Okay.... So, DC-DC is more efficient than AC-DC. Don't think anyone would argue with that. And he's advocating DC 24V lighting. Great - more efficient - agreed. But in all the off-grid DC systems I know about, you have to either buy all new appliances that run on DC, or have expensive inverters to run standard appliances that run on AC, or a combination. Totally agree it would be nice to get away from that dilemma.
But I'm confused - how would all our normal appliances work on this system? As some have already mentioned - DC running on our AC lines isn't very good for transformers in all our appliances...