Entropy. You cannot look at a system purely from an energy conservation stand point. Take Carnot efficiency for instance. That’s the extreme case where it teete

Entropy. You cannot look at a system purely from an energy conservation stand point. Take Carnot efficiency for instance. That’s the extreme case where it teeters on the fully recoverable entropy. For your example, the entropy price has to be paid somewhere in the system (usually in the heat to work ratio).