We've become very good at the thermal energy differential -> mechanical energy -> rotational mechanical energy -> electrical energy system, just because it's tr

We've become very good at the thermal energy differential -> mechanical energy -> rotational mechanical energy -> electrical energy system, just because it's trivially easy to get that first step since nearly every form of energy can be converted to heat. Some of our energy production machines use only a subset of these steps (e.g. internal combustion engines just use mechanical energy -> rotational mechanical energy), but pretty much everything save solar uses at least one of these conversions. So I find anything outside this cycle very interesting.