When I was in high school I looked into making a micro-power plant using the Seebeck effect for the Intel Science Talent Search. I thought about using liquid sodium as a heat sink, which is what some heliostats use. Solar power towers use the captured energy to power turbines, but this isn't very efficient, so I thought I would add thermoelectric generators to capture some of the energy that is lost as heat.

I ended up not doing this because the Seebeck effect isn't really a useful power-plant (in the broad sense of the word) when you have a small temperature gradient because it is really inefficient, although it is useful for thermometers and other low power items, and for some exotic things like Radioisotope Thermoelectric Generators, which is what powers Voyager and other long distance spacecraft. It becomes worth using when you have a large, consistent energy source, which is usually geothermal energy. But the small temperature difference between the human body and the flashlight and the low efficiency of thermocouples means that this project won't seriously compete with battery powered flashlights. However, it is a cool idea and could have some niche uses.