Hmmm... Nokia was teasing solar technology on their conversations site not long ago (something to the tune 'summer is coming' in Feb? might've been overinterpreted by MNB and it was just about upcoming summer announcements, no idea). The OH gives this quite a spin. With a solar panel the size of normal back cover solar is not an option with today's tech, you might prevent the charge going down on a sunny summer day, maybe gain a couple of percents of charge after keeping the phone idle for a few hours. With OH: deployable back cover making the area 3x (or 5x) larger, this might work. So futuristic too (queue in ads showing space probes/ships deploying solar panels, future is now, in your pocket...)