With DC, you can put solar power directly into the distribution grid without conversion inefficiencies and phase synchronization issues.
You still have the same system wide frequency compensation and phase margin (not related to AC phase) problems which overshadow AC phase matching.
Not only is solid state DC voltage conversion more power efficient than passive transformers, you do not run into nasty polarity and phase issues, which can be huge infrastructure liabilities.
DC is only more efficient when long distance high voltage transmission lines are used. DC allows a higher voltage to be used without excessive current and radiative losses. The transmission line itself takes a lot less metal for the conductors.
For distribution AC has the advantages of better arc interruption, easy passive impedance matching via transformers, and easy passive isolated current sensing. Ever notice how a given switch, circuit breaker, or fuse has a much lower DC than AC voltage rating? This has implications for high voltage DC connectors as well.
While high efficiency motors can make better use of DC, that excludes all other AC motors which are too small to make that economical and motors are pretty efficient already so there is not much to be gained there.