Yeah, like @jennswall said mostly the extreme shifts in day lengths and the long periods without light. In order to be effective you would either need huge battery capacity to store the energy for the months that pass without sunlight or you would need huge infrastructure overhauls to bring solar power in from closer to the equator. I don't know very much about batteries or power lines, but I do know that in general the more you use of each, the lower your energy yields are as you lose a good amount to heat. Also, I believe batteries still require the use of a lot of precious metals that we get through pretty exploitative methods in poorer countries. So imo why not just throw up a bunch of windmills in the arctic circles and save the headache?

Like in pretty much everything else, diversification is our best bet.