HVDC is not a silver bullet. Converter stations are very expensive and also take more space. You need one every time you tap in/out of the transmission line, g

HVDC is not a silver bullet. Converter stations are very expensive and also take more space. You need one every time you tap in/out of the transmission line, great for point to point links say Offshore windfarm to major IC, but general transmission gets tapped into and out of much more frequently. Even if today you plan for this link to be P2P from city A > city B today what happens tomorrow when someone builds a generation plant, or a new town, datacentre campus on that route? The "efficiency" gain is debatable, you do lose less on transmission but you now have this cost of getting from DC>AC AC>DC which costs roughly 1.1-1.6% - in the grand scheme of things for most schemes any overall efficiency gain is marginal to nil. Overall the most flexible thing to do is build AC at the highest voltage your towers/interconnect points support (and consider increasing that). In the UK we are building more lines and converting more substations from 275KV to 400KV.