I'd also think another challenge is the issue of timescales. "Green" energy sources like wind and solar can have large fluctuations, on the timescale of minute

I'd also think another challenge is the issue of timescales. "Green" energy sources like wind and solar can have large fluctuations, on the timescale of minutes. I don't know much about desalination plants, but I'd imagine they cannot be started and stopped just like that. (This, incidentally, is a reason I've heard power engineers give for preferring natural gas to e.g. coal, aside from cost considerations: generators are faster to start and stop.)