This Green Circuit is an example of the Joule Thief Circuit board. This one was made by Dawn DuPriest, and is freely available on her youtube page.
The Materials List and how-to manual is available on the e-store (under construction)
It uses 1 AAA NiMH to power 10 LEDs. The interesting part is that the 1.25 Voltage of a single AAA NiMH battery should not be strong enough to light the LEDs. On first glance, it appears as though it is stealing energy, hence the name. One advantage is that the solar panel only has to produce a bit more than 1.25 V to charge the battery.