Further looking into HVDC, it seems to be about $500k/km. Over distances of 4000km, that's $2/Watt ($2.20 with losses) or about the cost of producing the electricity in the first place.
Better than fuels at present, but inherently fragile so not a complete solution. Also those are just claimed building costs not including operation (and assuming it lasts about as long as the pv), and the natural monopoly spawned always winds up being a massive tax money sink, so it's not clear that building thousands of hvdc lines is going to work out.
What is inherently fragile in HVDC compared to conventional transmission?
AFAIU it is even less fragile because it's usually 'point-to-point', which means to integrate it into the grid you need very modern substations with the ability to 'transform' the DC into the AC of whichever pre-existing grid by means of mass cascaded https://en.wikipedia.org/wiki/Insulated-gate_bipolar_transis...
Which in turn makes the grid around these substations smart, the more, the smarter. Because you have much better ability to switch and regulate(diversion from same frequency in AC-grid due to dynamic load or failure) much faster.
Think of the difference between the large external 'power-brick' for older laptops vs. the small switching power-supplies for contemporary notebooks. Just in reverse.
> What is inherently fragile in HVDC compared to conventional transmission?
Nothing? The point is transmission is extremely fragile. To physical conditions (weather, accidents, faults). To market effects (massive price gouging during those failures due to lack of buffer). And to market failures (harmful monopolies always form around private utilities and neoliberals always privatize utilities).
Then if the oceans are involved, cost becomes a non-starter.
Better than fuels at present, but inherently fragile so not a complete solution. Also those are just claimed building costs not including operation (and assuming it lasts about as long as the pv), and the natural monopoly spawned always winds up being a massive tax money sink, so it's not clear that building thousands of hvdc lines is going to work out.