See also the toplevel.

I've been looking at a lot of power options. The 9W panels I'm looking at are about 10x9 inches (or 255x225 mm) and provide roughly 1.5A at peak sunlight. The 6W panel I got to start with is about 9x7 inches (220x175 mm) with about 930 mA at peak sunlight.

One thing that has to be considered is the thermal characteristics of the various components. The Pi seems to be the limiting factor here, with a max temperature of about 70C - I think this should be okay. If I 3D print the chassis, ABS plastic has a glass transition temperature of about 105C, which is kind of the limit when the system is powered off.

I bought a book [1] on building lithium battery packs, and I think the best option might be to build a custom 18650-based battery pack and charger. Otherwise, I have to start stacking battery packs, and neither of the charging options I've been looking at (the Adafruit solar charger [2] and the Sparkfun Sunny Buddy [3]) seems to support this kind of configuration. All of the system boards I've looked at accept 5V power; stacking batteries means I'll probably get 7.4V out of the power pack.