Think about how little cooling is needed on a big electric motor. Even motors made 100 years ago are very efficient. By contrast anything that qualifies as a

Think about how little cooling is needed on a big electric motor. Even motors made 100 years ago are very efficient. By contrast anything that qualifies as a "heat engine" (including internal combustion) is limited by Carnot's law to be low-efficiency. If it weren't for the extraordinary energy density of combustible fuels they wouldn't be competitive.