7 Signs Your Solar Panels Need Cleaning, and 4 That Point to Something Else

Check your numbers first

Open your monitoring app, pick a clear, sunny day this month and one in the same month last year, and type in the daily kWh for each.

The 7 signs

1. Clear-day output is down more than about 3%

Panels lose about half a percent a year to normal aging, so compare like with like and take that off first. A small gap is often weather. A gap of 3% to 6% with no new shade is usually dirt. One Las Vegas owner on Reddit saw only about a 4% drop after three years without washing, which shows how slowly plain dust builds up here.

2. You can see white droppings on the glass

Droppings matter more than dust. Safety trainers at ISCA explain that a dropping shading one row of cells can cut that panel’s output by about a third, and a weak panel can drag down others wired with it. See bird droppings cleanup.

3. Pigeons coo at sunrise, or droppings land on your patio

If birds fly under the panels and disappear, there is almost always a nest. The panels will keep getting dirty until the gap is closed with pigeon proofing.

4. A dirty band along the bottom edge

On flat or low-slope panels, rain and dew pool at the lower frame and dry into a line of dirt. It shades the bottom row of cells first. See does rain clean solar panels for why.

5. One panel lags behind the rest in your app

Systems with microinverters or optimizers, such as Enphase or SolarEdge, can show each panel’s output. If one or two panels sit well below their neighbors on a sunny day, look at those panels for droppings or a shadow.

6. Mud streaks after a monsoon storm or dust storm

Light rain that falls through dusty air leaves streaks and spots. If they are still there a few days later, see cleaning after dust storms and monsoon.

7. White spots after sprinklers or a hose

Las Vegas tap water averages about 280 ppm hardness. Overspray from sprinklers or a past hose rinse leaves mineral spots that rain won’t remove. See hard water spots on solar panels.

4 signs it isn’t dirt

What you notice	More likely cause	What to do
Output dropped sharply overnight	Inverter fault, tripped breaker or a dead string	Check the inverter and app for an error code, then call your installer or a solar electrician
Zero production on a sunny day	System off or an electrical fault	Don’t clean. Get the system checked
Lower output only in the afternoon	New shade from a tree, a neighbor’s addition or a patio cover	Trim or accept it. Cleaning won’t help
Browning, cracks, bubbles or burn marks	Panel damage or wear	Photograph it and book an inspection

If your panels have a problem like this, a cleaning won’t fix it, and a fair company should tell you that before it takes your money. Our solar panel warranty guide explains who to call for damage.