I think HVDC is a game changer for renewables. Any long East-West grid connection is going to improve the total fraction of power that can be generated using renewables because effectively windpower = solar power and having a longer East-West stretch makes the amount of sun hours during a day longer. And any North-South lines will help offset local conditions during the day.
I wanted Russia to invest in a transiberia-HVDC line and solar collectors instead of a war. They could even sell excess capacity to the countries on their southern border. I think Reddit panned this idea last time I proposed it because the longest HVDC line was only 2100 miles long.
HVDC can be made cheaper by making the voltage higher...
As voltage goes up, the thickness of metal needed goes down. The insulator thickness goes up - that either means taller towers or thicker plastic.
Conversion from regular AC grid voltages to high voltage DC was previously very expensive, with custom made semiconductors costing millions.
With the advent of electric cars, there are now off the shelf cheap power electronics. They can be stacked, perhaps 20x in package to get to 10kV, and then 100x packages to get to 1 million volts.
That should dramatically reduce the cost of moving large amounts of power long distances.
I think that would actually be more expensive as you still have the all the hard problems. Like how do you isolate the power electronics. You can use air which is cheap but needs a lot of space. (i learned that you need 1mm per 1kV)
You need a lot of space which has to be very secure.
etc
Additionally you need to control 5000 converters without getting oscillations etc. (probably over glas)
Also they will probably need a lot more space.
We need about four HVDC lines through the Sierras, to connect the US wind belt (the Texas panhandle north to Canada) to the West Coast. Plus lines east to Chicago and beyond.
An oversimplified explanation is that AC has less transmission losses over medium distances while high voltage DC has less transmission losses over extremely long distances. I found this stack-exchange post that goes into some of the details better[1]. It also explains some other advantages of DC.
1. Long lines become a "transmission line" in the sense that you get reflections. These have to Z matched and you also have to get the phase angle right.
2 Capacitance loss to ground. The lines are a massive capacitor to ground. The longer the line the more power shorts to ground
2a Because of 2. You dont use AC lines underwater. The increased dielectric means that you loose too much power from anything but the shortest runs.
You could change the frequency to a do the long runs at a lower f, and itd have its benefits, but its outweighed by the drawbacks (namely transformer saturation)
As the headline says, 3 grids that are not synchronized . You cannot interconnect them using AC. It would basically be a shortcut.
Edit: You could of course keep the DC step within one site and do all lines in AC. But as the other answers say DC transmission also has benefits, so doing it inside one site you'd need all the equipment but wouldn't get all the benefits.
First some background, sorry for the long comment but I can see you need a bit of a primer before we get to your question:
Transmission lines and generators such as solar panels and wind turbines work at very different voltages. Once you need to convert the extra step to convert from AC to DC or VV isn't a really big challenge. Solar panels output anywhere from 20 to 100V, these are ganged into strings and strings are then coupled to inverters to create relatively low voltage AC, or each panel has its own inverter (not very common in solar farms). Those inverters feed into a local parallel grid which is then stepped up to join the national grid using a feed line (typically 10 to 50 KV, depending on the size of the farm and the local grid). Very large solar farms can have their own local understation where the voltage is stepped up to long haul voltage.
Sometimes there is co-generation with another source (such as solar/wind, solar/natural gas or some other combination).
Wind Turbines usually have generators that output anywhere from 10KV to 50KV depending on the capacity and the manufacturer. This can be variable frequency current or, in a tightly grid coupled turbine it can be at the grid frequency (you can tell the difference from a distance because all of the turbines in a wind farm like that will move in lockstep with each other, this is a good indication that they are AC synchronized). At the base of every turbine you will find a an inverter and/or a step up transformer like with the solar farms. A typical turbine will do anything from 1 MW (which really is small these days, but which used to be state of the art not all that long ago) all the way up to 14 MW behemoths.
These are most impressive up close, to put it very mildly, think of an Eiffeltower but it rotates...
HVDC transmisison lines themselves are super high technology and you're definitely not going to find these running from every Wind Turbine to the grid, what you will most likely find is a local, intermediate AC network from a bunch of wind turbines and/or a number of solar farms to a concentration point and then a much higher voltage line from there to the national grid.
'intermediate' for shorter connections is anywhere from 10 KV to 50 KV, and for longer interconnects up to several 100 KV, all the way up to 800 KV for the longest and most power carrying lines. The engineering behind all this stuff is super impressive.
AC suffers from something called the skin effect, it essentially means that only a small part of the cross section of a powerline carries current, effectively limiting the carrying capacity of the line to a fraction of its theoretical DC limit. So by using DC rather than AC for very long connections line losses can be minimized and much more power can be transferred through a line because those losses translate into heat generated in the line. So HVDC makes very good sense for the long haul links coupling remote areas. They might even make sense intercontinentally (though I'm a bit more skeptical about this after the pipeline attack on the NS pipelines, HVDC lines would be quite fragile and very difficult to repair after an attack).
Note that you always have these losses, but the overhead of the AC->DC->AC conversion is such that it only makes sense for longer lines or lines carrying a very large amount of power. But even the shortest AC line suffers from that skin effect.
I’m sure you’ve heard something like “alternating current is more efficient than direct current for transmitting power”, but this is only true in specific conditions. At very high A/C voltages, the magnetic field created by the alternating current “pushes” elections away from the core of their conductor. This has the same effect as using a smaller diameter conductor, increasing heat which increases resistance and reduces efficiency. At sufficiently high voltages and distances, DC can have less loss and also has the added bonus of not needing to consider differences in A/C frequency when transmitting power between areas that have dissimilar electrical grids.
Does transatlantic HVDC make sense? Something that connects the US/Canada with mainland Europe through Greenland, Iceland, the Faroe Islands, and the UK/Norway.
The biggest problem with this is that the geography doesn't really make sense. A line from the east coast US to Europe goes right over Quebec which provides a large portion of the east coast's electricity through hydro already. Instead of spending billions on a trans-atlantic cable, you can just build a ton of renewables in the US and use Quebec's hydro as a giant battery.
It might be technically possible. The most ambitious project along those lines I’ve heard of is proposed from northern Australia (with lots of room for solar panels) to Singapore (which does not have a lot of room for anything). 5,000 km of HVDC undersea cable!
Not guaranteed to get off the ground, but I haven’t heard any serious reservations about the technical feasibility.
>Skelly is behind a previous transmission development company, Clean Line Energy, which dissolved in 2017 when a multi-state project failed to secure state regulatory approval.
We desperately need the feds to take over these approvals under the interstate commerce clause. We will need a ton of transmission infrastructure over the next decade, and we can't have things being held up or denied by the states just because they happen to be in the path. See the vote in Maine over the proposed line from Canada to NY.
It seems pretty clear to me that neighborhood level power grids are the way to go here. Large grids, long distance transmission and massive infrastructures are all a waste. Imagine if you could cut up a coal plant into small pieces and distribute it? Maybe a simple local neighbor grid sharing to cover a single failure.
I don't think power companies can (or want to) shift their thinking to local. Are their profits lost? Government subsidies lost?
> Large grids, long distance transmission and massive infrastructures are all a waste. Imagine if you could cut up a coal plant into small pieces and distribute it?
Smaller infrastructure is actually more wasteful. Since you suggested a coal plant, consider the sheer number of extra jobs it would take to hire people to drive the coal truck to the neighborhood plant and handle the offloading of coal. At the scale of per-neighborhood, you might even need someone to literally shovel coal into a furnace, I don't know if the coal conveyor lines make sense at that tiny a scale. Double that because you need to transport the resulting fly ash as well. Then there's the extra instrumentation you need, the duplicate emissions mitigation points. And this is before considering the literal better efficiency of larger boilers/blowers/etc. themselves.
In a concrete example I have familiarity with: I worked for a large water treatment plant that supplied water for about a million people. It required 2 engineers being present 24/7/365 to keep it running. Replace it with a water treatment plant that is 1/100th the size, and you still need 2 engineers present 24/7/365. Go much smaller than that, and the inability to economically provide on-site permanent engineer oversight leads to the idea of controlling the water treatment plant remotely via the public internet, with all of the increased risks that entails.
It is a lot cheaper to build transmission lines compared to providing storage.
In the future the vast majority of electricity will come from wind and solar. If production does not match consumption then it is almost always the best option to move the electricity somewhere else.
(That said: Of course storage will be needed, but only if there are no better options to balance the grid otherwise.)
[+] [-] jacquesm|3 years ago|reply
The more the better, especially intercontinental.
[+] [-] undersuit|3 years ago|reply
[+] [-] xupybd|3 years ago|reply
https://en.m.wikipedia.org/wiki/HVDC_Inter-Island
[+] [-] wil421|3 years ago|reply
https://en.m.wikipedia.org/wiki/List_of_HVDC_projects
[1] https://en.m.wikipedia.org/wiki/Mercury-arc_valve
[+] [-] londons_explore|3 years ago|reply
As voltage goes up, the thickness of metal needed goes down. The insulator thickness goes up - that either means taller towers or thicker plastic.
Conversion from regular AC grid voltages to high voltage DC was previously very expensive, with custom made semiconductors costing millions.
With the advent of electric cars, there are now off the shelf cheap power electronics. They can be stacked, perhaps 20x in package to get to 10kV, and then 100x packages to get to 1 million volts.
That should dramatically reduce the cost of moving large amounts of power long distances.
[+] [-] nuriaion|3 years ago|reply
Additionally you need to control 5000 converters without getting oscillations etc. (probably over glas) Also they will probably need a lot more space.
[+] [-] voxadam|3 years ago|reply
Why insulate the lines at all? HVAC lines aren't insulated.
[+] [-] xupybd|3 years ago|reply
[+] [-] Animats|3 years ago|reply
We need about four HVDC lines through the Sierras, to connect the US wind belt (the Texas panhandle north to Canada) to the West Coast. Plus lines east to Chicago and beyond.
[+] [-] toomuchtodo|3 years ago|reply
https://soogreen.com/
https://www.eenews.net/image_assets/2019/03/image_asset_5031...
[+] [-] excitom|3 years ago|reply
[+] [-] miteyironpaw|3 years ago|reply
[1] https://engineering.stackexchange.com/questions/19758/transm...
[+] [-] sbaiddn|3 years ago|reply
1. Long lines become a "transmission line" in the sense that you get reflections. These have to Z matched and you also have to get the phase angle right.
2 Capacitance loss to ground. The lines are a massive capacitor to ground. The longer the line the more power shorts to ground
2a Because of 2. You dont use AC lines underwater. The increased dielectric means that you loose too much power from anything but the shortest runs.
You could change the frequency to a do the long runs at a lower f, and itd have its benefits, but its outweighed by the drawbacks (namely transformer saturation)
[+] [-] usr1106|3 years ago|reply
Edit: You could of course keep the DC step within one site and do all lines in AC. But as the other answers say DC transmission also has benefits, so doing it inside one site you'd need all the equipment but wouldn't get all the benefits.
[+] [-] Aloha|3 years ago|reply
HVDC is desirable because it allows non-synchronous connection of different synchronized grids.
[+] [-] michael1999|3 years ago|reply
[+] [-] jacquesm|3 years ago|reply
Transmission lines and generators such as solar panels and wind turbines work at very different voltages. Once you need to convert the extra step to convert from AC to DC or VV isn't a really big challenge. Solar panels output anywhere from 20 to 100V, these are ganged into strings and strings are then coupled to inverters to create relatively low voltage AC, or each panel has its own inverter (not very common in solar farms). Those inverters feed into a local parallel grid which is then stepped up to join the national grid using a feed line (typically 10 to 50 KV, depending on the size of the farm and the local grid). Very large solar farms can have their own local understation where the voltage is stepped up to long haul voltage.
Sometimes there is co-generation with another source (such as solar/wind, solar/natural gas or some other combination).
https://group.vattenfall.com/press-and-media/newsroom/2019/v...
Wind Turbines usually have generators that output anywhere from 10KV to 50KV depending on the capacity and the manufacturer. This can be variable frequency current or, in a tightly grid coupled turbine it can be at the grid frequency (you can tell the difference from a distance because all of the turbines in a wind farm like that will move in lockstep with each other, this is a good indication that they are AC synchronized). At the base of every turbine you will find a an inverter and/or a step up transformer like with the solar farms. A typical turbine will do anything from 1 MW (which really is small these days, but which used to be state of the art not all that long ago) all the way up to 14 MW behemoths.
https://www.ge.com/renewableenergy/wind-energy/offshore-wind...
These are most impressive up close, to put it very mildly, think of an Eiffeltower but it rotates...
HVDC transmisison lines themselves are super high technology and you're definitely not going to find these running from every Wind Turbine to the grid, what you will most likely find is a local, intermediate AC network from a bunch of wind turbines and/or a number of solar farms to a concentration point and then a much higher voltage line from there to the national grid.
'intermediate' for shorter connections is anywhere from 10 KV to 50 KV, and for longer interconnects up to several 100 KV, all the way up to 800 KV for the longest and most power carrying lines. The engineering behind all this stuff is super impressive.
https://en.wikipedia.org/wiki/High-voltage_direct_current
Then, to answer your question:
AC suffers from something called the skin effect, it essentially means that only a small part of the cross section of a powerline carries current, effectively limiting the carrying capacity of the line to a fraction of its theoretical DC limit. So by using DC rather than AC for very long connections line losses can be minimized and much more power can be transferred through a line because those losses translate into heat generated in the line. So HVDC makes very good sense for the long haul links coupling remote areas. They might even make sense intercontinentally (though I'm a bit more skeptical about this after the pipeline attack on the NS pipelines, HVDC lines would be quite fragile and very difficult to repair after an attack).
Note that you always have these losses, but the overhead of the AC->DC->AC conversion is such that it only makes sense for longer lines or lines carrying a very large amount of power. But even the shortest AC line suffers from that skin effect.
I hope this answers your question.
[+] [-] xnyan|3 years ago|reply
[+] [-] 0xDEF|3 years ago|reply
Transatlantic HDVC might need actively cooled superconducting transmission lines: https://en.wikipedia.org/wiki/SuperGrid_(hydrogen)
[+] [-] adgjlsfhk1|3 years ago|reply
[+] [-] rgmerk|3 years ago|reply
Not guaranteed to get off the ground, but I haven’t heard any serious reservations about the technical feasibility.
[+] [-] entropicgravity|3 years ago|reply
[+] [-] plorg|3 years ago|reply
https://en.wikipedia.org/wiki/Tres_Amigas_SuperStation
[+] [-] xxpor|3 years ago|reply
We desperately need the feds to take over these approvals under the interstate commerce clause. We will need a ton of transmission infrastructure over the next decade, and we can't have things being held up or denied by the states just because they happen to be in the path. See the vote in Maine over the proposed line from Canada to NY.
[+] [-] readthenotes1|3 years ago|reply
[+] [-] bilsbie|3 years ago|reply
[+] [-] ianschmitz|3 years ago|reply
[+] [-] braingenious|3 years ago|reply
https://en.m.wikipedia.org/wiki/ISO_(disambiguation)
[+] [-] PaulDavisThe1st|3 years ago|reply
[+] [-] packetslave|3 years ago|reply
[+] [-] unknown|3 years ago|reply
[deleted]
[+] [-] swamp40|3 years ago|reply
I don't think power companies can (or want to) shift their thinking to local. Are their profits lost? Government subsidies lost?
[+] [-] jcranmer|3 years ago|reply
Smaller infrastructure is actually more wasteful. Since you suggested a coal plant, consider the sheer number of extra jobs it would take to hire people to drive the coal truck to the neighborhood plant and handle the offloading of coal. At the scale of per-neighborhood, you might even need someone to literally shovel coal into a furnace, I don't know if the coal conveyor lines make sense at that tiny a scale. Double that because you need to transport the resulting fly ash as well. Then there's the extra instrumentation you need, the duplicate emissions mitigation points. And this is before considering the literal better efficiency of larger boilers/blowers/etc. themselves.
In a concrete example I have familiarity with: I worked for a large water treatment plant that supplied water for about a million people. It required 2 engineers being present 24/7/365 to keep it running. Replace it with a water treatment plant that is 1/100th the size, and you still need 2 engineers present 24/7/365. Go much smaller than that, and the inability to economically provide on-site permanent engineer oversight leads to the idea of controlling the water treatment plant remotely via the public internet, with all of the increased risks that entails.
[+] [-] hannob|3 years ago|reply
In the future the vast majority of electricity will come from wind and solar. If production does not match consumption then it is almost always the best option to move the electricity somewhere else.
(That said: Of course storage will be needed, but only if there are no better options to balance the grid otherwise.)
[+] [-] nkingsy|3 years ago|reply
[+] [-] mastax|3 years ago|reply