I assume these are all communications cables, but I'm curious if anyone knows what the logistical issues would be to laying high-capacity high-voltage DC lines

I assume these are all communications cables, but I'm curious if anyone knows what the logistical issues would be to laying high-capacity high-voltage DC lines across oceans? The idea being that as renewable and specifically solar power becomes a larger percentage of electrical generation, it'd be really nice to be able to buy and sell power between the Americas, Europe, Asia, and Africa. It's either that or use a lot of batteries, and power lines seem like they ought to be the more efficient, effective solution. HVDC losses can be reasonably low even for thousands of miles* [1]. I'm thinking of having undersea links, for instance, between Brazil and Western Africa, or Canada to Greenland to Iceland to mainland Europe, or Alaska to Russia. (Wikipedia shows a number of short-distance undersea HVDC links in Europe [1].) * "Depending on voltage level and construction details, HVDC transmission losses are quoted at 3.5% per 1,000 km, about 50% less than AC (6.5%) lines at the same voltage." [1] https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current