Using an HVDC overlay to move the US to national 48-state electric system, rather than the current regional one, a new study shows 78% CO2 reductions with electricity cost of 8.5 to 10.2cents/kWh, compared to the current national average of 12.7cents
The Cheapest Way to Scale Up Wind and Solar Energy? HVDC Power lines
https://www.renewableenergyworld.com/2016/01/28/the-cheapest-way-to-scale-up-wind-and-solar-energy-high-tech-power-lines/