The Power Gorilla folks sell solar and batter-powered rechargers for portable devices. Their latest invention is the Power Gorilla, spare battery for laptops that can run a device for about TK hours on one charge. You can pair it with their solar panels to power your laptop with the sun. They’ve had one laptop running on solar power for about a month now, which is pretty impressive.
You might find them in some stores in the US, so keep an eye out. The Gorilla should be out in the summer.