Can You Clean Solar Panels With a Garden Hose and Tap Water?
Yes, plain water from a garden hose on a gentle spray is safe for the panel itself. The catch in the Treasure Valley is the water: most of our tap water is hard, so it can dry into white mineral spots on the glass.
Is it safe to clean solar panels with a garden hose?
For the panel, yes. Our guide on how often to clean solar panels in Boise says to use a soft brush and plain water, and that still holds. There’s just one thing to add: plain water is safe for the panel, but tap water can leave mineral spots as it dries.
A hose does best on loose dust and pollen. Bird droppings need a good soak and a soft brush, and oily films like wildfire smoke don’t rinse off with water alone.
Why does tap water leave spots on solar panels?
Most Treasure Valley water is hard: it carries calcium and other minerals. When hose water dries on the glass, the water leaves and the minerals stay behind as white spots and a cloudy film. The U.S. Geological Survey names hard water as one of the most common causes of cloudy dishes and glassware. A solar panel is a big sheet of glass sitting in the sun.
Spots form fastest when water dries fast: hot glass, full sun, a dry summer afternoon. Around here, that describes most summer afternoons.
Can hard water hurt solar panels?
One rinse won’t hurt anything. The trouble is what builds up. Every time tap water dries on the glass, it leaves a little more behind, and a film of mineral spots is one more layer between the sun and your cells. Rain won’t take it off, because the minerals are stuck to the glass.
It’s the same thing that happens when sprinklers hit your windows. On windows, minerals left long enough can etch the glass for good, and panel glass is still glass. Here’s more on hard water spots on windows, since the minerals are the same.
What do panel makers say about water?
Every brand has its own cleaning instructions, so start with yours. As one example, First Solar’s cleaning guidelines for its panels say:
- Reverse osmosis water gives the best results. Without it, use low-mineral tap water or deionized water.
- If you do use hard water, squeegee it off so the minerals don’t build up as scale.
- Its panels with an anti-reflective coating shouldn’t be squeegeed or scrubbed wet except to spot clean, and hard water isn’t allowed on them.
- Don’t spray straight at the junction box, edge seals or connectors.
Other brands set other rules, and some warranties spell out how panels should be cleaned.
Why do pros use pure water on solar panels?
Pure water has zero minerals, so there’s nothing in it to dry into spots. That’s how a pro can leave panels clear without soap and without wiping every panel dry.
On solar panels, we use soft brushes and pure, filtered water at low pressure, with no harsh chemicals. We bring our own water, so you never need to provide any.
How to rinse your own panels without leaving spots
Panels on the ground, or on a low mount you can reach from the ground, are easy to look after yourself. Our solar panel cleaning guide covers the basics. To keep tap water from spotting the glass:
- Go in the cool of the morning or evening. Water dries slower, so you can finish before spots form. Never put cold water on hot glass: First Solar’s guidelines say the water shouldn’t be more than 20°C (36°F) warmer or colder than the panel.
- Rinse, brush, rinse. Wet the glass, loosen the dirt with a soft brush, then rinse from the top down so the dirty water runs off the bottom edge.
- Don’t let tap water dry on the glass. If your panel maker allows it, pull the water off with a clean, soft squeegee. On a small ground array, a last rinse of distilled water from a clean pump sprayer leaves far fewer minerals behind.
- Keep it gentle. No pressure washer, abrasive pads or harsh cleaners.
- Turn the sprinklers. If your sprinklers reach ground-mounted panels, aim the heads away, or you’ll be fighting fresh spots all summer.
- Skip the hose in winter. Water can freeze on cold glass. Let snow slide off on its own, and wait for spring to rinse off the dull film that inversion weeks leave behind.
Rooftop panels: stay off the roof
This is the big one. Panels on the roof mean ladder and roof work, and that’s where most of the risk is, not in the water. OSHA says falls are among the most common causes of serious work-related injuries and deaths, and a roof wet from a hose is even slicker.
- Never walk, kneel or lean on the panels. Your weight can damage them, even when nothing looks broken.
- Don’t spray up from the yard instead. A hose aimed at the roof can’t scrub, and it leaves hard water drying on glass you can’t reach.
- Look for damage first. First Solar warns that cracked or broken panels are a shock hazard, and the risk goes up when they’re wet. If you see a crack, don’t spray it. Call your solar installer.
When to call a pro
Call us if your panels are on the roof, if your hose keeps leaving spots, or if you’d rather spend the morning doing something else. A typical home system takes about 1 to 2 hours. We’re fully insured, and you can add solar panel cleaning to an outside window cleaning, so the panels and the glass get done in one trip. We clean panels on commercial buildings too.
We serve homes from Boise, Meridian and Eagle out to Kuna, Star, Middleton and Emmett. Want spot-free panels without the ladder? Get a free quote or call or text (208) 484-5207, Monday through Saturday, 8am to 7pm.