[Nateman]

I wonder if there’s really a net gain.

Sad to say not only is energy always conserved but you can't even break even. Some of the energy becomes waste heat. A typical heat engine (like a car) only converts about 20% of the chemical energy into useful work.

[PLMerite]

“A typical heat engine (like a car) only converts about 20% of the chemical energy into useful work.”

Some things pass muster just because they’re the lesser of evils.