hey Ben, try and build a Peltier cell phone charger maybe using a cpu heat sink for cold side. a heat sink with candle\s on the hot side and then a 5v regulator attached to a usb plug. Ill leave the details up to you .
check this one out...
https://www.youtube.com/watch?v=_TuTGLS8nqI
https://www.youtube.com/watch?v=PIkyF_xR4pM