High-power thermoelectric generator utilises thermal difference of only 5°C
The Carnot efficiency of a heat engine is 1 - T_low/T_high. When operating between 305K and 300K (room temperature(ish)), for example, this is 1 - 300/305, or about 1.6%. In other words, the absolute most amount of energy a device operating over a 5 K temperature difference at room temperature is pretty dismal. Just because their band gap (for lack of a better term) is small does not make this device "useful."For all stories about heat engines running between smaller temperature differences, the smaller the temperature difference, the less excited you should be. For example, I have a device that reaches the Carnot efficiency across temperature gaps of 0K! HINT: It's a rock. Or a paper clip. Or a wet tissue. Or...