"Because many modern devices operate internally on direct current (DC)"
But notably the high power consumers like electrical stove, air conditioning, washing machines etc. do not. And it's not that with DC throughout there are no conversions. Solar cells' output varies greatly, hence it needs to be DC/DC converted to a fix voltage to be of any use. The same, albeit to a much lesser extend, applies to batteries. Further, there is no one single voltage, AC or DC, which is optimal for all uses. Even for devices which receive DC voltage, e.g. laptops, there are internal DC/DC converters.
Removing the AC/DC conversion seems hardly worth the trouble. High efficiency AC/DC converters can be constructed. It's rather a question on how much one is willing to spend on such.
Yes, you cannot reasonably run these high-power devices on low-voltage DC (12-48V), this is also said in the article. But the reason is not that these devices cannot run on DC in principle, the problem is cable loss. For running devices which need >1kW on low-voltage DC, we are talking at least 20-80A, depending on the voltage. So you need thick cables, which are expensive and hard to deal with (amount of space needed, securing connections, avoiding bending, everything becomes problematic with these cables). Any little mistake done with cabling is immediately a fire hazard.
So in the end, the article says: say good bye to your washing machine, dish washer, electric kettle, electric stove, etc. I mean, the site is called "low tech magazine" for a reason...
In-sync AC grids are an engineering marvel; high-voltage AC lines are comparatively lossy due to the skin effect among other things; a frequency of 50 or 60Hz yields what are, by modern standards, comically huge step-down transformers; etc. It's worth considering whether the relative ease of running AC motors makes all the difficulties of AC supply worth it.
(It's worth remembering that the "modern", i.e. 1930s, three-phase power grid is built primarily to power motors on factory floors. I don't know if these are the highest load these days, but wouldn't be surprised if not.)
So all efficient (switching) voltage conversion involves AC. Your stock plug-in DC power supply is actually a AC->DC->AC->DC device yet it's trivial to get above 97% and miniscule quiescent (minimum) load. High-frequency AC isn't a problem for efficiency.
What's NOT easy is efficiently making 60 Hz AC at low quiescent power. Most inverters always burn 2-5% of maximum power with no load, while 1% would be considered far excessive if the output was DC (maybe 0.1% would be generally okay?). Part of this is lack of regulation; consumer devices have low-quiescent power supplies originally because of government mandates and, now, economies of scale. The government mandate didn't apply to inverters so there isn't an initial push to shift to low-quiescent topologies and prevent the first movers from being undercut.
So just for that reason, lower-voltage DC distribution can overall be more efficient if you are off-grid, even if some other portions of the system have increased losses. 120Vdc distribution would be superior from an efficiency standpoint in every way, but you're going to spend a lot on switches and protection equipment.
Most of the high power consumers could run on DC power with only slight modifications (in design, not aftermarket).
Heating elements can run on DC more or less unmodified. Also electric motors can run on DC efficiently (see electric cars). Back in the days 3-phase power was needed to run strong electric motors (very common in Europe, but i think it exists also in the US for factories and businesses). But there are many easy solutions nowadays to just run them on DC.
> But notably the high power consumers like electrical stove, air conditioning, washing machines etc. do not.
An electric resistance stove (radiant or exposed coil) would work just fine on DC, although, if it’s controlled using a TRIAC, that would need to change.
An induction stove uses rather high frequency AC, and that could be generated just fine from a DC supply.
Modern air conditioners use variable frequency drives, and those generally work by first converting the AC supply to DC.
I imagine that many modern washing machines also use some sort of variable frequency drive or DC-powered motor.
> Solar cells' output varies greatly, hence it needs to be DC/DC converted to a fix voltage to be of any use.
This is simply wrong. It is true that modern MPPT solar regulators use PWM to extract the maximum power, but for years, a simple on/off regulator was used to prevent overcharging.
The reality is that a solar panel is essentially a "Constant Current" supply, so the panel puts out the same current over a wide range of battery voltages. It is the battery which puts out a Constant Voltage at whatever current the load requires.
With more and more DC generation and consumption on the network, I think the AC mains is becoming very noisy, i.e. there are spikes, which we are not so used to handling.
It is easier to turn AC at the wrong voltage into DC than it is to turn DC at the wrong voltage into the right voltage. Particularly if you care about efficiency of the device.
> Dutch researchers managed to reduce total cable length in a house down from 40 metres to 12 metres. They did this by moving the kitchen and the living room (where most electricity is used) to the first floor, just below the roof (where the solar panels are), while moving the bedrooms to the ground floor. They also clustered most appliances in the central part of the building, right below the solar panels
That's not great, since entertaining guests it is preferable to have these rooms on the ground floor, and the bedrooms which can be private on the upstairs floor.
What's happening in their living room to use so much electricity? I figured TVs, computers and lighting use a fraction of what they used to use.
My mom is in a typical suburb tract housing development, and the kitchen is right above the service entrance and the HVAC/mechanical room is right at it.
Great they're applying the same logic to solar-first systems, but it's not a new concept at all.
It’s actually not that crazy. Many multi story houses have their plumbing and hvac built this way to save on copper pipe and get you hot water faster. All the bathrooms etc backing a central plumbing chase.
Something I didn’t find in the article is that in AC systems sparks are self-extinguishing because of the zero-crossing.
There are a few domestic circuit breaker teardowns on youtube. I suggest watching one and then asking the question: how can we break a high current _DC_ surge?
Not mentioned so far: AC->DC adapters also provide galvanic isolation. In many power supplies, that electric isolation comes 'for free', as you don't want device(s) connected to high voltage wiring anyway. AC vs. DC as input isn't that big a deal really.
In situations where power source (solar!), storage and most consuming devices are low-voltage DC, just use a DC based setup if more practical.
I'm on a boat & most everything electric here is low voltage DC. But I do have a 12V->230V AC converter when needed.
In short: AC & low voltage DC can live happily side-by-side. The DC vs. AC debate is kind of a moot point these days.
Few devices other than switching power supplies are designed to work over a wide range of DC input voltages. There's an electric pump which will run slowly on an low input voltage and faster at a higher voltage.[1] Those are driven from windmills and solar. It's not cheap. It has to be self-protecting against too high and too low voltages.
This is part of the reason why a fully compliant USB-C cable is so expensive and stiff. It should carry thick power lines, and also a number of high-speed serial lines, and some electronics to configure and drive all that on either end.
If DC in houses became popular, it seems like they'd follow the same model as RV's -- low power devices like lighting, water pump, maybe refrigerator all run on 12VDC, high power devices like air conditioning, microwave, etc run on 120VAC (sometimes inverted from battery).
That limits the high gauge wire to the short run from battery to inverter, otherwise you'd need very expensive and heavy large gauge cable running to those high power devices.
I think that, if DC appliances as used in RVs became genuinely popular, they would move to reasonable voltages. 12VDC is absurd. 48VDC would be much, much better.
Just sitting here speculating, not even a web search yet...
In the USA we have both ground and neutral wires at every outlet along with the hot (120VAC nominal) wire.
Why couldn't we raise the ground wire to +12VDC (or whatever) with regard to the neutral? The ground would have a very sensitive detector so that if electrical conditions exceeded some preset threshold it would collapse to zero nearly instantly, allowing the circuit protection to function as expected.
You could make a plug that only has a neutral and ground pin to tap into the low voltage side, or use all three pins to provide low power standby mode.
Now I'll do a search to find out that it is impossible because of a, b or c reasons or that it has already been patented somewhere and abandoned. Yay Internet...
The GND (or Earth/GND) is there for safety and equipotential bonding. It’s not meant to carry current and running current through it will trigger your RCD, because that’s how a ground fault is detected. And detecting that is important so when you trip with your hairdryer into the bathtub you won’t kill yourself.
Even if plug is polarized (plug goes in only in 1 orientation), you can't assume any of the high voltage wires to be touch-safe. Wiring mistakes (swaps) can & do happen.
In-house AC systems are designed to remain safe when that occurs. But it prevents using any of those wires in ways like what you suggested.
One problem is that many older houses don't have grounding. Half my outlets are ungrounded and I use GFCI to get three-prong plugs. Or the grounding is done through pipes and conduit which aren't suitable for running current.
The standards for grounding make them unsuitable for running current. The ground wire in box are frequently bare. Metal boxes are grounded. The center screw is grounded. If you run current over the ground, those are live.
You have invented a way to electrocute lots of people.
Currently the ideal balance of price, performance and availability of off the shelf components is 48v dc power.
There is a telecom industry standard (perhaps only loosely standardized) for DC converters which are called "isolated DC-DC converters bricks."[2]. These are reasonably priced and reasonably high efficiency DC converters that fit into a set of standard form factors, e.g. 1/4 brick, 1/2 brick, etc. They are small sealed modules and a variety of outputs ratings are available for < $100 with efficiency > 85% and many newer examples are > 90% efficient.
The setup I've settled on is the following, based on 48v nominal[2] system.
Solar Array
80-100v
|
Solar Charger
|
LiFePo4
Battery
[40-53v]
|
Circuit
Protection
| <- Standard house wiring to point of use
|
| --- [12v DC Brick] -- short wire --> 12v devices
|
| --- [5v DC Brick] -- short wire --> 5v devices
Note that multiple devices could run on a single DC brick. It can, for example, provide an array of USB ports for devices to source power. The 5v or 12v power wiring is short so there isn't a need for oversized wire to combat voltage drop.
DC power never went away in serious ISP/telecom applications. It's more popular than ever. And things like the DC power distribution within an open compute platform standard rack, for large-scale numbers of individual small servers.
Same here. The problem is that there's no consensus on what voltages. I might prefer 48v for lower losses but you might want 24v since it's "safer" and my neighbor might want 192v since he's already an electrician.
There are multiple things that we really need to make it viable. A standard for the plug that separates it from any AC standard, a standard voltage and current and then standard DC to DC convertors for adjusting the voltage. I guess also we need a completely different light bulb fitting socket too that only fits DC light bulbs. Lots of different commercial DC convertors of varying sizes to replace the AC convertors in all sorts of devices.
I do wonder how much in practice would be gained given the DC to DC conversions are guaranteed for every device.
When I built out a van into an RV, I got to run a new electrical system for it — one based around the 12V automotive battery.
It turns out that there is a small industry out there that serves both RVs (and boats as well) that is 12V/DC based. Lights, pumps, refrigerators, fans, all running straight off a 12V power bank. "Cigarette lighter" outlets stand in for wall outlets for USB-style chargers, etc.
The 12V/DC battery system in the van is of course charged from both solar on the roof of the van and from the van's alternator (when the van battery is topped off and the van is under power of course).
I did add an inverter to supply 110V/AC for a pair of traditional electrical outlets I installed in the kitchen area of the van/RV. These are primarily used for plugging in wall-wart style chargers for the laptops.
(My Kill-A-Watt suggests that my rice cooker and even the electrical kettle would, just barely, function on the current provided by the inverter but RV-life tends toward minimalism so those extra appliances I've left behind.)
In any event, the whole experience did have me wondering if I could run a parallel 12V/DC electrical system in a new home and do away with a lot of the step-up/down of AC.
Definitely could do with some kind of modern outlet (USBC?) rather than the cigarette lighter outlets, ha ha.
What would be nice is a residential power over Ethernet standard. With standard crimp connections.
Some advantages power limited and low voltage means it's safer[1]. Ethernet means you can control lights and other devices. Smaller diameter wiring means it's cheaper. Not needing a licensed electrician to install it saves $$$.
[1] Can imagine for a non North American not having to deal with 230VAC would be a big bonus.
What would make the most sense to repurpose AC wiring for DC. The big problem is that only circuit goes to each spot and putting in duplicate circuits would be expensive.
The standard AC wiring is probably enough for 720W with 48V. The problem with choosing 48V is lock to medium power. Appliances would require 240V or 480VDC to get enough power.
The big problem is that there is no standard for DC power outlets or plugs. Would need to be different from AC and would also need to be different for different voltages.
There's already a somewhat common standard for DC wiring in homes and offices, though it's probably not exactly what you had in mind: it's Power over Ethernet (PoE), which provides around 48V over standard twisted pair Ethernet wiring, while still allowing it to be used for data.
[+] [-] guenthert|2 years ago|reply
Removing the AC/DC conversion seems hardly worth the trouble. High efficiency AC/DC converters can be constructed. It's rather a question on how much one is willing to spend on such.
[+] [-] deng|2 years ago|reply
So in the end, the article says: say good bye to your washing machine, dish washer, electric kettle, electric stove, etc. I mean, the site is called "low tech magazine" for a reason...
[+] [-] mananaysiempre|2 years ago|reply
(It's worth remembering that the "modern", i.e. 1930s, three-phase power grid is built primarily to power motors on factory floors. I don't know if these are the highest load these days, but wouldn't be surprised if not.)
[+] [-] coryrc|2 years ago|reply
What's NOT easy is efficiently making 60 Hz AC at low quiescent power. Most inverters always burn 2-5% of maximum power with no load, while 1% would be considered far excessive if the output was DC (maybe 0.1% would be generally okay?). Part of this is lack of regulation; consumer devices have low-quiescent power supplies originally because of government mandates and, now, economies of scale. The government mandate didn't apply to inverters so there isn't an initial push to shift to low-quiescent topologies and prevent the first movers from being undercut.
So just for that reason, lower-voltage DC distribution can overall be more efficient if you are off-grid, even if some other portions of the system have increased losses. 120Vdc distribution would be superior from an efficiency standpoint in every way, but you're going to spend a lot on switches and protection equipment.
[+] [-] andix|2 years ago|reply
Heating elements can run on DC more or less unmodified. Also electric motors can run on DC efficiently (see electric cars). Back in the days 3-phase power was needed to run strong electric motors (very common in Europe, but i think it exists also in the US for factories and businesses). But there are many easy solutions nowadays to just run them on DC.
[+] [-] amluto|2 years ago|reply
An electric resistance stove (radiant or exposed coil) would work just fine on DC, although, if it’s controlled using a TRIAC, that would need to change.
An induction stove uses rather high frequency AC, and that could be generated just fine from a DC supply.
Modern air conditioners use variable frequency drives, and those generally work by first converting the AC supply to DC.
I imagine that many modern washing machines also use some sort of variable frequency drive or DC-powered motor.
[+] [-] Johnythree|2 years ago|reply
This is simply wrong. It is true that modern MPPT solar regulators use PWM to extract the maximum power, but for years, a simple on/off regulator was used to prevent overcharging.
The reality is that a solar panel is essentially a "Constant Current" supply, so the panel puts out the same current over a wide range of battery voltages. It is the battery which puts out a Constant Voltage at whatever current the load requires.
[+] [-] kzrdude|2 years ago|reply
[+] [-] hinkley|2 years ago|reply
[+] [-] marcosdumay|2 years ago|reply
Maybe outputting a square wave from that solar generator would be optimal.
[+] [-] amelius|2 years ago|reply
Now this is dedication ...
[+] [-] kabouseng|2 years ago|reply
[+] [-] brtkdotse|2 years ago|reply
So they sacrificed the freedom of design to save €100?
[+] [-] Scoundreller|2 years ago|reply
My mom is in a typical suburb tract housing development, and the kitchen is right above the service entrance and the HVAC/mechanical room is right at it.
Great they're applying the same logic to solar-first systems, but it's not a new concept at all.
[+] [-] unknown|2 years ago|reply
[deleted]
[+] [-] ip26|2 years ago|reply
[+] [-] huppeldepup|2 years ago|reply
There are a few domestic circuit breaker teardowns on youtube. I suggest watching one and then asking the question: how can we break a high current _DC_ surge?
[+] [-] weare138|2 years ago|reply
[+] [-] RetroTechie|2 years ago|reply
In situations where power source (solar!), storage and most consuming devices are low-voltage DC, just use a DC based setup if more practical.
I'm on a boat & most everything electric here is low voltage DC. But I do have a 12V->230V AC converter when needed.
In short: AC & low voltage DC can live happily side-by-side. The DC vs. AC debate is kind of a moot point these days.
[+] [-] Animats|2 years ago|reply
Few devices other than switching power supplies are designed to work over a wide range of DC input voltages. There's an electric pump which will run slowly on an low input voltage and faster at a higher voltage.[1] Those are driven from windmills and solar. It's not cheap. It has to be self-protecting against too high and too low voltages.
[1] https://www.dankoffsolarpumps.com/product/solar-slowpump/
[+] [-] blendo|2 years ago|reply
Easily enough power for a monitor/TV, or for a small desktop computer.
https://audioxpress.com/news/usb-specification-revision-defi...
And Anker now makes the honkin’ big hubs you need for that: https://www.anker.com/products/a2342-240w-gan-charger
[+] [-] nine_k|2 years ago|reply
[+] [-] Johnny555|2 years ago|reply
That limits the high gauge wire to the short run from battery to inverter, otherwise you'd need very expensive and heavy large gauge cable running to those high power devices.
[+] [-] amluto|2 years ago|reply
[+] [-] amelius|2 years ago|reply
[+] [-] jakedata|2 years ago|reply
In the USA we have both ground and neutral wires at every outlet along with the hot (120VAC nominal) wire.
Why couldn't we raise the ground wire to +12VDC (or whatever) with regard to the neutral? The ground would have a very sensitive detector so that if electrical conditions exceeded some preset threshold it would collapse to zero nearly instantly, allowing the circuit protection to function as expected.
You could make a plug that only has a neutral and ground pin to tap into the low voltage side, or use all three pins to provide low power standby mode.
Now I'll do a search to find out that it is impossible because of a, b or c reasons or that it has already been patented somewhere and abandoned. Yay Internet...
[+] [-] _fizz_buzz_|2 years ago|reply
[+] [-] RetroTechie|2 years ago|reply
In-house AC systems are designed to remain safe when that occurs. But it prevents using any of those wires in ways like what you suggested.
[+] [-] ianburrell|2 years ago|reply
The standards for grounding make them unsuitable for running current. The ground wire in box are frequently bare. Metal boxes are grounded. The center screw is grounded. If you run current over the ground, those are live.
You have invented a way to electrocute lots of people.
[+] [-] tzs|2 years ago|reply
[+] [-] 20after4|2 years ago|reply
There is a telecom industry standard (perhaps only loosely standardized) for DC converters which are called "isolated DC-DC converters bricks."[2]. These are reasonably priced and reasonably high efficiency DC converters that fit into a set of standard form factors, e.g. 1/4 brick, 1/2 brick, etc. They are small sealed modules and a variety of outputs ratings are available for < $100 with efficiency > 85% and many newer examples are > 90% efficient.
The setup I've settled on is the following, based on 48v nominal[2] system.
Note that multiple devices could run on a single DC brick. It can, for example, provide an array of USB ports for devices to source power. The 5v or 12v power wiring is short so there isn't a need for oversized wire to combat voltage drop.1. There are lots of sources for dc-dc "brick" converter modules, such as these: https://www.artesyn.com/power-supplies/cat/148/isolated-dc-d...
1.1 Another affordable and available option is mean-well chassis-mount dc converters like this one: https://www.digikey.com/en/products/detail/mean-well-usa-inc...
2. "48v nominal" means anywhere from something like 44v to 60v depending on battery chemistry, state of charge and current loads on the system.
[+] [-] dang|2 years ago|reply
Slow Electricity: The Return of DC Power? (2016) - https://news.ycombinator.com/item?id=28216968 - Aug 2021 (230 comments)
[+] [-] limaoscarjuliet|2 years ago|reply
[+] [-] walrus01|2 years ago|reply
[+] [-] thsksbd|2 years ago|reply
Yes HVDC exist and are awesome for very long lines and for underwater uses. Yes, most appliances in a house today are DC.
That doesn't mean that making the in-between DC makes sense.
[+] [-] bad_alloc|2 years ago|reply
[+] [-] msandford|2 years ago|reply
[+] [-] PaulKeeble|2 years ago|reply
I do wonder how much in practice would be gained given the DC to DC conversions are guaranteed for every device.
[+] [-] JKCalhoun|2 years ago|reply
It turns out that there is a small industry out there that serves both RVs (and boats as well) that is 12V/DC based. Lights, pumps, refrigerators, fans, all running straight off a 12V power bank. "Cigarette lighter" outlets stand in for wall outlets for USB-style chargers, etc.
The 12V/DC battery system in the van is of course charged from both solar on the roof of the van and from the van's alternator (when the van battery is topped off and the van is under power of course).
I did add an inverter to supply 110V/AC for a pair of traditional electrical outlets I installed in the kitchen area of the van/RV. These are primarily used for plugging in wall-wart style chargers for the laptops.
(My Kill-A-Watt suggests that my rice cooker and even the electrical kettle would, just barely, function on the current provided by the inverter but RV-life tends toward minimalism so those extra appliances I've left behind.)
In any event, the whole experience did have me wondering if I could run a parallel 12V/DC electrical system in a new home and do away with a lot of the step-up/down of AC.
Definitely could do with some kind of modern outlet (USBC?) rather than the cigarette lighter outlets, ha ha.
[+] [-] Gibbon1|2 years ago|reply
Some advantages power limited and low voltage means it's safer[1]. Ethernet means you can control lights and other devices. Smaller diameter wiring means it's cheaper. Not needing a licensed electrician to install it saves $$$.
[1] Can imagine for a non North American not having to deal with 230VAC would be a big bonus.
[+] [-] ianburrell|2 years ago|reply
The standard AC wiring is probably enough for 720W with 48V. The problem with choosing 48V is lock to medium power. Appliances would require 240V or 480VDC to get enough power.
The big problem is that there is no standard for DC power outlets or plugs. Would need to be different from AC and would also need to be different for different voltages.
[+] [-] amelius|2 years ago|reply
[+] [-] cesarb|2 years ago|reply
[+] [-] adrianN|2 years ago|reply
[+] [-] Physkal|2 years ago|reply
[+] [-] George2515|2 years ago|reply
[deleted]
[+] [-] George2515|2 years ago|reply
[deleted]
[+] [-] Podgajski|2 years ago|reply
[+] [-] Johnythree|2 years ago|reply
And neither type are a health hazard.