Step 2: Get Some Peltier Cells Online
Peltier cells utilize semiconductor technology much like standard solar cells. Two polarized semiconductors convert heat flow into electrical current. Naturally, the greater the heat gradient, the more current is produced. A set of 10 peltier cells can be purchased for $70. Surprisingly, this price is cheaper (since I last checked in 2007) per watt produced than solar cells. Peltier cells are often used in heating and cooling applications because when current is passed through a peltier cell, one side becomes hot, and the other side becomes cold.
It is highly recommended that a cooling element (heat sink) is placed in the opposite side of the peltier cell (the side not touching the Fusion Jr.). This allows for a greater cooling gradient. In some cases, fans or even ice can be used as a coolant to allow for a gradient. Don't let the peltier cells get too hot or they will melt though!
Placing the cells just right for them to get a maximum heat gradient is optimal. Use aluminum tape to attach the cells.
If you do not wish to use peltier cells, other technology can be used as well such as small steam engines or stirling engines. Both can produce enough power to charge batteries or small appliances.