One reason DC power is more viable nowadays is (as others here have mentioned) the use of DC-DC converters. They internally actually use AC to do the conversion (usually at much higher frequency to save weight and cost on inductive elements). But they're not super cheap (not cheaper than transformers) and they can also be inefficient.
But part of my problem with this article is it kind of sandbags the efficiency. We can get pretty high efficiency inverters and rectifiers. >90% is common and 95-98% is feasible (and not uncommon). Low voltage DC (like 12V) requires MUCH thicker cables for the same power, which means a lot more copper (and copper mining). Typical line voltage can be very lightweight.
With DC, nothing is really at the same voltage, so you need DC-DC converters all over anyway, so you're not saving anything (although not losing much, either!).
Another important thing that really drives some of the advantages is: breakers, relays, and (much less important) current measurements of existing cables. All these are feasible for both DC and AC, but cheaper and easier with AC. AC is self-extinguishing as it crosses zero 120 times a second. That means you can switch a circuit on or off when the applied voltage is very low, meaning you can use cheaper and lighter power electronics. Plus, at a given voltage, there's a safety advantage as arcs will more easily stop with AC.
I actually think it's funny to see this in a "low tech" blog. DC ubiquity is something really only practical for significant use (i.e. beyond automotive or RV) with modern 21st century power electronics.
-48V DC has been a thing with telco equipment for decades: it's what a landline telephone uses for signalling.
* https://www.servertech.com/blog/48vdc-power-and-the-backbone...
If we'd use anything DC, it would probably be that.
You can even design the system so that the batteries are in parallel with the power supply and load making the system uninterruptible by default.
A lesser known standard is 110V DC used in electrical substations and switchgear. They cover a lot of ground and cable runs can be hundreds of meters so the higher voltage allows longer distances with minimal line loss.
Power hogs like refrigerators, window-AC units would no doubt still run on 110/220.
But I already have mixed voltage AC in my home: otherwise 110V but purpose-placed 220V for electric stove/oven (in kitchen) and electric clothes dryer (in garage).
In my perfect future only those high-current outlets would remain — the rest of the house would have 12V plugs and lighting.
There are actually scant few things in modern houses that inherently want to run on 60Hz single phase AC - basically just fixed-speed induction motors [1]. And the amount of those are shrinking as more and more appliances get "inverter" technology for the energy savings.
The transformers on the poles are bona fide 60 Hz devices (and I'll take the electricity I can get). Industrial customers with large 3 phase induction motors want 60Hz AC. But for household use, DC would be straightforward.
I agree about the self-extinguishing arcs, although it seems like moving to solid state switches would solve much of that.
[0] power factor correction
[1] And actually, "single phase" induction motors don't even want to run off of a single phase. They all contain capacitors to create a second phase so the motor rotates.
DC-DC converters are cheaper than the classic transformers. There's a reason that you almost never see the classic "big chunk of iron" wall-warts anymore: not only are they inefficient, they're more expensive.
> Low voltage DC (like 12V) requires MUCH thicker cables for the same power, which means a lot more copper (and copper mining). Typical line voltage can be very lightweight.
Yes, a low voltage DC bus doesn't make much sense except for specific applications. Even in small spaces like recreational boats it's more common to use 24V or 48V these days. I think around 50V makes sense, as it's not very dangerous so there are fewer safety regulations. Look at PoE, for example. Unprotected runs of fairly thin cable transmitting up to 52V.
> With DC, nothing is really at the same voltage, so you need DC-DC converters all over anyway, so you're not saving anything (although not losing much, either!).
DC-DC buck converters are the simplest, cheapest, and most efficient category of power converters at the moment. (Of course a specific converter may be worse than a specific converter of a different category, but this is broadly true) Buck converters that support up to 50V are only marginally more expensive than lower-voltage ones. As an electronics engineer, I would be very happy if I could get away with only needing buck converters from now on; they're very easy.
If the DC source is required to be galvanically isolated and to have it's own transient suppression than the DC devices can get away with much less input protection than AC devices require. Could be a significant cost savings.
> Another important thing that really drives some of the advantages is: breakers, relays, and (much less important) current measurements of existing cables. [...]
Absolutely. I don't see high voltage/high power DC becoming popular in homes any time soon for that reason. There shouldn't be any difficulty with arcing at 50V though. (Yes, switch contacts still arc but it's not any more difficult than 120VAC) Also high power applications in houses tend to work just fine on AC (motors and restive heaters), though that may be a chicken-and-egg thing.
This may be the case now, but it's just through historical lack of standardisation, resulting from AC having been the one true standard. It's not inherent to DC.
USB PD is attempting to address this issue. It is standardising voltages for DC-powered devices.
1. Any time you mix motors and electronics, motors produce brownouts and spikes which can cause directly connected electronics to malfunction. DC-DC converter mitigates that. LEDs are particularly prone to overload with just minute increase in voltage and dim/flicker with decrease.
Not inherent to DC but same thing happens with poorly designed appliances that emit RF which then interferes with everything connected to the circuit.
2. Voltages. You can't standardize electronics power supply to 12V because semiconductors are most efficient at lower voltage, which depends on particular technology.
> One way to solve the problem of high power devices is simply not to use them -- this is the approach that's followed in sailboats, motorhomes and caravans
> Obviously, this strategy implies a change in our way of life. It would mean that electricity is used only for lighting, electronics and refrigeration, while non-electric alternatives are chosen for all other appliances. Not coincidentally, this is quite similar to how DC grids were operated in the late nineteenth century, when the only electric load was for lighting -- first arc lamps and later incandescent bulbs.
> Thus, no dishwasher, but doing the dishes by hand. No washing machine, but doing the laundry in a laundromat or with a manually operated machine. No tumble dryer, but a clothes line. No convenient and time-saving kitchen appliances like electric kettles, microwaves and coffee machines, but a traditional cooking stove operated by (bio)gas, a solar cooker, or a rocket stove. No vacuum cleaner, but a broom and a carpet-beater. No freezer, but fresh ingredients. No electric warm water boiler, but a solar boiler and a small wash at the sink if the sun doesn't shine. No electric car, but a bicycle.
Simple, instead of grocery shopping twice a month, ditch that wasteful freezer and walk to the farmers' market down the block before dinner each night.
Was it cloudy yesterday? Simple!, take a whore-bath¹ at the sink and be thankful your meetings are on Zoom these days :)
Ok, ok, those are caricatures of the final paragraphs, but that's what I hear when the word "simple" is abused that way.
[¹] Or, "PTA", which isn't much nicer. Any ideas on what to call this that's less vulgar, but still derisive?
My question is, if those people actually tried that by themself before suggesting it, or if they just picture the women doing it somewhere.
I mean in this specific instance I can imagine they tried. And I did too, while off grid. It gives you a special connection to your clothes. But suggesting this as a general way of life is a bit offworlds.
Middle class Victorians, in England at least, had things delivered. I imagine that quite a lot of cosplay characters are middle class.
In fact food delivered to homes of all types was a normal feature of life in England when I was a child in the 50s and 60s. Milk, eggs, etc., every weekday morning delivered directly to the door before breakfast, grocery van came to the street once a week, bread van twice, another van came a bit less often selling lemonade and other drinks.
Of course these services were not universally available, we were lucky to live in a moderately affluent town with a prosperous working class.
We didn't have a freezer until 1966 and I'm not sure that we suffered from the lack. But once everyone had both a freezer and a car those services became unprofitable and eventually disappeared.
I like bird bath for this.
I agree with your overall sentiment, I do also aknowledge that we (as a society) are very wasteful with resources. I would like to see some form of incentive for using less power and producing less waste.
My energy provider during the first lockdown actually paid us to use electricity because it was being produced at renerwable plants and would otherwise go unused. We set our washing machine to start during the period they would pay us and did our morning routine a few hours earlier. That small incentive was enough to change our behavior
Sponge bath?
> 1. A quick sponge bath by hand, using a wet washcloth or a pre-moistened towelette, to extend the interval between showers or clean up after casual sexual intercourse.
This might be a positive though. Having moved to the UK years ago, the average trip to the supermarket is for around a few days of food, a week at most here. The supermarket is 7 minutes by foot or a 4 by car. It means we buy a lot more fresh items, and this is natural due to the limited amount of freezer space we have (60/40 fridge and no chest freezer in our house). It's arguably better than the experience I had back in Canada plus for the same quality of food, it's much cheaper over here.
So it isn't exactly the same as the olden days with wet markets and whatnot, but it's much closer to it (they even have manned meat, fish and deli counters at our local).
Not particularly derisive, but I've always called it a “pits & bits” wash. I've heard it called a “got lucky rinse” too, presumably a variant on the whore-bath.
Making something both simple and easy is a highly sought art.
I think the same applied for the majority of population in underdeveloped / developing countries.
(Though I do think that Americans uses clothes dryers _much_ more than they should. Most other G20 countries do not. In our household we hang dry any load of laundry that doesn't involve our heavy blankets, and that usually ends up extending the life of our laundry as well, while taking just a few additional minutes. (See, "often impractical" not "always impractical").)
And a kettle is so low impact anyway. It uses a high amount of power for a very short time and spends almost all of its life turned off. The faster you heat the water the less waste there is as it cools during the heat process.
There are many reasons for this. Some of them are cultural, and other are legal.
Many Americans simply don't remember drying clothes on a clothes hanger outside, and aren't used to hanging them indoors as many Europeans do. And to be fair, indoor clothing hanging is time consuming in comparison to "transfer clothes from one machine to another".
But what many don't know is that it's often banned in many home owners' associations, and banned in many apartment leases, meaning that hanging your clothes outside is actually a luxury that many simply can't partake in.
Meanwhile the thing that has actually gotten people out of their cars is the ebike. It turns out it’s much more effective to produce a more convenient and comfortable solution for people rather than just demand that they go back a century or two just because.
0 - It’s also telling that such advocates never seem to actually say who should be stuck doing all the labor that machines like washing machines now do for us. Washing clothes and dishes by hand is hard labor, and someone is going to have to give up their career or free time to do it if we’re going to ban these machines. No extra credit if you figure out who will get stuck with the task…
Yeah lol I always find this the funniest part of Low Tech Magazine. While they're always breathlessly moralizing, they rarely think through (or at least write about) the social ramifications of the changes they propose. They do have some interesting ideas though, such as the use of thermal cookers, and burning biomass in a rocket stove may not be the worst idea if you live in an area with a temperate climate and a dirty grid. Perhaps more practical though would be just incentivizing ordering at a restaurant, since a restaurant will be more energy efficient at preparing food than an individual will.
They are probably not actually closet misogynists or anything like that, they probably just haven’t thought that far ahead.
This is not my experience. People just put their ebike on a rack and drive it somewhere to ride it for fun.
Tech products footprint is either during consumption (most of the devices requiring heat or cold) or during production (the other devices like smartphones).
Obviously this rule is a trend and countries with low carbon electricity are exceptions.
While most people are OK for lasting a smartphone a bit longer, the same logic would imply to reduce the heat/cold consumption.
So yeah in this sense, a freezer is a luxe we can't afford.
If you want governments to do whatever needs to be done to limit climate change, you also need to be willing to "pay the price" in the form of reduced material comfort.
Besides, there are quite a few people (a big chunk of the world population actually) living today without dish washers, without microwaves and without coffee machines.
Which is why nothing significant has been done, nor will it.
The 380-volt DC sounded nice, so long as DC to DC is more efficient than AC to DC, but I have no idea if that’s true.
Consumer devices vary, but it’s a safe bet that modern cool-to-the-touch GaN power adapters are far more efficient than those old black bricks from the 1990s.
Saving a few % just isn’t worth all the incompatibility and inconvenience of rewiring your entire house for.
380-volt DC sounds dangerous!
Instead of driving to the gym and bike 1h you may commute by bike (with enough safe paths its pretty nice, not perfect but pretty nice and health improvements come very rapidly as a bonus).
I have no idea where they got that picture either. Edison's Pearl St. station did not work that way, and that was the first power station. The generator shown is Edison's famous "long-waisted Mary Ann". But Edison never built a one generator per bulb power station. He was able to calculate ROI [1]. This is probably some conceptual drawing of what would have been necessary had the "subdivision of the electric light" (a hot issue around 1889)[2] had not been accomplished.
"In other words, a DC electrical system could make a solar PV system more energy efficient." Not clear that it matters much in terms of raw conversion efficiency. Solar inverters are now up around 96-98% efficiency. If you're going to have batteries, you need something that handles battery charging, discharging, and some constant output, and while you can get all that stuff for 12VDC or 24VDC, it's not any more efficient than outputting 120VAC.
The real argument they're making is to save power by using small boat or RV sized appliances. They're available, efficient, undersized, and about 3x as expensive as line-powered units.[3]
[1] https://www.hup.harvard.edu/catalog.php?isbn=9780674423640
The best inverters convert solar DC to household AC at 97.6 % efficiency. [1]
Adding more solar is a question of adding another panel.
The inversion loss is a small price to pay for safe power. [2]
DC is probably not coming back as a way to wire houses and buildings.
[1] https://www4.enphase.com/sites/default/files/downloads/suppo...
[2] https://www.businessinsider.com/tesla-solar-panel-fires-beco...
otherwise you chain a bunch of panels together in series and track the max power point there. This means that you don't quite optimise for each panel
It's more convenient to simply plug into a low voltage DC current wiring with a LED fixture than to install a AC-DC converter.
It's certainly something I've entertained doing for my own place.
802.3bt Type 4 allows for sending 100W down Cat 6A cables, but only 71W is available at the other end. That's highly inefficient.
* https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i...
The only reason PoE makes sense at all is because it uses 48V, but due to the flimsy cables the losses are still 15-20%. Not great.
Power over Ethernet would be a pretty cool way of doing it if it was practical...that way you get the data to control the lights as well as the power to run them.
Does anything like this exist in a way that won't get me fired by the builder for even mentioning it?
[1] https://www.boatus.com/expert-advice/expert-advice-archive/2...
V=RI and W=VI
WireLossInWatt = RI²
at 120V you need 1A so you lose 1²A² × 7ohms = 7W
at 12V you need 10A so you lose 10²A² × 7ohms = 700W
I’m also looking at whole house USB-PD, https://voltekinc.com/dc-power-advantage/
Thermostats and doorbells are low-voltage AC. The transformer is standard. If you can find 24-volt AC lights, an open-minded electrician should be able to figure it out.
Related: My old house built in the 1960s had an intercom system that was ripped out by a previous owner. I found a warm transformer attached to a bare bulb light socket in the basement with nothing else running from it. I happily removed it.
I had a battery fridge in a caravan (trailer) and it was very small and pretty rubbish, certainly not suitable for home. However, for a short stay, it could keep some basic foods cool enough to be safe.
As others have said, although it is fine on paper, as soon as you start talking about significant power, you are talking lots of amps, which means more risk of overheating and fire, potentially significantly larger (and therefore expensive) cabling and all of the switchgear that can support a few amps AC will not support the same current at DC so all your switchers are larger/electronic. There is also an issue of RFI which could be significant if you are switching high current DC loads.
At least here Europe/Italy there are bus-based systems from various manufacturers.
Example:
https://professionisti.bticino.it/catalogo-prodotti/myhome-i...
(not too bad in google translate)
Basically normal wires (here 220-250 V AC) Live+Neutral+Ground and a signal (bus) 2 wire cable arrive to each and every electrical box/light point.
Then you can install into the box any kind of device, switches, outlets, etc., and you can configure them.
The bus wires (the protocol is called SCS):
https://en.wikipedia.org/wiki/Bus_SCS
allows also (low power) 27 V DC trasmission.
The protocol and compliant devices were first introduced between 1996 and 2000 and are by now well tested and reliable:
https://en.wikipedia.org/wiki/OpenWebNet
Legrand also uses the same protocol:
https://developer.legrand.com/documentation/open-web-net-for...
Just be aware many jurisdictions have minimum lighting requirements that your low voltage lights may not meet, but you could always just leave those lights off
We'll see how things go, but on paper at least this makes a lot of sense if you don't try to run things at 12V (why do people still try?). 48V is a voltage that is still safe, but cuts your amperage and losses to reasonable numbers.
While designing my own LED drivers, I found that most LED panels will internally work with a Vf of 36V, which you can efficiently get from your 48V installation.
Even in an AC-powered home, if you have lots of LED lighting in one place, it makes sense to use a single high-power converter to get 48V DC and then drive LEDs off that. Small AC to DC converters are inefficient.
> AC won, mainly because of its higher efficiency when transported over long distances.
AC is not actually more efficient at long distance transmission, it’s less efficient due to the skin effect. AC is just easier to convert.
1) The line connects two synchronized grids. It's much easier to convert electricity to DC and back to AC on receiving end, than to synchronize grids or to implement something similar with AC.
2) The line runs under sea water for a significant distance. Due to the conductivity losses DC is more efficient in such contexts that AC.
And surprise, a lot of DC-DC topologies require a transformer too.
Transformers still soundly beat solid state conversion on cost, and efficiency at above the wall outlet voltages.
You can't run away from that entirely. If you were to give a free hand to a good EE to redesign the electric grid from scratch, I doubt the result will differ much from what the world has already.
Transformers still have their place but they're still basically big dumb (uncontrollable) chunks of copper and iron.
This is incredibly important to note. Buck-boost converters enjoy efficiencies beyond 90% in even the most pedestrian implementations. This makes their efficiency directly competitive with transformer-based designs (95-99%).
So everyone saying how it's fantasy to expect peoples behaviour to change, just remember if you haven't tried it you are likely highly over estimating how much effort it is, and not aware of many of the unexpected advantages.
As much as I personally hate them, would it not be better to install 120% of solar cells required to match the load upfront. Given the energy is free at generation write off this small inefficiency as being built into the system. It's not like the sun will come after you for capturing more than your fair share.
This feels like a problem for 2100 imo once we've moved to much lower carbon supplies.
There is an argument for using DC over AC but avoiding conversion losses is not a compelling part of it.
Is this actually true though? I just bought a reel of 30 high power mosfets from digikey for ~$450. Each of these bad boys can rock ~1kW continuous switched output/input. Magnetics for the HV boost section of a 30KW DC-DC converter circuit are a mild additional cost.
Compare this to how much money you would have to spend for a more traditional copper & iron monstrosity of similar rating (well over $1000).
Weight is also a huge factor when you start talking about megawatts.
This is absolutely untrue. You may be safer from shocks, but it's a much _worse_ fire hazard. The currents need to be higher at lower voltages. Higher voltages need less current for the same power, decreasing the fire risk.
(Water heating dominates the energy used in those, the mechanical sloshing around takes trivial power compared to it).
There's not many people living in these areas though like the sibling comment points out.
What would work best for this?
They have an automatic transfer switch built in for anti-islanding (your mains entry goes through it), so it disconnects you from the grid if it goes down but your local side still operates. I think it can also have two AC outputs, one for loads powered by either grid or battery, and one that is only on when the grid is present (if you have a grid). You can use any type of battery so you’re not locked in (LiFePO4 are some of the best at the moment).
I have an AC solar inverter and 5kW of panels on my roof, which would be about enough, but I’m going to add another four panels (bit less than 1.5kW) that are DC-coupled through an MPPT charter (Victron SmartSolar MPPT) to solve the bootstrap problem for prolonged outages (which are very rare here, but still). Not sure if that’s the normal term, but I mean where the batteries run out, so without the grid to put some charge in them, the inverter/charger can’t produce an AC waveform for the PV inverter to lock to, so the PV inverter won’t switch on. Having some solar on the DC charger lets that work.
As I type this my house is running from a backup generator. The power company has their repair crew in route to whatever the issue is. I'm looking into how/if I can add solar to the system as well.
Check out options like the Yeti 6000x. You can buy a transfer switch to go with it for powering a few circuits. The 6kwh battery could run things like your fridge and computers for at least a day.
I camp a bit and spend more than enough time dealing with 12V lighting, recharging drone batteries from car/aux batteries, etc. Always end up wondering how much of my house actually needs AC, where in the house that occurs (fridge, ducted heating/cooling unit?) and what could get by without it. More and more of my power tools are battery based too. Would AC to the kitchen and garage be enough?
I still do think AC is still advantageous in a lot of ways for power grids though, just not on that particular point.
We have this article that discusses changing home design in order to limit cabling losses (crazy) and not using "high power" appliances that we associate with modern life... and another article discussing Livermore labs achieving net positive fusion, a milestone that seemingly hints we're on the cusp of a carbon free renaissance of power generation.
Schrodinger comes to mind
I wonder what would happen if we redesigned the grid today? Would it be AC or DC? If AC, would it be a higher frequency? (Smaller transformers) Is modern DC-DC voltage conversation easier than AC-DC? What voltages would we use?
The biggest factor is AC is a lot safer. Switches and branch protection devices (fuses) work best on AC. For low voltage DC we can make them work, but for high voltages we don't - instead we put in the protection on an AC side, then convert that to DC.
You can even get Anderson Powerpole wall sockets: https://powerwerx.com/powerpole-connector-outlet-box-coverpl...
I lived on a boat for a while and I used almost exclusively DC - it worked out pretty well. I used hard wiring and cigarette lighter plugs and that worked fine. The problem with wiring a house is that DC losses start to be huge over decent distances (100+ feet starts to be really tough.) I feel like that's one reason why DC is only really standard on cars/boats/motorhomes.
I don't necessarily think it's wise to do 5 amps over USB-C, but it is a standardized DC outlet. Personally, USB-A is still a more useful power outlet, but nobody is insane enough to shove 240W over it.
Transitioning to this sort of system would actually be simple, you'd just have to make DC power supply boxes that plug into a regular 110 or 220 AC outlet -- sort of like multi-port USB power adapters, but designed for more power and probably higher voltages: perhaps +/- 12 volts and ground.
A more sophisticated system might be that the DC power supply can supply a different voltage/current to each port, and it negotiates with the device to supply to current power. (I think this is basically how DC fast chargers for EVs work -- the car tells the charger what it can accept, and the charger supplies that the car.)
Maybe "dumb" devices that don't know how to do the handshake just default to 5v DC or something.
Also you can't exactly have a USB-C PD power strip of 10+ plugs without it costing a fortune because of all the negotiation needed per-port. Now they're onto some GaN bullshit just to make the PD adapters smaller.
The standards are a shitshow, there are incredible number of non-compliant USB-C cables.
802.3at PoE is slightly better, you can get 24+ ports for a couple hundred bucks, most cables advertised to meet PoE specs do in fact meet them.
But really the best would be straight up 48V on 2 rails and a bunch of plugs. No negotiation, no bullshit, no GaN, just 2 wires. Equipment, cabling, power strips would be dirt cheap. Individual devices can have very compact, efficient buck converters to get the voltage they actually need.
It can. Cree's JR5050 24‐V LEDs run on 24V. They have 30V and 36V versions as well.
I'm using my ipad while plugged into a 120V USB charger, and the charger isn't even warm.
120VAC plugs e.g. standard IEC computer power plugs can be hit with bricks and rammed into furniture while they are plugged in and they won't get damaged. All forces of impact get transferred to the chassis, not the PCB. That's good design.
I break about a USB-C cable a week because they just aren't designed for the ruggedness that consumer use cases demand, which are typically higher than military.
I don’t know… that seems excessive, even people I’ve known to handle all of their stuff like it’s free have managed to go mostly through 1-2 cables a year.
12V would need some fat wiring to avoid incurring voltage drops for normal amounts of loads.
48V is nice because you can use much thinner wiring, and it's about the highest "safe" voltage to accidentally touch with normal dry skin.
Sorry to be so pessimistic on my first post, but I don't see this happening for a long, long time.