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Comment by AngryData | Hacker News Reader

It isn't technology that holds back water desalination, it is energy availability/cost. Even the most promising desalination tech is only a small efficiency boost over simpler established methods. Yeah efficiency gains certain help over the long term, but the overall energy costs are still enormous and nearly require dedicated power plant for any significant amount of clean water.

The best bet in actually desalinating population scale levels of water would be investment into nuclear power. And the desalination could double as a buffer for the nuclear plant so that it could be run at peak power and efficiency nearly full time.

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Wouldn't solar be much better for powering desalination than nuclear power? It is way cheaper per energy produced than nuclear, especially in those countries, which need desalination most. Also, it doesn't take a decade to set up. Not even mentioning proliferation issues.

Solar doesn’t provide nearly as much energy and for desalination you need a surprising amount.

Nuclear is a great use-case since the problem with nuclear is it needs a constant water source. If you’re desalinating you’ve got that problem covered.

Does nuclear need fresh water? I'd imagine salt water would wreck all the equipment, and you probably don't want to use up all the fresh water you generate...

You need very pure water for most portions of a nuclear power plan.

that'd depend on the reactor type, no?

Not really. Pure heavy water along with pure uranium and pure CANDU reactors are imported components. The quality of cooling water and feed water doesn't matter much.

Remember, nuclear power plant is merely a very large heat engine. The main problem is terrorism there.

The turbines do but you can recycle much if not nearly all of that water by cooling the steam and condensing it, which you could use sea water to heat exchange to for it.

The water is just there for thermal mass to conduct waste heat away from the condenser. The water that gets heated by the reactor core and turns the turbines is isolated and highly purified, since many of the internals can only be accessed during refuels. Some designs go further and separate the reactor coolant system from the steam generator to prevent contamination, but AFAIK there isn't a single commercial design that allows outside water to feed into the reactor cooling or power generation systems. The parts of the condenser that touch the external body of water are basically just blocks of metal that have to be scrubbed on the outside from time to time.

You have heat exchangers between saltwater and clean freshwater that circulates through the sensitive parts of the plant.

> Solar doesn’t provide nearly as much energy and for desalination you need a surprising amount.

Are there numbers for this? One one hand solar might provide more energy than nuclear if you're only interested in heat generation, but on the other hand using heat to desalinate (ie. boiling water) is also less efficient than using reverse osmosis.

Solar doesn’t provide nearly as much energy and for desalination you need a surprising amount.

That statement doesn't make any sense to me. If you need more power, install more panels. Space certainly isn't an issue in like northern Africa. It is cheaper to order a gigawatt or more of solar panels than building a new nuclear reactor, and faster to set up too. Even Germany today has way more solar capacity than it ever had in nuclear, and it is less a great place for solar than Africa.

> Even Germany today has way more solar capacity than it ever had in nuclear

That's because it never had much nuclear capacity, not because it now has a lot of solar

I don't know what you mean by "much", but Germany has a peak power capacity of 56 GW of Solar. On good days the output comes close to the nuclear output of France, which is mostly nuclear in power production. German wind power occasionally eclipses French nuclear power production.

The vast majority of our freshwater comes from sources that cost us effectively zero in energy: the water cycle moves water towards higher elevations and it flows down towards our populations. Worst case scenario, water in ancient underground reservoirs is pumped to the surface.

If we had to desalinate all that water and actively distribute it instead, it'd be a significant fraction of our current global power consumption. The power sources need to be concentrated near the desalination plants and at least half the world lives 100km+ away from a coastline. At 3 kWh per m^3 of water[1] and ~3.5 m^3 per person per day [2], that's an extra ~3800 kWh per year, which would increase per capita energy consumption by 25-30% [3] in the United States just for desalination.

We have enough challenges replacing existing power infrastructure with solar and wind. Placing the burden of desalination on top of that is unrealistic, especially since the NIMBY fight over solar installations of that size would probably be just as fierce as for a nuclear reactor.

[1] https://res.mdpi.com/d_attachment/energies/energies-12-00463...

[2] https://www.usgs.gov/special-topic/water-science-school/scie...

[3] https://data.worldbank.org/indicator/EG.USE.ELEC.KH.PC?locat...

I have never claimed, that we would replace all fresh water used on this planed by desalinated water. This certainly is neither feasably nor necessary. At best, it can be an important contribution to water supply in many regions.

I was only answering to the original post which suggested we would build nuclear power plants to desalinate water. There I commented that solar would be cheaper (and more environment friendly) for the same task.

Last I checked Algeria has a bit of solar energy hitting it. :)

Nuclear power is severely restricted and building a nuclear power plant in a country dealing with active terrorist movements is probably something to be avoided.

Solar is relatively inefficient, but it can't be used to build a dirty bomb or worse. With large patches of uninhabit{ed,able} desert, many African countries have more than enough space to build large solar farms if they can find a solution to the sand blowing onto the panels.

The Sydney desalination plant is entirely powered by Wind:

https://www.sydneydesal.com.au/caring-for-the-environment/10...

Yes, solar is dirt cheap energy and you wouldn’t need much of a battery (or any?) in this case, since you can store the excess product water in a tank.

I power my water maker with about 1400 watts and can make 35 gallons an hour. The panels, electronics and water maker were ~ $5000. I did the work myself at a slow pace, so not sure what the labor costs would be.

I set my system up in about 2 weeks. The requirements are a bit of time, seawater access and some capital.

https://seawaterpro.com/

$5000 in a third world country is quite a lot.

For context, according to CEIC data [1], the average salary in Algeria is about $300 per month. That "dirt cheap" project of yours is more than a year's worth of labor.

Locally priced goods may be cheaper, but the US does benefit from a more direct shipping line with China (where most of these products come from, especially cheap solar panels). There's repair costs to be taken into account and if these become a necessity, you'll also have to take into account some kind of protection for when those without the means to buy one of these setups become desperate.

It's true that solar is relatively safe and cheap compared to other power sources, but projects like these are difficult to map to places where they can make a life-or-death difference. If things were that easy, we'd probably cover a patch of Sahara desert with solar panels and power the entire African continent for decades, with power to spare to export to other continents.

[1]: https://www.ceicdata.com/en/algeria/average-monthly-wages

Yeah, it’s tough out there. I think the capital cost might be around $15 to $40 a month depending on how generous the lender is.

Evaporative is interesting too, but solar isn’t too bad to maintain. Most of the maintenance would probably be keeping the filters, pumps and membranes in working order.

That seems like a lot of cost and complexity for a rural installation in a 3rd world country. How does the water output compare with, say, spending $1000 a simple evaporation design? The size of the evaporation pool would be larger than 1400W worth of solar, but it's much simpler and easy to repair.

I agree there is more complexity, but it may be worth it. Making electricity buys a good deal of versatility. If you have a bit extra, you can run an inductive burner, charge your phone/laptop or charge a house battery (if/when you can afford one).

I think in either system, teaching the locals to setup the system and maintain it themselves is important for keeping the costs down.

But my question is, what's the cost benefit?

$1000 would buy a pretty large solar still and you can spend the extra $4000 on a solar phone charger if that's something the locals need. Meanwhile there's little that can go wrong with a solar still and if something does go wrong, they can likely fix it (even if temporarily) with duct tape. Losing their cell phone charger and cooktop to electrical failure sounds like less of a problem than losing their water source.

An inductive burner, cell phone charger, desalinator, etc all sound great on a $200,000 boat where the owner is wealthy enough to keep it maintained and probably keep spares. But putting expensive and complicated electronics in a village so remote that they don't even have reliable water seems like a mistake.

I wouldn’t discount people’s ability to do some basic electrical repair. And maybe the neighbors can lend you some water till you get back up and running.

You might be right though, if it’s remote enough and you have room, perhaps a solar still is the cheapest and simplest option. It seems like it would have to be very large to give comparable amounts of water. Do you know someone selling such kits?

In any event, maybe this gives folks some ideas for lowish cost options.

Yep, evaporator + condenser works very well in nature for billions of years.

For example: https://news.mit.edu/2020/passive-solar-powered-water-desali...

That's true from an engineering standpoint, but many of the places which are short of fresh water also lack the capital and industrial infrastructure to support large nuclear plants. Solar power seems more realistic from an economic and political standpoint, even if less efficient.

If it’s extremely hot, using solar energy should IMO be the first choice.

I don’t find https://en.wikipedia.org/wiki/Solar_desalination an easy read, but I think it says using PV to get electricity and that electricity to drive reverse osmosis is one of the best solutions.

Certainly, given that solar power is cheaper than nuclear (in the current political climate), nuclear can’t be the better choice for peak loads, which happen when there’s a lot of sunlight.

There's also a capital investment problem - good equipment is expensive to set up, even leaving aside the operating costs problem.

Achievable, yes, but only for the rich for now. eg Gulf Arab states and Israel are early adopters, the latter with some EU subsidies to defuse water rights as an point of conflict in the Jordan watershed.

I have never believed this. The energy cost of operating a modern (or even moderately old) desalination plant is far, far lower than the cost of water in the Bay Area. It’s not even close.

Capital and permitting costs presumably dominate.

> The best bet in actually desalinating population scale levels of water would be investment into nuclear power.

FWIW on several occasions we came lose to losing the North American Great Lakes to nuclear accidents, the second largest freshwater stores in the world.

What about osmotic pumps? https://science.sciencemag.org/content/183/4121/157

This isn't technically accurate, we have access to abundant long term (multi-century) reserves of natural gas which can be used to provide power needed for desalinization. Nuclear is in no way a "blocker". Certainly, cost is a substantial barrier especially in less wealthy nations.

Carbon emissions

If the choice is reducing emissions or saving lives from dehydration, I wonder which is the appropriate course of action.

Which could completely destroy modern civilization over time. Once certain tipping points are crossed most of the earth could become uninhabitable for large parts of the year.

Problem is, carbon emissions make the dehydration worse by heating up the planet. It's counterproductive.

Probably something else.

Gas burns and makes CO2 which increases temperature which increases the likelihood of more dehydration events in future. This is the wrong choice. Actually the long term right choice is not to burn gas anymore.

Letting people die is obviously the wrong choice too.

When all choices are wrong we must find another choice that can be right. Somebody wrote solar energy, somebody wrote nuclear energy, somebody argued that both are wrong. I don't suggest a solution but I point out that limiting ourselves to binary choices is the wrong way to think.

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