On this page
The panels sit in full sun, yet the output reads lower than it did last season. Issues with solar panels usually come down to a short list: dirt on the glass, shade across part of the array, damage to the glass or frame, a loose connection, or a warning on the inverter. The sections below work through each cause in turn, with the checks that separate them, and the cleaning steps at the end cover the most common fix.
SolarKitHQ earns a commission when you buy through links on this page, at no extra cost to you. As an Amazon Associate I earn from qualifying purchases. Affiliate disclosure.
Issues with solar panels: what to check first
Start with a visual check from the ground, then look at the inverter display and the output over recent days. A panel covered in dirt looks different from a panel with cracked glass, and a shaded panel behaves differently from a panel with a loose connection. Work through the causes below in order, and note which one matches what you see.
| Issue | What you see | What to do |
|---|---|---|
| Dirt on the glass | Film, droppings or sap on the glass | Clean with a soft brush and water |
| Shade | A shadow moves across the array | Trim the branch or move the object |
| Damage | Cracked glass, bent frame, lifted seal | Call a qualified installer |
| Loose connection or inverter warning | A warning on the inverter display | Note the code and call a qualified installer |
Step 1: Dirt, droppings and dust on the glass
Dirt, dust, pollen, ash, bird droppings, tree sap, hard water stains, smoke residue and other pollutants sit on the glass and block light, so a dirty panel makes less power than a clean one, and the loss grows as the layer thickens. Look at the glass in daylight: a film of dust, a patch of droppings or a ring of sap points to cleaning, not to a fault in the panel. The cleaning section below gives the steps and the kit figures.
Step 2: Shade across part of the array
Shade from a tree, a chimney, a roof edge or a nearby building cuts the light that reaches the cells. A panel in shade makes less power, and shade that moves across the array through the day makes the output rise and fall with it. Check the array at several points in the day and note where the shadow falls: shade in the morning only, or in the late afternoon only, points to the object that casts it. Trimming the branch or moving the object is the fix; a panel that stays shaded keeps making less power.
Step 3: Damage to the glass or frame
Cracked glass, a bent frame or a broken seal lets water in and weakens the panel. Look for cracks across the glass, chips at the edges, a frame that no longer sits square, or a seal that has lifted. A cracked panel can still make power, but the damage spreads with weather, and water inside the panel brings corrosion. Do not try to repair cracked glass yourself: a damaged panel needs a qualified installer to judge whether it stays in service or comes off the roof.
Step 4: Loose connections and inverter warnings
A loose connection between the panel and the rest of the system stops power from flowing, and the inverter shows the result as a warning or an error. Look at the inverter display for a warning light or an error code, and note the code before doing anything else. Do not open wiring or change connections yourself: the system carries DC voltage, and a loose connection needs a qualified installer. If the inverter shows no warning and the panels look clean and unshaded, the fault sits further down the system, and the installer is the next call.
Step 5: Low output with no visible cause
Sometimes the panels look clean, the array sits in full sun, and the output still reads low. Compare the output with the same time on a clear day, and look for a slow fall over weeks rather than a sudden drop: a slow fall points to dirt building up, while a sudden drop points to a fault or a new shade source. Note the pattern before calling the installer, since the pattern tells the installer where to look. A panel that reads far below its neighbors points to that panel, while the whole array reading low points to the inverter or the connection to the house.
How to clean solar panels
Cleaning is the most common fix, and the kits in the listings show the shape of it: a soft brush on a long pole, fed with water, with a soap dispenser for stubborn dirt. Buyplus lists a 20 inch brush on a 5 to 24 ft pole with 4 nozzles and a 180 degree adapter, and VEVOR lists a 30 ft pole with 2 water jets, a 65.6 ft hose and a soap dispenser. The pole lets you work from the ground, and the brush head turns to fit the panel angle. Use soft bristles only: the listings name high-density nylon bristles that protect the panel surface, and a hard brush or a scraper can scratch the glass.
Connect the brush to a garden hose, wet the panel, brush gently with soap on the dirty patches, and rinse. Solar Shine lists a 32 fl oz concentrated formula that treats up to 20 panels or about 300 sq ft, and its sprayer reaches up to 30 ft, so the ground does the work. BVOHVN lists a pole that extends to 12, 20 or 24 ft, and Veebuyla lists a 40 ft hose for full mobility at full extension. Solar Shine says cleaning can increase energy production by up to 30% when panels are properly cleaned and maintained, and that figure is the maker’s claim. Work in the cool part of the day so the water does not dry on the glass and leave marks, and rinse well after the soap.
When to call a professional
Call a qualified installer for cracked glass, a bent frame, a broken seal, a warning on the inverter that stays after cleaning, or any fault that involves wiring. Do not climb on the roof to reach a panel: the kits above work from the ground, with poles that reach 30 ft, and a ladder adds a fall risk. If the output stays low after cleaning and the panels look clean and unshaded, the installer checks the connections and the inverter.
Ways to keep the panels working
- Check the glass after a storm, a dust spell or a bird visit, and clean it before the layer thickens.
- Note the shade line through the day, and trim the branch that casts it.
- Keep the inverter display in view, and note any warning code before calling the installer.
- Clean with soft bristles and water, and rinse well after soap.
FAQ: power away from the grid
Why is solar panel output low?
Dirt on the glass, shade, damage, a loose connection or an inverter warning are the usual causes. Clean the glass first, check the shade line through the day, look for cracked glass, and read the inverter display for a warning. If the output stays low after cleaning, call a qualified installer.
How often should solar panels be cleaned?
There is no fixed schedule in the listings: clean them when the glass looks dirty, after a storm or a dust spell, or when the output falls without another cause. A visual check from the ground tells you when the glass needs it.
Can solar panels be cleaned with a garden hose?
The listings say yes: the brushes connect to a garden hose, and the water runs through the brush head. Buyplus lists a 20 inch brush with 4 nozzles fed by the hose, and VEVOR lists a 65.6 ft hose with quick connectors for a standard garden hose. Use soft bristles and rinse well after soap.
What causes hot spots on solar panels?
A hot spot is a cell that runs hotter than its neighbors, often where shade, dirt or damage blocks part of the panel. The shaded or dirty cell makes less power while the rest of the panel keeps working, so the blocked cell heats up. Clean the glass, clear the shade, and call a qualified installer if the spot stays.
Related solar guides
See the DIY solar panel kits, the solar charge controller size, the solar generator calculator and the solar panels hub.
