I'm a gadget queen so I had to work out something to keep my kit going during my upcoming extended cycle tour. Now, there's a lot of dynohub-and-battery-charger arrangements coming to market, but I lack the dynohub and don't want to tie stuff to one bike (or any bike). Solar is the obvious candidate, and most of the commercial "backpacking solar" is expensive and rather underpowered. Here's what I settled on:
An Extreme USB smart charger, which will charge up 4 AAs (and AAAs) from USB or mains power and will drain those batteries to charge USB devices. Since I'm standardized on AAs, this ticks all my boxes. 4 full AAs will feed a phone more than twice over, and in case of emergency, disposable batteries can be used to feed the phone too.
A stack of Vapex AA NIMH batteries. At 2900 mAH, they're more capacity for half the price of rechargeable Energizers. They even come with little cases, bless. They are fat little buggers though, and they jam in tight torch barrels.
And a Voltaic Systems 2w 6v solar cell from Adafruit (yes, the geeks on the cover of the latest Wired, home of the Mintyboost and the SpokePOV (one day) and other nerdy goodness). Output peaks at 330mW, and the panel is vanishingly light and weatherproof.
By sweet serendipity the charger is tolerant of a range of inputs: it kicks in weakly in low cloudy gloom and rages away when south-facing at just the right angle at noon. The panel's output plug even matches the charger's input! Plans were afoot to molish a fancy-pants regulator-and-low-light-boost, but this Just Works. So the solar cell goes under the clear map-trap in the handlebar bag, the charger lurks inside somewhere, and Robert is your mother's brother.
I think, for about the price of a big Powermonkey, I've got about half as much electrickery and a lot more flexibility. Stay tuned to mock this prognostication in late May when I get back!