Occasionally a system becomes so filthy that very few people have the necessary equipment to clean it. In this case the amount of light reaching the solar panel surface was minimal due to a combination of airborne dirt and bird faeces.
Aside from the obvious reductions in electricity that result from a layer of dirt this thick, leaving panels in this condition will eventually cause hot spot damage and module failure – and it would be a tricky conversation to try to argue for warranty replacements under the circumstances.
PV modules are expected to generation electricity for at least 25 years from the date of installation – and can go on for much longer if well maintained. Considerable investment can be rendered useless if light can not reach the panels and generate electricity.
If no light at all can get to the silicone then the panels will never reach the point where they deliver enough electricity to the inverters, which may then also develop issues related to their attempts to re-start continuously.
If left to get into this kind of condition, the cleaning process becomes more difficult an time consuming, so we would always recommend routine cleaning be scheduled to avoid reaching this kind of situation in the first place.