Enlarge (credit: Oregon DOT / Flickr) Solar energy is really starting to get its wings, with utility and residential installation growing at a rapid clip. While these systems generally operate for two or three decades, there inevitably comes a time to take photovoltaic panels down for replacement. What happens then has a lot to say about solar's long-term bottom line. The opportunity is there to turn old PV panels into new ones, reducing the technology's environmental footprint.