This is a decade old, but I think that the proportions are still about right: https://desline.com/Geneva/Banat.pdf https://desline.com/Geneva/Banat.pdf See the

This is a decade old, but I think that the proportions are still about right: https://desline.com/Geneva/Banat.pdf https://desline.com/Geneva/Banat.pdf See the slide "Cost composition for a typical seawater RO (reverse osmosis) plant" Fixed charges (primarily capital cost): 31% Energy: 26% Maintenance and parts: 14% Membrane replacement: 13% Supervision and labor: 9% Chemicals: 7% Really cheap solar electricity could reduce the second largest expense (energy costs), but right now that's just an improvement for daylight hours. Battery-stored solar electricity is getting cheaper but it's not cheap enough to actually reduce nighttime desalination costs yet. And if you run the plant only during the day, you get less value out of the very largest expense (capital cost).