I had some 4" x 6" one sided copper pcb (5 ounce!), so I'm using that, and 8 of these:
AC Filter Caps. 8 of these buggers!
8 of them are rated for 80 amps RMS, which is good enough for my purposes.
Now I just need a basic charge controller. Basically, I think I can just set a homemade buck charger to 100% duty until the battery bank reaches some max level, and then I start to reduce the duty to keep the voltage constant, until it gets dark. At that point, you live on the battery power, and in the morning, you do it all over again! haha.
The nice thing about the film caps is, they are rated for 60,000 hours at very high temperatures, so it's probably more like double that since they won't get too hot. I won't be close to their rated RMS amps.