There are many fancy headphones on the market. HELIOS happens to be a pair of headphones with solar panels to draw energy from natural light. You can also recharge the battery through an AC outlet. HELIOS lets you listen to your music and phone calls without having to worry about running out of battery. The battery is good for 15 hours of music. You get half an hour of music after 1 hour of exposure to natural light. You can find out more information about it here.