For long distance high power transmission DC over normal conductors is more efficient and ultimately cheaper than AC - despite the horrendous cost of the power converters.
But superconductors won't replace AC for lower power (ie under 100MW) stuff any time soon because transformers are so relatively cheap and reliable and the losses aren't that bad.
And anyway - we don't have useful normal temperature superconductors.
You will always need AC for long distance power transmission.
Now if you connect superconductors with a localized battery powered by wind an solar, you can greatly reduce the long distance power needs and make the overall power grid more robust.
