I was asked to call by and look at a 150 kW solar PV ground mounted system that we installed around 7 years ago. This most likeable client wanted to take care of the system himself so did not want to enter into a maintenance contract at the end of the first year.
When I visited today I was disappointed to see the state of the both the panels and the site in general.
The panels had never been cleaned and had a substantial amount of moss and hard lichen deposits. Self seeded small trees had grown up all over the site and were even poking through the panels in places. No surprise that the output was below forecast and this was before the trees came into leaf.