It has been calculated that a supergrid alone without special off-the-grid energy storage could potentially eliminate any need for fossil fuels for electric production.
However, my best guess is the best strategy would be to combine supergrid with off-the-grid energy storage and that off-the-grid energy storage should use either flow batteries or magnesium-sulfur batteries (which have yet to be properly developed).
There is also the currently massively under exploited marine current power;
antialias_physorg
Apr 16, 2018