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Comment by thelastgallon | Hacker News Reader

Water probably isn't grid connected like electricity. Nor does the supply need to perfectly match the demand every second. There is quite a bit of water storage in the system.

There might be pumps, in addition to just gravity assisted transportation of water. When energy is cheap, we can do both desalinate + transport.

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But mainland desalination plants are connected to the electricity grid.

The problem with only running them part of the time is that the fixed capital and other operational costs of the plant are now split over a smaller amount of water produced so that water is more expensive than if you ran the plant all the time paying more for electricity at other times of the day.

There is certainly a trade off there, does the cheaper electricity compensate for the fact that you need to add say 20% extra capacity and the accompanying costs to your desalination plants as they will now be idle during low renewable production/times of high electricity costs.

If it's solar powered, more like 60% extra capacity to compensate for that annoying daily power down.

You're missing the point. If you need 24 m^3/day of fresh water, you can have a desalination plant producing 1 m^3/hour and a water tank to match supply to demand. But if you only want to run the plant for 3 hours/day when electricity is cheap, you now need a plant which can produce 8 m^3/hour.

There's a tradeoff -- spending more building the desalination plant makes it possible to run at a lower duty cycle so you can spend less on the electricity.

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