string, end of dry season |
|---|---|---|
| Uncleaned | None | −6.94% |
| Water-cleaned | Tap water and a brush | Reference |
| Solar Wash Protect (SWP) | Cleaning solution at 1:50: spray, brush, rinse | +3.22% |
| D-Solar Defendor (DSD) | Hydrophobic coating, 1:1,000 in distilled water, soft brush | +2.01% |
| Industrial Glass Protect (IGP) | Ready-to-use hydrophobic coating, 5–10 mL/m² on degreased glass | +1.89% |
The test covered two seasons. In the dry-season cleaning period, the cleaned strings were washed on 12 and 26 August, 10 September, 10 October and 10 November 2021. Through the rainy season, from November to April 2022, only rain cleaned them. The paper describes nine months of operation; its monitoring data run from 12 August 2021 to 10 April 2022.
Performance indicators followed IEC 61724, with continuous DC monitoring, a meteorological station on site, and I–V curves traced after the cleans in the first 60 days, corrected to standard test conditions under IEC 60891.
What the dust was. X-ray fluorescence of local dust found calcium oxide at 25.55–36.47%, silica at 17.11–31.83% and phosphorus pentoxide at 15.85–23.01%. The authors trace the calcite, dolomite, phosphorus and quartz to local industry and construction.
Results
- Cleaning period (first three months): the treated strings averaged around 10% higher efficiency than the uncleaned string.
- Non-cleaning period: around 5%, after six months of exposure.
- Against water-only cleaning: a cumulative energy gain averaging about 3%, led by SWP (see the table). By the end of the dry season, the uncleaned string had fallen 6.94% behind the water-cleaned one.
- Seasons change the ranking: SWP did best in the dry season. In the rainy months of March and April, IGP overtook SWP and DSD by a small margin.
- Water and time: the paper reports that SWP used 50% less water. On the day-30 clean the SWP string needed 2.25 L, half the 4.5 L per string used on the water-only clean at day 15; the water-cleaned string used 4 L that day. Cleaning time fell from 12 minutes with water to 10 with SWP (Green Energy Park report).
Mind the baselines. The 10% and 5% compare the treated strings with a string that was never cleaned. The 3% compares them with water cleaning, and is the fairer measure for a plant that already washes.
What this means for a South African plant
- Dry spells. South Africa gets about 490 mm of rain a year, about half the world average (WWF-SA), and soiling builds when it doesn’t rain. South African dry-season rates are in soiling losses in South Africa.
- Rain changes the answer. Here the hydrophobic IGP did best in the rainiest months, and SWP in the dry ones. In a published Northern Cape trial, a hydrophobic coating increased dust soiling (du Plessis et al., 2020). Coatings are site-specific.
- Dust. This dust was rich in calcium, as limestone and cement dust are, which makes the result relevant to plants near cement works and quarries.
- Water. SWP’s 50% saving comes from the first two monitored cleans, so treat it as indicative and measure it with your own water.
- Method. Our pilots follow the same logic at a smaller scale: treated strings beside matched controls, under the same sun. Soiling monitoring then tracks the seasons.
