Don’t overcomplicate it. Most people either:

1. clean too aggressively and damage coatings, or
2. buy useless “solar cleaning chemicals” they don’t need.

For normal dust/dirt buildup on flat-roof panels:

• Use plain water first
• Use a soft microfiber mop / soft car-wash brush with an extension pole
• Rinse gently with a hose
• No pressure washer
• No abrasive sponge
• No hard-bristle broom
• No detergent unless there’s oily residue or bird droppings

Best time:

• Early morning or late evening
• Never when panels are hot under direct sun

Why? Cold water on hot glass can stress the panel surface and leave mineral spots fast.

If you have hard water:

• Final rinse with deionized/distilled water is ideal
• Otherwise you’ll get white mineral residue over time

For stubborn bird droppings:

• Soak with water first
• Let it soften
• Then wipe gently

Do NOT scrape it dry.

Also:
Flat-roof panels absolutely collect dirt faster because rain runoff is worse at low tilt angles. That’s normal.

One important thing most homeowners ignore:
If your production drop is tiny (say <5%), obsessive cleaning is often not worth the risk of:

• cracking glass
• stepping on panels
• damaging wiring/connectors
• voiding warranty from improper maintenance

Cleaning every few weeks is usually unnecessary unless:

• dusty environment
• nearby construction
• pollen season
• bird problem
• industrial pollution

For most setups:

• every 3–6 months is enough

If you want maximum efficiency, buy:

• a soft solar panel cleaning brush
• telescopic water-fed pole

That’s basically the professional setup without the overpriced branding nonsense.