TEGs aren't the only technologies that can do what steam does. There are closed cycle gas turbines, for example, which do not combust a fuel but rather use heat

TEGs aren't the only technologies that can do what steam does. There are closed cycle gas turbines, for example, which do not combust a fuel but rather use heat differentials to convert energy. There's also Thermoacoustic generators as well, which are quite efficient and interesting to boot. Both of these have practical efficiencies that are already much higher than TEGs.