You think way too high: zero Hz forever.
I'm actually being serious. There's now the idea of HVDC lines coming out. I think this is a great idea, actually because you can drastically lower the amount of copper by eliminating the third line in 3 phase. The lower diameter wire can be used because DC current can flow through the whole wire, as opposed to the skin effect of A/C. Not to mention that the nasty power factor problem goes away.
You mean the third line in split phase? 3 phase often has 4, 3 phases and a neutral (Wye configuration, Delta doesn't.) You also need a safety for 5 wires.
You technically only need two wires coming in for residential, the transformer can split the phase at the final distribution point.
Skin effect at 60Hz isn't that much of a problem. Your biggest problem is going to be the massive losses of the DC system (AC is theoretically sum-zero) and the problem of getting it down to a useful voltage that isn't thousands of volts. AC is why Westinghouse's system worked for distribution and Edison's didn't.
If we really wanted to do it right, we'd all go to 400Hz and be like the military.
Well, I keep hearing that power factor is a big problem and there are plenty of circuits to correct that. If it wasn't such a problem, there would be no need to correct for power factor loses. I admit, that residential use probably doesn't care about power factor loss that much.
DC losses are only at low voltages. If you bump DC up to say 300KV, the losses are a lot less than a few hundred of volts. In my own home, I use 48 volt DC primarily for my inverters. This seems to be convenient. My solar panels output about 120 volts DC (I string a bunch of them in series). I wanted to run lower gauge wire.
Now there are conversion losses from going to A/C. But for long haul power transmission, I think HVDC is the way to go.
Power factor can be a problem, but that's very easily fixed with the addition of a capacitor on a motor.
Current and voltage tend to get out of sync when you have an inductive load, as the resistance (reactance in AC) starts to become a complex number - by complex I mean [R -j Z] as in a polar number, or a number represented by a phasor. A capacitor drags it back to a purely resistive load, which is an easy solution. It is a problem with AC systems, but is very easily corrected. This has the effect of reducing apparent power consumed by a device, and keeps things in sync. (Capacitve reactance goes the other way, but since we don't have that many capacitive-input devices, correcting it with inductors isn't really that much of a thing but it does happen.)
When I say losses, you're not sending DC hundreds of miles along a cable without losing most of your voltage due to resistance of the cable (generating massive amounts of heat) - sending it 1500 feet from your solar panels to an inverter is meaningless in this sense. AC has less of an issue with that because, as I said, it's theoretically zero. DC over longer distances needs massively sized cables to cut resistive losses down to something manageable.
You also have the problem of getting that HV down to a reasonable level. AC is easy with a transformer, and that's what made our modern distribution system possible. Converting high DC to anything is a very expensive prospect because you'll need to have a massive HV switching supply to get it reasonably low. High voltage parts are expensive, and you're going to need to get down to 24V or so to be reasonably safe at high currents.
If you wanted to have an internal DC system at something like 24 or 48V, that's fine - but also remember that you're going to need a higher voltage if you want to have any kind of motorized or heating devices without drawing massive amounts of current for the power consumed.
Sure, you can do it like you're doing it. Bulk power generation and distribution isn't going to happen like that because physics says no. That's not even getting into the fact that actually switching high-current DC and isolating it from adjacent conductors can be black magic of it's own. (Check out a relay sometime...some will say switches 120VAC/36VDC. DC will arc long before AC will for a given current.)
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