The US does not really have a 'national' grid. It is a mishmash or local, state, and regional grids that have little overall coordination. The consequence is expensive, slow and inefficient power distribution since much of the grid components are controlled by local utilities, other by regional forces (the TVA for example).
The other extreme is China, which at present has no nationwide grid (until recently even China's banking system had no national clearing so used MasterCard's for national clearing). Now National Grid, perfectly named is building massive UHV lines to distribute electricity from area with solar, hydroelectric and wind power to area that need the electricity. The US has no UHV lines IIRC.
China has the enormous advantage of going from zero to something. The US began electrifying more than 125 years ago, and lives with the ageing infrastructure and nearly incomprehensible regulatory and ownership structures. The trump administration states that it will fix all that. I hope they will. It will be a massive undertaking physically, but the patchwork ownership and regulations make it far more challenging and complex to establish a functioning national grid. Exacerbating the complexity the Northeastern US buys a large among of electricity from HydroQuebec which makes this an international issue.
The best short-term solutions seem to be those that address weaknesses in existing State and regional grids. The enormous success of West-Texas wind power (11% of Texas electricity consumption today) happened in part because Texas is large enough to deal with the issue locally. They still use the lower voltage grid, though.
China’s Electricity Sector « Energy Map
I am not an electrical engineer nor am I claiming technical expertise. I simply have read a bit on the subject. Some people on this thread are likely to be competent to speak to this issue from their own direct knowledge.