Running an HVDC grid to grid electricity superhighway is especially interesting when one side has substantial hydropower capacity, since that is a market that has a stockpile of quickly dispatchable power that is able to benefit from the UHVDC transmission capacity in both directions, buying power that is cheaper than the price that effectively ration the available supply of hydropower when available, and in turn being able to sell that hydropower capacity that has been freed up at a higher price.

On the side of that HVDC line where at some times the excess immediately harvested sustainable power is coming from and where at some other times the higher price bid for the hydropower capacity is coming from, there's an incentive to have at some local stored power capacity as well. If some of that local stored power is piles of biocoal by a thermal generating plant, then that seems likely to be complementary with some more quickly dispatched power store such as battery or modular hydro or whatever (eg, compressed air or compressed hydraulic power store), for the time period required between cold start and generating power, with similar production capacity but substantially less total power storage.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.