The author seems very confused about whether they're talking about the grid or devices.
"DC power is significantly more energy efficient than AC power." -> the examples go on to specify end points for electrical energy but we already use DC there, AC is mainly used in transmission, so the claimed advantages of DC are irrelevant.
"DC motors and appliances have higher efficiency and power to size characteristics." -> Brushed DC motors aren't efficient, just cheap. Brushless DC motors actually require a separate circuit to turn DC into something resembling a sinusoidal current (i.e. AC).
"DC is inherently compatible with renewable sources of energy such as solar and wind." -> solar generates DC but wind generates AC.
"requiring storage (batteries)" -> chemical batteries require DC but other forms of storage like dams require AC to drive motors or turbines.
"Most energy storage technologies are DC-based" -> at a local level (mobile phones, cordless power tools), sure. At a grid level, we're often talking about hydro.
"Electronic equipment operates on DC power." -> equipment that deals with computation. Electric fans, washing machines and many industrial consumers of electricity use AC. Plus, the existing grids and existing generation infrastructure are built on AC.
Yes, but a wind turbine is allowed to spin at variable speeds - its rotation is not synchronized to the grid frequency in the same way that hydroelectric and thermal turbines are.
In order to get a wind turbine's power output to match the grid frequency, it goes through an AC -> DC -> AC conversion in a component known as a double-fed induction generator (DFIG).
The author seems very confused about whether they're talking about the grid or devices.
Which is surprising, given his background, a degree in electrical engineering and jobs with power companies.[1]
This may be an argument for using more DC-DC converters and fewer transformers. The classic problem with shipping DC around is that voltage conversion is expensive. DC-DC converters have improved a lot. This article may be a dumbed-down version of that argument.
A nice thing about large transformers is that those big hunks of copper and iron have a lifespan of 30 to 75 years. Replace those with a DC-DC converter, and it will probably have semiconductor lifespan problems. Plus someone will add on a data connection, firmware updates, a web server, and an antivirus program.
> "DC power is significantly more energy efficient than AC power." -> the examples go on to specify end points for electrical energy but we already use DC there, AC is mainly used in transmission, so the claimed advantages of DC are irrelevant.
DC is more efficient for transmission too.
The reason the grid uses AC is that high voltage is always[1] more efficient for transmission than low voltage--regardless of whether you're talking about AC or DC--and in 1900 the only way to step voltages up or down was to use transformers, and transformers require AC. That's unfortunate because for a given voltage, it's more efficient to transmit it as DC than AC.
But today we have power electronics which can step DC voltages up or down, which means we are free to convert the grid to DC.
[1] The single exception is superconducting cables which can transmit low voltage power just as efficiently as high voltage power. But they are not yet cheap enough to be practical except over short distances.
In terms of motors, yes -- virtually all motors need to provide AC to the coils to run, so DC motors need to use an inverter.
But increasingly these days, even AC motors are being run from variable-frequency drives, in order to squeeze out a bit more efficiency, because the savings from better matching the load more than makes up for the losses in the drive. Many jurisdictions are starting to incentivize or require VFDs for HVAC applications. And typically the first thing the VFD does is rectify the AC input to DC.
DC is generically more efficient for transmission than AC. That is why it is used for very long lines. It used to be that you needed to stay AC to use transformers to step up the voltage but those days are long past.
>Brushless DC motors actually require a separate circuit to turn DC into something resembling a sinusoidal current (i.e. AC).
Typical split phase AC induction motors used in residential applications are not very efficient and have various other deficiencies. There is a tendency to do a AC>DC>AC thing to a 3 phase these days for smaller electric motors and get variable speed as a bonus.
>...wind generates AC.
But not at any particular frequency. So typical wind turbines have a AC>DC>AC converter to allow them to sync up with the grid.
If you wanted to efficiently make an efficient deeply variable speed modern motor run on AC, you might very well turn the AC into DC then back into AC in a brushless motor controller.
Indeed, changing the frequency of an AC wave programmatically is incredibly difficult (but possible through a CVT, I guess), you're better off turning it into DC then back into AC through some some form of function generator.
So indeed, the widespread use of BLDC motors is a point in favour of DC electric circuits in the home.
Same goes for variable velocity generators, you will generally have an AC-DC-AC conversion in a variable speed generator. Either that, or a gearbox, those are your two options.
The case for DC is named microgrids: keeping the frequency on a microgrid is hard, inverters react too slowly for most loads (that does not ramp up/does down power slowly) while DC devices can be far quicker. The case for AC is large grid and safety.
AFAIK wind turbines, as opposed to conventional turbines in power plants, don't directly connect to the 60Hz Grid but go through DC and an inverter. This is done so they can efficiently work at different speeds at not just a few mechanically selectable ones
The author gets a few things wrong or mixed up (mostly covered in other comments).
None of the other comments also talk about galvanic isolation, you need transformers (therefore AC) for that.
But the article is trying to sell you on DC, like there are lot of marketing around hydrogen and such. I would say the right approach would use the right technology where it is the best option. HVDC to replace HV AC transmission, sure if it makes sense for your use case. DC-ify all homes and appliances just because? Definitely not. DC-ify parts of home lighting? Why not. Tho lighting is usually at 24VDC or 48VDC and then you are going to need either very thick cables (insane waste) or DCDC converters and where is the advantage there?
Besides transmission line level of DC, rest of the article is pretty much noise, generation is where we have big problems at the moment.
Also AC frequency is currently used as signaling mechanism to regulate grid power-balance and stability, spinning reserve and all that jazz. With DC you need some other signaling mechanism, first to mind is Voltage but with all the smart semiconductor devices my guess is that the signal gets lost as these devices tend to compensate. So you'd need a dedicated signaling mechanism like software...
You don't need AC for isolation, you need transformers. Isolated DC to DC is a big area of power supplies. You've also got cabling size backwards: you need thinner conductors for higher V due to lower I.
The major thing that is unaddressed is the inertia of the extant built environment.
We know that lead paint is bad for people, especially kids, but we haven’t remediated it in much of the pre-1976 housing stock. Why? It is expensive and the places where it is worst are not high-value areas.
Similarly, there are many homes in America with low voltage knob and tube which is an uninsulated wire. Would you retrofit homes with a second DC circuit or use the existing AC infrastructure and be constrained by the choice of 12/14GA wire? Would new homes have two systems? Would you have a second set of DC distribution wires or a home inverter (with its own inefficiencies and failure modes)?
The supposed efficiency of DC for residential applications will be overwhelmed by the efficiency of doing nothing.
It's a tangent, but worth pointing out that like asbestos, lead paint remediation is often more dangerous than doing nothing. Paint over it, and it isn't hurting anyone. Sand it off, and now you have super fine lead particles floating in the air and settling all over the place just waiting to be disturbed and kicked up again.
Lead pipes are an entirely different matter, and remediation is usually (wrongly) deferred due to cost.
The author appears to be Gregory Reed, Professor at the University of Pittsburgh who focuses on grid things. He's also the Chief Science Advisor for: https://www.emergealliance.org/
Definitely seems like someone who would have appropriate knowledge to make statements like those in the article, though maybe with a vested interest in things.
There is some validity to using DC distribution within a building or domicile, it can make it cheaper and more reliable to have a central power supply and battery system.
That is not a new idea obviously, that exact approach has been in use in the telecom industry for decades. There is a AC feed to a system of rectifiers that converts the AC from the grid to -48VDC and continuously charge a string of batteries. There is a Generator that will go on automatically if the power from the grid fails and takes over.
The -48VDC is distributed throughout the central office to the equipment bays. There are a number of benefits to doing it this way, the batteries help maintain a constant voltage level and provide back up until the generator can fire up or if the generator should fail to start it buys you time to get it going.
For a home, I could see having a DC distribution system using USB 48V standard or maybe a 12VDC system with a wall battery and perhaps Solar system. Assuming that you could power all your devices off DC, it would eliminate the need for an Inverter. Most devices in homes today can be powered with 12VDC versions, with some exceptions.
Since we are doing DC-DC, I'd say we go with the highest DCV we can get away with. 12V is just simply too low and the associated I^2R losses will be unacceptable.
Correct me if I'm wrong but isn't the whole point of using AC that it's easy to convert voltages super-efficiently with transformers?
Having DC power at home seems like the worst of both worlds. Low voltage DC at home causes large losses in the wiring, and high voltage DC causes large losses in the step-down regulator (leaving you with a buck-type regulator operating at the low extreme of its duty cycle). After all, DC-DC conversion relies broadly on turning the DC into something vaguely sinusoidal and using an inductor - so its basically DC-AC-DC anyways.
I think 24vdc is pretty much ideal. It's low enough not to be dangerous (48 volts is right at the threshold of danger) while it could supply enough power via the 12 or 14 gauge copper that's already in most US homes to handle all lighting needs plus probably a decent fraction of other loads.
When you decrease the voltage to 12 you start having to think about fatter wire--especially in larger homes--and that retrofit would be expensive.
> Direct Current (DC) electric power is an emerging disruptive technological area that has the potential to stimulate economic growth, inspire innovation, increase research and development opportunities, create jobs, and simultaneously advance environmental sustainability.
Was this published in the early 1900s? There is no date and DC is definitely not emerging nor disruptive.
DC won't replace AC for those who rely on remote power production.
DC is great for transmitting power. You crank the voltage, use all of the copper wire (no pesky skin effect), and sync to the grid at the DC-AC conversion point.
The limiting factor to DC was conversion losses. The Pacific DC Intertie needed to use gigantic, toxic mercury vapor tube diodes for the conversion for a very long time.
Now that we use high voltage semiconductors, that's no longer a problem. We easily convert between DC voltages as well as AC with quite remarkable efficiency.
For grid transmission over longer hauls it will definitely be the standard, for shorter runs and local distribution we will likely be using AC for a long time to come, possibly forever.
There is an interesting effect with AC distribution that leads to the statement "the amount of power produced must balance that consumed" that you sometimes hear.
On first thought this is a ridiculous statement: voltage is a measure of potential energy after all. If load is reduced, the voltage just hangs there and less power will be consumed.
But with AC distribution what you have is essentially a large rotating machine. The more power you put into it, the faster it spins. When you connect a generator to the grid, you phase match the AC waveforms, connect it, then start pushing the grid faster to inject power.
So the statement is true. If the load is too low, the frequency starts to go up. But it's also not true.. if each generator independently self limits the frequency, we would be back to the potential energy situation. But power plants want to push power into the grid- this is how they earn money.
So some plants self regulate and some do not, see:
Ones that self regulate get to charge a premium for their unused capacity.
Even with DC only, you would be in the same situation. A power plant wants to make money, so it will want to push power into the grid, which for DC means pushing the voltage up.
> There is an interesting effect with AC distribution that leads to the statement "the amount of power produced must balance that consumed" that you sometimes hear.
You have the same problem with DC. It nothing to do with 'AC' per say. It's a issue of large scale power plants.
> On first thought this is a ridiculous statement: voltage is a measure of potential energy after all. If load is reduced, the voltage just hangs there and less power will be consumed.
Voltage is a measurement of the difference of two electrical potentials. "Potential Energy" is something else entirely.
Voltage is not a measurement of energy.
Voltage works in a similar way that pressure does. Imagine you have two pressure cylinders and one of them is 200 PSI and the other is 220 PSI. If you were using a voltage-style measurement between the two cylinders you'd say that the there is 20 PSI different or 'potential' between them.
That gives you zero information as far as the actual energy potential.
A 16 ounce canister at 100 PSI is going to have a lot less energy potential then a 500 gallon tank at 100 PSI, for example.
This is why you can go and get a static electrical shock that involves thousands of volts and your skin doesn't burst into flames.
> But with AC distribution what you have is essentially a large rotating machine.
No with AC, or DC, what you is LITERALLY a large rotating machine. A rotating machine larger then most houses running of of hydro electric, coal, or nuclear power take time to have their energy output adjusted.
They don't work like car motors were you press a button to go "zoom" and another to go "woah".
The generators that can quickly adjust are small ones. Generally natural gas turbines. They are a lot like jet engines. In fact many of them used to be the same type of engines used in jet planes.
And they are much more expensive to operate and less efficient overall, but they are the ones people are moving to because they can keep up with the extremely poor quality electrical output (read: highly unpredictable) you get from solar and wind.
> Even with DC only, you would be in the same situation. A power plant wants to make money, so it will want to push power into the grid, which for DC means pushing the voltage up.
You somehow seem to have "laws of physics' confused with "making a profit".
Of course you are not wrong with the power plants operators wanting to get paid to work for a living and there are plenty of shady things they do that you should be irritated about, but you are barking up the wrong tree here.
For example: the massive scam that is government-subsidized grid-tied residential solar. How that the plant operators have colluded with the regulators to ensure that they have remote control over your inverter's output. Which means that with the hundreds of thousands of solar panel installations that people are proud of and think they can make money from 'selling back to the power plant' are actually operating at a only a tiny fraction potential output.
Which means that home owners that do pay tens of thousands of dollars for these setups are getting burned WHILE accomplishing nothing to help the environment.
And when the grid goes down so will those grid-tied installations. For "safety" reasons, despite the fact that ICE-based generators have had reliable failsafes for generations that automatically prevent any electrical feedback into downed power lines.
--------
The fact of the matter why DC is better then AC for power transmission has to do with inductance.
Every time the wire is subject to electrical current it generates a magnetic field. The higher the current the more powerful the magnetic field. By winding a cable around a iron core you can concentrate that field and make a powerful electro-magnet. The effect is still present in the miles of electrical cable used for power distribution. It's just spread out over a massive area.
With AC that magnetic field needs to be torn down to zero, reversed, and then torn down to zero again 60 times a second. Sure much of that energy is returned to the wire on each field collapse, but it is still something you have to deal with and fight with. It shows up as significant inductance.
The AC/DC debate has raged for over a hundred years because each side has some merits over the other, but overall the differences are relatively minor compared to the cost of ripping up an existing AC or DC system and replacing it, or even switching to one system or the other going forward. PG&E isn't going to scrap all of the transmission towers they have on order just because DC might save them a few dozen watts.
I keep wondering if there might be some value in a derivative high-efficiently USB-C PD standard (since distance, and other factors come in) for whole house. IE, could you add DC power via USB connections to a bunch of different devices with a high-efficiency power supply for all of the different connections, rather then having low-efficiency power supplies in lots of other devices?
Most modern (GaN) USB-C chargers are already highly efficient. Since USB-C PD can only be used as a point-to-point connection (since a voltage level is negotiated), a sane architecture would likely use a high voltage (>100V to minimize resisitve losses) DC line with local step-down. At that point, the dc-dc step down shouldn't be integrated into the cabeling but into an external unit or into tne device, since the idle power, size and cost of a 500W PC power supply and a 5W headset charger is very different (even using DC).
The losses from the AC conversion aren't very high and the most energy intensive consumers (resisitive loads, ACs, Fridges) don't benefit much from switching to DC.
With high voltage DC safety becomes another concern, with arcing being a huge issue.
I've always wanted something like this, and I imagine the global efficiency benefit would be monumental in the long term, despite the enormous cost of enforcing a change. Though I also have trouble wrapping my head around a USB washing machine.
AC is still way better for power transmission, and I don't mean giant power lines spanning from one city to another, I mean from the curb to your home, or within the walls of your home. Electroboom has a video on this topic https://www.youtube.com/watch?v=S7C5sSde9e4 and its been repeated elsewhere, but transmitting dc power with any meaningful voltage is dangerous, like burn your whole house down dangerous, and if its not high voltage, you're just losing too much power to resistance.
> AC is still way better for power transmission, and I don't mean giant power lines spanning from one city to another, I mean from the curb to your home, or within the walls of your home.
First you say AC is way better for transmission, which is false - you should look into what HVDC is.. and second what you’re talking about “curb to home” is power distribution, not transmission - so your post is confused on a few levels - it’s hard to understand what you’re trying to even claim.
> its been repeated elsewhere, but transmitting dc power with any meaningful voltage is dangerous, like burn your whole house down dangerous
Would you like to specifically reference in your linked video where that claim is made? Because I didn’t see that, and I am puzzled what you’re referring to. Quite the opposite he demonstrates at household voltage, DC is safer than AC from a shock standpoint (see 2:08). Why do you think high voltage DC is inherently less safe than AC?
This video seems to demonstrate the basic historical concept that AC is superior for transmission due to the typical ease in converting to high voltage low current and back - the key point is that it is high voltage for lower current and lower loss and this has traditionally been easier achieved with AC. It doesn’t really get into modern power conversion which has changed things somewhat.
AC won out historically because it's easy to change the voltage of AC using a transformer. If we reach a point where modern DC-DC converters are cheaper or better than a traditional transformer, then I don't see why we wouldn't just use DC everywhere. (I don't know if we're actually there yet.) With DC, you can transmit more power over the same wire you'd use for AC (no skin effect), electric shock from moderate DC voltages isn't as bad as AC, and you mostly get rid of 60-hz RF noise.
One argument for AC though is that it's easier to make AC switches, since those have a self-extinguishing arc. Maybe even household light switches can be replaced by solid-state devices?
Aside from the difficulty of making reliable switches, I'm not aware of anything about DC that makes it inherently more dangerous than an equivalent AC voltage.
I'm not sure if that's the moral of that video. Just watched (had seen before), and his conclusion is that you shouldn't transmit power with low voltage because it means you need lots of current.
HVDC has some tradeoffs over HVAC, but you should be able to transmit power just fine with either.
Consider also having to rebuild things from scratch. Say a solar flare knocked out all your electronics or you are at war with your only supplier of rare earth metals. How quickly can you replace missing generators and appliances with devices that may be less efficient or clean and may only supply a small fraction of current power levels, but will at least let you turn lights and fridges back on? If mechanical turbines can generate A/C without advanced electronics and mechanical motors can run on that, it's not a bad precaution to keep these around.
This may be a dumb idea, but, would it be more efficient and useful to use DC battery storage in series up to 120V rather than up/down-converting between 120 and 12?
Ohms law is the same for AC and DC at any given moment in time. That is, in an instant where an AC voltage in a wire at 120V, it will have identical resistive loss as DC voltage at 120V.
Pretty much all device in a household can function using only DC and now we can also generate DC directly DC at home, thanks to Solar. So we can cut the losses switching to AC and DC.
Counter-example: Motors consume >= 25% of all electrical power, and the majority of household and industrial motors are AC. Think air conditioners, fans, compressors, etc.
Cool, let me know how much the copper will cost you when you'll need to wire your entire household with at least 2 tons (and I am on low estimate here) of them, because you'll need them thick to drive the increased Ampere juice. Remember P (power) == U (voltage) x I (intensity). As you'll lower your voltage, your intensity will rise to meet the same power consumption. Meaning thick copper wires, at least 2cm diameter, not your current 3mm diameter you currently have.
In what way is AC safer than DC? Ohm’s law says V=IR, that means your resistive body is gonna get shocked regardless of whether the voltage is constant or changing.
After skimming this post history I'm not sure if it's AI, a joke, a troll or something else all together. AC computers and sin + cos = consciousness are just the beginning.
Youden|3 years ago
"DC power is significantly more energy efficient than AC power." -> the examples go on to specify end points for electrical energy but we already use DC there, AC is mainly used in transmission, so the claimed advantages of DC are irrelevant.
"DC motors and appliances have higher efficiency and power to size characteristics." -> Brushed DC motors aren't efficient, just cheap. Brushless DC motors actually require a separate circuit to turn DC into something resembling a sinusoidal current (i.e. AC).
"DC is inherently compatible with renewable sources of energy such as solar and wind." -> solar generates DC but wind generates AC.
"requiring storage (batteries)" -> chemical batteries require DC but other forms of storage like dams require AC to drive motors or turbines.
"Most energy storage technologies are DC-based" -> at a local level (mobile phones, cordless power tools), sure. At a grid level, we're often talking about hydro.
"Electronic equipment operates on DC power." -> equipment that deals with computation. Electric fans, washing machines and many industrial consumers of electricity use AC. Plus, the existing grids and existing generation infrastructure are built on AC.
Reason077|3 years ago
Yes, but a wind turbine is allowed to spin at variable speeds - its rotation is not synchronized to the grid frequency in the same way that hydroelectric and thermal turbines are.
In order to get a wind turbine's power output to match the grid frequency, it goes through an AC -> DC -> AC conversion in a component known as a double-fed induction generator (DFIG).
Animats|3 years ago
Which is surprising, given his background, a degree in electrical engineering and jobs with power companies.[1]
This may be an argument for using more DC-DC converters and fewer transformers. The classic problem with shipping DC around is that voltage conversion is expensive. DC-DC converters have improved a lot. This article may be a dumbed-down version of that argument.
A nice thing about large transformers is that those big hunks of copper and iron have a lifespan of 30 to 75 years. Replace those with a DC-DC converter, and it will probably have semiconductor lifespan problems. Plus someone will add on a data connection, firmware updates, a web server, and an antivirus program.
[1] https://grid.pitt.edu/people/gregory-f-reed
dreamcompiler|3 years ago
DC is more efficient for transmission too.
The reason the grid uses AC is that high voltage is always[1] more efficient for transmission than low voltage--regardless of whether you're talking about AC or DC--and in 1900 the only way to step voltages up or down was to use transformers, and transformers require AC. That's unfortunate because for a given voltage, it's more efficient to transmit it as DC than AC.
But today we have power electronics which can step DC voltages up or down, which means we are free to convert the grid to DC.
[1] The single exception is superconducting cables which can transmit low voltage power just as efficiently as high voltage power. But they are not yet cheap enough to be practical except over short distances.
jbay808|3 years ago
But increasingly these days, even AC motors are being run from variable-frequency drives, in order to squeeze out a bit more efficiency, because the savings from better matching the load more than makes up for the losses in the drive. Many jurisdictions are starting to incentivize or require VFDs for HVAC applications. And typically the first thing the VFD does is rectify the AC input to DC.
upofadown|3 years ago
>Brushless DC motors actually require a separate circuit to turn DC into something resembling a sinusoidal current (i.e. AC).
Typical split phase AC induction motors used in residential applications are not very efficient and have various other deficiencies. There is a tendency to do a AC>DC>AC thing to a 3 phase these days for smaller electric motors and get variable speed as a bonus.
>...wind generates AC.
But not at any particular frequency. So typical wind turbines have a AC>DC>AC converter to allow them to sync up with the grid.
sudosysgen|3 years ago
Indeed, changing the frequency of an AC wave programmatically is incredibly difficult (but possible through a CVT, I guess), you're better off turning it into DC then back into AC through some some form of function generator.
So indeed, the widespread use of BLDC motors is a point in favour of DC electric circuits in the home.
Same goes for variable velocity generators, you will generally have an AC-DC-AC conversion in a variable speed generator. Either that, or a gearbox, those are your two options.
simonebrunozzi|3 years ago
kkfx|3 years ago
danhor|3 years ago
jnsaff2|3 years ago
None of the other comments also talk about galvanic isolation, you need transformers (therefore AC) for that.
But the article is trying to sell you on DC, like there are lot of marketing around hydrogen and such. I would say the right approach would use the right technology where it is the best option. HVDC to replace HV AC transmission, sure if it makes sense for your use case. DC-ify all homes and appliances just because? Definitely not. DC-ify parts of home lighting? Why not. Tho lighting is usually at 24VDC or 48VDC and then you are going to need either very thick cables (insane waste) or DCDC converters and where is the advantage there?
Besides transmission line level of DC, rest of the article is pretty much noise, generation is where we have big problems at the moment.
Also AC frequency is currently used as signaling mechanism to regulate grid power-balance and stability, spinning reserve and all that jazz. With DC you need some other signaling mechanism, first to mind is Voltage but with all the smart semiconductor devices my guess is that the signal gets lost as these devices tend to compensate. So you'd need a dedicated signaling mechanism like software...
R0b0t1|3 years ago
DoingIsLearning|3 years ago
Citation needed? Other then HVDC links or micro-generation I can't see a practical use for DC unless you are entirely off-grid.
naikrovek|3 years ago
article author is either sole owner of a huge copper deposit or isn't articulating themselves very well. DC makes no sense for distribution at all.
contingencies|3 years ago
dpierce9|3 years ago
We know that lead paint is bad for people, especially kids, but we haven’t remediated it in much of the pre-1976 housing stock. Why? It is expensive and the places where it is worst are not high-value areas.
Similarly, there are many homes in America with low voltage knob and tube which is an uninsulated wire. Would you retrofit homes with a second DC circuit or use the existing AC infrastructure and be constrained by the choice of 12/14GA wire? Would new homes have two systems? Would you have a second set of DC distribution wires or a home inverter (with its own inefficiencies and failure modes)?
The supposed efficiency of DC for residential applications will be overwhelmed by the efficiency of doing nothing.
zdragnar|3 years ago
Lead pipes are an entirely different matter, and remediation is usually (wrongly) deferred due to cost.
userbinator|3 years ago
fatnoah|3 years ago
Definitely seems like someone who would have appropriate knowledge to make statements like those in the article, though maybe with a vested interest in things.
zw123456|3 years ago
That is not a new idea obviously, that exact approach has been in use in the telecom industry for decades. There is a AC feed to a system of rectifiers that converts the AC from the grid to -48VDC and continuously charge a string of batteries. There is a Generator that will go on automatically if the power from the grid fails and takes over.
The -48VDC is distributed throughout the central office to the equipment bays. There are a number of benefits to doing it this way, the batteries help maintain a constant voltage level and provide back up until the generator can fire up or if the generator should fail to start it buys you time to get it going.
For a home, I could see having a DC distribution system using USB 48V standard or maybe a 12VDC system with a wall battery and perhaps Solar system. Assuming that you could power all your devices off DC, it would eliminate the need for an Inverter. Most devices in homes today can be powered with 12VDC versions, with some exceptions.
It's an interesting idea.
dhdc|3 years ago
arcticbull|3 years ago
Having DC power at home seems like the worst of both worlds. Low voltage DC at home causes large losses in the wiring, and high voltage DC causes large losses in the step-down regulator (leaving you with a buck-type regulator operating at the low extreme of its duty cycle). After all, DC-DC conversion relies broadly on turning the DC into something vaguely sinusoidal and using an inductor - so its basically DC-AC-DC anyways.
Am I missing something?
dreamcompiler|3 years ago
When you decrease the voltage to 12 you start having to think about fatter wire--especially in larger homes--and that retrofit would be expensive.
kimpeek|3 years ago
Was this published in the early 1900s? There is no date and DC is definitely not emerging nor disruptive.
DC won't replace AC for those who rely on remote power production.
bsder|3 years ago
DC is great for transmitting power. You crank the voltage, use all of the copper wire (no pesky skin effect), and sync to the grid at the DC-AC conversion point.
The limiting factor to DC was conversion losses. The Pacific DC Intertie needed to use gigantic, toxic mercury vapor tube diodes for the conversion for a very long time.
Now that we use high voltage semiconductors, that's no longer a problem. We easily convert between DC voltages as well as AC with quite remarkable efficiency.
jacquesm|3 years ago
orf|3 years ago
jhallenworld|3 years ago
On first thought this is a ridiculous statement: voltage is a measure of potential energy after all. If load is reduced, the voltage just hangs there and less power will be consumed.
But with AC distribution what you have is essentially a large rotating machine. The more power you put into it, the faster it spins. When you connect a generator to the grid, you phase match the AC waveforms, connect it, then start pushing the grid faster to inject power.
So the statement is true. If the load is too low, the frequency starts to go up. But it's also not true.. if each generator independently self limits the frequency, we would be back to the potential energy situation. But power plants want to push power into the grid- this is how they earn money.
So some plants self regulate and some do not, see:
https://www.e-education.psu.edu/ebf483/node/705
Ones that self regulate get to charge a premium for their unused capacity.
Even with DC only, you would be in the same situation. A power plant wants to make money, so it will want to push power into the grid, which for DC means pushing the voltage up.
hushpuppy|3 years ago
You have the same problem with DC. It nothing to do with 'AC' per say. It's a issue of large scale power plants.
> On first thought this is a ridiculous statement: voltage is a measure of potential energy after all. If load is reduced, the voltage just hangs there and less power will be consumed.
Voltage is a measurement of the difference of two electrical potentials. "Potential Energy" is something else entirely.
Voltage is not a measurement of energy.
Voltage works in a similar way that pressure does. Imagine you have two pressure cylinders and one of them is 200 PSI and the other is 220 PSI. If you were using a voltage-style measurement between the two cylinders you'd say that the there is 20 PSI different or 'potential' between them.
That gives you zero information as far as the actual energy potential. A 16 ounce canister at 100 PSI is going to have a lot less energy potential then a 500 gallon tank at 100 PSI, for example.
This is why you can go and get a static electrical shock that involves thousands of volts and your skin doesn't burst into flames.
> But with AC distribution what you have is essentially a large rotating machine.
No with AC, or DC, what you is LITERALLY a large rotating machine. A rotating machine larger then most houses running of of hydro electric, coal, or nuclear power take time to have their energy output adjusted.
They don't work like car motors were you press a button to go "zoom" and another to go "woah".
The generators that can quickly adjust are small ones. Generally natural gas turbines. They are a lot like jet engines. In fact many of them used to be the same type of engines used in jet planes.
And they are much more expensive to operate and less efficient overall, but they are the ones people are moving to because they can keep up with the extremely poor quality electrical output (read: highly unpredictable) you get from solar and wind.
> Even with DC only, you would be in the same situation. A power plant wants to make money, so it will want to push power into the grid, which for DC means pushing the voltage up.
You somehow seem to have "laws of physics' confused with "making a profit".
Of course you are not wrong with the power plants operators wanting to get paid to work for a living and there are plenty of shady things they do that you should be irritated about, but you are barking up the wrong tree here.
For example: the massive scam that is government-subsidized grid-tied residential solar. How that the plant operators have colluded with the regulators to ensure that they have remote control over your inverter's output. Which means that with the hundreds of thousands of solar panel installations that people are proud of and think they can make money from 'selling back to the power plant' are actually operating at a only a tiny fraction potential output.
Which means that home owners that do pay tens of thousands of dollars for these setups are getting burned WHILE accomplishing nothing to help the environment.
And when the grid goes down so will those grid-tied installations. For "safety" reasons, despite the fact that ICE-based generators have had reliable failsafes for generations that automatically prevent any electrical feedback into downed power lines.
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The fact of the matter why DC is better then AC for power transmission has to do with inductance.
Every time the wire is subject to electrical current it generates a magnetic field. The higher the current the more powerful the magnetic field. By winding a cable around a iron core you can concentrate that field and make a powerful electro-magnet. The effect is still present in the miles of electrical cable used for power distribution. It's just spread out over a massive area.
With AC that magnetic field needs to be torn down to zero, reversed, and then torn down to zero again 60 times a second. Sure much of that energy is returned to the wire on each field collapse, but it is still something you have to deal with and fight with. It shows up as significant inductance.
With DC you don't have to do that.
phendrenad2|3 years ago
InTheArena|3 years ago
danhor|3 years ago
The losses from the AC conversion aren't very high and the most energy intensive consumers (resisitive loads, ACs, Fridges) don't benefit much from switching to DC.
With high voltage DC safety becomes another concern, with arcing being a huge issue.
Mizza|3 years ago
seanalltogether|3 years ago
danachow|3 years ago
First you say AC is way better for transmission, which is false - you should look into what HVDC is.. and second what you’re talking about “curb to home” is power distribution, not transmission - so your post is confused on a few levels - it’s hard to understand what you’re trying to even claim.
> its been repeated elsewhere, but transmitting dc power with any meaningful voltage is dangerous, like burn your whole house down dangerous
Would you like to specifically reference in your linked video where that claim is made? Because I didn’t see that, and I am puzzled what you’re referring to. Quite the opposite he demonstrates at household voltage, DC is safer than AC from a shock standpoint (see 2:08). Why do you think high voltage DC is inherently less safe than AC?
This video seems to demonstrate the basic historical concept that AC is superior for transmission due to the typical ease in converting to high voltage low current and back - the key point is that it is high voltage for lower current and lower loss and this has traditionally been easier achieved with AC. It doesn’t really get into modern power conversion which has changed things somewhat.
elihu|3 years ago
One argument for AC though is that it's easier to make AC switches, since those have a self-extinguishing arc. Maybe even household light switches can be replaced by solid-state devices?
Aside from the difficulty of making reliable switches, I'm not aware of anything about DC that makes it inherently more dangerous than an equivalent AC voltage.
dudeofea|3 years ago
HVDC has some tradeoffs over HVAC, but you should be able to transmit power just fine with either.
HVDC doesn't suffer from the skin effect that AC does: https://www.allaboutcircuits.com/textbook/alternating-curren...
HVDC is however harder to make/break contact with compared to HVAC as AC crosses zero volts many times: https://electronics.stackexchange.com/a/325608
EDIT: Sorry, didn't mean to pile on this comment with everyone else
cat_plus_plus|3 years ago
system2|3 years ago
jl2718|3 years ago
b33j0r|3 years ago
But right now, resistive heat losses make DC a silly solution. That’s why we rectify only when the energy reaches “the edge.”
thehappypm|3 years ago
sabareesh|3 years ago
nickff|3 years ago
unnouinceput|3 years ago
Overtonwindow|3 years ago
thehappypm|3 years ago
dhdc|3 years ago
stevespang|3 years ago
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chrisp_how|3 years ago
cfraenkel|3 years ago
CyberDildonics|3 years ago