Helpful video reference. We reference this UK-specific "Solar Panel Cleaning in the UK" tutorial for its practical guidance on safe ground-level cleaning, correct product choice and what to watch out for on a typical UK roof installation. Worth watching before you buy any equipment.
1. Decide whether cleaning is actually needed
Most domestic solar panels in the UK are self-cleaning to a reasonable degree - the tilt angle and UK rainfall handle light dust and pollen. The jobs that rain cannot shift are:
- Bird droppings (acidic, cling to glass, block cells directly underneath)
- Leaf and twig debris that has settled at the lower edge of the array
- Mud splash from low-hanging gutters or adjacent flat roofs
- Lichen or moss growth (normally only on older panels in shaded positions)
The easiest way to spot a problem is your monitoring app. If your system is consistently generating 10-15% less than it was at the same time last year, and the weather pattern is similar, dirty panels are a likely culprit. Check before you wash.
2. Inspect from the ground first
Before you pick up a pole, spend five minutes looking at the array from street level or the garden. You are checking for:
- Cracked or discoloured glass (stop - this needs a professional check)
- A panel frame that has visibly shifted
- Nesting birds under or between panels (you cannot disturb an active nest legally during breeding season; call a specialist)
- Loose wiring or junction boxes that have come open
If you see damage, do not clean. Call your installer or a solar maintenance company. Washing damaged equipment risks water getting into live parts.
3. Choose the right products
Cold or lukewarm water is all most dirty panels need. If the grime is particularly stubborn - thick bird droppings, for example - use a cleaning fluid designed specifically for solar panels. Check that it is non-abrasive and pH-neutral.
Things to avoid:
- Washing-up liquid or household detergents (leave residue and can damage the anti-reflective coating)
- Bleach or any solvent-based cleaner
- Abrasive cloths, scourers or hard-bristle brushes
- A pressure washer (jets water behind frames and into junction boxes)
- Hot water (can cause thermal shock to cold glass on a frosty morning)
De-ionised or purified water leaves no limescale smear, which matters if your tap water is hard. Most professional window cleaners using water-fed poles already carry purified water as standard.
4. Clean from the ground with a water-fed pole
A water-fed extension pole with a soft-bristle brush head gives you safe reach to a standard single-storey or most two-storey pitched roof arrays. You can hire one from a local tool hire shop if you do not want to buy.
Method:
- Start at the top of each row and work downwards so dirty water runs away from the area you have already cleaned.
- Use gentle circular motions with the brush - you are loosening dried grime, not scrubbing.
- Rinse thoroughly from top to bottom once the debris is broken up.
- Keep water away from the junction boxes on the back of each panel (usually visible at the edges of the frame) and away from cable connectors.
Early morning or an overcast day is the best time. Washing panels in direct summer sunshine causes water to evaporate quickly and leave smear marks - and the glass is also hot enough that a thermal shock risk exists.
5. Let panels dry and check the output
Give panels 30 minutes to air dry before judging the results. Then open your inverter monitoring app or web dashboard and compare the output per kWp with a similar clear-sky day from the previous year. A clean gain of 5-15% on visibly dirty panels is typical.
If output remains noticeably low after cleaning and the sky is clear, the issue is elsewhere - shading that has grown (a neighbour's new extension, a tree that has leafed out further), a struggling string or inverter, or a failed panel. Time to call your installer.
6. Set a simple maintenance schedule
In east Kent, most domestic arrays need proper cleaning once or twice a year. A practical schedule:
- Spring (March/April): clear winter grime, bird debris and any moss that has grown over the darker months.
- Late summer (August/September): clean before the equinox when sun angles lower and any soiling has more impact on autumn and winter output.
- Quarterly: a quick inspection from the ground - look at the junction box covers, check no debris has built up at the lower frame edges, and glance at monitoring data for any sudden dip.
If pigeons have found a gap under the panels to roost, netting is the proper solution. Cleaning helps short-term, but pigeon-guarding is a one-time fix that pays for itself.
When to call us
The cleaning itself is a homeowner job. But if you have noticed a drop in output, a warning light on the inverter, or a problem with the AC side of the installation, Richard can carry out a solar health check. We also offer EICR inspections that cover the electrical installation associated with your panels.
Solar panel question in Sandwich or east Kent?
Richard can advise on solar health checks, inverter faults and any electrical work connected to your system.
Contact Richard