solar panels have come a long way. a lot more efficient, and a lot more output (better voltages)
even if the solar was not strictly for charging, a battery is a good idea as a buffer/regulator/backup for the power the cells put out.
here's a long video about an R/C plane and he does a good job describing what's going on with the solar cells, battery, etc. saw this a while ago and thought it was a really good example of the possibilities of solar.