Do solar panels need to be cleaned?

Sometimes, but less often than door-to-door cleaning offers suggest. Panel makers disagree on how often: one says rain keeps tilted panels clean enough, another recommends regular cleaning. Your own panel's manual sets the rule for your warranty, and your monitoring data tells you whether dirt is actually costing you power. When cleaning is needed on a roof-mounted array, it is a job for a pro.

What the panel makers say

The U.S. Department of Energy notes: "Solar energy production can be affected by season, time of day, clouds, dust, haze, or obstructions like shadows, rain, snow, and dirt."^[3] How much that matters depends on the panel and the site, and manufacturers' own manuals differ.

Canadian Solar's manual says: "Modules with sufficient tilt (at least 15°), generally may not require cleaning (rain will have a self-cleaning effect)."^[1] JinkoSolar's manual takes a stricter line: it recommends cleaning its panels preferably once a month, and more often in dusty conditions,^[2] because "A buildup of dust or dirt on the module front face will result in a decreased energy output."^[2]

Flat or low-tilt arrays, homes near farm fields or gravel roads, and panels under trees tend to collect more than steep, open roofs. Canadian Solar's maintenance section talks about keeping modules clear of snow, bird droppings, seeds, pollen, leaves, branches, dirt spots and dust,^[1] and in Virginia spring pollen and bird droppings are often the reason panels look dirty.

Is cleaning worth paying for?

Your monitoring app is the test. Compare this month's production with the same month last year, or with your installer's estimate, and look for a drop that a few rainy days do not fix. Visible soiling that rain leaves behind, such as caked bird droppings or a film of pollen on a low-tilt array, is worth a closer look. If production is down but the panels look clean, the cause is more likely shade, weather or an equipment fault; our answer on why solar panels produce less than expected covers those.

Why roof-mounted panels are a pro job

The risk is not the dirt. Canadian Solar's manual warns: "The voltage and current present in an array during daylight hours are sufficient to cause a lethal electrical shock."^[1] It adds: "Cracked or broken modules represent an electric shock hazard due to leakage currents, and the risk of shock is increased when modules are wet."^[1] Its cleaning section requires that the circuit be disconnected, and the array disconnected from the inverter, before cleaning starts,^[1] and it addresses its cleaning guidelines to professional installers.^[1] JinkoSolar's manual likewise rules out cleaning a panel with broken glass or other signs of exposed wiring, because it presents a shock hazard.^[2]

Add a ladder, a sloped roof and wet glass, and this is roofing and electrical work combined, which is why Loclis treats it as a job for a pro.

The warranty is the other reason. Canadian Solar's manual states: "Damages induced by inappropriate cleaning procedures will void Canadian Solar Inc. warranty."^[1] JinkoSolar notes that using chemicals may affect the module warranty and energy yield.^[2]

What to ask a cleaning company

You do not need to do the work to judge whether a cleaner knows it. Ask how they will follow your panel maker's manual, and listen for the points both manuals stress:

• The circuit is disconnected first. Canadian Solar requires the circuit and the array to be disconnected from the inverter before cleaning starts.^[1]
• Soft, non-abrasive tools and gentle methods. Both makers rule out abrasive material, and Canadian Solar recommends avoiding rotating brushes, which can cause micro-cracks, and says dry dirt must never be scraped or rubbed off, which leaves micro-scratches on the glass.^[1][2]
• No harsh chemicals. Canadian Solar rules out abrasive cleaners, degreasers, and solutions containing hydrofluoric acid, alkali, acetone or industrial alcohol, and JinkoSolar says chemicals may affect the module warranty.^[1][2]
• The right water and a gentle flow. Both makers call for low-mineral, near-neutral water, and both set a pressure limit for hoses and sprayers.^[1][2]
• Not in the hottest part of the day. Cleaning in the early morning or late afternoon avoids thermal stress and reduces the risk of electrical and thermal shock.^[1][2]

A crew that shows up with a household pressure washer and a bucket of detergent, and no idea which panels you have, is the wrong crew.

Snow

Snow stops production until it clears, and as the photo above shows, it can cover an array completely. Removing it from a roof is not worth a fall or a scratched panel, so waiting for it to melt is usually the safer choice, and a pro should handle anything more.

The rest of the upkeep

Cleaning is a small part of looking after a system. JinkoSolar recommends a preventive check every six months of the junction box sealing, the wiring for rodent damage and weathering, tight and corrosion-free connections, and the grounding.^[2] It also calls for keeping grass and plants under and around ground-mounted arrays trimmed so they do not shade the panels.^[2] Canadian Solar says electrical or mechanical inspections and maintenance should be performed by qualified personnel only.^[1]

When to call a licensed pro

Call your installer if monitoring shows a lasting drop, if you see cracked glass, scorch marks or loose wiring, or if snow or debris has sat on the array for weeks. Repairs belong with a licensed contractor: the alternative energy system (AES) specialty covers installing, repairing and improving solar generation systems from the customer's meter, but not electrical work,^[4] so wiring faults need a licensed electrician too. For any service agreement, DPOR's hiring guide advises: "Since a written contract protects you and the contractor, all agreements should be put in writing."^[5] Before hiring someone new, check their licence on DPOR's record.

Browse solar installers on Loclis, find electricians in Blacksburg, or read more electrical answers.

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