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The US is currently an AC grid. HVDC is not currently in any meaningful use in North America (yet)

That may be true but the number quoted there is 6.7%/1000 km for AC which is very far from 20%/1000km.

And now some people will have read his comment but not yours, and this will be anti-renewable energy propaganda forever.

There is a large HVDC corridor up the west coast, but I dont know of anything else.