Solar panels are one of the best investments you can make for your home — but only if they're working at full capacity. What many homeowners don't realise is that dirty panels can lose a significant amount of their energy output, costing you money every single day they're left uncleaned.
How Much Efficiency Do Dirty Panels Lose?
Studies consistently show that dirty solar panels lose between 15% and 25% of their energy output. In some extreme cases — particularly where bird droppings or heavy lichen are involved — losses can exceed 30%. That's a substantial chunk of the energy you're paying to generate, effectively going to waste because of a layer of grime.
Even a thin film of dust reduces the amount of sunlight reaching the photovoltaic cells. The effect is cumulative: a little dust becomes a lot of dust, and before long your panels are underperforming without any obvious visual warning from the ground.
What Causes Build-Up on Solar Panels?
Several factors contribute to solar panel soiling, and here in Somerset we see most of them regularly:
- Bird droppings — The most damaging contaminant. A single bird dropping can block an entire cell, creating a "hot spot" that reduces output across the whole panel. Somerset's proximity to the Levels means large bird populations, particularly starlings, pigeons, and gulls.
- Pollen — Spring and early summer bring heavy pollen loads, especially from rapeseed fields and hedgerows common across Somerset farmland.
- Dust and agricultural particulates — Harvest season throws up enormous amounts of fine dust. Properties near arable land see noticeably faster build-up from late summer onwards.
- Lichen and moss — Somerset's damp climate encourages organic growth, particularly on panels with a lower tilt angle where moisture sits longer.
- Tree sap and leaf residue — Overhanging trees deposit sticky sap that binds other dirt to the panel surface.
Why Rain Doesn't Clean Your Panels
A common misconception is that rainfall keeps solar panels clean. It doesn't. Rain can wash away loose surface dust, but it leaves behind mineral deposits as it dries — the same water spots you see on car windscreens. Bird droppings, tree sap, and lichen are not water-soluble, so rain simply runs around them, sometimes spreading the contamination further.
In fact, light rain can make things worse by dampening dust into a sticky film that then bakes on in the next sunny spell.
How Often Should Solar Panels Be Cleaned?
For most properties in Somerset, once or twice a year is sufficient. We recommend a clean in early spring to clear winter grime before the high-output summer months, and optionally a second clean in autumn after harvest dust and leaf fall. Properties near farmland, under trees, or with heavy bird activity may benefit from more frequent cleaning.
Why You Shouldn't Clean Them Yourself
It's tempting to grab a hose and a sponge, but DIY solar panel cleaning carries real risks:
- Warranty issues — Many manufacturers specify that panels must be cleaned by professionals using approved methods. Using the wrong cleaning products or abrasive tools can void your warranty entirely.
- Risk of damage — Panels have a delicate anti-reflective coating. Harsh chemicals, pressure washers, or rough cloths can scratch or strip this coating, permanently reducing efficiency.
- Safety — Solar panels are on your roof. Working at height without proper equipment and training is dangerous. Falls from ladders remain one of the most common causes of serious injury in the UK.
How Professional Cleaning Works
Professional solar panel cleaning uses purified water and soft-bristled brushes — nothing else. The purified water (with dissolved minerals removed) lifts dirt without leaving residue, and the soft brushes agitate stubborn deposits without scratching the panel surface. It's gentle, effective, and completely safe for your panels and their warranty.
The whole process is done from the ground or using safe access equipment, with no need for anyone to walk on your roof. Most domestic installations take under an hour.
Protecting Your Investment
Your solar panels are a long-term investment — typically with a 25-year lifespan. Keeping them clean ensures you're getting the maximum return on that investment throughout their life. A professional clean once or twice a year costs a fraction of the energy you'd lose by leaving them dirty.