Casing out a solar bag for one of the green tech enthusiasts on your holiday list this year? Consider the Piggyback Solar-Powered Gadget bag from ThinkGeek (which comes to us via Red Ferret), designed to strap over an existing bag, be it a backpack, messenger bag or otherwise. The result is the solar "electrification" of any existing bag, providing power on the go, via renewable energy, for all of your favorite mobile gadgets.
The straps and buckles here are designed to make sure you don't have to give up your favorite bag to get in on this solar bag thing: the Piggyback straps directly onto whatever you may already be toting, and offers two more zippered pockets in the process: one large (8" x 12" - big enough for an iPad), and one small (8" x 5" - big enough for a Kindle). The Piggyback's sizable (8 x 12 inch) super-efficient flexible solar panel turns full sun into 1000 mA at 5.6 volts -- enough (according to ThinkGeek) to charge your iPhone with ease.
On a sunny day, of course, the Piggyback will be your gadget's best friend, but if you haven't already drained all the juice produced by this device while the sun was shining, you can tap those reserves on cloudy days via the included 800mAh Lithium Ion battery pack. The device includes built-in channels for running USB cables between pouches, so you can also charge more than one device at one.
At $119.99, this isn't the cheapest solar bag we've seen, but it certainly is the most adaptable. Transitioning smoothly from the backpack to briefcase -- or, we imagine, even a larger handbag -- means truly mobile solar charging.