> question is whether it uses less electricity to desalinate and flood irrigate, or pay for the electricity to allow ultra high density, water efficient farms

Nobody desalinates & floods fields, surely. (That's what you do if you live before the invention of water-pipe, or have a use-it-or-lose-it quota.) The Israelis are I think world leaders in growing stuff outdoors with minimal water, delivered directly to the roots. And indoors, they have greenhouses, just not the same design as in cold climates obviously.