More Than a Cosmetic Problem

A single gull dropping on a south-facing panel in Plymouth or Penzance can look like nothing more than a mess the next rain shower will rinse away. In reality, it is an obstruction sitting directly in the path of the sunlight your array depends on. Panels are wired in series, so the output of an entire string is limited by its weakest-performing cell. A mark the size of a 50p piece can quietly trim several percent off your daily generation, and if it dries and hardens it may stay put for months.

Bird mess is one of the few maintenance issues a homeowner or facilities manager can actually see from the ground. That makes it worth understanding, because catching it early is far cheaper than living with the consequences.

How Droppings Turn Into Hot Spots

When shade falls on a single cell, that cell stops producing electricity while the current from its neighbours still tries to push through it. The result is resistance, heat, and what installers call a hot spot. Bypass diodes offer some protection, but they work at the level of groups of cells, so you can lose far more output than the physical size of the mark would suggest.

Over time the effects compound:

• Shading losses – reduced yield on every sunny day until the glass is cleaned.
• Thermal stress – repeated heating and cooling gradually degrades the encapsulant and backsheet.
• Micro-cracking – cells weakened by heat are more vulnerable to cracking, particularly on older arrays.
• Warranty questions – manufacturers expect reasonable upkeep, and prolonged neglect can complicate a performance claim.

Fresh droppings are acidic and mildly abrasive. Left through a hot spell, they can etch the anti-reflective coating, leaving a faint ghost mark that survives cleaning.

Why the South West Sees More of It

Coastal towns from Weston-super-Mare round to Bournemouth support large gull populations, and gulls are heavy, messy birds that favour high vantage points. A roof with a chimney stack, a dormer or an old television aerial is an obvious perch, and the panel plane below becomes the landing strip for everything they drop.

Inland, the pressures are different but no less real. Pigeons roost on chimney pots and barn ridges. Rookeries and starling flocks gather near farmland, and estuaries along the Severn and the Tamar attract cormorants whose droppings are especially corrosive. The region's mild, damp climate adds another factor: mess stays soft and smears across the glass rather than drying to a flake the wind can carry away.

Businesses with rooftop arrays on agricultural or warehouse buildings often face the sharpest problem, because a roosting flock in one spot can shade the same group of panels week after week.

Spotting Trouble Early

You do not need to climb a ladder to keep an eye on things. A quick check from the garden with binoculars, or a look at your inverter app, will usually tell you what you need to know.

• Visible streaks and white splashes on the glass, especially along the bottom edge where mess collects.
• A drop in daily yield compared with the same week last year, adjusted for weather.
• One string underperforming while others look normal – a classic sign of localised shading.
• Persistent marks that remain after rain has washed the rest of the roof clean.
• New nesting activity nearby, which predicts more mess in the months ahead.

Thermal imaging during a service can confirm whether a hot spot has developed, and it is far better to find one at that stage than after a cell has failed.

Cleaning Without Doing Damage

Solar glass is tougher than it looks, but it is not indestructible. A soft microfibre brush on an extending pole, plenty of water, and a steady hand will deal with almost everything the South West's birds can throw at a roof.

• Clean in the early morning or late evening when panels are cool, not in direct midday sun.
• Never use abrasive pads, cream cleaners or a pressure washer at close range.
• Use deionised or filtered water in hard water areas to avoid limescale spots.
• Do not walk on the panels, and stay off the roof unless you have proper access equipment and training.
• Work from the top of the array downwards so dirty water does not run back over cleaned glass.

For most homes, one or two cleans a year is enough, timed after nesting season and again in late summer. Commercial arrays on large roofs often benefit from a scheduled visit, particularly where birds are roosting nearby.

Prevention and a Workable Routine

Stopping the mess at source is cheaper than cleaning it off. Bird spikes, tensioned wire systems and mesh fitted to ridges, chimney pots and parapets can discourage the perching that leads to droppings. Netting works well over large flat roofs but must be fitted properly so birds cannot become trapped. Trimming back overhanging trees also reduces the traffic passing above your array.

A sensible routine looks like this:

• Spring – check for nesting activity and clean off winter grime.
• Late summer – clean again once fledglings have gone and the worst of the season has passed.
• After storms – inspect for new damage or debris carried onto the glass.
• Annually – book a professional check of output, connections and mounting, alongside a clean.

Solar arrays in the South West are a genuinely good investment, and they reward a little attention. Keeping the glass clear means every panel works as intended, hot spots never get the chance to develop, and your system keeps generating the energy you paid for year after year.