Solar AA Charging

System

Hey all, I've been toying around with the idea of making an AA charger out of some solar panels I have. The panels can generate either 800mA @ 4.25V (850mA Isc and 5V Voc) or 1600mA @ 2.13V (1900mA Isc and 2.5V Voc) depending on how I wire them up.

They actually work, in clear and unobstructed sunlight, as a direct USB source for a lot of devices when hooked up in series (5V "mode"), even high powered devices as they can put out 500mA @ roughly 4.7V (a little below spec).

I've hooked them up to an AA Eneloop Mobile Booster and under clear skies, it powers it fine. But, since the Eneloop wants 500mA, if there are clouds, it doesn't work. So I'm going to need a charging circuit that will operate when cloudy and I don't have so much current. It seems I always have around 100mA available, even when heavily overcast.

I've found this article here which seems to describe a circuit fairly similar to what I need. The source and battery voltages are different, but it seems like, with some tweaking, it would work. (But I'm no EE, so I might be way off here).



I'm not sure this is the best place to ask, but I've seen some knowledgeable posts here and if anyone has some advice on how I might modify this circuit for my purposes, or perhaps another route altogether. I'm trying to use this project as a way to learn about electronics, so please, be gentle!

Thanks!