How to clean solar panels: when, how and fatal mistakes

A 5-10% layer of dust drops your solar output by 15-25%. Cleaning is the highest-ROI maintenance task you can do. Here's how to do it without breaking anything.

How often

• Wet region with regular rain: 1×/year or when you see output drop
• Dry or dusty area: 2-4×/year
• Near roads, farms or industry: every 2-3 months
• After a dust storm or wildfire smoke: always
• Leaf buildup in fall: as needed

What to use (exact list)

• Soft tap water (use distilled if you have hard water)
• Telescopic soft-bristle brush (NO metal, NO stiff)
• Mild dish soap (Dawn) for grease or sticky grime
• Squeegee or microfiber wipe to remove excess water
• Safety harness if working at height

Correct steps

Do it early morning or at dusk (cool panels avoid thermal shock). Wet first to soften dust. Brush in smooth parallel lines. Rinse. Stubborn spots: diluted soap and generous rinse. Never use pressure washers.

Fatal mistakes that destroy the panel

• Pressure washer: breaks the seal and forces water inside
• Midday cleaning on 140 °F panels: thermal shock can crack the glass
• Abrasive products, straight vinegar or bleach: damage the anti-reflective coating
• Going up barefoot or without a harness: many injuries every year
• Strong solvents: melt the frame's plastic

When to hire a pro

If your array is more than 16 ft high or the roof is steeper than 30°, pay $90-180 for a yearly pro cleaning. They use deionised water and you avoid roof falls.

Also read solar maintenance cost and how production is hit by shading and dirt.