The comment about powering a few anemic lightbulbs on 60W was assuming 12V, but otherwise it's all pretty independent of voltage.
You could get the current 1800W of energy out of a branch circuit with 15A at 120VDC and all the limitations/massive wires I described.
If you wanted to run 1800W DC as we run current power (14/2, hundred foot+ runs, etc) you'd be looking at something like 720VDC at a couple amps.
There's three main things I see as limitations to really pushing DC up to those levels:
1. Safety, plain and simple.
2. Switching. You generally require larger contacts and bigger gaps to switch DC because you don't get the benefit of it crossing over a 0 point several times a second. This gets worse the higher the voltage goes. This requires much more involved switching equipment. E.g., it's common to see a relay rated for switching 120VAC/30VDC.
3. Economies of scale. This one isn't some law of physics, but most current equipment you can find is 12/24/48VDC outside of very expensive industrial stuff. Also you're gonna need some pretty big transformers to step this stuff back down to usable voltages since everything we need it for is generally running at single-digit voltages. (Efficient, but just another big thing on the BOM for every single device.)
That said, I'm just a hobbyist so I may be missing something fundamental here.
Ohms law plays a big part in all this. Resistive losses are governed by the square of current multiplied by the resistance of the wire. As such running higher voltages minimises these losses. We use this all the time with our power transmission lines which generally run at 500kV AC if I recall correctly.
1. Safety is relative. 10-20mA is enough to kill a person. In AC voltage we measure it as root mean square, the actual peak to peak voltage is greater than Double that.
2. There are such things as solid state switching. Solid state relays and field effect transistors come to mind. This is also how we down convert DC power to lower voltages, very fast switching giving an average voltage that is the target (see buck converters).
3. DC power is everywhere and it is easy to do DC to DC conversion. Single chip solutions exist. Hell your car is entirely 12V (if ice powered, EV's are a different matter)
> You could get the current 1800W of energy out of a branch circuit with 15A at 120VDC and all the limitations/massive wires I described.
15A at 120VDC wouldn't require massive wires. I'm not sure why you think it's drastically different from 120VAC for wire sizing. If dropping 10% of the AC voltage is OK, dropping 10% of DC is presumably OK, too, and either is I * R. About 96 meters to drop 12V, or 48 meters out and back.
It's not a good idea for plenty of other reasons, but...
You could get the current 1800W of energy out of a branch circuit with 15A at 120VDC and all the limitations/massive wires I described.
If you wanted to run 1800W DC as we run current power (14/2, hundred foot+ runs, etc) you'd be looking at something like 720VDC at a couple amps.
There's three main things I see as limitations to really pushing DC up to those levels:
1. Safety, plain and simple. 2. Switching. You generally require larger contacts and bigger gaps to switch DC because you don't get the benefit of it crossing over a 0 point several times a second. This gets worse the higher the voltage goes. This requires much more involved switching equipment. E.g., it's common to see a relay rated for switching 120VAC/30VDC. 3. Economies of scale. This one isn't some law of physics, but most current equipment you can find is 12/24/48VDC outside of very expensive industrial stuff. Also you're gonna need some pretty big transformers to step this stuff back down to usable voltages since everything we need it for is generally running at single-digit voltages. (Efficient, but just another big thing on the BOM for every single device.)
That said, I'm just a hobbyist so I may be missing something fundamental here.