Strictly speaking, the energy it consumes is the gravitational potential energy of the ore they're mining, which would be consumed anyway in the form of, well, gravity, acting on the ore on the way down. They're just using it productively instead of dissipating it as heat from the brakes. Using only energy that ordinarily would have been wasted is of course very neat, but it's not breaking any laws of physics.

~~energy is converted and never destroyed so it's true~~

I think it means that the net energy consumption is zero. It can use energy, but it generates enough to offset it.