A little background: Thomas Edison's first commercial power distribution was DC; it was Westinghouse who adopted alternating current, and he pounded Edison into the ground because AC can easily be stepped up to huge voltages, lowering resistive losses over long-distance transmission lines, and then back down to less-dangerous voltages for consumption. Long-distance transmission at dozens or hundreds of kilovolts is still somewhat lossy, but much much better than if we transmitted power at voltages that were safe in your house.
The solution to this coordination problem is to segment the grid and use DC interconnects, so that a 70-year-old hydro plant whose turbines spin down a bit under high load doesn't take the entire grid down every August. But how to transmit it? Even from one side of a substation to the other, direct current is just not the right tool for transmitting lots of power.
Enter superconductive transmission lines. Superconductors are DC-only affairs (the magnetic flux of an AC line destroys the superconducting effect), so they're a good match for this problem. They still need liquid nitrogen temperatures to work, but liquid nitrogen is cheap. And so serious work is being done to bring superconducting DC interconnects on line in the near term.
It's the stuff of science fiction, brought to reality.