you'll probably be interested in reading https://en.wikipedia.org/wiki/High-voltage_direct_current. it says typical losses are 3.5% per 1000km, and typical voltages are 100–800 kilovolts, but china built a 12-gigawatt 1100-kilovolt link over 3300km in 02019

unfortunately i don't have a good handle on how efficient that link is. the numbers above suggest it would be about 89% efficient, but those are for lower-voltage systems

in general you expect the resistive losses in the cables, at a given diameter and power, to scale with the inverse square of the voltage, so an 1100-kilovolt link should have 47% less resistive losses than an 800-kilovolt link at the same power level running over the same cables. however, corona-discharge losses increase at higher voltages rather than decreasing, and i don't know which one is dominant. so i don't know if that link is closer to 89% efficient or closer to 95% efficient

the distance from the north or south pole to the equator is of course 10000 km, but people don't build very near the poles. for example, from svalbard to algiers is 4700 km. so, yeah, there are hvdc transmission lines already spanning those kinds of distances, but not quite that far yet

transmission lines require utterly insignificant quantities of raw material, but where they cut through forested terrain, they do require upkeep. in the meeting of a tree and a megavolt, neither one comes out unscathed

for some calculations on how much you need to over-provision solar, see my earlier comment at https://news.ycombinator.com/item?id=40724349 considering a counterfactual where somehow norway had to use solar. 6.1 average kilowatts per norwegian at a capacity factor of 6% works out to 102 kilowatts peak per norwegian. if you're using low-cost 16%-efficient solar panels (as i assumed you would in my cost estimate, even though mostly people spring for the more efficient 'mainstream' ones) that would require 635 kilowatts of sunlight per norwegian, which is 635 square meters per norwegian (we rate solar panels on the assumption that sunlight is 1000 watts per square meter). 635 square meters is 25 meters square, .000635 square kilometers per norwegian. multiplying that by 5.5 million norwegians gives you the truly immense area of 3500 square kilometers of solar panels

but wait! that's not all! you can't just lay the panels out flat on the ground and expect them to get a 6% capacity factor. you have to angle them toward the equator and spread them out so they don't shade each other. oslo is at 60° north, so your panels need to be angled at 60° from the horizontal, toward the south. maybe a bit more if you want to increase power production in winter, say 69°. so you have to space them out by 1/cos 69° ≈ 2.8. so actually you need 9800 square kilometers for your €340 billion of solar panels. how much space will you have left?

a lot, it turns out. norway is 385000 square kilometers, so this is still just 2.5% of the country

so norway, despite being the #2 highest user of energy per capita in the world after canada, and having cities that are literally inside the arctic circle, could switch to all solar. it's totally feasible. fortunately they have plenty of hydropower and wind so they don't need to