This is a thread about thermoelectric generators (TEG) of all kinds and shapes.
They are using the Seebeck effect.
In short it is a ceramic plate with two wires that make electricity from the temperature difference of two items that cools and making heat.
Read also about the Peltier effect used in thermoelectric coolers, those are related but different, one can use a TEC as a TEG if the temperature is more low.
TEC are often used to cool a fridge box using a battery or mains power tranformer. They are not energy efficient compared to a compressor fridge in our homes so dont build a large one, but they are good in a small cooler for cooling food/soda in a car for example, they are in those 12V cooling box one can buy.
TEG can handle more heat than TEC and there is also minor differences in the internal design to make them fit their purpose better.
The cheap TEG's at ebay or aliexpress can tolerate 150 celcius it says.
More expencive TEG's can handle more heat than the cheap ones, i bet one finds good ones in wood stove fans.
TEG's can be useful for making light and power for mobile charging on a propane cooker, camp fire or a wood stove, a example here.
Thermoelectric Power Generation On Wood Stove
They can add power to a tea lamp candle so it makes lots more light and also charge USB.
THERMOELECTRIC GENERATOR | TEG | PELTIER
DIY Candle Powered USB Charger
I did buy some TEG's to test what they can do.