It's not engineering problems. It's assumptions about how humans will behave!
Maybe the region where solar needs can be scaled is not in your country. Maybe you're at war with that country. Or maybe the company producing that power would only sell you the power at some outrageous price that you don't want to pay. Maybe you want to be the one selling not buying that power, you want to be the one making profit. Maybe your neighbor just considers you're an inferior race so he will not even sell you the power for the flood dams or the desalination plant. Or maybe you're the bad guy, but now because people won't sell you what you need at realistic prices you contemplate of... maybe nuking some sense into them, because if 1mil of your people might die of hunger, why not have 2mil of theirs die burned and irradiated?
Any solutions that assumes people working well together in some "perfect world order" are very dangerous. Humanity ain't "a giant organism". We're a bunch of warring tribes with carefully disguised racist, xenophobic and even purely sadistical tendencies just waiting for an excuse to come out!
We need more technologies that just work and can be used SUSTAINABLY in any random place and at any scale regardless of how bad we fucked up or we're planning to fuck up.
Energy diversity and energy security are important.
On the one hand, global trade can strengthen relationships between nations and make war less likely. On the other hand, look at how Russia uses the threat of turning off gas supplies to pressure european countries.
A solar farm has higher energy density than you might think. New York City could get ~100 gigawatts of solar power without importing anything. Further, if anyplace used close to as much energy as provided by sunlight it would get really hot.
Sure there's engineering challenges in that, but no more than some hypothetical case where we need an entire fusion plant in some locality right now.