[davedx]

If the world could run power along all these submarine telecoms cables then we'd be a lot further towards solving the problem of renewable power generation. I wonder how these kinds of cables compare to HVDC cables in terms of size and cost.

[ccakes]

They do, any cable over about 1000km has active repeaters on the seabed which need to be powered.

There is HVDC equipment on both ends and typically each end is sufficient to power the entire cable independently to allow for the cable to continue running through maintenance, shunt faults (basically something earthing out on sea water) or a single failed repeater.