[crote]

The problem is that all of those DC devices don't operate on 48V either. The vast majority of chips require a 5V or lower input, so with a 48V DC supply you're still going to need a per-device PSU to do DC-DC conversion. In other words: no getting rid of power bricks.

Efficiency isn't as straightforward either. You're still being fed by 120V/230V AC, so you're going to need some kind of centralized rectifier and down converter. It'll need to be specced for peak use, but in practice it'll usually operate at a fraction of that load - which means it'll have a pretty poor efficiency. A per-device PSU can be designed exactly for the expected load, which means it'll operate at its peak efficiency.

We also don't use 5V DC grids because the wire losses would be horrible, so a domestic DC grid should probably operate at pretty close to regular AC voltage as well. In practice this means the most sensible option would be to have a centralized rectifier and a grid operating at whatever voltage it outputs - but what would be the point?

As to PoE: I personally really like the idea, but I don't believe it'll have a bright future. For its traditional use the main issue is that there doesn't seem to be a future for twisted-pair beyond 10Gbps. 25GBASE-T might exist as a standard on paper, but the hardware never took off due to complete disinterest from the datacenter market, and it is too limited to be of use in offices and homes. I fully expect that 25G will arrive in the home and office as some form of fiber-optic interconnect - with fiber+copper hybrid for things like access points.

On the other hand, for a lot of IoT applications PoE seems to be too complicated and too expensive. It makes sense for things like cameras, but individual lights, or things like smoke sensors are probably better served in office/industrial applications by either a regular AC supply or a local DC one, plus something like KNX, X10, CAN, or Modbus for comms: just being able to be wired as a bus rather than a star topology is already a massive advantage. And for domestic use the whole "has a wire" thing is of course a massive drawback - most consumers strongly prefer using Wifi over running a dedicated wire to every single little doodad.

[matt-p]

What if all homes had battery storage and or solar? You could then simply use it's rectifier as needed or direct 48v from the solar panels. That would be even more efficient than 230v.

[ssl-3]

That'd be neat. But there's no standard for voltage for home solar: The batteries might be 12, 24, 48v, 60v, or even much more. Meanwhile, the panel arrays commonly output anything as low as 0V and up to ~600V. There's not much for rules and norms here.

Even if we were to standardize a low (<50V) voltage for DC distribution within homes, we'd still need ~120/240VAC to power big stuff, or we'd instead need even-larger conductors (more copper) than we use today to do the same work with low voltage.

But, sure -- we can play it out. So let's say we have an in-home 48VDC distribution standard and decide that this is the path forward and we enshrine it in law.

We need to convert whatever the solar system has available to 48VDC. Then, we need to distribute that 48VDC using a completely separate network of cabling. Finally, we still need to convert 48VDC to whatever it is that devices can actually use.

That's not representative of a reduction in steps, or an increase in efficiency.

That is instead just an increase in installed infrastructure expense, and a decrease in device compatibility. It takes what we have, which is simply universal (at least within any given geographical area) and adds complexity.

And for what? What's the perceived benefit?

[matt-p]

Almost all home batteries are 48v, I think it would be reasonable to standardise on that.

[ssl-3]

So 48v it is.

Is the juice worth the squeeze, though? Two sets of home wiring voltages? Substantially bigger copper wire inside the walls instead of existing copper, in order to do the same work? Two sets of appliances (of all sizes) on shelves at the store? More adapters?

Billy now needs to bring 2 wall warts to make sure he can charge his portable gear at a friend's house instead of just 1, because he's never sure until he gets there if they've got a 120 or 240v house like they all used to be, a combination house, or if it's one of those solar-only places that only has the weird plugs.

What we have now is 1 cable plant connecting the rooms of a home, and an increasing number of hybrid solar inverters that -- on a sunny day -- cheerfully convert solar power directly from whatever the panels are outputting to the 120/240 VAC wiring that both existing and future appliances know how to use. At night, these hybrid systems do do the same thing from whatever voltage the battery uses and convert that to AC. There's only 1 voltage, and only 1 plug; Billy brings 1 wall wart and knows he can charge his stuff.

To be sure: What we have not strictly ideal, but then neither is changing things without a clear positive benefit.

Again: What's the qualitative advantage of changing this, other than change for the sake of change?

DC might feel nice and neat, but in reality it doesn't seem to be shaped that way at all to me.

[marcosdumay]

I'm not sure converting the solar and battery to 48V, distributing it around, and converting it to the needed voltage at the point of use is any more efficient than inverting it into 230V and distributing it around.

Also, you'll need wires that 5 times thicker. Instead of needing a reasonably 1mm^2 for a normal 16A line, you'll need 5mm^2 for the same power.

[matt-p]

Solar and battery are already at 48v in most cases, so you are avoiding converting it to AC.

I agree, it's unserious to suggest a cooker or something high power is going to run off of 48v. But for loads like lights, PC/Laptop/TV/Audio 16a at 48v is ~770W which is adequate for these devices.

[marcosdumay]

Both solar and batteries voltages vary wildly and require a converter to use.

[lillecarl]

We live on societies, switching from AC to DC because your low-power home appliances doesn't need AC makes no sense. Home power usage is dominated by heating and cooling not by your 45w laptop charger.

DC infrastucture makes sense in highly specialised environments.... Like new gigawatt AI farms

[shiroiuma]

Large home appliances probably mostly need DC power these days too. Look at clothes washers: they all have variable-speed reversing motors, so they're probably using brushless DC motors (which use motor drives that are fed with DC, and output variable-frequency and variable-amplitude sinusoidal waves to drive the motor). HVAC seems to be similar, with variable-speed motors and compressors.

I don't think that much stuff is left which actually needs AC power (usually to run an AC induction motor).

[matt-p]

[HVAC] true for the fans and controllers but surely you wouldn't DC feed a compressor.

[shiroiuma]

Aren't compressors these days usually variable-speed?