Solar and wind power are the
cheapest sources of energy right now. But they do have one slight
drawback, they don't generate when the sun sets or there's no
wind. And we can't control either of these things. Wind
doesn't blow continuously in one specific area and while the sun
might shine all day long, come evening, it dips over the
horizon, leaving you in darkness for hours. However, there's
always daylight on half the planet, and it's always windy
somewhere. So if we could connect these various energy
generating locations, we would have an uninterrupted supply of
renewable power regardless of the time of day or weather
conditions. But what about long distance or intercontinental
connections across seas and oceans? After all, we've been
connecting loved ones across the Atlantic since the laying of the
first transatlantic telegraph cable in the 1850s. So can we do
the same with electricity cables? The answer is yes, it
can be done with high voltage direct current (HVDC)
interconnectors. In this video, I'm going to explain how these
differ to regular AC (alternating current)
transmission, the recent technology advances that are
causing HVDC interconnectors to start popping up all over the
place and what challenges remain to be solved if we're going to
connect places as far flung as Europe and North America. I'm Rosie Barnes. Welcome to
Engineering with Rosie. Connecting renewable energy
plants is relatively easy to achieve across short distances
by existing electricity grids. Australia is a good example of
the benefits this can provide, we've got a really really long
grid. And when you connect wind farms way down in the south of
Australia with ones in the north, there's not much
correlation between the wind in those two locations. And I mean,
this is kind of obvious with solar as well. If you can
connect grids east to west then you get a few extra hours of
solar power in your system. There are two ways we transmit
high voltage electrical power from region to region and that's
with alternating current (AC) and direct current (DC). We use
high voltage because that's how you can transmit a lot of power
without a very high current. Power losses from resistance in
the powerlines are related to current so lower current means
higher efficiency and efficiency is the name of the game when it
comes to long distance transmission because even low
percentage losses per kilometer add up if your cables are
hundreds or even 1000s of kilometers long. Most of the
high voltage overhead power lines you see are AC because in
the early days of electricity, AC voltage could be stepped up
and down using transformers. That meant you could transmit at
high voltage and therefore high efficiency and then easily
stepped down to a manageable voltage in people's homes and
offices. However, since about the 1950s, we've been developing
better and better ways to step up and down DC voltage. So
that's less of an issue and inefficiencies due to line
losses are becoming more important. There are three types of line
losses: resistive, capacitive, and inductive. And ACs fairs
worse than DC in all three. First is extra resistive losses
in AC due to a phenomenon called the "skin effect" where the
majority of AC current tends to flow close to the outer surface
of a cable. It occurs because AC's constantly changing current
creates a magnetic field around the conductor which in turn
pushes the flow of electrons towards the outer surface of the
wire. This means the effective diameter of the wire is reduced
making its resistance higher so more energy is lost as heat.
Next is line inductance. That's a property of cables that
resists changes in the current flow by creating an opposing
voltage due to the magnetic field generated by the current
it's like the lines natural reluctance to let the current
change too quickly. Then we have capacitance, a transmission line
together with other nearby conductive elements like the
ground or ocean act like the plates in a capacitor. When you
connect a capacitor to a voltage source, electrons are drawn to
one plate making it negatively charged while the other plate
loses electrons making it positively charged. In an AC
system, the voltage is always oscillating which causes the
charges of the transmission line to constantly move back and
forth. This continual shuffle of charges doesn't contribute to
the energy transmitted, it just generates heat and results in
energy losses. Because a DC system's voltage is constant, it
doesn't suffer any of those three issues. It still has
losses from resistance in the cable which AC does too. But
overall, it's much more efficient than AC and the longer
the transmission line, the bigger the difference. For short
distances AC still wins due to its cost effective
infrastructure. However, for longer distances, power losses
dominate and DC systems are cheaper due to the higher
efficiency. There's a breakeven distance
somewhere around 500 to 900 kilometers for overhead lines
beyond which HVDC becomes more economical than AC and for
underground or subsea interconnectors. That distance
is much shorter because the capacitance effect is more of an
issue when the cable is so close to the ground or water. Okay, now let's take a look at
an HVDC cable and what it's made of. HVDC cables are comprised of
several layers, each serving a specific function. On the inside
there's a conductor usually copper or aluminium. This is the
part that actually carries the electric current there's an
insulation layer surrounding the conductor preventing electrical
current from escaping to nearby conductive elements. These days
most cables use crosslink polyethylene (XLPE) as
insulation, a significant improvement over the previous
norm of gas and oil impregnated cables. XLPE can withstand high
electric fields in HVDC cables offering excellent electrical
and mechanical properties. Moreover, it's durable and leak
proof enabling higher voltage transmission over longer
distances. compared to what was possible before its use. Then
there is a semiconductor insulation screen, a metallic
sheath and armouring layer and lastly an outer covering,
typically made of a polymeric material, provides an overall
protection to the cable from the external environment and
prevents corrosion. And in some cases fibre optic cable elements
are included for communication and monitoring. There has been a lot of recent
HVDC action around the world a few of which particularly
interest me. The first is ElecLink, a 51 Kilometer HVDC
interconnector that runs between the UK and France through the
Channel Tunnel built by the owners of the "Chunnel",
ElecLink runs inside the tunnel itself, negating the need for
subsea cabling. Because ElecLink uses existing infrastructure,
technologically speaking, it's not particularly special, but
its financial results have piqued the interest of big
businesses and governments. ElecLink costs around 600
million euros to build and it went into operation in May 2022.
By the end of that year, it had already generated 480 million
euros in revenue, extrapolate that out just a tad and it's
clear that ElecLink probably more than paid for itself within
its first operational year. So how does it make so much money?
Basically, it's down to energy arbitrage. The company buys
electricity when it's cheaper on one end of the cable than the
other and sells it at a profit at the other end. For example,
if it's windy in Scotland, ElecLinkn might buy cheap wind
power from the UK and sell it to France or if it's sunny in Spain
they'll buy cheap solar power from the continent and sell it
to the UK. The next really interesting
project is the North Sea link that runs from Kvilldal in
southwestern Norway to Blyth in the northeast of the UK. It's
also in the energy arbitrage business with the North Sea Link
effectively taking cheap wind energy from the UK and selling
it to Norway and then selling cheap hydro from Norway to the
UK. The 720 Kilometer cable is currently the world's longest
and it's a joint project of Statnett, a Norwegian
state-owned transmission system operator, and National Grid PLC
the British multinational utility company that owns and
operates the electricity and national gas transmission
networks within the UK. Construction originally began in
March 2015. And the project went into operation in June 2021,
having cost an estimated 2 billion euros. Now that might
sound like a lot but it's generated a net income of 2.75
billion euros in 2022 alone, you do the math as they say. So
that's what's going on in Europe where projects seem to be able
to more or less stand on their own economically. But now let's
move on to Australia, the world's smallest continent or
largest island depending on how you want to think about it. In
particular, let's focus on a smaller island, Tasmania, which
I think provides a perfect example of the future of
interconnectors. Tasmania might have a small population of about
545,000 people, but it has a whole heap of hydropower. Now, I
don't feel I can talk about Tassie's hydropower without
mentioning that these are the result of dams that flooded some
very important and beautiful ecosystems. And if we were
talking about building them today, I would for sure oppose
them. But personal thoughts aside, those dams are there now
and they provide the vast majority of Tassie's own power
needs. Some 750 kilometers away on the mainland, sits Melbourne
and the rest of Australia's east coast grid, which is
incorporating more and more variable renewables. Now, if
you've been watching my channel for a while, then you're well
aware that more variable renewables means more storage is
needed, and storage is the expensive part. Tasmania is connected to
Melbourne by the Basslink interconnector So in effect,
Tasmania's hydro can play the role of a battery for mainland
Australia. It helps fill in some of the "dunkelflaute" on the
mainland, that's period with no wind and no sun, and in return,
Tassie gets some of the low costs sometimes even negative
cost electricity during windy sunny periods, which means it
can save its water for times when it can get paid more for
the hydro. Tasmania is currently a bit constrained with the
capacity of the 500 megawatt Basslink interconnector but
there are plans to expand the connection by adding a 1500
megawatt Marinus link, a proposed 250 Kilometer subsea
interconnector plus 90 kilometers of underground land
cables. However, in stark contrast to ElecLink in Europe,
this is not a project that's going to pay for itself within
one year for various reasons, including Victoria's own shift
towards renewables and the cost of Marinus is expected to be
double that of what Basslink cost. Because of this, there's
currently a bit of a squabble going on about which side should
pay for Marinus. But assuming it does get built, this will enable
Tassie to start developing more of their own wind resources,
which they don't really have domestic demand for nor spare
capacity in the Basslink to export it to the mainland. And
Marinus isn't the only exciting future project. There's another
Australian plan. The Australia Asia Powerlink aka Sun Cable, a
mega project that will build up to 20 gigawatts of solar
generation from what would be the world's largest solar farm
in the Northern Territory desert. The project also
incorporates what would be the world's longest subsea HVDC
cable of 4200 kilometers to transport the electricity to
Singapore via Indonesia. Elsewhere, the proposed 16
billion pound Xlinks Morocco to UK Power Project is also
claiming to be the world's longest with 10 and a half
gigawatts of solar and wind farms and 20 gigawatt hours of
battery storage to transmit via a 3.6 gigawatt interconnector
from Morocco to the UK. Such is the enormity of Xlinks that
according to them, there doesn't exist the manufacturing
capability to Make enough cable for the project in a timely
fashion and nor are there any ships capable of carrying and
laying such a huge amount of cable. Xlinks' solution is to
begin manufacturing HVDC cables themselves and they'll be
designing and building the ships as well. So that's 2 world's
longest, but I suppose that any number of people can claim their
project is the biggest when everything is still only
blueprints. Of course, as with any mega scale project, there
are challenges but as I said, right at the beginning of this
video, we've been laying communications cables across the
Atlantic for over 150 years. So why can't we connect an HVDC
interconnector to connect Liverpool to Montreal? These east to west
interconnectors would effectively create up to 20
hours of daylight per day as far as solar power is concerned, and
the cable could be used to transmit power in both
directions in contrast to the Xlinks or Sun Cable plans, which
are just one way, in fact, I've heard that there are actually
plans to build such a cable, although it's currently in the
very early planning days, but we can get a sense of the issues
they're going to face by looking at what aa smaller cousin Xlinks
is facing such as the necessity to build ships capable of
holding and laying so much cable. There are other technical
issues too as HVDC cables get longer. Although DC is far more
efficient than AC for long distances, there are still
losses. Typically an HVDC cable will encounter around 3%
electrical losses per 1000 kilometers and across extremely
long distances this will add up. To minimize these resistive
losses you have to make cable cores thicker, but of course
thicker cable cores means heavier, less flexible cables
that can't be spooled as tightly so they take up more space on
ships and they have to be installed in shorter lengths.
Another issue is the fact that cable cores are tending to move
from copper to aluminium because it's lighter and therefore
easier to handle in length. However aluminium's fatigue
strength is lower than copper's, so failures are more likely if
there's a lot of bending of the cable during installation and
operation. Much of the costs associated with subsea cables is
in their installation. Operating a cable laying ship can cost up
to $750,000 per day and delays because of weather drive up
those costs even further. So repairing a subsea cable can
cost nearly as much as its installation. Not only is there
the cost of ships, but that of specialists undersea workers and
specialised equipment. Planning exactly where to lay an
HVDC cable so it won't be affected or harmed by shipping
and fishing will be vital in future subsea interconnector
projects. All of these engineering problems can be
solved and no doubt will be within the next few years. But
they might be a different showstopper that no amount of
technical innovation or clever logistics can solve, politics.
There's a big energy security question when one country
supplies a large chunk of another country's electricity
supply, as we've all seen with Russia's supply of natural gas
to Europe. Politics has the potential to ruin the Morocco to
UK or Australia to Singapore interconnector projects. A few
years ago, China announced plans to link up the whole planet with
an HVDC network, but I think political barriers are likely to
stop that one from ever getting past the talking stage. Despite
the immense technical benefits such a system would bring to the
global energy transition, the ramifications of one nation
wielding so much control over a global power supply are probably
insurmountable. I do you think it's inevitable that we'll end
up with HVDC interconnectors, linking out much of the world's
grids but I expect it will be done project by project and
international agreement by agreement and definitely between
politically friendly countries first. Anyway, all that's politics and
I've veered too far away from my actual sphere of expertise,
which is engineering. So I'll stop at that. If you've enjoyed
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