The site and the test
Soleden Power maintains a commercial rooftop solar plant of about 300 kWp in India, for an owner it doesn’t name. The roof sits in an industrial complex, and the soiling is greasy fumes from the surrounding factories, plus fine dirt and dust. The plant is cleaned by hand with brushes, about once a month in the dry season, and not at all in the rainy season. The test set out to measure two things: the energy gain, and how easily the soiling came off and stayed off.
- Strings: two, of six panels each.
- Treated string: cleaned and protected with Chemitek Solar Wash Protect (SWP), applied by hand: diluted, sprayed on, brushed thoroughly and rinsed to remove the dirt and any excess product.
- Control string: cleaned with water only, as the baseline.
- Duration: one month, according to the report. Its daily table covers 16 consecutive days, from 22 December 2022 to 6 January 2023.
- Measure: each string’s energy at the inverter, compared day by day. Both strings saw the same irradiation and ambient temperature.
Results: ahead on every day
- 5.05%22 Dec
- 4.93%23
- 4.99%24
- 4.82%25
- 5.12%26
- 5.09%27
- 4.78%28
- 4.92%29
- 5.07%30
- 5.79%31
- 5.7%1 Jan
- 5.24%2
- 5.51%3
- 5.36%4
- 4.7%5
- 5.28%6
Ahead on every one of the 16 days, 22 December 2022 to 6 January 2023 (Chemitek case).
The 16-day average is +5.15%, which Chemitek reports as +5.1%. Chemitek’s table prints the January dates as 2022; they follow 31 December 2022, so they are January 2023.
During the clean, the O&M team found the soiling came off faster and more easily than on the water-only string. Water use fell sharply, because water was needed only to dilute the product and rinse. After the test, Soleden moved all its cleaning to Solar Wash Protect.
How to read it. This is a small test: 12 panels on a roof of about 300 kWp, over 16 published days. The gap was about 5% from the first day in the table and a little higher in the second week, so most of it was there from the start. That points to SWP lifting more of the greasy film than water did, rather than a gap that built up as the water-cleaned string re-soiled. But the report has no comparison of the two strings before cleaning, so part of the gap could be a difference between the strings themselves. Read +5.1% as a clear signal on one pair of strings, not as a figure for the whole roof.
What this means for a South African plant
- Industrial roofs. C&I roofs on industrial estates can collect fumes as well as dust, as this one did. A film that water doesn’t lift keeps costing energy after every water-only clean. Identify the deposit before you choose the method: see our soiling assessment.
- Water. SWP needed water only to dilute and rinse. South Africa gets about 490 mm of rain a year, about half the world average (WWF-SA), so a clean that uses less water counts. See low-water cleaning.
- Warranty. Solar Wash Protect carries letters of conformity from module makers, valid when it is used within each maker’s cleaning conditions. We check your modules’ manual before any product touches the glass; see cleaning and your module warranty.
- Test design. A pilot on a large C&I roof uses more than one string on each side, matched for position and exposure, with a baseline recorded before the first treatment.
Running a large C&I roof? Our pilots measure treated strings against matched controls, and are free for utility-scale and large C&I plants. If your facilities team or cleaning contractor already washes the array, order just Solar Wash Protect with our dilution advice.
