USA: A study by the National Renewable Energy Laboratory suggests that the percentage of energy from renewable sources could be increased up to 90 percent with a national grid consisting of high voltage DC (HVDC).
Currently the American grid is getting only 30 percent of its energy from renewable sources. The hindrances against implementing HVDC are rather of political nature than financial. HVDC lines need the permit to cross state borders, after that they can be built without increasing the utility costs.
Wyoming and Kansas are states rich in renewable energy, and North Dakota could switch from carbon capture to wind energy. Thus, revamping the national grid would bring many economic and logistic benefits.