Lichen takes a lot of scrubbing off whatever you use, if panels are up on a roof its pretty near impossible to get enough downward pressure on to remove it, Hypo will bleach it but it will return and surely must be contra indicated for use on them, if they are low-lying you may have a chance,
Have a look on how Lichen is so strongly attached to pavement flags and ask what equipment you could use to clean them-? You have an answer straight away.