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You are assuming that electricity is the only cost involved.

Based on the numbers in the article, the plant runs at 38-megawatts, consumes 100,000,000 gallons of sea-water a day, and produces 1 gallon of drinkable water per 2 gallons of sea-water.

Assuming a cost of 15.2 cents/kwh [0] (california seems to be one of the most expensive states), this comes out to an electricity bill of $451.70/acre-foot. A non-trivial portion of the total cost, but there is plenty of room for cost savings without reducing electricity usage.

Its also worth keeping in mind that Isreal exists, relies heavily on desalination plants, and is an agricultural exporter so we know the situation is solvable [1]

[0] https://www.npr.org/sections/money/2011/10/27/141766341/the-...

[1] Although will likely involve less wasteful agricutlure.

> Isreal exists, relies heavily on desalination plants, and is an agricultural exporter so we know the situation is solvable

Israel also has a lot of reclamation systems. Most of their sewage gets filtered and the fresh water reused. In most of North America, we give minimal safe treatment to sewage and then dump it back into our water sources.

That is a very expensive process, but cheaper than desalination usually. We just need to get over the ick factor.

"Gray water" use for irrigation is pretty common in dry areas. I don't know if it used for farms producing food for humans, though.

That is interesting to hear, I grew up in the alps, where water plays an important role in my province (90% of the enery comes from water). You can drink the water from the lakes etc.

The idea not to perfectly clean the sewage water you created, would sound irresponsible to anybody living here, as the water cycle becomes very apparent even to the craziest right wing nut when you live in the mountains.

Political slam unnecessary.

Would it be feasible for a desalination plant to also process and sell sea salt as a byproduct? Alternatively, could the salt be used for molten salt energy storage?

Humans have come up with tons of interesting ways to generate and store energy. I think we'll see some truly innovation solutions combining these methods to solve our biggest problems.

The brine waste from desal is full of nasty stuff you don't want concentrated even further and sold as food. Removing the long list of chemicals and heavy metals is not going to be viable costwise and even the most foolhardy consumer would think twice over regular salt.

A responsible desal plant does studies on how to pump and disperse it in the ocean as best possible. Sadly in the gulf the Saudis aren't doing this and have completely ruined the local ecosystem.

https://www.bloomberg.com/news/articles/2019-01-08/saudi-thi...

Desalination typically only raises the concentration by 2 in the non fresh water output. So it would be another process on top of the desalination.

Doesn't mean it doesn't make economic sense. Just that it's not an easy win.

Your comment sorted below one saying the KSA has ruined the gulf because of intensive hypersaline solutions in the water.

So.. can you help reconcile your optimistic and their pessimistic assumptions? Whats the difference? Gulf doesn't wash out well. Maybe the dumped water doesn't disperse?

There was an article on this not too long ago on HN with a good comments section, you should be able to find it by searching. From what I recall the situation is basically

- Locally it doesn't disperse fast enough, 2x is a lot when talking about sealife.

- They add copper (and maybe some other stuff) to prevent fouling of the pipes, which is bad for you.

If the primary cost is electricity and not equipment this can double as a "battery" by only running when electricity is cheap, lowering the price further.

> Its also worth keeping in mind that Isreal exists, relies heavily on desalination plants, and is an agricultural exporter so we know the situation is solvable

https://www.aljazeera.com/news/2016/06/israel-water-tool-dom...

Fair enough! I didn't know some of those numbers, maybe there's more hope :)

It's worth keeping in mind that residential water use is a tiny number when expressed in acre-foots. The vast majority of drinking water is used by farming.

Desalination, even at today's costs, is not ruinously expensive for drinking water; but it might make farming inefficient crops (i.e., almonds) nonviable in the desert.

Farming might just move geographically, or use water more efficiently. Neither of these are necessarily bad outcomes.

Israel is a leading desalinator and major almond exporter, using less water per bushel than California by a factor of 30.

Their secret? Each tree has a pipe about one meter deep. Water goes into the pipe instead of being sprayed on the ground.

There are huge amounts of low-hanging fruit in California agriculture. Water is priced too low to make it worth taking advantage of.

You’ve touched on another problem:

New/increased usage gets charged the average price.

Meanwhile, new capacity is the most expensive.

So you get subsidized if you switch to a more water-intensive crop.

I think the calculus should get a bit better with cheap renewables - desalinating only when more energy is produced than can be reasonably used.

I think if we can find a bunch of things that can effectively use excess power but aren't time sensitive, it'll also make renewables much more attractive.

The lower the capacity factor of the plant the longer it will take to recover the capital cost of building it. Whether this is economic depends on the ratio of energy cost to capital cost. Do you know what that ratio is?

> only when more energy is produced than can be reasonably used

But when would that ever happen. They'd just get used up in e.g. mining $coins.

Clean energy cost is still going down rapidly and is already cheaper than coal and other fossil fuels. Existing desalination approaches will get progressively cheaper as well simply because of energy price reductions. IMHO, solving cheap, plentiful, clean energy solves a lot of problems as most other problems boil down to being energy problems as well. E.g. food production is bottlenecked on water. Solve cheap energy, you get clean water as well. Solve that, and food production becomes cheaper as well. The water crisis is an energy crisis.

I do agree we need to be smarter how we use the land and water. E.g. California draining its natural resources to provide cheap water in LA is not sustainable. There's no excuse for that city to not have extensive desalination as its primary means of supplying water; other places in the world are managing just fine. That 25$ cost is basically about not factoring in the true cost of destroying natural resources. Also, farming practices in California are kind of wasteful and result in lots of water being wasted.

Great point. Especially given how wasteful we are with drinking water there is far more room for efficiency on the demand side than the supply side.

This source says we use 80-100 gallons (304-380L) per day (in the US) https://water.usgs.gov/edu/qa-home-percapita.html

At $2000 per acre-foot, 100 gallons costs 61 cents.

That's right, $2000 per acre-foot is $0.0061 per gallon.

So even at that cost all you have to worry about is the consequences of using the energy, the cost is no problem.

Wonder if we'll ever run dual source systems...like salt water is just fine for pooing in.

It’s a thing for Hong Kong. Something like 80% of toilets are flushed with sea water.

Chlorination is easy: just electrolyse the water on its way in.

Not sure what impact this has on sewage treatment.

Very interesting concept that I never considered. Shower with salt water and then rinse with regular water. Pay one price for salt, one price for regular water.

The salt water would probably be too corrosive to pipe significant distances, which would make that difficult to get enough scale to make it feasible.

Most of the dual-use water systems I’ve read about were fresh water vs gray water.

Much piping these days (>75% for major distribution pipes, and increasingly common in residential use) is PVC, which doesn't corrode.

Salt and minerals get into fittings, destroy valves, and coat everything when the water evaporates. Probably not a great solution.

You would have to purge your system and shower head with vinegar every day just to keep things clean.

You are assuming that only metal pipes exist. Nowadays most pipes are made by either concrete for the big ones (canal like) or plastic connected with glue that is rated for hot or cold water.

This is assuming the current energy costs though, right? If we can get cheaper energy, say via fusion, it could go down.

For sure! But cheap energy is hard :( I'm cheering for Solar, renewables and Nuclear Fission to become cheaper and more widespread. Fusion... well it would be nice, but given that it's never been demonstrated in a form suitable for commercialization, it's hard to hold out for that.

Anyone know why we don't just use nuclear fission as the heat source in desalination?

I mean, other than the implications of your nuclear purified drinking water.

For the same reason we don’t utilize fission in other areas, people are ignorant and terrified of it, politicians are trying to be re-elected, and as a result real problems such as distributed rather than centralized storage of waste emerge. There are also real issues with processing vast quantities of seawater in a way that doesn’t destroy littoral ecosystems. Then there’s disposal whatever heavy metals and pollutants are concentrated as a byproduct of the process, regardless of your power source.

Still, it’s feasible to overcome the last two issues, but I’m pretty sure that ignorance is going to kill us.

I used to work in the nuclear power industry. When I came on board out of college in my first month or so I was given a bunch of books to read and free time to read the history of the company and industry in the company library. I came across a 1980's feasibility study to use nuclear power for desalinization in a boiling water reactor. The tldr of the report was "not economic" so the project died.

I asked my boss about it since he was around at the time and he hadn't work on the project but did hear about it. He said the study was paid for by Saudi Arabia and that the deal killer wasn't the cost of nuclear heat but fouling of the pipes from mineral deposits in the heat ex-changer and desalination chamber. The coatings killed the thermodynamic efficiencies of the system so there would be really high maintenance costs for continually cleaning and/or replacing the pipes. Like a lot of engineering projects it was a material science problem but nobody wanted to pay for the research to solve.

With renewables due to changing weather and demand, prices for electricity at international markets are falling regularly, sometimes even becoming negative (keeping the frequency is must), only to rise again when there is more demand than supply.

Desalination plants have the advantage that, as long as you have overcapacities compared to the average needs around, they can be turned on when energy is cheap and off when it's expensive. While they are operating, they would fill reservoirs that would provide a continuous supply of water.

There might be a thermodynamic limit onto how much energy you need to desalinate water, but the limits of harvesting renewable energy are far from being reached. We might make the sahara green, in this very century.