Solar chargers already exist. I don't think they work for Sony Ericsson phones yet.

But I have a bunch of them tied to my bookbag so they collect power when I walk to class. And then they only work for NTT DoCoMo FOMA or Softbank Japan 3G phones. Since Docomo and Softbank phones (mostly Toshiba/Sharp/Panasonic) all use the same charger/data port so they just make one type of cabling and it works for over 30 different devices.