Poweradd ™ 7W Foldable Solar Charger with USB Port for iPhone 5S 5C 5 4S, Android smartphones, tablets (not supported Samsung Tablets) and other USB devices (7 Watt) (Electronics)
In full sunshine a good alternative to the socket, then you can eg charge a battery pack good. Like all solar cells is the power on cloudy days, of course, only a fraction of what is possible in direct sunlight.