Any appliance with strong motors should be more efficient with AC supply. But almost anything else can be regarded as a heater that doesn't care much as long as it is fed with the correct voltage. Which is actually the core issue.
A DC household would have to choose a trade-off between multiple lines with different voltages or fewer voltages that need to be adapted to the appliances. And we're right back at the AC situation, but worse since DC voltages are more difficult to change.
But consumers like datacenters can very well plan ahead and standardize on a single DC voltage. They already need beefy equipment to deal with interruptions, power sourges, non-sinus components, and brownouts, which already involves transformers, condensators, and DC conversion for battery storage. Therefore almost no additional equipment is required.
What qualifies as a strong motor here? Are you comparing to a brushed DC motor? Do you think a washer/dryer would have worse overall efficiency with a BLDC in a DC home compared to what we have today? If so, that’s news to me. Where can I learn more about that?
The trade-off between, say, one (relatively) high voltage DC bus throughout the home vs many branches with lower discrete voltages is indeed a problem. With AC, we took the bus approach, running 120v everywhere (in the U.S., higher elsewhere). I’m inclined to say we should keep doing that for flexibility and predictability. But it’s a trade off, like you said. It would obviously help if regulatory and standards bodies came out with official recommendations.
Things like washing machines, dryers, dishwashers, air conditioners, or fridges spend a lot of energy by running powerful electrical motors, which should benefit from AC.
Everything else I can think of in a typical household is basically a mere heater that in principle works equally well with AC and DC of the correct voltage. Even computers can be said to mostly care about the correct voltage since AC->DC conversion is vastly easier than voltage conversion.
>Things like washing machines, dryers, dishwashers, air conditioners, or fridges spend a lot of energy by running powerful electrical motors, which should benefit from AC.
No, they don't, not at all.
Most modern appliances have variable-speed motors these days. You can't do that by just connecting AC to a motor; you need a control board to generate the waveforms necessary to make the motor turn at the speed and direction you want. That control board has to be fed with DC power. (Source: I used to design BLDC motor control systems)
Only really simple appliances, like old-fashioned horribly-inefficient clothes dryers, still use AC induction motors, and those are mostly being phased out. (Bathroom fans also need AC; they're usually cheap synchronous reluctance motors.)
So it really doesn't matter much whether the incoming power is AC or DC these days, unless you have a bunch of ancient appliances that still use induction motors. If it's AC, it's going to be rectified and fed into a DC-to-DC converter to create the lower DC voltages needed. If it's a higher DC voltage, we can skip the rectification step and not worry much about ripple.
Probably 90% of my devices run 5V DC or similar, but you can't run that through a home so you're back to needing AC. If you're going to have AC and DC then you might as well just have AC.
> Probably 90% of my devices run 5V DC or similar,
Indeed. And that’s quite normal. Our electrical system should serve our modern needs.
> but you can't run that through a home
5V might be too low for that length of wire. But you could most definitely have a low voltage line in your house that we could design around, maybe 12V. Electric vehicles are moving towards 48V for accessories. It seems like lack of a standard is holding us back more than anything else.
Or we could just keep doing 120V in the walls, with a DC supply. Modern DC-to-DC voltage converters are very efficient and small. But maybe I’m wrong. A lot of people seem to believe they are still not good enough yet for such a change to make sense.
> If you're going to have AC and DC then you might as well just have AC.
I arrive at the opposite conclusion. Most things are natively DC. So therefore, power in the walls should be DC and we should covert it to AC near the endpoint where necessary.
A DC household would have to choose a trade-off between multiple lines with different voltages or fewer voltages that need to be adapted to the appliances. And we're right back at the AC situation, but worse since DC voltages are more difficult to change.
But consumers like datacenters can very well plan ahead and standardize on a single DC voltage. They already need beefy equipment to deal with interruptions, power sourges, non-sinus components, and brownouts, which already involves transformers, condensators, and DC conversion for battery storage. Therefore almost no additional equipment is required.