Firstly, the power is primarily related to the range – shortwave typically covers much larger areas than MW and FM techniques, and thus needs more energy in total, but less per square km covered.
Secondly, much of the energy can be saved in digital mode since DRM does not require a carrier: AM carriers account for about 60% of the energy in a shortwave signal, this energy can be saved by removing it when broadcasting in DRM.
Thirdly, analogue AM broadcasts cannot contain stereo sound or data streams, whereas DRM can.
Thus, shortwave DRM provides a better-quality broadcast, with integrated data streams, all while saving around 40% of the electricity to cover the same transmission area compared to analogue shortwave transmissions.