this post was submitted on 29 Oct 2023
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This makes me wonder if we'll see a return to homes having DC for power instead of AC just to skip transforming DC to AC for homes that go totally off grid.
With high efficiency DCDC converters now cheap and good, we totally could do it.
So the issue is that nothing wants the same DC level. You have one device that wants 12V, another that wants 48V, and another that wants 5V. You end up with layers of conversions that each take an efficiency hit. Better to have one AC line and convert at point of use like we do now.
I can see in the future a standard for DC power with a completely different power socket that saves up the round trip of DC to AC then back into DC for all our electronics. There are fairly substantial benefits to be had but as I think it through the usable DC is 3 to 12V and appreciable load will mean those cables will push a lot of amps. Not sure the economics will work out without it being high voltage and that fits nothing DC today. If it's high voltage then everything needs a converter again.
Setting a DC standard today will be a world wide nightmare, we need it but it's got to be dumb for longevities sake. It's far off I think.
PoE is 48V. That's high enough to avoid too many losses over wiring distance, but also low enough that it doesn't have to be installed by a licensed electrician.
POE also is point to point, and currently tops out at 30W per link. You could split it off in a socket - but that reduces the available power per device even more.
Or we could use the current AC cabling where we use a single wire over multiple sockets and get a combined 3600W over a standard 16A fuse over 1.5mm2 wire - which with ground and neutral is about the same thickness as a shielded ethernet cable.
PoE type 4 can go to 90W, and this is plenty to power modern lights and charge smartphones and laptops. It has the side effect that smart devices no longer need wifi/zigbee/bluetooth/whatever; they get power and network from one cable.
12/3 romex costs about $200 for 100ft, or the same length of 14/3 for $80. 250ft of solid copper (not copper clad aluminum) cat6a costs around $200. You don't need a licensed electrician for 48V wiring. You may not even need to pull a permit on a retrofit. Very few individual things need more than 90W. We can cut the amount of romex going around way down in exchange for a lot more wired networking ports that have other side benefits than just power.
I've pulled a setup like this in my own house. Fishing a bundle of six cat6 cables through a hole isn't much more difficult than a single romex cable.
USB is the new defacto standard DC outlet. It's only suitable for fairly low power (240W) though. That's enough to charge your laptop but not enough to run a gaming PC.
USB-C power delivery can charge laptops. If there's going to be a DC outlet, though, it should be PoE.
Not for the reason you're thinking. DCDC conversion has gotten more efficient, but the problem is that nothing wants a specific voltage. Your LED strip might want 12 or 24 or 48V. Your phone wants 5V. Your single board computer might want 3.3V. Meanwhile, what's flying out of your solar panel array might be over 300V (depending on how they're wired together). You end up with layers of conversions that each take an efficiency hit. Add it all up, and it's better to convert the solar output to AC and then convert once to DC at the point of use. Which is exactly what we're doing.
Plus, items with larger draw, like a clothes dryer or electric stove, are going to want AC, anyway.
However, there's another thing that might make DC lines viable in houses. Power over Ethernet equipment has gotten relatively cheap. The base power levels are easily enough to run lights or charge a phone, and the more powerful versions can handle a laptop. What makes it especially interesting is that you don't need a licensed electrician to run it. You can't be a complete imbecile installing it, but don't need a license, either. That could dramatically reduce install costs in new homes. You need a proper electrician to install the breaker box and run a few high draw lines, but skip the rest.
As a bonus, any smart controlled devices no longer need wifi or zigbee or bluetooth or anything. They're already connected to the network by being plugged in.
PoE has been mostly an enterprise thing, but mass production for residential use should further bring prices down.
What about all the appliances expecting AC input?
There would still be a need to convert DC to AC, both for that reason and for export to the grid, but the first thing a lot of appliances do is internally convert to DC anywhere. If it became the norm for homes to have a distributed DC supply, there could well be a cottage industry in replacing the PSU component springs up.
There was a time early in the electrification of America with Edison, he pushed for DC over AC. https://en.wikipedia.org/wiki/War_of_the_currents
The last DC utility turned off in 2007. http://www.jaygarmon.net/2010/11/in-what-year-did-last-of-new-yorks-dc.html
As far as answering your question, you can run a transformer, but new construction and new appliances will likely be built with DC service in mind.
Most things with a motor would prefer AC. Alternatively, they use DC, but it's a brushless motor with more complicated electronics and are more expensive for it. This would apply to anything with a heat pump, which includes air conditioning and hybrid water heaters.
Things that run electric resistive heating is fine with either AC or DC, but it has to be higher voltage. The benefits of DC disappear because nothing wants to run at the same voltage.