Blast, I are a thermoelectrics engineer. At least I was one at one point.
The challenge with thermoelectric power generation and cooling is that you need a material that has high electrical conductivity but low thermal conductivity. God saw fit to make most electrically conductive materials good heat conductors and most electrical insulators good heat insulators. Oh, by the way, the material needs to have a high Seebeck voltage as well.
In a generator, very little of the heat used is converted to electric power. Most of it is simply transfered by plain old conduction from the hot side to the cold side where you need to get rid of it.
Your typical measurement thermocouples have an output of tens of uV/C. Even with a 1000 degree delta-T, you'll need thousands of thermocouples in series to get a few volts to charge your cell phone.
That being said, I once built a unit with commercial cooling modules that was about the size of a 4" cube (mostly two extruded aluminum heat sinks). It output about 200mA at 12V sitting on top of a kitchen stove burner set to low. Most of the 200mA was used to run the computer fan that kept air moving across the cold side heat sink
The real challenge in a consumer product is preventing overheating. Ferinstance, some "High Temp" modules start melting at only 200C.
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