Side topic, but I wonder if there's a pivot point coming where household appliances could be offered in DC versions. It would be great to avoid the inverter efficiency loss / point of failure. Could there be a standard DC interior wiring system with line voltage for the fridge / dishwasher / laundry machines and let's say LED lights, phone chargers, etc? The need for AC power is just an artifact of long transmission distances, right?
High-voltage DC is actually more efficient for long-distance transport, and makes it easier to interconnect grids. Efficiency is not why we use AC. Installation cost and history is, because you need converters everywhere you connect it to an AC grid.
Up until recently a lot of standard pieces of equipment weren't practical for HVDC lines. Electrical breakers, for instance: They existed, but tended to have short lifespans. That's because DC lines never go to zero power, whereas AC lines do so a hundred times per second.
Modern technology has changed that. The equipment is still more expensive, but that would be made up for by the reduced transmission losses... if we were starting from scratch. We're not.
DC is definitely better for charging batteries but most of those other appliances don't require inverters. Converting AC into heat, light, or rotation is pretty simple.
Many solar cell installations use maximum power point trackers with an internal high voltage DC bus - you could presumably tap that and distribute it directly throughout the house (often it's also directly attached to lead-acid battery banks, if used). In fact, you can often take ~170VDC and directly power many passive PFC power supplies with it. You still need inverters for AC motors though, which are a big portion of the load (compressors, fans).
I believe the biggest issue right now with internal DC wiring is you need much higher gauge wire, which translates to more expensive cabling throughout the house. You also still need a way to step the voltage for each device, so it's not clear what the savings are. It may be beneficial for lights where a clear standard for voltage can be determined, but everything else will still have it's own requirements.
You can use the same gauge wire if the voltage stays the same. The downside is that all of the switches and circuit breakers need to be replaced with ones rated for DC as arcs are harder to break.
Most DC installations are <50v to take advantage of existing DC powered gear and circuits under ~50v don't need a licensed electrician to do the work (in most locations).
