Short answer
Pure water or osmosis water (TDS < 30 ppm) is the right choice for panel cleaning. Combined with soft nylon brushes, it is sufficient on its own. You don't need any chemical additives.
Water types — detailed comparison
✅ Pure water (Demineralized)
Water with all minerals removed. Leaves no residue when it dries. The first choice for professional cleaning. Produced via filter systems; small and large infrastructure options exist.
✅ Osmosis water (Reverse Osmosis)
Highly purified water. Performance is similar to pure water. TDS should be below 30 ppm. Possible to produce on-site by installing an RO unit on your site's water source.
⚠️ Rainwater
Naturally pure but can pick up dust and sediment from the atmosphere. Usable if filtered. Not sufficient on its own; useful for pre-cleaning.
❌ Tap water (municipal supply)
In most regions, water hardness is high. Lime deposits leave white marks on the panel surface. Those marks block light — sometimes worse than the original soiling. Don't use.
❌ Well water
Mineral content varies wildly by region. Risky without a TDS measurement first.
Chemicals — absolutely not
None of the following should be used to clean solar panels:
- Detergent / dish soap: Degrades the anti-reflective coating over time.
- Glass cleaner: Most contain ammonia, harmful to the coating.
- Vinegar / acids: Cause permanent surface damage.
- Bleach: Chlorinated compounds damage the frame and cell contacts.
- Acetone or solvents: Never, under any condition.
Exception: special cleaners explicitly recommended by the panel manufacturer for very stubborn oil or paint marks. Even then, pure water + mechanical brushing is usually sufficient.
Doka FK robots' water management
FK-1000-V3 and FK-600-V2 models run with 6 — 30 L/minute adjustable water flow. Water tank integration is available; osmosis water can be fed directly into the robot. The operator adjusts flow rate from the remote based on site soiling level.
In dry mode, the robot uses no water at all — just the soft imported Nylon 6.6 brush to remove loose dust. This mode is critical for desert and remote sites.