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Solar power from Africa to Europe ?
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emordnilap



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PostPosted: Tue Sep 12, 2017 10:35 am    Post subject: Reply with quote

Monbiot did some investigating into high-voltage undersea DC lines, primarily looking at Africa as a solar source, feeding Europe. Apparently, HVDC is almost lossless.

How feasible is it, adam2?
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adam2
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PostPosted: Tue Sep 12, 2017 7:49 pm    Post subject: Reply with quote

Not sure about HVDC being almost lossless ! Ohms law still applies.

Despite losses the idea has some merit and is entirely doable. The main objections would seem to be political and human rather than technical.

Africa as a continent has a reputation for tribal conflict, wars, coups, revolutions, poor governance and corruption.
Whom is likely to risk a billion pounds or more on a facility that is at risk of destruction in the next conflict, or of being nationalised or confiscated by the next regime.
The European hard left will no doubt want the electricity given to the local poor, of whom there are uncountable millions, rather than being "taken away" to the profit of "the 1%"
Add to that a few witch doctors claiming that it is all a western plot to make black people sterile, or spread "bad juju" or some other nonsense.

I would not care to risk my money in such an uncertain venture.
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clv101
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PostPosted: Tue Sep 12, 2017 8:32 pm    Post subject: Reply with quote

Technically (and even economically) it's fine.

Politically (even before the 'Arab Spring') it's hopeless.
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fuzzy



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PostPosted: Tue Sep 12, 2017 8:46 pm    Post subject: Reply with quote

The interconnectors between europe - UK are DC. Apart from not drawing more current through capacitance under the sea [imagine trying to push water that is rapidly reversing direction through a 50 mile long spongy tube], it allows different mains supplies that are not synchronised to swap power. In an ac system all generators have to be exactly in phase or things go bang.

http://www2.nationalgrid.com/About-us/European-business-development/Interconnectors/france/
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cubes



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PostPosted: Tue Sep 12, 2017 10:01 pm    Post subject: Reply with quote

Sounds like a good excuse for interventionism and new wave of colonialism.
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emordnilap



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PostPosted: Wed Sep 13, 2017 9:44 am    Post subject: Reply with quote

adam2 wrote:
Not sure about HVDC being almost lossless


But less lossless than AC?

As to the political and social objections, in an ideal world, the Africans themselves would be the capitalists, selling their product to the Europeans, as opposed to Europeans colonising and exploiting Africa.

As I said, ideal world. We have a long way to go before then.
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adam2
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PostPosted: Wed Sep 13, 2017 10:17 am    Post subject: Reply with quote

HVDC is more efficient than AC if the distance is great enough.
AC has a loss per mile, so presuming that other factors remain unaltered, a 200 mile line has twice the losses of a 100 mile line.
There is no definite upper limit to transmission distances for AC, given a high enough voltage, but a few hundred miles is often considered to be the sensible limit.

AC transmission is generally limited to about one mile for every thousand volts of system voltage, but still preferably also no more than a few hundred miles.
DC transmission is also subject to the rule of thumb of a mile per thousand volts, though greater distances are possible at the cost of greater losses.

HVDC has a lower loss per mile, but also fixed losses in the converting plant at each end, these losses remain no matter how short may be the line.

As an aside it may be noted that the HVDC link between the UK and France is shorter than would be economic, on strictly economic grounds AC would have been better. HVDC was chosen to avoid having to synchronise the UK and French grids.

Some AC lines in the USA are longer than is sensible, but the system was not properly planned, it "just sort of grew" in an ad-hoc way.
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emordnilap



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PostPosted: Wed Sep 13, 2017 10:39 am    Post subject: Reply with quote

Interesting and informative as usual, adam2. Thanks.
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vtsnowedin



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PostPosted: Wed Sep 13, 2017 11:41 am    Post subject: Reply with quote

adam2 wrote:
.......

Some AC lines in the USA are longer than is sensible, but the system was not properly planned, it "just sort of grew" in an ad-hoc way.

Major lines in the USA built over the last twenty five years or so are mostly HVDC. Notably the ones bringing Canadian Hydro power to Boston and New York markets. Older AC lines that are longer then optimum have not yet been replaced but as the grid is upgraded that will eventually come about.
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BritDownUnder



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PostPosted: Fri Sep 15, 2017 9:14 am    Post subject: Reply with quote

adam2 wrote:
HVDC is more efficient than AC if the distance is great enough.
AC has a loss per mile, so presuming that other factors remain unaltered, a 200 mile line has twice the losses of a 100 mile line.
There is no definite upper limit to transmission distances for AC, given a high enough voltage, but a few hundred miles is often considered to be the sensible limit.

AC transmission is generally limited to about one mile for every thousand volts of system voltage, but still preferably also no more than a few hundred miles.
DC transmission is also subject to the rule of thumb of a mile per thousand volts, though greater distances are possible at the cost of greater losses.

HVDC has a lower loss per mile, but also fixed losses in the converting plant at each end, these losses remain no matter how short may be the line.

As an aside it may be noted that the HVDC link between the UK and France is shorter than would be economic, on strictly economic grounds AC would have been better. HVDC was chosen to avoid having to synchronise the UK and French grids.

Some AC lines in the USA are longer than is sensible, but the system was not properly planned, it "just sort of grew" in an ad-hoc way.


DC is more efficient in several ways. Both AC and DC suffer the same effects of resistance equally.
1) DC voltage is always the maximum whereas the AC voltage is only maximum at the peak of each cycle so more power can be pushed down a DC cable. Note that overhead power lines and underground cables are rated to a certain maximum voltage that depends on facts such as height of lines above ground, separation between different phases (in AC) or poles (in DC). in cables the insulation type has a maximum voltage rating.
2) AC cables suffer from problems with inductance (overhead lines especially) and capacitance (in underground/underwater cables especially) which reduces voltage and causes other complicated problems which do not affect DC cables or power lines. The capacitance effect in particular effectively reduces the maximum length of an undersea AC cable to less than 90 kilometres. I understand that the longest AC cable in the world is from the UK mainland to the Isle of Man.
3) On very long power lines AC suffers from the standing wave effect which limits their theoretical maximum length to 1200km.
4) As mentioned by Adam DC lines can link two UNsynchronized grids. this is not usually the main reason for them but the UK to France link "could" be AC if the UK and France didn't mind synchronizing their grids and it is probably less than 90km long.
5)From what I have read a 1 million volt DC link will lose about 10% of its power due to ohms law in 3000 kilometres. Basically the higher the voltage for a given power then the lower the current and hence resistive losses. Good luck in finding a cable that can take 1 million volts but I think there is a 2400km power line in China supplying Shanghai.
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kenneal - lagger
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PostPosted: Fri Sep 15, 2017 1:17 pm    Post subject: Reply with quote

There was some talk a while ago about building thermal generating plants in Iceland using their volcanism and bringing it here via HVDC lines. That would have the benefit of a constant supply although some of the North African proposals involved concentrated solar which could result in stored heat and therefore 24hr supply.
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Potemkin Villager



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PostPosted: Fri Sep 15, 2017 9:37 pm    Post subject: Reply with quote

BritDownUnder wrote:




........ the UK to France link "could" be AC if the UK and France didn't mind synchronizing their grids and it is probably less than 90km long.



Laughing I wonder why they mind synchronising their grids so much?

No doubt is down to those untrustworthy frogs and their inferior engineering standards again. If this predudice could be got over the additional cost, maintenance overhead and losses of the ac/dc converters at each end would have been avoided.

This link seems to be quite relatively unreliable and regularly down. One suspects this is to do with the ac/dc converters rather than the line itself. I imagine the semiconductor devices used are not off the shelf and available by return from RS components!
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BritDownUnder



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PostPosted: Fri Sep 15, 2017 10:05 pm    Post subject: Reply with quote

kenneal - lagger wrote:
There was some talk a while ago about building thermal generating plants in Iceland using their volcanism and bringing it here via HVDC lines. That would have the benefit of a constant supply although some of the North African proposals involved concentrated solar which could result in stored heat and therefore 24hr supply.


The UK might get one or two gigawatts from Iceland - not much but useful. The UK government would have been better making Iceland "an offer they could not refuse" when the Iceland banks started going bust rather than using the terrorism act against them.

Two problems I can see. the lines will have to go through Scotland and if they became independent would be problematic (check what Quebec does to Newfoundland's electricity on it's way to the US - They are considering using HVDC to goaround Quebec). Iceland may also want to use the power for other things, e.g. making cheap aluminium for China.

I would advise Europe to not even think about the Desertec idea. Too many problems to even start. I am all for north Africa developing their own economies using solar power and from the one North African I have spoken to, they are keen to do this.
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BritDownUnder



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PostPosted: Fri Sep 15, 2017 10:14 pm    Post subject: Reply with quote

Potemkin Villager wrote:
BritDownUnder wrote:




........ the UK to France link "could" be AC if the UK and France didn't mind synchronizing their grids and it is probably less than 90km long.



Laughing I wonder why they mind synchronising their grids so much?

No doubt is down to those untrustworthy frogs and their inferior engineering standards again. If this predudice could be got over the additional cost, maintenance overhead and losses of the ac/dc converters at each end would have been avoided.

This link seems to be quite relatively unreliable and regularly down. One suspects this is to do with the ac/dc converters rather than the line itself. I imagine the semiconductor devices used are not off the shelf and available by return from RS components!


It was built in the sixties and maybe that was the prevailing attitude then about France - also may account for the unreliability. I think that all of mainland Europe from Portugal to Poland and except Scandinavia is now one synchronised grid. There is probably a loss of sovereign control in synchronising your grid whereas HVDC is just straight power flow. Even New Zealand has two UNsynchronised grids on its two islands linked by a DC link. The Australian Eastern energy market also has a few DC links between parts of a synchronised grid and also across to Tasmania to its own separate grid.

I think we can see a lot of power-politics in future however even after Brexit the UK cannot have enough DC links to other countries. They already have links to Ireland, France and Netherlands and are actively considering links to Belgium, another to France, one to Scotland and 'could' get them to Iceland, Norway, Denmark and Germany with existing technology. I think it may reduce reliance on gas but will not save the UK any money IMHO.
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Last edited by BritDownUnder on Sat Sep 16, 2017 8:53 am; edited 1 time in total
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vtsnowedin



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PostPosted: Sat Sep 16, 2017 12:29 am    Post subject: Reply with quote

While you occasionally have a country that can deliver surplus power to a power hungry neighbor, such as Canada to the USA, in most cases the logistics and the politics make it unwise or impracticable. A country needs to generate and use the bulk of it's electricity at home with complete control in it's own hands and not being subject to being cut off by an aggressive supplying neighbor.
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