Solar PV owner John noticed a drop in his solar PV output recently so called on the services of suitably qualified, safety-attired person to check the solar array on his two-storey home.

What he discovered gave him a surprise -  pigeon poo and lots of it. Sun-baked poo was caked on to many of his 20 solar panels. Poo clogged in the gutters and had even started to nurture plant life.  John reckons he first noticed the birds about 15 months ago but hadn’t put much store by it. What he didn’t know was that a single pigeon is capable of dumping around 11kg of poo a year. Pigeons are prolific breeders that can breed up to nine times a year with offspring likely to return to the nest site.

output dropped from 1604kW in 2013 to 1489kW in 2014 and 1234kW this year 

It all started when John noticed his the mid-May to mid-August output over three years had declined. As the graphic above shows, the output dropped from 1604kW in 2013 to 1489kW in 2014 and 1234kW this year. That represented a 12.3 per cent decrease on his average daily exports, which by his calculation equated to about $112.  Australian Bureau of Meteorology data show Townsville experienced about the same amount of solar energy levels for each of the three years so it wasn’t due to a shortage of sunshine.

Panel design and installation generally encourages 'self-cleaning' when it rains, but as John has discovered, the tenacity of poo and a lack of rain due to a failed wet season might have contributed to his solar output decline. A 2013 study by the University of California shows that paying for regular washing of dusty panels isn’t all that economical   - the cost of washing dust twice a year isn’t recouped by any energy efficiency gains.

However, the study added that bird poo requires a stronger solution than falling rain – so manual labour is likely when it comes to cleaning.  This raises the next issue - safety. Clambering around roofs and cleaning solar arrays can be hazardous for the inexperienced (and something John does not recommend). Put safety first and leave it to the experts. Pest controllers and solar cleaning services are a mere Google search away.

So scrubbing the stuff away raises the economic, or money aspect. Bird poo is caustic and can cause problems if left unattended. Poo-clogged gutters can result in rainwater damage to roof spaces, the stuff can build up in rainwater tanks or clog pump filters.  So while it will cost solar panel owners money to clean soiled panels, it is money well spent if the owner is concerned about declining output and the panels are difficult to access.

John's 20 panels were cleaned, the mess removed and so his 5kW system is ready for the summer production. And as for the panel pests?  They are up in the air because anti-pigeon measures have been installed. 

Which could mean there’s a flock looking for a new roost.

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Links and Sources:

Australian Bureau of Meteorology.
http://www.bom.gov.au/climate/data/index.shtml?bookmark=200

California research.
http://ucsdnews.ucsd.edu/pressrelease/cleaning_solar_panels_often_not_worth_the_cost_engineers_at_uc_san_diego_fi

Pigeon facts.
http://ovocontrol.com/pigeons/pigeons/