What about a 8th module, a thick soft one-piece additional plastic over-cover. To protect the phone when it falls, with edges topping/protruding from the screen to spare scratchs. Something a bit like the yellow part here : http://www.electricien-quimper.fr/wp-content/uploads/2013/01/testeur.jpeg
It would be equipped with solar cells at the back (something robust, no expendable panels), and would be pluggable in the standard battery reload port of the FP2 (for instance)(with a USB port pointing from inside the over-cover towards the FP2).
It would enhance battery lasting period simply with the habit of laying the phone back-on-top on tables. We’ll need a flashing activity led here, but some softwares simply use regular flash-light for this. We could wear the phone on an arm-band, cells on top, like joggers.
Transparent solar panels are very attractive, but what I suggest here is possible right now.
Solar charging would be more efficient in some countries than in others, but it would provide a hope that the phone won’t shutdown when critically needed… Or that you would be able to starting it again despite everything else, simply waiting near a strong light source. (Remember “Castaway on the moon” movie ?)
Ok we can reload phones regularly at work, at home, in some trains… But if I don’t have to plug it in, because solar pannels are working, I would enjoy the enhancement. I always forgot to plug my phone, and take some time to find my cable back…
I have a solar Casio watch, it just works, it’s a pleasure. Phones require more power, but lets start with something.