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.

Why Solar Panel Glass Is Different 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 microscopically thin layer applied to the surface that reduces light reflection and increases the amount of sunlight reaching the cells. This coating is what gives newer panels their characteristic dark, non-reflective 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

Windex, and most household glass cleaners, are formulated for standard glass. Using them on coated solar glass damages the coating — permanently reducing your panel’s light transmission, and therefore its output.

What Windex Does to Solar Panels

1. Ammonia Degrades the AR Coating

Windex’s active cleaning ingredient is ammonia (ammonium hydroxide). On uncoated glass, ammonia evaporates cleanly and 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

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 microscopically thin film on the glass surface.

This film:

• Has slightly higher surface energy than clean glass — dust particles adhere 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 stay dirty permanently.

3. Streak Risk

Windex contains dyes and fragrance compounds that 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.

Other Common Household Products to Avoid

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 — at concentrations that 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 and see this problem faster.

What You Should Use

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, so 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 specifically designed for solar glass. These are 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

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.

The Bottom Line

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

Understanding the Australian Context

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, accelerating 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 in Australia use: Every reputable commercial solar cleaning operation in Australia uses deionised water systems — water purified to below 10 ppm TDS. The water is delivered through brush-fed poles and leaves panels with zero mineral or chemical residue. It costs them roughly $0.50 per litre to produce on-site, which is why it 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, making the total DIY cost under $20 — far less than any professional glass cleaner.

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