Why pigeons and starlings crawl under your solar panels

Solar panels don't lie flat on your roof. They sit on a mounting system, which leaves a gap of several centimetres between the roof tiles and the underside of the panel. That gap is there on purpose: it lets air flow, so the panels can get rid of their heat. Birds, however, see something completely different in it.

Dry, warm and sheltered, all three at once

A bird looking for a nesting site checks three things: does it stay dry, is it sheltered from the wind, and can a cat or crow get to it? Under a solar panel, the answer is favourable on all three counts. The panel acts as a roof above the roof, so rain doesn't get in. The space is usually closed at the top because the row is up against the ridge, so draughts are limited. And the opening is low and narrow, so no bird of prey can get in from above.

Then there's the warmth. On a sunny day panels get very warm and also give off that heat on the underside. In early spring, exactly when pigeons and starlings are looking for a spot, the space under a panel is one of the warmest places on your entire roof.

Which birds you'll come across in practice

In the Netherlands, it is usually these three:

• Feral pigeons. They breed all year round and aren't fussy. If there is an opening of ten centimetres or more somewhere, a pigeon will fit through it.
• Starlings. They specifically look for a narrow, hollow space and like to nest in colonies. Once one pair has moved in, more often follow.
• House sparrows. Smaller, and they squeeze through a gap a pigeon would never get through.

Jackdaws and crows rarely nest under a panel, but they do pull out nesting material that is there, spreading the mess across your roof.

Why they don't leave by themselves

Birds are creatures of habit. A pigeon that has successfully raised a brood under your panels will come back the following year, and the young often look for a spot near where they grew up themselves. That is why the problem almost never goes away by itself and usually gets bigger: one pair in the first year, several spots by the third.

Scaring them away only helps for a short while. As long as the space stays open, it will be occupied again within a few days. The only thing that works for good is to physically seal that space, without blocking the ventilation underneath.

Sealing without choking the airflow

That is exactly what a brush strip does. The bristles fill the gap and wedge themselves between the roof tile and the edge of the panel, but air keeps moving freely between those bristles. A bird can't get through, but heat can.

It's important that the brush is slightly thicker than the gap at its narrowest point. If it's too loose, a gap remains at the bottom, and that is enough for a sparrow. How to measure the gap and which diameter goes with it is explained in the article on measuring. If you already know your size, the size finder sets out in a few steps how many metres you need.

The best time is before it starts

If there are no nests yet, sealing is simple: you'll be done in an afternoon. If there is already a brood, the order changes and you first need to check whether there are still young inside. A separate article covers that. In this case, prevention really is easier than clearing up.