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Solar panel cleaning is more delicate than it looks. Done incorrectly, it can permanently scratch the anti-reflective coating, void the panel warranty or cause a workplace accident. A poorly executed cleaning can produce worse outcomes than no cleaning at all.
Here are the practices distilled from 160+ Doka field projects.
4 fundamentals of correct cleaning
1) Timing: clean while the panel is cold
Start when the panel surface is below 30 °C — early morning or evening is ideal. Cold water on a hot surface causes thermal shock; micro-cracks form and reduce performance over time.
2) Water type: pure or osmosis water
Tap water contains lime — it leaves marks when it dries and reduces light transmission. Professional cleaning uses osmosis water (TDS < 30 ppm). Rainwater also works if you're sure it's free of sediment.
3) Brush: soft, non-damaging
Use nylon soft brushes or microfiber. Doka FK robots use imported Nylon 6.6 brushes — soft enough not to scratch the anti-reflective coating. Never use steel wool, hard synthetic brushes or abrasive sponges.
4) No chemicals
Detergent, glass cleaner, vinegar solutions or soap degrade the anti-reflective coating over time. Use water only; for stubborn stains (oils, etc.), refer to specialty cleaners recommended by the panel manufacturer.
How manual cleaning is done
Manual cleaning can make sense for small rooftop installations with 10-30 panels. Steps:
- Put on safety gear (harness, non-slip footwear). Never approach the roof edge.
- Remove loose dust with a dry brush or air blower first.
- Apply osmosis water through a telescoping brush — top to bottom, parallel strokes.
- Don't press hard; the brush's own weight is sufficient.
- Rinse the panel; don't dry it manually — let air-dry to avoid streaks.
This method is fine on small sites but impractical for 100+ panels: a single technician cleans 50-80 panels per day, taking weeks on large plants.
How robotic cleaning is done
For mid-scale and large plants of 500+ panels, robotic cleaning is both fast and standardized. Steps with the Doka FK series:
- The robot is placed on the end of a panel row by a single operator (FK-600-V2 is 18.5 kg; one person can carry it to a roof).
- Select dry/wet/hybrid mode on the remote control.
- In FK-1000-V3's semi-automatic mode, the robot scans the panel automatically; edge-detection sensors reverse direction at panel edges.
- One pass cleans 1080-1800 m² per hour.
- When done, the robot goes to charge (2 hours to full) and is ready for the next row.
A typical 5 MW plant can be cleaned in 2-3 days with FK-1000-V3; the same site would take 3-4 weeks manually.
Top 5 mistakes
- Cleaning in the heat of the day: Thermal shock causes micro-cracks. Always early morning or evening.
- Using high-pressure washers: Breaks panel seals. Stay below 3-4 bar.
- Tap water with lime: Leaves white marks over time. Pure water is essential.
- Using detergent or vinegar: Permanently damages the anti-reflective coating.
- Wrong cleaning frequency: Too often (weekly) wears the surface; too rarely (yearly) causes yield loss. See our frequency guide.