[londons_explore]

Power cables are getting cheaper and cheaper. The expensive part used to be the voltage conversion stations at the ends, but with mass production of MOSFETs for EV's these have now become far cheaper than the JFET's and other exotic silicon that used to be used.

In turn, that means voltages can be higher, letting one use more of the cheaper PVC or XLPE insulating material and less expensive aluminium for the same amount of energy delivered a large number of kilometers.

To be honest, I don't think we're many decades away from the cable+conversion stations themselves cost being irrelevant, and the administration costs, land purchase costs, etc dominating.

[coryrc]

> The expensive part used to be the voltage conversion stations at the ends, but with mass production of MOSFETs for EV's these have now become far cheaper than the JFET's and other exotic silicon that used to be used.

Why do you believe these things are related?

HVDC lines operate in the hundreds-of-kilovolts range. For example, https://en.wikipedia.org/wiki/Basslink operates at 400kV. There are no MOSFETs or JFETs directly involved in stepping down that power.

[londons_explore]

Semiconductors are stackable to get higher voltage. They're parallelizable for more current. Cost scales linearly with voltage and current, and is therefore constant WRT to system power.

[tim333]

Apparently they use thyristors https://en.wikipedia.org/wiki/Thyristor#HVDC_electricity_tra...

https://en.wikipedia.org/wiki/HVDC_converter#Thyristor_valve...

[londons_explore]

Thyristors require you have at least one transformer operate at AC line frequency (50/60Hz). That costs a lot, since you need enough steel to store 20 milliseconds of your total power as a magnetic field. Thyristors are on-off devices (like most semiconductors when used for power conversion), but cannot turn off without zero current, which precludes a bunch of high frequency designs which are better for harmonics and weight-of-steel.

Overall, they were a popular choice in the 90's and 2010's, but I don't think we'll see any new designs installed with them.

[tim333]

Ah - right you are. Seems IGBTs are the thing now.

[coryrc]

I've never heard of MOSFETs being used in extra-high voltage systems, but I have not been following the industry for a while. Do you have any links? I've only seen IGBTs or older technology used.

[bhy]

Why higher voltages can result in cheaper insulation materials? Wouldn’t it be the opposite?

[londons_explore]

Nah - the insulation material costs ~ $0.80/liter, whereas aluminium conductor costs $6.50/liter.

If you can have the conductor 1mm^2 thinner (capable of carrying less current for the same heat production) and the insulation 1mm^2 thicker (capable of handling a higher voltage) and transfer the same power, then you'd save money.

It only works up to a certain limit obviously - the relationship is non-linear and there is an optimal point.

The actual tradeoff involves a lot more modelling, because you need to consider all kinds of other factors, not just the costs of the conductor and insulator.

[ikekkdcjkfke]

Would they be using AC or DC? I heard that very long cables using AC can be more lossy

[jaidan]

The problem with long distance AC is the reactive power component caused by the capacitance, and the voltage rise caused by the Ferranti effect.

The reactive component has significant impact on the generation equipment and grids. It also causes the Ferranti effect, where the voltage along the cable rises. This can make managing the voltage within the cable difficult because at no load, the load end has a higher voltage than the source, and when loaded, the middle of the cable has a higher voltage than both ends.

During stable operation these effects can be managed with Statcoms, shunt reactors and voltage regulation tap changers. However during transient operation you will be relying upon the static protective devices such as surge arrestors, depending on how large the transient is.

DC transmission does not suffer from the same reactive power component and has less losses, but it does require large convertor stations at both ends.

[goodcanadian]

It doesn't seem like anyone directly answered your question. As far as I am aware, all long distance undersea power cables are high voltage DC. I believe this has to do with the efficiency of power transfer over long distances.

[immibis]

AC loses power by inductively and capacitively coupling to nearby objects. It's manageable at medium distances above ground, cheaper than a pair of converter stations. However, water is much more conductive than air and losses from an underwater AC cable would be much greater.

[londons_explore]

AC is a sine wave, of which the peak is a factor of Sqrt(2) higher than the DC voltage. That means your insulation needs to be sqrt(2) thicker - ie. 41% more insulation material.

On top of that, you also have losses to the cables capacitance with AC.

But DC has the cost of the conversion stations to consider - both capital cost and efficiency causing operational cost.

[tdrz]

> But DC has the cost of the conversion stations to consider - both capital cost and efficiency causing operational cost.

I suppose you mean AC-DC conversion stations. Assuming only solar energy will be "pumped" over the wire, then the "only" conversion stations that are needed are at the consumer, right? I said it before, I don't know much about electricity, so please correct me if I'm wrong.

[lazide]

It’s really difficult to make solid state components that work at million+ volts.

It’s comparatively quite easy to make transformers that work at million+ volts.

So anytime you need to do any sort of voltage boosting, conversion, or the like, DC is going to be expensive and relatively fragile compared to AC.

If it’s just once, that’s not bad. If it’s often, that sucks.

[sangnoir]

> It’s really difficult to make solid state components that work at million+ volts.

You can split (or add up) the million volts as transmitted at either end so the individual components only work across a small fraction of the 1MV potential difference. This is how can get 12V from 1.5V batteries or use 1V LEDs from a 12V line.

[londons_explore]

That principle doesn't work as well at high voltages because generally it's a pain for a rack of equipment (such as solar panels) to have a potential between them and ground of 1 million volts.

[BillSaysThis]

This is Australia, it's AC/DC!

[contingencies]

For the confused that is a reference to https://en.wikipedia.org/wiki/AC/DC

Amusingly (IMHO), The band's line-up remained the same for 20 years until 2014 when Malcolm retired due to early-onset dementia, from which he died three years later; additionally, Rudd was charged with threatening to kill and possession of methamphetamine and cannabis. Stevie, who replaced Malcolm, debuted on the album Rock or Bust (2014). On the accompanying tour, Slade filled in for Rudd. In 2016, Johnson was advised to stop touring due to worsening hearing loss. So a rocker's fate: forgot what planet they were on, went mad on drugs becoming threats to society, lost their hearing, or kept touring indefinitely with a changing lineup cashing in on past glories.

Similar period https://www.youtube.com/watch?v=XfR9iY5y94s https://en.wikipedia.org/wiki/Down_Under_(song)

[nsonha]

is there any thing special about the nature of such project that makes you ask this question? By default, long range transmission is always DC for that exact reason.

[Kuinox]

What material is made the power cable ? I thought copper was getting more and more expensive ?

[londons_explore]

Some use Copper, but usually Aluminium is used.

Aluminium is far less dense, which in turn makes the whole cable bigger, which has other costs (eg. fewer kilometers of cable fit in a boat). Usually it's still the best choice overall though.

[Kuinox]

Thanks for the reply