New Zealand has had a 600V HVDC link from the South Island to the North Island for quite some years - most of the power is generated by the hydro lakes in the south, then delivered via a 610km link to a substation in the north, where it is fed into the normal high-voltage transmission grid.

http://en.wikipedia.org/wiki/HVDC_Inter-Island

So it is a proven technology to have this as a long distance link (been in operation since 1965) and it is capable of bi-directional power transfer as well.