Solar Panel Cleaning Procedure

Why this matters

Soiling reduces solar production. Dust, pollen, leaves, bird droppings, and snow all block sunlight from reaching the panel surface. The effect varies by location: a clean residential panel in a moderate climate may lose 5-10 percent annual production to soiling, while a panel near a dusty road or in an agricultural area may lose 20-30 percent. Routine cleaning recovers this lost production. The work is straightforward but has specific techniques to avoid panel damage.

When to use this procedure

• Annual or semi-annual cleaning service
• Customer reports lower production than expected
• Heavy soiling (visible accumulation)
• Bird droppings concentrated on specific panels
• After major events (dust storm, fire smoke, construction)
• Snow removal (specific to winter)
• Pre-warranty assessment (verify production claims)

Tools and materials

• Soft-bristle brush (specifically labeled for solar; standard automotive brushes may scratch)
• Telescopic pole with brush head (5-25 ft)
• Garden hose (NOT pressure washer)
• Squeegee (for water removal)
• Bucket
• pH-neutral cleaner (specialty solar cleaner OR diluted mild dish soap)
• Distilled water (for spot-free finish on premium installations)
• Ladder rated for the working height
• Safety harness + roof anchor for roof access (if needed)
• Microfiber towels
• Gloves and eye protection

Safety

The single most common solar service injury is the fall from the roof during panel cleaning. The customer can do their own cleaning from ground level on a ground-mount; roof-mount cleaning is a specialty service.

Procedure

Step 1: Time the visit

1. Early morning or late afternoon (panels cooler)
2. Avoid noon-day sun (panels can be 130+ °F; thermal shock from water)
3. Avoid rainy or stormy weather
4. Check the weather forecast; reschedule if conditions are wet

Step 2: Site survey

1. Identify the panel array location
2. Identify safe access (roof ladder, dormer, etc.)
3. Verify the customer's roof condition
4. Identify the array boundaries (don't work outside the array safely)

Step 3: Set up safety

1. Anchor harness to a secure roof point
2. Set ladder at the appropriate angle (1:4 ratio per OSHA)
3. Wear hard hat, eye protection, gloves
4. Have a partner ready (preferred for roof work)

Step 4: Pre-rinse

1. Use garden hose with light flow
2. Hose down each panel
3. Loose dirt washes away
4. Soaks any dried debris (bird droppings, leaves stuck to surface)
5. Pre-rinse loosens material for the next step

Step 5: Soft-brush cleaning

1. Use the soft-bristle brush (no abrasion)
2. Light pressure; let the brush do the work
3. Brush gently in the direction of the panel framing (typically downhill)
4. Pay attention to:

• Bird droppings (require more attention)
• Pollen accumulation (often greasy; soap helps)
• Mineral deposits (calcium from hard-water spray; specialty cleaner may help)
• Soot / smoke residue (from fires or industry)

1. Don't scrub aggressively - soft pressure, multiple passes if needed

Step 6: Soap if needed

For greasy or stubborn soil:

1. Apply pH-neutral solar cleaner (diluted per label)
2. OR mild dish soap solution (1 tablespoon per gallon)
3. Light scrub with the soft brush
4. Dwell for 1-2 minutes
5. Rinse thoroughly

NEVER:

• Use abrasive cleaners
• Use acidic cleaners (vinegar can etch some glass coatings)
• Use solvents (degrade EVA encapsulant in panels)
• Use hard water spray (mineral deposits form)

Step 7: Final rinse

1. Thoroughly rinse all panels with clean water
2. Verify no soap residue (residue attracts dirt)
3. For premium service: distilled water final rinse for spot-free finish

Step 8: Squeegee dry (optional)

For premium service:

1. Squeegee each panel from top to bottom
2. Removes water beads that would otherwise leave spots
3. Wipe edges with microfiber

Step 9: Inspect

While cleaning, look for:

• Damaged panels (cracked glass, browning)
• Damaged or corroded connections
• Vegetation growing under or around the array
• Pest activity (birds nesting, etc.)
• Damaged or missing rapid shutdown components

Document any issues with photos.

Step 10: Wrap up

1. Restore power to the array (if disconnected for service)
2. Verify the system is producing normally (check the monitor)
3. Document the cleaning in the customer file
4. Photo before/after for the customer
5. Schedule the next service

What NOT to do

• Walk on the panels - glass cracks
• Use pressure washer - too much force; damages panels
• Clean during peak sun - thermal shock risk
• Use abrasive cleaners or stiff brushes - scratches the glass
• Skip the safety equipment - fall risk
• Clean a panel array damaged from hail without checking the system first (cracked glass is sharper than expected)

Snow removal

For winter service in snow regions:

1. Light snow: typically slides off as the panel warms
2. Heavy snow: may require removal
3. Use a soft-bristled snow rake or solar-specific snow remover
4. NEVER use a metal snow rake or shovel (scratches the glass)
5. Brush snow off, don't shovel
6. The panel design typically prevents snow buildup; modern panels shed snow well

Some installations use snow guards or specialized racking that prevents heavy snow buildup. Others rely on the customer's tolerance for reduced winter production.

Frequency

For automatic cleaning systems (industrial / commercial), water and labor savings can justify the technology.

Soiling effects on production

Approximate production impact:

The cleaning visit recovers these losses. The customer's electric bill reflects the difference.

Self-cleaning options

For some installations:

References

• IEC 61215 (Photovoltaic Module Standards)
• UL 61730 (PV Module Safety)
• OSHA 1926 (Construction Industry, including fall protection)
• NFPA 1 (Fire Code)
• Manufacturer cleaning recommendations (specific to panel model)
• Manuall internal: Solar Maintenance Cleaning SOP, Diagnose Production Drop, Solar Monitoring Troubleshooting