Bird droppings, nests and Saharan dust: how they affect your solar panels

Bird droppings: small, but very harmful

Dust forms a more or less even layer. A dropping, on the other hand, is an opaque patch that almost completely covers one or more cells. Because the cells in a module work in series, the one receiving less light holds back the rest.

A study published in Sustainability analysed the effect of dust, water droplets, droppings and shading separately. Droppings reduced system performance by about 7.4%, and partial shading had an even bigger effect: covering a quarter of the module cut power by 33.7% [1].

The danger of hot spots

When one cell is shaded while the rest are still in the sun, it stops producing and starts behaving like a load: it turns its neighbours' energy into heat. This is known as a hot spot. Researchers at the Politecnico di Milano reproduced this phenomenon and confirmed it with a thermal camera on a real installation [2]. If it keeps happening for months, it can degrade the cell, damage the solder joints or mark the panel permanently.

Pigeons nesting under the panels

The gap between the panels and the roof is a perfect shelter for pigeons: it is shaded, protected from the wind and high up. The result is a build-up of droppings, feathers and nest debris right under the installation and in the gutters, plus constant dirt on the panels themselves.

The most effective solution is to close off the perimeter with bird-proofing mesh: a physical barrier that prevents access without harming the birds or drilling into the modules. Ideally it should be installed right after a clean, so the area is left free of debris.

Saharan dust: two effects in one

The "calima" is Saharan dust suspended in the air. It affects your panels in two ways:

1. While it is in the air, it blocks and scatters sunlight. A University of Jaén study of the March 2022 dust event found that direct radiation was the most affected component [3]. A study published in Renewable Energy covering events from 2019 to 2023 estimated that, with extremely high dust concentrations, output in Spain fell by 16.3% to 19.8% [4].
2. Afterwards, it settles. If it coincides with rain, you get the well-known "muddy rain", which leaves a layer of fine dust stuck to the glass.

The first effect cannot be avoided, but the second can: after a dust event with muddy rain, it is worth inspecting and cleaning the installation.

BEFORE

AFTER

What to do in each case

About the sources: the water quality, pressure and temperature figures in this article come from the cleaning guidelines of First Solar, one of the largest US manufacturers of solar modules, which makes thin-film modules; silicon modules, more common on rooftops, may have slightly different specifications. Each manufacturer publishes its own, which is why at TARRAMED we always follow those of your panels' manufacturer.