Seems to me the author is understating his own argument, and missing the point, to some extent. The devices he excludes ("Appliances like electric ovens, electric water heaters, and air conditioners will [still] require 110VAC") are precisely the ones that take most of the power, probably 80% in aggregate. So, if you want significant savings, those would have to be DC as well, but it would have to be 220VDC or at least 110VDC, because for 12 volts you would need at least finger-sized copper bus running all through the house. In fact, the most efficient new air conditioners / heat pumps (e.g. Daikin Altherma) run on DC, i.e., they convert the AC to DC which then powers inverter-controlled synchronous motors. A water heater, even an existing one, could just as easily run on 110/220 VDC, you'd just need to replace the control unit. What you'd probably want is a system with at least 2 voltages, say 24V and 220V, each with its own battery charged by its own solar array, so you don't need to do DC/DC voltage conversion (which also has losses though probably not as much as an inverter). Most of the house would only have 24VDC wiring, 220VDC would only go to the kitchen and utility room, just as it does now in AC systems.