How to Clean Solar Panels: A DIY Maintenance Guide

The “Self-Cleaning” Myth

Salespeople love to tell you that “rain will clean your panels.” While true for loose dust, rain does not remove bird droppings, pollen, soot, or tree sap. Over time, this grime bakes onto the glass, forming a cement-like layer that blocks sunlight.

Google conducted a study at their Mountain View campus and found that cleaning their flat panels doubled their energy output. While tilted residential panels fare better, a dirty system can easily lose 10% - 25% of its annual production.

When to Clean

Frequency: Once or twice a year.
Timing: Late Spring (to clear winter grime/pollen) and Late Autumn (to clear falling leaves).
Time of Day: CRITICAL. Only clean early in the morning or late in the evening. Spraying cold water on hot glass at noon can cause “thermal shock,” shattering your panels instantly.

Step-by-Step Cleaning Guide

1. Safety First

Never climb a roof without a harness. If you aren’t comfortable, hire a pro ($150-$200). It’s not worth a broken leg.

2. The Tools

YES: Garden hose, soft sponge, soft brush, squeegee, de-ionized water (if available).
NO: Pressure washers (High PSI strips the anti-reflective coating), abrasive pads (scratch the glass), harsh detergents (Windex/Bleach leave residue).

3. The Process

Shut Down: Turn off the system at the rapid shutdown switch or breaker (safety precaution).
Rinse: Hose down the panels to remove loose dirt.
Scrub: Use a soft brush (like a car washing brush) on an extension pole. Mix a tiny amount of mild dish soap (like Dawn) if there is heavy grease, but plain water is usually best.
Rinse Again: Thoroughly remove any soap suds.
Dry (Optional): If you have hard water, squeegee them to prevent calcium spots.

Conclusion

A clean solar panel is a happy solar panel. If you notice your production dropping in your monitoring app compared to last year, look up. A simple 20-minute wash could save you hundreds of dollars in lost electricity.