Between smartphones, laptops, ipads and ipods, the 21st century is all about being constantly switched on and hooked up, and there's nothing more frustrating than when a dead battery takes you off the grid. Thankfully, with the latest strides in portable solar panel technology, you might be able to bury those dead battery worries for good.

You may remember back in the summer we featured the Eco Arcs Voltaic Converter Solar Backpack, a rucksack with solar panels attached that enables you to charge your gadgets on the go? A great festival must-have, its only drawback was the fact that you couldn't remove the panels when they're not needed. Well now ThinkGeek have come up with the solution.

The Piggyback Solar-Powered Gadget Bag is a PV solar array that's designed to strap over an existing bag – enabling you to use it when needed, but protect the panels and ditch the extra weight when your charging needs are covered. With its sturdy straps, it enables anyone to get in on the solar bag action without having to invest in a brand new bag in the process.

The Piggyback's flexible and extremely efficient PV solar panel turns direct sunlight into an impressive 1000mA at 5.6V. For the technophobes among you, that means it should charge your smartphone with ease. Even more impressively, with two extra pockets included, one small (8" x 5" - big enough for a Kindle), and one larger (8" x 12" - big enough for an iPad), and built-in channels for running USB cables between them, you can actually charge more than one device at a time.

Naturally, if you don't use up the Piggyback's full power capacity when the sun is out, the clever gadget's 800mAh Lithium Ion battery will store any left over rays for a more cloudy day. This sort of technology doesn't come cheap. But at $1i9.99 from US stockists, it's not overpriced either, given the infinite hours of free energy you've got ahead of you.

What do you make of the Piggyback? A bold green fashion statement? Or something that should be left in the shade?

To bag yourself a bag, or to find out more about ThinkGeek's other green tech ideas, head to www.thinkgeek.com