solar panels are the wrong dc voltage, so some sort of conversion is needed. I'm no EE, but my understanding is you go through AC and a transformer anyway in most cases.
Virtually all off-grid solar installations use some kind of an MPPT controller with a battery setup. The controller is always charging the battery (when there is power output from the panels), and the consumer power output is supplied by the batteries. This way you get much higher peak current output than the panels could provide, you also ensure stability.
In fact, many cabin installations don't even use inverters to convert into AC. They instead use DC appliances. So no, going through AC makes no sense in this scenario.
As for DC voltage levels, that of course is dependent on solar panel configuration and battery cells configurations/packing. Virtually all electric cars have a built in charger with a switching power supply that's already doing the DC voltage conversion. What I was remarking was that there is a lot of duplicate electronics that perform the same function and that a lot of intermediary steps can be eliminated.
Off grid is going to be designed to fit and probably cheap. Not always best. If you panels are near the batteries and near the load what you say can make sense (though I wouldn't be surprised if the charger had a AC step internally, that is clearly optional)
That isn't what you would do for anything tied to the grid. This is far more common (economies of scale mean the parts are cheaper). There you would take advantage of AC's ability to change voltage easily to allow the panels to be farther from the rest of the system. You would also want to use the grid as a backup for any system failures in the solar setup.
