It doesn't need to be done as a single super-project. Each step along the way could be a sensible, contained, and iteratively beneficial project. Lots of countries are already building up solar; as that progresses they could construct cross-border grid connections to balance out the load, then further build up solar capacity to be able to transmit your daytime excess to countries further from your solar peak. At that point it would only take a couple cross-ocean power lines to go from multiple continent-wide power grids to a single global one, and then everyone involved is even more incentivized to build excess solar capacity.

It's not a piece of cake, but it's not a wild idea either. Adding a pair of LK-99 lines alongside each existing undersea optical line potentially gets you there by just increasing the maintenance budget. Lossless power transmission could change a lot of previously fundamental assumptions.

Many grids are interconnected already and the electricity distribution is already an international business, if the lk-99 becomes available as a final product I don't see why would be hard to built a SC backbone. Not only electricity but international pipelines that move fossil fuels to thousand of kilometres away are already a common thing.