Because of the negative lift of the horisontal stabilizer, the main wing needs to provide more lift than the weight of the airplane. This increased lift requires flying the wing at higher angle of attack, which always comes with increased drag (https://en.wikipedia.org/wiki/Lift-induced_drag). Increased drag means lower efficiency.

Analyzing energy transformation is not so useful, because most drag ultimately ends up heating the air. (A little will heat the airplane skin.) There are several different mechanisms that makes that happen, and no easy way to figure out how large it is, but it's definitely not minimal. It's why (most) airplanes need an engine to stay up...