Will cleaning chemicals void my panel warranty? Letters of conformity explained

Can cleaning void a solar panel warranty? Module makers expect their modules to be cleaned. LONGi’s O&M manual, for example, asks for cleaning at least every 20–30 days in dry areas. What the makers control is how: which products, what water, how much pressure, which brushes and who does the work.

So the risk isn’t cleaning. It’s cleaning outside the maker’s instructions: the wrong chemistry, water outside the limits, too much pressure, or a brush the maker warns against. For chemicals, the maker’s written approval takes the form of a letter of conformity.

A letter of conformity is a module maker’s written statement that a named cleaning product, or a cleaning method using it, may be used on its modules. Chemitek collects these letters product by product and publishes the count for each.

What a letter does:

• records the module maker’s approval of a named product for use on its modules;
• sometimes names the module series it covers;
• sets conditions for use.

What a letter does not do:

• It is not a warranty guarantee. The sample LONGi letter says so, and lists its conditions: wet cleaning only, a pressure limit, a specified brush type and trained staff.
• It doesn’t cover products it doesn’t name. A letter for Solar Wash Protect says nothing about another cleaner, or about another Chemitek product.
• It may be limited or preliminary. The Canadian Solar letter on file for Solar Wash Protect, dated 26 May 2020, approves the cleaning method with two module series (CS6K-P and CS6U-P) and states that the module warranty remains valid. It also calls itself a preliminary approval, with final approval subject to further testing. If you run Canadian Solar modules, ask for the current letter for your series.

1. Solar Wash Protect18
2. Antistatic Solar Armor 2.017
3. Inorganic Removal Agent8
4. Lichen Removal Agent4
5. D-Solar Defendor3
6. Water Softening Agent3
7. Metal Oxides Removal Agent3
8. Paint Removal Agent3
9. Drone Solar Cleaning Agent3

Solar Wash Protect: the 18 makers

• Aiko
• Astronergy
• Canadian Solar
• CSun
• EVVO
• First Solar
• GCL
• JA Solar
• Jinko
• LONGi
• ReneSola
• Risen
• Runergy
• Seraphim
• Suntech
• Trina
• Ureco
• Znshine

Inorganic Removal Agent: the 8 makers

• Canadian Solar
• JA Solar
• Jinko
• LONGi
• Risen
• Runergy
• Suntech
• Trina

Counts from Chemitek, September 2026. Industrial Glass Protect is not counted; JA Solar’s letter names it. The makers for the other products are listed on request.

Counts from Chemitek (September 2026). JA Solar’s 2025 letter approves ten named Chemitek products for its modules: Solar Wash Protect, Antistatic Solar Armor 2.0, D-Solar Defendor, Industrial Glass Protect, Inorganic Removal Agent, Metal Oxides Removal Agent, Lichen Removal Agent, Paint Removal Agent, Water Softening Agent and Drone Solar Cleaning Agent.

Conditions differ by maker and by letter, but they fall into four areas. Check each one against your method before the first wash:

• Method: wet or dry, manual or mechanical. LONGi’s sample letter allows wet cleaning only.
• Water quality: hardness, TDS, pH and sometimes chloride and turbidity. Limits are in water quality for solar panel cleaning.
• Pressure, brushes and temperature: the maximum water pressure at the module, the brush type, and how close the water may be to module temperature. Limits are in warranty-safe methods.
• People: LONGi’s conditions include trained staff.

This creates a tension worth knowing about. Chemitek says Solar Wash Protect works with manual brushes, rotating brushes, robots and tractors. A product’s letter doesn’t override the module maker’s method rules: where they differ, follow the module maker. Brush and pressure rules are in warranty-safe methods.

Yes. A coating stays on the glass for months, so check its letter as carefully as a cleaner’s. Antistatic Solar Armor 2.0 has 17 letters of conformity and D-Solar Defendor has 3, and Industrial Glass Protect is named in JA Solar’s 2025 letter.

Each coating also comes with application rules, and following them is part of using it within the conditions:

• Antistatic Solar Armor 2.0 is dosed at 1 kg per 1,000 L of cleaning water and applied with rotary brushes, robots or tractor-mounted brushes. Chemitek advises against manual brushing with it and recommends Solar Wash Protect for manual crews.
• D-Solar Defendor must be diluted in soft or demineralised water. In TÜV SÜD testing it passed an alkali-stability test at pH 8 but failed at pH 9, so keep alkaline water and products away from it.
• The first coat needs fully clean glass, so the coating bonds to the glass rather than to dirt.

Then prove the effect on your own plant. In a Northern Cape trial, a hydrophobic coating increased dust soiling (du Plessis et al. 2020). An approved coating that doesn’t suit your dust is still a poor investment.

Are Chemitek products independently tested? Yes, and the wording matters. Chemitek’s PV cleaning and coating products are tested by ÉMI-TÜV SÜD for safety on module glass, anti-reflective coatings and frames. That is a product test rather than a blanket certification, so the accurate phrase is “tested by ÉMI-TÜV SÜD”. Before you rely on it, ask for the current test report for the product you plan to use and check its date.

Chemitek’s quality management is certified to ISO 9001:2015. Its products’ biodegradability is tested to OECD 301F by Portugal’s Centre for Waste Valorisation (CVR), and Chemitek describes them as readily biodegradable.

• Abrasives. Abrasive methods damage the anti-reflective coating, whatever chemistry you use with them. In Chemitek’s cement case studies on a carport in Chile and a 160 kWp plant in Israel, scrapers and high-pressure washing were ruled out for exactly this reason: they would damage the modules and void the warranty (Case study: Chemitek (Portugal), with Ecomundo; Case study: Chemitek (Portugal), with Girasol).
• Unapproved chemistry. Before any product touches the glass, ask for its letter of conformity for your module brand. No letter, no use.
• Bad water. Washing with high-TDS well water can leave the glass worse than no wash. See the Malaysia case. Water outside the limits can breach the conditions and cost yield at the same time.
• The wrong product for the job. Solar Wash Protect and Antistatic Solar Armor 2.0 are pH 7 ± 1, but Drone Solar Cleaning Agent is pH 11–13 and made for drone application. Use every product only as its datasheet and letter allow.
• Untrained crews. LONGi’s conditions include trained staff. Keep a written method statement and train the crew on it.
• Environmental conditions. Your environmental authorisation may add rules of its own. Check it against each product’s safety data sheet.

This is the checklist we work through before the first wash:

1. Identify the module maker and series, and get the current installation or O&M manual.
2. Match each product to a letter of conformity that names that maker. For Canadian Solar, check that the letter for your series is final, not preliminary.
3. Test the cleaning water on site against the maker’s limits: hardness, TDS, pH and, where listed, chloride and turbidity.
4. Choose brushes and pressure within the maker’s rules. See equipment selection.
5. Write the method statement and train the crew on it.
6. Record what was used, where and when: product, dilution, water test and equipment. It’s your evidence if a claim is ever questioned.

This is what our warranty-safe methods service covers, alongside cleaning-water testing. If an O&M contractor does the cleaning, we work alongside them: see working with your O&M team. For every Chemitek product and its approvals in one place, see the Chemitek range and Chemitek products explained.