Yeah, but all these things (even the heat transfer from exhaust toncoolant in the Prius) need to transfer many kilowatts of energy to actually work. A kilowatt

Yeah, but all these things (even the heat transfer from exhaust toncoolant in the Prius) need to transfer many kilowatts of energy to actually work. A kilowatt-class liquid heat exchanger is the size of a large coffee cup. A kilowatt-class TEG is the size of a car engine. See for instance the paper linked below, Fig. 12, their module is 1 m x 0.3 m x 0.35 m. For comparison the Ford 1.0 Ecoboost engine is famously said to fit on an A4 sheet of paper and produces 100 kW. So adding a TEG you would more than double the size of your engine for a 1% efficiency gain. https://pangea.stanford.edu/ERE/db/WGC/papers/WGC/2015/26009.pdf https://pangea.stanford.edu/ERE/db/WGC/papers/WGC/2015/26009...