florinc:
Its a very inefficient way to charge AA batteries.
By "inefficient" you mean that there energy is lost somewhere, or it's just a slow?
In real-world designs energy is always "lost", even running current through copper wire uses a small amout of energy. 
But seriously it would be slow, even though a nominally 15 VDC solar panel could charge 9 (possibly 10 in strong sunlight) AA batteries at a time. If the AA batteries have a 2500 mAh capacity, and the average current from the solar cell is 100 mA; it would take at least 25 hours to fully charge the batteries (in real-life it would probably be somewhat slower). Given that most places on Earth have less than 12 hours of sunlight during the majority of the year, that's about three days total... Unless of course you only plan to use this charger within either the Arctic or Antarctic Circle during their respective summers, then it would be just over a day.