It is dramatically more expensive running HVDC under water than above ground, as the cables need to be incredibly tough even compared to buried land cables. I ran across a price quote that seemed like 10x the cost per km installed. If you can do suspended overhead cables, even cheaper. HVDC has pros/cons around the inversion/rectification on either end.
Yet essentially all planned or existing HVDC lines (at least ones notable enough for the map), are undersea cables.
They seem non-notable enough I had a hard time finding a good combined list anywhere.
I ran across plenty of references to HVAC being used for offshore wind turbines and the like too.
And they were the default standard (and still are for shorter runs and where the grid frequency matches). There are AC solutions for lack of grid frequency matching and the like.
I can’t find a list or easy map for major new on land grid connections - if you can find one, that would be great. Might be national security concerns or something?
Maybe because they can be implemented with only one pole/conductor for the underwater part. AFAIUI two poles go to the shore, where one pole ends in a metal-mesh underwater, using the salty sea as conductor until the remaining single cable reaches the other shore, where another underwater metal-mesh exists, and from that emerges the remaining piece of dual pole HVDC overland.
I know of at least one such solution between Germany and Sweden trough the Baltic Sea.
It’s even easier to do that on land by the way. You’d use large Earth grounds, which also don’t corrode as badly as grounds in saltwater. And running it on land (minus permitting, right of way, etc) is dramatically cheaper as the cable itself also doesn’t need to be as sturdy.
AC has a capacitance/inductance issue in any sort of run where it is surrounded by metal or metallic elements. Usually the runs are short enough and inconsistent enough it doesn’t matter. Metal shielding (required for undersea and most underground) and certain types of soils are pretty much terrible. That said, for ‘short’ runs of less than a couple hundred km, the cost of the HVDC inverter/rectifier drowns out the losses most of the time, so AC still wins most of the time. Sometimes there are still niceties around HVDC (like easier load management) that can still tip the scales.
If it’s a 1000km single run, the math is definitely different, but there aren’t a lot of those. If there are transformers, taps, generators, or other live equipment in the middle, those also change the equation, and in a grid environment, there are a ton of those.
Yet essentially all planned or existing HVDC lines (at least ones notable enough for the map), are undersea cables.
Why would that be?
There are definitely undersea HVAC interconnects - https://www.nkt.com/products-solutions/high-voltage-cable-so...
They seem non-notable enough I had a hard time finding a good combined list anywhere.
I ran across plenty of references to HVAC being used for offshore wind turbines and the like too.
And they were the default standard (and still are for shorter runs and where the grid frequency matches). There are AC solutions for lack of grid frequency matching and the like.
I can’t find a list or easy map for major new on land grid connections - if you can find one, that would be great. Might be national security concerns or something?