The idea of solar-powered headphones is certainly a worthy one, but we're not sure how well products like this will fare in hotter climes. The "Soltronix Headphone Radio" looks a little bulky for summertime wear and, as we've noted many times in this space, we're morally opposed to anything that might draw perspiration.
And as Ubergizmo notes, plastic tends to warp and crack if left in the sun too long. But if they do hold up, this $50 headset can get 19 hours of playback time on a four-hour charge.
Just remember, unless you've got an outdoor dance floor, you'll need a more conventional pair of headphones to play DJ inside. When you do venture out, though, perhaps you can stay a bit cooler with a solar fan hat.