Planning on being away from a wall outlet with your MacBook for a long time? QuickerTek has released a pair of solar chargers for your laptop, letting you carry a power outlet around with you...at a fairly steep price.
The whimsically named Apple Juicz comes in two models, which generate 27 watts and 55 watts respectively. Lay it out in bright sunlight, stake it through the included corner grommets if it's windy, and plug the MagSafe connector to your MacBook. You'll be fully charged in six to twelve hours, depending upon which Juicz and MacBook you have--and, of course, whether you're using your MacBook at the same time.
The 27-watt model is a step down from the 45 watts, 60 watts, and 85 watts you'd get from your Air, MacBook, or Pro wall chargers respectively. It's unclear from QuickerTek's documentation whether you can fire up your MacBook immediately with a completely dead battery and an Apple Juicz; doing the math, I'd assume you'd want to store up some charge first to avoid a local brownout.
The Juicz comes with a carrying case and folds up to the size of letter paper, but it spreads out like an oversized beach blanket. The 27-watt model unfolds to 3.5 by 2.5 feet; the 55-watt to a whopping 5 by 3.5 feet. It might be portable, but you'll want a lot of untrammeled space to deploy this.
Finally, there's the price tag: the 27-watt panel is $700, and the 55-watt panel is $1,200. Sure, it's green, theoretically unlimited, and lightweight, but I note that Amazon will sell me nearly 30 additional batteries for my MacBook for $1,200. Unless you're expecting to be away from reliable power for days at a time or you're truly committed to renewable energy use, an older MacBook and a few spare batteries is probably the way to go. But if your travels take you further afield, this would be a nifty addition to your travel bag.