The United States has multiple regional grids, operated by organizations called RTOs or ISOs (Regional Transmission Operators, Independent System Operators). Co

The United States has multiple regional grids, operated by organizations called RTOs or ISOs (Regional Transmission Operators, Independent System Operators). Components of the grid, including transmission lines, may be owned by government agencies or by private companies, though private companies are more common. As I mentioned in another comment, the hardest part of building big interstate transmission projects in the US is getting approval from every state and land owner between two distant points. 4 out of 5 involved states can approve a plan quickly but then the plan can languish for years trying to get approval from the 5th state involved. Long distance transmission projects do get built, but they generally take a long and uncertain time to reach approval. That's one of the factors that prevents sunny states from just exporting solar power to less sunny, more densely populated states. The other big factor is that these big infrastructure projects are also expensive to construct, but in my opinion it's the delays and uncertainties that are the bigger obstacle.