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Comment by BurningFrog | Hacker News Reader

Desalination seems ideal for cheap but unreliable energy like solar or wind. You just need a water reservoir to act as "battery".

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https://www.moderndescartes.com/essays/factobattery/

Using the above methodology, I ran numbers for a desalination factobattery and it's really bad, like two orders of magnitude more expensive than just buying a Li battery to buffer the unreliable energy and running desal 24/7.

This right here. Even low grade continual energy supply is better for desal.

By "battery" here, I just mean a dam that holds a few days worth of fresh water.

I think you misunderstood the comment. I agree there has to be a buffer somewhere. You're arguing that we can get a free buffer by piping the water behind a reservoir, but the cost is that the very capital-expensive desalination plant will be idle half of the time. I'm proposing that the more economical option is to buy a lithium ion battery to buffer the renewables and run the desal plant 24/7. (You can still pipe the water behind a reservoir if you want)

I see. It's better to have a half as big plant running 24/7 with a battery.

Thanks for educating me!

Even with battery degradation?

See: collapsing European industry, finally now even in Germany, due to thinking "demand-side response" was a good solution.

Desalination plants do REALLY badly when run infrequently. All the salt water, brine, etc. creates absolute havoc when it sits for random period of time, and maintenance costs are already a huge part of opex for desal plants.

Also, the concentrated brine is a real problem in any area that has regular sealife. Maybe not a big problem in the salt ponds already, but it will kill off anything normal.

Yeah, it isn't going to hurt the salt ponds. What is more, we did the math and found you could harvest more salt faster for less money when starting with a higher salinity brine which would be a win for Morton.

The problem, of course, is utilization.

Amortized capital costs for desalination runs about 40%,[0] so if you "charge" for 12 hours and "discharge" for 12 hours then your facility doubles in size, so your desalination cost increase by (at least) 40%. This doesn't even account for added maintenance btw.

If you charge for 6 hours (ie the solar peak) and discharge for 18 hours, you need a facility 4x as large, and your desalination costs increase by at least 160%.

Desalination isn't 'free' energy storage.

[0] https://www.advisian.com/en/global-perspectives/the-cost-of-...

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