solar works well for cell batteries like aa and aaa, but the bigger batteries like video cameras and dslr use just don't charge well, especially on the AT where you've got canopy cover almost all the time. I knew a few hikers that would use the towns to recharge, but if you plan on more then just sporadic shooting, you'll be using the towns quite a lot.
charging batteries was a big concern to us, and my solar charger was one of the first things that got scratched from the needs list while still in georgia.
we had a little extra weight as my wife is diabetic(type I) which added a bit of a twist to hiking the AT.
back to the subject though, it comes down to how much blue blazing you want to do if you plan on seriously making a documentary, and how good your resupply and support is.
if you have a good resupply network, you can always carry a couple of batteries and have a couple of charged batteries ready to mail out to you. having someone that can receive your dead batteries and send you good ones and keep that up is a good work around, as i'm sure you've looked into setting up your drops, it's not too much of a concern or hard to work around. we did that with xd cards, we carried three and had three shipped back and forth as we went once we filled them up. so we always had access to empty cards and didn't worry about having full cards with us.
as far as resupply, the AT these days is too easy to hike when it comes to supply points. without trying you can usually go 4-5 days tops as supply is available just about everywhere. kind of takes away from the whole experience, but thats the reality of nature versus construction expansion. even the 100 mile wilderness isn't really that anymore.
before you go, do a couple of hikes with a video camera and equipent to see how it works for you.
i wish you two luck and hope you enjoy your AT hike. you'll find no matter how experienced you are, it's a pleasently different experience, and a challenge you'll never forget. i would say some day i will go back and do some section hikes on the AT but i doubt i'll ever go back to the east coast again. now we are eyeng the pacific crest
