Power line capacity is designed around the maximum power that must be delivered. Solar power by itself reduces the mean, and possibly the minimum as well, but never the maximum.
In some places the annual peak demand is for summertime cooling, but in others the annual peak demand is for wintertime heating. It's too strong to say "never [reduce] the maximum" as the parent post did, but there are substantial regions where solar power can't reduce the needed power line capacity.