Watt would be a good size of panel (lookin for the maximum output) to use on a lead acid battery to keep topped off without having a charge controller. What is the effect of a panel, in the sun, and in addition then redirecting the sun via a mirror to the panel? Possibilly creating a "hot spot" depending on the focus of the mirrow.
And while on the subject of mirrows, years ago at one of many jobs i had the opportunity to install some mirrows that were plexiglass, i think. Anyway they were flexible and could be bent into a concave position. Does this have any "intensity" factor