A device is usually either in your palm or your pocket, you don't put it screen down on the table to charge. I would prefer large flexible external charger, which can be hung on the pocket, bag or backpack or left on the table without stopping you from using the device.

But the device looks beautiful... And raises ecological awareness.

It is entirely possible to make a theme based on this device, if somebody likes to see 'happy' battery

A practical phone with a solar panel on the back would have to:
1. use small amount of power, like, have e-ink screen;
2. be carried in transparent bag/pocket to recharge.