[r9etb]

“Low energy” tells me this is interesting only from a scientific perspective, not an economic one.

It depends. If we scale energy sources from "low" to "high," I think that "cold fusion" might well end up being on roughly the same level as the gasoline engine. "Hot fusion," by contrast, being a very high energy source.

[broncobilly]

“Hot” or “Cold”, “Low energy” or “High energy” has to do with the energy of the participating ingredients needed to make the reaction go, not the amount of energy available if the reaction goes.