This kit is from adafruit.com
With a little soldering, you can make this battery-less blinking skull. That's right, there's no coin battery! Instead, a 1 Farad super capacitor is used to store energy. It takes around an hour to make and, when you finish, you can charge it either with a USB or with the power of the sun. It takes less than 2 minutes or so to fully charge through the USB and 15 minutes from direct sunlight. In darkness, it'll last for almost 90 minutes.