Wind power is huge here in the UK. It makes up over 1/3rd of our grid. Solar on the other hand is about 1/15th: it's not as viable for much of the country.
The only difficulty we have is getting the power to where we need it. More high-capacity lines are needed.
Sorry, I shouldn't have said only issue. There's also the issue of intermittency and load-shifting. More capacity is needed, more work to do to keep the grid frequency stable.