After reading your post I started looking around for other battery power systems like that one. Amazon has a bunch of very cheap 5v USB charging systems with both AC input and a mini solar panel (e.g. http://www.amazon.com/SunPlug-Solar-1350-rechargable-battery/dp/B0019ZH5N0/ref=sr_1_1?ie=UTF8&s=electronics&qid=1268367867&sr=1-1). I'm wondering if I can use one of those as a super cheap charge controller. Since the AC charging input is actually just a DC input from an AC wall wart, I wonder if I could run my solar panel (with a voltage regulator) into that AC input on the battery as an external power source, then splice the a USB charging cable from the output for a nicely regulated power source for my camera. For $11 its probably worth trying out.
I find no specs on what input voltage those use. I suspect that it being advertised as charging from AC or USB that input voltage might be limited to ~5v, same as its own solar-cell specs. Keep in mind too that if you use a standard voltage regulator to drop the voltage from the typical solar-panel array (15-18v) that this is a lossy process. The nice thing about the DC-DC converters with that DigiPower unit is that they don't waste energy as heat. Miniature DC-DC converters are also very pricey, if you've ever tried to hunt some down, even as bare-bones electronics components. As I said, those were worth the price of the unit alone. But you say you already ordered a DPS-9000 so you'll have your bases covered in either case.
The main problem I see is whichever battery you plan on using. And this will all depend on how much solar-panel you use as well as the frequency of shots taken, and the power-draw for each shot which depends on which camera features they are using. I find no mAh specs on my battery here, but searching online I see estimates of 1850-2200 mAh for the DPS-9000. (Which seems about right, when compared to the size of my Li-Ion battery in one of my cameras which rates at about 1250mAh.) With the semi-lossless DC-DC converter going from 7.2v (8.2v on full charge) to 5v, that's probably around 2700-3000 mAh of useful charge at 5v from the DPS-9000. If you are going to use a standard voltage regulator at any spot in your current path, then after the 5v to lower it to your camera's input will be the most energy-efficient spot to use one. Though in the end I think it will take a few days of tests in sunlight and cloudy conditions to be certain if solar-panel and battery-capacity will be enough for your required shooting rate. (From your blog: "Frame rate: 12 images an hour, ~200 per day (One image every five minutes, +/-16hrs a day)") For my trips I used three 1-watt solar panels. One of them being compact and foldable which was used/carried most often to the more remote places. It could charge a depleted DPS-9000 in about 3-5 hours of bright sunlight. Keeping the charge curve well ahead of daily photography uses, clear-skies permitting.
I recall seeing a CHDK page somewhere of them doing a test on all camera functions and how much current that each one will draw. It might be worth trying to find that. Then you'll be able to gauge how much solar-panel and battery-capacity is needed to keep up with whatever time-lapse task you choose. The surprise in that list is that manual-focus mode drew much more current than auto-focus modes.
So many variables to consider.
