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Press release No. 20/2012 of 30 October 2012

Biofilms on solar panels impair performance

They can be found at the North and South Poles, on the summit of K2, in hot desert regions and now also on solar panels in Germany: black fungi. Together with cyanobacteria, they form pinpoint-sized dark colonies on the glass of solar panels in just a few years’ time. Scientists of the BAM Federal Institute for Materials Research and Testing have found that the resulting biofilm then impairs the efficiency of the solar system.

It has been known for quite some time that cyanobacteria and black fungi can settle on solid surfaces, including glass, to form so-called biofilms. However, little has been known up to now about the colonisation on the surface of solar power systems which are also usually made of glass. BAM’s biologists have looked into these issues and investigated several photovoltaic modules for biofilms. First results: black fungi and cyanobacteria do settle on these particular glass surfaces.

This is not just an aesthetic problem because they "swallow" a lot of light: "Biofilms on solar panels absorb a large amount of light, especially in the wavelength range of 300 to 1000 nanometres. And solar radiation is captured in this range in solar panels for electricity," says Steffi Noack-Schönmann who carried out the tests at BAM.

Not only is the performance of the equipment impaired, the organisms can extract minerals from the glass and damage it. Filamentous cells of fungi, called hyphae, penetrate the glass and cause physical and chemical destruction over time. Even if the biofilm is removed, the glass is no longer smooth and the light is scattered.

The organisms do not need particularly favourable conditions. Black fungi are very stress tolerant – which is confirmed by their presence in inhospitable locations. Their thick cell wall, which contains the pigment melanin as well as a compact colony structure, make them resistant to heat, dehydration, cold and UV radiation. Therefore, these organisms, also called extremotolerant, can be found in many regions of the earth which are characterised by extreme conditions. They are also considered pioneers of the colonisation of solid surfaces that come into contact with air.

Mistakenly, the grey-green-black coating of black fungi, cyanobacteria and green algae on façades is still considered dirt and its importance overlooked.

The work of an entire research group at BAM deals with these biofilms. Whereas a lot is known about biofilms in general, investigation of solar systems is in its infancy. So far, three solar facilities from different locations and various ages have been investigated. The results are very different. No biofilm has been found on a more than 10-year-old system mounted on the middle strip of a motorway. At the same time, biofilm was detected on a three-year-old system installed on a roof. The investigation of other facilities is pending. It also should be tested which facilities are most affected and what factors affect colonisation. The angle of inclination and the glass surface of the panels may play a role. Pure isolates of black fungi were taken from samples of solar facilities, which are available as reference organisms for further tests and will be offered to manufacturers in the future to be used in their own experiments.

Currently, many manufacturers assume a lifetime of 25 years for their installed modules without taking into account black fungi. There are also pathogenic species among black fungi. However, the species on the walls of buildings and solar panels are harmless to humans and mainly cause economic and aesthetic problems.


Dr. rer. nat. Steffi Noack-Schönmann
Department 4 Material and Environment

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