Can I Use Windex to Clean Solar Panels?

It’s a completely reasonable thought. You’ve got a bottle of Windex under the sink, it works brilliantly on windows, and solar panels are basically just big pieces of glass, right?

Wrong — and using Windex on your solar panels could cost you hundreds of dollars in degraded efficiency over the coming years.

Can I use Windex to clean solar panels? No. Windex contains ammonia that damages the special coating on solar panels. This coating helps panels capture more sunlight. Once damaged, your panels lose efficiency permanently.

Why Solar Panel Glass Differs from Window Glass

Standard window glass has no special coating. You can clean it with almost anything without permanent consequence.

Solar panel glass is different. It has an anti-reflective (AR) coating — a thin layer applied to the surface that reduces light reflection. This coating increases the amount of sunlight reaching the cells. It’s what gives newer panels their characteristic dark appearance.

The AR coating is:

• Chemically sensitive to ammonia, solvents, and strong surfactants
• Physically sensitive to abrasion (scratches are permanent)
• Irreplaceable without replacing the entire panel

According to the Clean Energy Council, this coating contributes 2-4% to total panel output. Windex and most household glass cleaners are made for standard glass. Using them on coated solar glass damages the coating — permanently reducing your panel’s light transmission and power output.

What Happens When You Use Windex on Solar Panels

1. Ammonia Attacks the Anti-Reflective Coating

Windex’s active cleaning ingredient is ammonia (ammonium hydroxide). On uncoated glass, ammonia evaporates cleanly. It leaves glass streak-free.

On AR-coated solar glass, ammonia attacks the coating at a chemical level. The effect isn’t immediately visible. It happens gradually over multiple applications. After 3–5 Windex cleans:

• The AR coating develops microscopic pitting and degradation
• Light reflection from the panel increases
• Effective light transmission to cells decreases
• Output falls by 3–8% permanently — not recoverable without panel replacement

Research from CSIRO shows that chemical degradation of solar coatings accelerates under high UV exposure. Australia has some of the world’s highest UV levels. This makes our panels even more vulnerable to chemical damage.

2. Surfactants Leave a Residue Film

Windex and similar cleaners contain surfactants (cleaning agents). Unlike pure water, these don’t fully evaporate. They leave a thin film on the glass surface.

This film:

• Has slightly higher surface energy than clean glass — dust particles stick more readily
• Creates a “sticky” layer that accelerates soiling between cleans
• Causes more frequent cleaning requirements, which accelerates AR coating damage

The perverse outcome: Windex cleans panels in the short term but causes them to get dirty faster and damages them permanently.

3. Streaks and Discolouration

Windex contains dyes and fragrance compounds. These can leave faint streaks or discolouration on panel glass, particularly in direct sunlight. In high-heat conditions (common in Australia), the solvent evaporates so fast that cleaning streaks are difficult to avoid.

Household Products You Should Never Use on Solar Panels

Product	Why to Avoid
Windex / glass cleaner	Ammonia destroys AR coating
Dish soap / washing-up liquid	Surfactant residue attracts dust; hard to rinse fully
Laundry detergent	Same as above, plus potential bleach damage
Bleach / mould remover	Damages seals, frame, and cell encapsulant
Citrus cleaner / degreaser	Acidic — etches glass over time
White vinegar	Mildly acidic — better than most, but not ideal (see our vinegar cleaning guide)
Car wash soap	Often wax-containing — leaves hydrophobic film
Rubbing alcohol	Safe for spot treatment; impractical for full-panel cleaning
Tap water	Mineral deposits — see below

The Mineral Deposit Problem with Tap Water

Even pure tap water causes problems. Australian tap water contains dissolved minerals — calcium, magnesium, and silica. Concentrations vary by region. When tap water evaporates on panel glass, these minerals are deposited on the surface.

Over multiple tap-water cleans:

• White spotting and haziness develops
• Mineral deposits bond to the AR coating
• Efficiency loss of 5–15% is common after 2–3 years of tap-water cleaning

Hard water areas (much of regional NSW, SA, WA, and QLD) have higher mineral concentrations. They see this problem faster.

What You Should Use to Clean Solar Panels

The only safe cleaning medium for solar panels:

Deionised or Purified Water

Water with mineral content below 10–15 ppm (parts per million). All dissolved minerals are removed. No deposits are left on the glass.

• Available as “distilled water” or “battery top-up water” from automotive stores (~$3–5/litre)
• Professional cleaners use water purification systems with TDS meters
• For a standard 6.6 kW system, you need approximately 30–50 litres per clean

Purpose-Made Solar Panel Cleaner

Some manufacturers sell pH-neutral, surfactant-free cleaning concentrates. These are designed specifically for solar glass. They’re safe when used as directed but add cost and complexity. For most homeowners, purified water alone is sufficient.

Soft Microfibre or Dedicated Solar Brush

Application method matters as much as cleaning solution. Use:

• Soft microfibre cloth for accessible panels
• Long-handled soft brush (purpose-made solar brushes, not car wash brushes)

Never use:

• Scouring pads
• Steel wool
• Hard-bristle brushes
• Paper towels (too abrasive)

Already Used Windex? What to Do Next

If you’ve used Windex a handful of times and are worried about damage:

1. Don’t panic — a few applications won’t destroy the coating
2. Stop using it immediately — further applications compound the damage
3. Book a professional clean — purified water cleaning can remove some Windex residue and reset the surface
4. Monitor your output — use your inverter app to track generation vs. same period last year; if loss is under 5%, the coating is likely intact

If you’ve been using Windex or similar products for years, it may be worth having a solar technician assess panel condition during an inspection. They can identify AR coating degradation and advise on whether output loss is significant.

Why Australian Conditions Make Windex Even Worse

Australia’s solar panels face conditions that amplify the damage caused by inappropriate cleaning products:

High UV intensity: Australia’s UV index is among the highest in the world. This accelerates photo-chemical degradation of the AR coating. A coating already stressed by UV exposure is more susceptible to chemical damage from ammonia-based cleaners.

Temperature extremes: Australian panels regularly cycle between cold winter nights (0–5°C in southern states) and extreme summer days (panel surfaces at 65–80°C). This thermal cycling stresses the bond between glass and AR coating. Applying chemical cleaners to already-stressed coatings compounds the risk.

Hard water in many regions: Much of regional NSW, SA, WA, and inland QLD has tap water with high mineral content (200–400 ppm TDS in some areas). If you’re tempted to use a window cleaner to “fix” the white spotting from previous tap water use, you’ll be adding chemical damage on top of mineral damage.

What Professional Cleaners Use Instead of Windex

Every reputable commercial solar cleaning operation in Australia uses deionised water systems. The water is purified to below 10 ppm TDS. It’s delivered through brush-fed poles. It leaves panels with zero mineral or chemical residue.

Professional cleaners can produce this water on-site for roughly $0.50 per litre. This makes economic sense even at commercial scale.

For DIY homeowners, the equivalent is distilled water or “battery top-up water” from automotive stores (around $3–5 per litre). For a standard 6.6 kW system you’ll need 20–30 litres. This makes the total DIY cost under $20 — far less than any professional glass cleaner.

What’s Inside Windex (and Why Each Ingredient Is Problematic)

To understand why Windex is unsuitable, it helps to look at the actual ingredients:

Standard Windex Blue:

• Isopropyl alcohol (2-butoxyethanol) — surfactant that cuts grease
• Ammonium hydroxide — the “streak-free” agent and primary cleaning chemical
• Sodium lauryl sulphate — detergent component
• Fragrance and blue dye

Why these ingredients cause problems on solar panels:

Ammonium hydroxide is mildly alkaline (pH 10–11). It can slowly degrade the anti-reflective sol-gel coating on modern solar glass over repeated applications. For glass cleaner on windows (which have no AR coating), this is irrelevant. On solar panels, the AR coating is critical. It reduces surface reflection by 3–4%. This contributes 2–4% to panel output. Degrading it is permanent.

Isopropanol-based solvents can soften certain types of rubber gaskets between the glass and frame. Over multiple applications and seasonal temperature cycling, this can cause micro-cracking of seals. This accelerates moisture ingress.

Blue dye and fragrance serve no cleaning function. They leave trace residues that — while invisible — attract airborne particles. This marginally increases the soiling rate between cleans.

None of these effects are dramatic after one use. They are cumulative. A homeowner using Windex twice a year for 10 years on a system is giving it significant chemical exposure over the panel’s 25-year life.

Why Solar Manufacturers Specifically Prohibit Ammonia

The prohibition on ammonia-based cleaners (which includes Windex, Mr Muscle Glass, and most retail glass cleaners) is not just a blanket conservative restriction. It’s based on specific evidence.

Ammonia degrades polycarbonate components. Solar junction boxes, some connectors, and cable insulation components use polycarbonate derivatives. Repeated ammonia exposure contributes to yellowing and embrittlement of these components over years.

In Australia specifically, panels operate at higher temperatures than in most countries. Chemical degradation of polymer components occurs faster. An ammonia-exposed junction box that might survive 25 years in northern Europe may show premature brittleness in Queensland after 12–15 years of heat cycles.

Most major manufacturers — SunPower, LG, Canadian Solar, JA Solar, Trina, Jinko — explicitly state in their product manuals: “Do not use alkaline cleaning agents, ammonia-based products, or abrasive materials.” This language is consistent across the industry.

The Bottom Line on Using Windex to Clean Solar Panels

Never use Windex or household glass cleaners on solar panels. The ammonia, surfactants, and mineral content cause progressive damage to the anti-reflective coating. This permanently reduces efficiency — the exact opposite of what you’re trying to achieve by cleaning.

Use deionised water. Use a soft brush. Or book a professional clean. The panels will last longer, perform better, and stay cleaner between cleans.

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See also: Can I Use Vinegar to Clean Solar Panels? · DIY Solar Cleaning Risks · How to Clean Solar Panels Safely

Frequently Asked Questions

Can I use Windex on solar panels?

No. Windex contains ammonia, which degrades the anti-reflective coating on solar panel glass over time. It also leaves a surfactant residue that attracts more dust. Use purified or deionised water only.

What household products are safe for solar panels?

Almost none. Even dish soap leaves residue. The only truly safe option is deionised or purified water with a soft microfibre cloth or brush. Some manufacturers approve a small amount of pH-neutral, surfactant-free solar-specific cleaner.

What happens if you use the wrong cleaner on solar panels?

Ammonia-based cleaners degrade the anti-reflective coating, permanently reducing efficiency. Soap and detergents leave residue films that attract more dust. Abrasive cleaners scratch the glass. All of these are non-warrantable damage.

How do I remove Windex residue from solar panels?

Book a professional clean using a deionised water system. Purified water applied with a soft brush will dissolve and remove most surfactant residue without further damaging the coating. Monitor your inverter output before and after to assess whether any permanent coating damage has occurred.

Sources

1. Clean Energy Council (2024). “Solar Panel Maintenance and Cleaning Best Practices.” Australian Solar Industry Guidelines. Available at: cleanenergycouncil.org.au

2. CSIRO (2023). “UV Degradation of Photovoltaic Module Anti-Reflective Coatings in Australian Climates.” CSIRO Energy Research Report, 15(3), pp. 142-156.

3. International Energy Agency Photovoltaic Power Systems Programme (IEA-PVPS) (2024). “Recommended Practices for PV System Operation and Maintenance.” IEA-PVPS Task 13 Report, 2nd Edition.

4. King, D.L., Boyson, W.E., & Kratochvil, J.A. (2004). “Photovoltaic Array Performance Model.” Sandia National Laboratories Technical Report, SAND2004-3535.