Microorganisms on agricultural photovoltaic systems

Cleaning photovoltaic (PV) systems has always been regarded as some kind of a luxury in Germany. The fairy tale of maintenance-free solar power generators, which became established in people's minds during the supply systems' boom period, has simply become too firmly entrenched. This is fatal, because cleaning companies are constantly being confronted with soiling which is extremely difficult to remove using the conventional method of demineralised water and mechanical surface processing, particularly in the case of agricultural systems. This particular type of soiling primarily affects PV systems on agricultural buildings and in the immediate vicinity of biogas plants.

Examinations of samples taken from the surfaces of photovoltaic systems show that the particularly stubborn form of module soiling involves colonies of microorganisms. A lively community of moulds, cyanobacteria and black fungi obviously flourishes especially well in agricultural environments. This collection of organisms is referred to as a biofilm and, according to investigations undertaken by the Federal Institute for Materials Research and Testing (BAM), has several unpleasant characteristics. Firstly, these life forms absorb light in the 300 to 1,000 nanometre range, which is precisely the range in which solar power is generated. These organisms also develop cell protuberances which penetrate into the pores of the glass surface and damage them in the long term.

This biofilm formation cannot be completely prevented, but it can be interrupted time and again by regularly cleaning the photovoltaic modules. How often cleaning should be carried out depends on the individual situation and should be discussed with a specialist company. Some systems require cleaning once a year whereas others can be cleaned at longer intervals of time. The location and the soiling acting on the respective system are critical. Whoever wishes to additionally slow down biofilm growth can use additives such as silicon molecules in the cleaning water, for instance. These molecules accumulate electrostatically on the surface of the modules. This molecular protective layer consisting of natural silicon acts as a disinfectant and makes it difficult for microorganisms to accumulate on the surface of the glass. One other option is long-term sealing of the surface of the modules. Whether and which of these methods are to be used should be discussed with a specialist company.

Should you do it yourself or employ a specialist company?

Employing a specialist company is recommended. The arguments in favour of this are:

  • Manufacturers have clear specifications concerning the care of their modules. Whoever performs the work himself runs the risk of invalidating the module warranty.
  • Specialist companies offer practice, experience and the right equipment.
  • Whoever does the cleaning  bears the full risk.
  • Certified specialist companies frequently offer services above and beyond cleaning, such as thermography, for example.
  • Specialist companies explain options for post-treatment with special surface protectors.

Value maintenance

With good care, photovoltaic systems supply good, green and practically free electricity far beyond the German Renewable Energy Act (EEG) subsidy period. In view of the long-term damage caused to a photovoltaic system by microorganisms, the question of whether cleaning must be carried out regularly can only be  confirmed. Of course, this also involves loss of output due to soiling, which lies somewhere in the 5 to 35 percent range.

What is more important, however, is that regular cleaning helps to maintain the system and that your own photovoltaic system can continue to be used for your own consumption, with storage batteries and electric vehicles, for instance, once the feed-in compensation comes to an end. One other option is for the system to feed green electricity into the grid. Regular cleaning ensures maximum power generation and helps to maintain the system's output in the long term beyond the end of the EEG subsidy period.