Desalination system could produce fresh water that is cheaper than tap water(eurekalert.org)
eurekalert.org
Desalination system could produce fresh water that is cheaper than tap water
https://www.eurekalert.org/news-releases/1002811
142 comments
Solar heaters are remarkably efficient, well above 95%. Solar water heaters are really quite efficient so there is no particular reason why with the right coatings such a device wont get quite close. Its actually surprisingly easy to make a solar water boiler and they aren't expensive. People heat pools with DIY water heaters.
If heating water is the goal then going directly to heating the water is more than 4x the power capture of a solar panel. Dropping one solar panel on your roof for a water heater pays off its just that the solar heaters are kind of expensive dealing with all the other aspects, like if the pump fails or its too cold and the water would freeze etc etc. Those other aspects are probably going to dominate the complexity and cost of the devices.
If heating water is the goal then going directly to heating the water is more than 4x the power capture of a solar panel. Dropping one solar panel on your roof for a water heater pays off its just that the solar heaters are kind of expensive dealing with all the other aspects, like if the pump fails or its too cold and the water would freeze etc etc. Those other aspects are probably going to dominate the complexity and cost of the devices.
I’ve always wondered how hard it would be to have standard solar panels water-cooled and use that heat for hot water storage.
The main problem is the expected lifetime (and payout periods) of the two parts. Cooling solar panels brings more efficiency so it feels like a reasonable fit, cool the panels and get hot water. Its less efficient water heating because the panels aren't the ideal coating but they do still get quite hot and a few of them can definitely do the job. The big mismatch is in life.
A solar thermal heater typically lasts 10 years, its a pretty harsh environment and they have pumps and expansion vessels and water in the heat range of -25 through +80 C is just damaging over time. Where as a solar panel has a rated 80% output at 25 years. That mismatch is problematic for Solar panel payoff, 10 years is only just past break even point. Whereas the solar thermal heaters typically pay off within a few years so the reduced lifetime isn't such a big problem (but both are driven by local gas and electrical prices).
Companies are trying to do this better and products exist to do it. The added installation complexity and reduced expected lifetime are all a bit of an issue. Currently I suspect most people are better off with a dedicated solar heater and solar panels separately, at least for now until the water channels in the panels at least are reliable enough that they meet the panel lifetime and then the pump is installed in the roof cavity so its cheap and easy to replace. Work still needs to be done to work out the details and make the parts that fail easily swappable.
A solar thermal heater typically lasts 10 years, its a pretty harsh environment and they have pumps and expansion vessels and water in the heat range of -25 through +80 C is just damaging over time. Where as a solar panel has a rated 80% output at 25 years. That mismatch is problematic for Solar panel payoff, 10 years is only just past break even point. Whereas the solar thermal heaters typically pay off within a few years so the reduced lifetime isn't such a big problem (but both are driven by local gas and electrical prices).
Companies are trying to do this better and products exist to do it. The added installation complexity and reduced expected lifetime are all a bit of an issue. Currently I suspect most people are better off with a dedicated solar heater and solar panels separately, at least for now until the water channels in the panels at least are reliable enough that they meet the panel lifetime and then the pump is installed in the roof cavity so its cheap and easy to replace. Work still needs to be done to work out the details and make the parts that fail easily swappable.
> Currently I suspect most people are better off with a dedicated solar heater and solar panels separately
Right now most people are better off (from a total cost of ownership perspective) with PV panels + heat pump water heater. The latter can achieve a COP of 3.0 (300% "efficiency"), and also can just use grid electricity on a cloudy day. Unless you are off-grid, the additional cost/complexity of running plumbing to the roof for a solar water heater doesn't pencil out.
Right now most people are better off (from a total cost of ownership perspective) with PV panels + heat pump water heater. The latter can achieve a COP of 3.0 (300% "efficiency"), and also can just use grid electricity on a cloudy day. Unless you are off-grid, the additional cost/complexity of running plumbing to the roof for a solar water heater doesn't pencil out.
Where are you finding COP for water heaters? The best I found was a field study by the Canadian government where it seemed like most units operating in ambient temperatures relevant for me (in central California) get about 2.5.
The COP is roughly equivalent (but more forgiving) than the UEF rating. Many new heat pump water heaters have a UEF of 4 [1], but this accounts for things like standby losses, so the COP of the heat pump itself is higher than that.
Some premium hot water heaters like the SanCO2 can achieve COP of up to 5.0 [2], so high that they don't need backup resistance elements, even in northern climates.
1. https://www.energystar.gov/productfinder/product/certified-w...
2. https://www.smallplanetsupply.com/small-planet-blog/2021/1/7...
Some premium hot water heaters like the SanCO2 can achieve COP of up to 5.0 [2], so high that they don't need backup resistance elements, even in northern climates.
1. https://www.energystar.gov/productfinder/product/certified-w...
2. https://www.smallplanetsupply.com/small-planet-blog/2021/1/7...
Here's the definition of UEF:
https://www.govinfo.gov/content/pkg/CFR-2016-title10-vol3/pd...
It would be really nice if manufacturers published delta-T vs COP curves.
It would be really nice if manufacturers published delta-T vs COP curves.
You can buy such things. Eg, https://dualsun.com/en/products/dualsun-spring/
(Not affiliated, no idea if that particular one is any good, it was just one of the first results)
(Not affiliated, no idea if that particular one is any good, it was just one of the first results)
There’s a company called RayGen trying something along these lines at grid scale.
They use concentrated PV to generate electricity directly, and the cooling water goes into a pond (with insulation on top) that reaches ~90C. They also have a “cool pond” cooled using a heat pump to just above freezing.
The combination of the heat and cold reservoirs are used to run a turbine with a low boiling point fluid.
Obviously with the low temperature differentials it’s not terribly thermally efficient, but the proponents claimed the cost of electricity combined with the storage will make it viable in sunny locations.
https://raygen.com/
They use concentrated PV to generate electricity directly, and the cooling water goes into a pond (with insulation on top) that reaches ~90C. They also have a “cool pond” cooled using a heat pump to just above freezing.
The combination of the heat and cold reservoirs are used to run a turbine with a low boiling point fluid.
Obviously with the low temperature differentials it’s not terribly thermally efficient, but the proponents claimed the cost of electricity combined with the storage will make it viable in sunny locations.
https://raygen.com/
The problem is you want your hot water much hotter than your solar panels so there may be limited use for this compared to a traditional solar water heater.
Heat pump water heaters exist. I would think running a warm water source past one would increase the efficiency since it lowers the delta-T
Can't you boost the efficiency by using heat recovery?
The steam is very hot, and the condensed fresh water is also pretty hot. You can use a heat exchanger to transfer this heat into your 16°C ocean water, preheating it so the sun doesn't have to do all the work.
This wouldn't mean magically getting free energy. Your output fresh water would otherwise be really hot, and that's where the energy comes from.
Obviously there are limits. If you have 100°C fresh water coming out and 16°C ocean water going in, a heat exchanger will at best average their temperatures to 58°C. You could in theory overcome this with a heat pump, but that's pretty elaborate.
(I'm not trying to design the perfect desalination system here. The point is there may be some easy efficiency wins.)
The steam is very hot, and the condensed fresh water is also pretty hot. You can use a heat exchanger to transfer this heat into your 16°C ocean water, preheating it so the sun doesn't have to do all the work.
This wouldn't mean magically getting free energy. Your output fresh water would otherwise be really hot, and that's where the energy comes from.
Obviously there are limits. If you have 100°C fresh water coming out and 16°C ocean water going in, a heat exchanger will at best average their temperatures to 58°C. You could in theory overcome this with a heat pump, but that's pretty elaborate.
(I'm not trying to design the perfect desalination system here. The point is there may be some easy efficiency wins.)
A simple system can do much better than the average. Picture the water flowing in a "U", with the hottest water at the bend. The coldest incoming water is warmed just a bit by the coldest outgoing water, then the slightly warmer incoming water is warmed by water a bit further upstream from the output. Carry that logic through and you recapture the heat with a fairly simple system (give or take longer pipes to let enough heat exchange happen).
A multi-stage or continuous heat exchanger can transfer a lot more than half the heat.
A countercurrent heat exchanger could transfer up to 99% of the heat from the steam to the ocean water: https://en.m.wikipedia.org/wiki/Countercurrent_exchange
It sounds to me like the 'condenser' is perhaps wrapped around the water intake.
I don't think they are boiling it. It read to me like they're just evaporating the water in some efficient way, rather than boiling.
What would the math look like if they aren't necessarily going to boil?
What would the math look like if they aren't necessarily going to boil?
Boiling is just evaporating water rapidly. No matter what you do, you need to put the same amount of energy in to convert some mass of water to vapor. Any efficiency gains would be in how you get this energy into the water (electric element vs. directly heated by the sun) not in the energy required.
Technically evaporation takes less energy than boiling as your product is ambient temperature water vapor instead of hot water vapor. You also don't have to replace heat lost to the environment by the hot water and steam during the boiling process. The difference can be lessened by good insulation and heat regeneration, but they still can't be perfect.
Of course on the flip side, your goal is fresh liquid water, so you need to condense the vapor. Condensing hot vapor is easy, just expose it to cooler ambient conditions. Condensing ambient vapor is harder, and will require you to run something like a refrigeration cycle or a chemical desiccant system which will need energy to be regenerated.
Most commercial systems use vacuum distillation which boils water at low temperatures and pressures, which has its own drawbacks but is generally more efficient.
Of course on the flip side, your goal is fresh liquid water, so you need to condense the vapor. Condensing hot vapor is easy, just expose it to cooler ambient conditions. Condensing ambient vapor is harder, and will require you to run something like a refrigeration cycle or a chemical desiccant system which will need energy to be regenerated.
Most commercial systems use vacuum distillation which boils water at low temperatures and pressures, which has its own drawbacks but is generally more efficient.
I just found out that the latent heat of evaporation itself decreases with increasing temperature and disappears at the critical temperature [1].
With regard to the energy expenditure for reaching that temperature: if we were merely raising the temperature of the water and then cooling it down again, I think it would be correct to say that with a completely efficient contra-flow heat exchanger, perfect insulation, and no pumping losses, the steady-state heat input could be arbitrarily low.
If we now modify this system to evaporate and then condense some of the water at the point of highest temperature, we would have to supply, and then extract, the latent heat at whatever temperature the evaporation is performed at. Once that has been performed, the outflow would comprise of the same amount of water as before (and at the same temperature), and it would be equally available to warm up the incoming stream as in the initial scenario (though now we would need two heat exchangers in order to keep the fresh water separate.)
Of course, both the heat exchanger and the insulation will have losses, but we are rejecting quite a bit of heat in the condenser, and it is at the highest temperature in the system. Would that, in principle, be available to make up for any losses elsewhere? This makes me wonder if, counter-intuitively, it could be more efficient to do the distillation at higher temperatures, at least up to the point where the diminishing latent heat can no longer compensate for the losses of running at a higher temperature?
I'm leaving out some considerations that I don't know how to handle (and probably others that have not occurred to me.) For one thing, there's the question of what happens if the evaporation occurs into a chamber containing some air, rather than just steam (my guess is that the relevant temperature is determined by the water vapor partial pressure.) For another, what difference does having salt dissolved in the water make? And this may all be moot, as this system has no moving parts, so the pressure is probably atmospheric (or somewhat below, if the condensation can be exploited to create a partial vacuum.)
I have no idea if any of this makes the slightest bit of sense, and it's probably wrong - as you say, most systems run at reduced pressure.
[1] https://www.engineeringtoolbox.com/water-properties-d_1573.h...
With regard to the energy expenditure for reaching that temperature: if we were merely raising the temperature of the water and then cooling it down again, I think it would be correct to say that with a completely efficient contra-flow heat exchanger, perfect insulation, and no pumping losses, the steady-state heat input could be arbitrarily low.
If we now modify this system to evaporate and then condense some of the water at the point of highest temperature, we would have to supply, and then extract, the latent heat at whatever temperature the evaporation is performed at. Once that has been performed, the outflow would comprise of the same amount of water as before (and at the same temperature), and it would be equally available to warm up the incoming stream as in the initial scenario (though now we would need two heat exchangers in order to keep the fresh water separate.)
Of course, both the heat exchanger and the insulation will have losses, but we are rejecting quite a bit of heat in the condenser, and it is at the highest temperature in the system. Would that, in principle, be available to make up for any losses elsewhere? This makes me wonder if, counter-intuitively, it could be more efficient to do the distillation at higher temperatures, at least up to the point where the diminishing latent heat can no longer compensate for the losses of running at a higher temperature?
I'm leaving out some considerations that I don't know how to handle (and probably others that have not occurred to me.) For one thing, there's the question of what happens if the evaporation occurs into a chamber containing some air, rather than just steam (my guess is that the relevant temperature is determined by the water vapor partial pressure.) For another, what difference does having salt dissolved in the water make? And this may all be moot, as this system has no moving parts, so the pressure is probably atmospheric (or somewhat below, if the condensation can be exploited to create a partial vacuum.)
I have no idea if any of this makes the slightest bit of sense, and it's probably wrong - as you say, most systems run at reduced pressure.
[1] https://www.engineeringtoolbox.com/water-properties-d_1573.h...
The latent heat of vaporization decreases, but the amount it decreases by is the same amount of heat you need to put in to raise the water to that temperature. You're still trying to do the same thing - overcome the intermolecular bonds, but at higher temperatures you've already invested most of the energy you need to do so.
With perfect insulation and heat recovery (zero loss) all that matters is the change in entropy between the starting and end products. Both the energy for raising the temperature and for the vaporization is theoretically recoverable (when you condense a vapor back to a liquid it releases the same amount of heat that it took to vaporize it). But you can't have perfect insulation and heat recovery in practice, and the losses become worse with increasing temperature - or more accurately increasing temperature difference, so trying to cool things down below ambient won't help you either.
With perfect insulation and heat recovery (zero loss) all that matters is the change in entropy between the starting and end products. Both the energy for raising the temperature and for the vaporization is theoretically recoverable (when you condense a vapor back to a liquid it releases the same amount of heat that it took to vaporize it). But you can't have perfect insulation and heat recovery in practice, and the losses become worse with increasing temperature - or more accurately increasing temperature difference, so trying to cool things down below ambient won't help you either.
> The latent heat of vaporization decreases, but the amount it decreases by is the same amount of heat you need to put in to raise the water to that temperature.
I Don't think that can be right - for example, at 18 °C, the isobaric specific heat of water is 4.18 kJ/(kg.K), while the rate of change of the latent heat with temperature is only 2.4 kJ/(kg.K), and at 100 °C, the figures are 4.22 kJ/(kg.K) and 2.7 kJ/(kg.K) respectively.
> Both the energy for raising the temperature and for the vaporization is theoretically recoverable (when you condense a vapor back to a liquid it releases the same amount of heat that it took to vaporize it).
Only up to a point: you cannot condense steam at 100 °C in a condenser where the incoming coolant is also at 100 °C. Using only passive methods (heat exchangers) you cannot, even assuming perfect efficiency, recover all of the heat needed in a distillation process for reuse within that distillation process.
While distilling at higher temperatures need not be anywhere near as inefficient as it seems if you don't include the use of heat exchangers, the numbers given above don't seem different enough to justify distilling at a higher temperature than necessary, under realistic assumptions of efficiency, which is not surprising, given that it does not seem to be done.
I Don't think that can be right - for example, at 18 °C, the isobaric specific heat of water is 4.18 kJ/(kg.K), while the rate of change of the latent heat with temperature is only 2.4 kJ/(kg.K), and at 100 °C, the figures are 4.22 kJ/(kg.K) and 2.7 kJ/(kg.K) respectively.
> Both the energy for raising the temperature and for the vaporization is theoretically recoverable (when you condense a vapor back to a liquid it releases the same amount of heat that it took to vaporize it).
Only up to a point: you cannot condense steam at 100 °C in a condenser where the incoming coolant is also at 100 °C. Using only passive methods (heat exchangers) you cannot, even assuming perfect efficiency, recover all of the heat needed in a distillation process for reuse within that distillation process.
While distilling at higher temperatures need not be anywhere near as inefficient as it seems if you don't include the use of heat exchangers, the numbers given above don't seem different enough to justify distilling at a higher temperature than necessary, under realistic assumptions of efficiency, which is not surprising, given that it does not seem to be done.
Vaporizing at 18 C produces vapor at 18 C, vaporizing at 100 C produces vapor at 100 C. Once you account for cooling the vapor back down to ambient temperature (specific heat pretty close to constant varying from 1.86 to 1.89 kJ/(kg.K) from 18 to 100 C) you get the same amount.
You use the cold incoming water to condense the hot vapor, thus pre-heating it prior to distillation. You get out all the heat you put in, the issue is that vapor has higher entropy than liquid water so you can't use that heat efficiently enough to vaporize the same quantity of water. That's in the efficiency term we are handwaving away.
You use the cold incoming water to condense the hot vapor, thus pre-heating it prior to distillation. You get out all the heat you put in, the issue is that vapor has higher entropy than liquid water so you can't use that heat efficiently enough to vaporize the same quantity of water. That's in the efficiency term we are handwaving away.
One way to bring the recovered energy higher could be to use some of the steam energy to drive a steam engine (with most still used in a heat exchanger). The steam engine, in turn, can provide at least some of the power needed to take the sea water in the last stage past 100°C.
If your water source is cooler than ambient air, is that still a problem?
If it works less well on cool days, well you don't need as much water on cool days as you do on hot ones.
If it works less well on cool days, well you don't need as much water on cool days as you do on hot ones.
Ambient here is referring to the temperature of the water. The hotter the air is, the higher the partial pressure of water can be, meaning you need to take even more heat out to get it to condense.
As long as you use the sea water to cool the steam, this is not really an issue. The more energy you extract from the steam, the less additional energy you need to evaporate the water.
Fair enough. I guess what I'm getting at is that the heat of vaporization sets a lower bound for how much energy you need to add, regardless of whether you boil the water or evaporate it.
You are correct that at ambient temperatures there is an ultimate lower bound for energy.
You are incorrect that at ambient temperature the lower energy bound is set by the latent heat of vaporisation, as others have pointed out this is theoretically recoverable.
At ambient temperature there is however still a fundamental physical limit: the solvation energy of the salt in the water: https://en.wikipedia.org/wiki/Solvation#Solvation_energy_and...
Now the whole globe does not have the same ambient temperature, and as you know about global warming it would be great to shed some energy in the form of heat.
There are many forms of desalination. Another way to desalinate is freezing: when salty water freezes, it pushes out the salt, so while desalinated water ice forms, the liquid water surrounding the ice will increase in salinity and become brine. One could then use simple nets or grills to separate ice from brine.
Suppose one has a space elevator, or even a tether from a balloon, but capable of carrying significant weight.
The temperature falls roughly adiabatically with height. Above the tropopause the atmosphere is essentially cloud-free, CO2 free and below freezing point (say -60 deg C). Hence the latent heat of fusion (freezing) can be shed to outer space. So it should be possible to lift salty water up an elevator, allow it to freeze over, separate brine from ice at the top, then lower the separated brine and ice.
The energy required to lift the brackish water is compensated by the energy released by lowering the freeze-distilled water and brine. What comes up must go down, so simplistically speaking a pulley in equilibrium, so that the only energy intentionally exerted is lost to pulley and air friction. Then one would be cooling the planet and receiving frozen freeze-distilled water at the same time.
The law of conservation of misery is typically not a fundamental law of nature, but imposed by reluctance to study of those who dictate artificial laws.
You are incorrect that at ambient temperature the lower energy bound is set by the latent heat of vaporisation, as others have pointed out this is theoretically recoverable.
At ambient temperature there is however still a fundamental physical limit: the solvation energy of the salt in the water: https://en.wikipedia.org/wiki/Solvation#Solvation_energy_and...
Now the whole globe does not have the same ambient temperature, and as you know about global warming it would be great to shed some energy in the form of heat.
There are many forms of desalination. Another way to desalinate is freezing: when salty water freezes, it pushes out the salt, so while desalinated water ice forms, the liquid water surrounding the ice will increase in salinity and become brine. One could then use simple nets or grills to separate ice from brine.
Suppose one has a space elevator, or even a tether from a balloon, but capable of carrying significant weight.
The temperature falls roughly adiabatically with height. Above the tropopause the atmosphere is essentially cloud-free, CO2 free and below freezing point (say -60 deg C). Hence the latent heat of fusion (freezing) can be shed to outer space. So it should be possible to lift salty water up an elevator, allow it to freeze over, separate brine from ice at the top, then lower the separated brine and ice.
The energy required to lift the brackish water is compensated by the energy released by lowering the freeze-distilled water and brine. What comes up must go down, so simplistically speaking a pulley in equilibrium, so that the only energy intentionally exerted is lost to pulley and air friction. Then one would be cooling the planet and receiving frozen freeze-distilled water at the same time.
The law of conservation of misery is typically not a fundamental law of nature, but imposed by reluctance to study of those who dictate artificial laws.
Ultrasound would do it without boiling?
Ultrasonic "steam" tends to aerosolize the total dissolved solids. Google "white dust" in regards to ultrasonic humidification. I suspect that this would not work for desalination.
Aside:
I have a home-built ultrasonic humidifier. If I run it with Boulder, CO tap water that is low in TDS, it only takes a day or so to have a PM2.5 >600 in my house. For this to work I had to install an RO filter in order to humidify with ultrasonic and not degrade air quality.
Aside:
I have a home-built ultrasonic humidifier. If I run it with Boulder, CO tap water that is low in TDS, it only takes a day or so to have a PM2.5 >600 in my house. For this to work I had to install an RO filter in order to humidify with ultrasonic and not degrade air quality.
Ultrasonic humidifiers need to be run with distilled or equivalent purity water, yes. Not just for the lack of salts being aerosolized, but also because anything that may incidentally grow in the water also will be aerosolized. Distilled water helps minimize growth.
Also the total undissolved bacteria and ameoba.
I don't think it matters whether you "boil" the water or not, you still need to put in enough energy to cause a state transition in the water you're evaporating. I see some papers on using ultrasonics to increase the efficiency of energy transfer from a heating element[1], but I don't think the second law of thermodynamics allows for a free lunch here.
[1] https://www.sciencedirect.com/science/article/abs/pii/S13594...
Edit: If you're thinking of something like an ultrasonic humidifier, I don't think these actually evaporate the water[2]. The mist these produce would still contain salt if you tried to use them for desalination.
[2] https://en.wikipedia.org/wiki/Humidifier#Ultrasonic_humidifi...
[1] https://www.sciencedirect.com/science/article/abs/pii/S13594...
Edit: If you're thinking of something like an ultrasonic humidifier, I don't think these actually evaporate the water[2]. The mist these produce would still contain salt if you tried to use them for desalination.
[2] https://en.wikipedia.org/wiki/Humidifier#Ultrasonic_humidifi...
That will give you bone lung
https://en.wikipedia.org/wiki/Legionnaires%27_disease
I didn't know that legionella can kill macrophages from the inside. That's nasty.
I didn't know that legionella can kill macrophages from the inside. That's nasty.
> I don't think they are boiling it. It read to me like they're just evaporating the water in some efficient way, rather than boiling
There are definitely efficiencies to be had, though I don't know enough of the math to judge one vs. the other. During my brief patent career, I wrote the patents for a distillation system where the main elements involved heating water that was distributed across rotating blades (heat + surface area + air movement) to evaporate the water. When the water was collected, it passed through a heat exchanger that exchanged heat with the in-flowing water. The result was a very efficient system on a small scale, at least.
There are definitely efficiencies to be had, though I don't know enough of the math to judge one vs. the other. During my brief patent career, I wrote the patents for a distillation system where the main elements involved heating water that was distributed across rotating blades (heat + surface area + air movement) to evaporate the water. When the water was collected, it passed through a heat exchanger that exchanged heat with the in-flowing water. The result was a very efficient system on a small scale, at least.
the swamp cooler panel seems more durable than rotating blades, maybe*. If i were going to desal it'd be with solar; which seems inefficient but one could precipitate "CO2" out of the water as calcium carbonate during the same process. Emergency water supply for tropical weather aftermath, during the quiet season park upstream from a coral reef that's in danger.
*edit: although window and wall unit HVAC use the blades to fling water around so the condenser gets the coolest possible air
*edit: although window and wall unit HVAC use the blades to fling water around so the condenser gets the coolest possible air
They have to “boil” but not get the water to 100ºC. Water evaporates in the air at any temperature; it’s faster when the water is warm, and the air is warm and dry. Technically, that’s boiling, even if it’s not exactly like how your kettle does it.
Essentially, they find an equilibrium between the cold water coming in, warming in the sun, an increasing amount evaporating into the warm, damp chamber, and the remaining brackish water being cooled by the new water.
Essentially, they find an equilibrium between the cold water coming in, warming in the sun, an increasing amount evaporating into the warm, damp chamber, and the remaining brackish water being cooled by the new water.
Thermodynamics can't be cheated. If you want to turn some liquid into gas at given pressure you need to deliver specific amount of energy regardless of how you do it.
However, you also need to turn the same amount of gas back into liquid, just somewhere else without the salt. It does seem like there's good potential for recovering and reusing that energy.
From some quick searches, it looks like 2257 J the energy used by the phase transition, so that part will probably be the same.
There are desalinization systems for boats. They are expensive but everything about boats is. I saw one model that produces 20gph and seems to use about 1200 watts.
Doesn't feel like there is a gross thermodynamic reason it wouldn't work.
Doesn't feel like there is a gross thermodynamic reason it wouldn't work.
20 gallons = 75.7 liters.
4 to 6 liters is 5-8% of that.
5-8% of 1200 watts is 60-96 watts.
If you remember the numbers right, that thing is already roughly in this range. A 100 watt solar panel might fold into a briefcase.
4 to 6 liters is 5-8% of that.
5-8% of 1200 watts is 60-96 watts.
If you remember the numbers right, that thing is already roughly in this range. A 100 watt solar panel might fold into a briefcase.
The fundamental limit to energy expenditure is not the heating and boiling of water (as others have pointed out, that energy can all be captured). Rather, the limit is set by the requirement for the entropy of the universe to not decrease when we reduce the local entropy in the salt-water system.
According to GPT4, the numbers come out to 760 J/L for seawater with a salt concentration of 35 g/L. That would mean a limit of around 2 L/s*m2 for full intensity sunlight.
According to GPT4, the numbers come out to 760 J/L for seawater with a salt concentration of 35 g/L. That would mean a limit of around 2 L/s*m2 for full intensity sunlight.
I had this same idea on an HN comment early this year lol.
Part of my idea is to use desalinated water to build artificial lakes and rivers. Specifically, a river system along interstate highways, especially in the US west and alongside that infra build highspeed railways. These two things along with interstate highway will allow new towns and cities to flourish which will help with economic activity recouping some of the cost but also solve homelessness, climate goals and even social unrest and instability. It passed my poorly done napkin math.
If hitler had plans to dam the mediterranean and turn the sahara into an fertile land and generate crapton of energy wth are we doing today with all the peace, economic health and insane amounts of technical progress? $300B in subsidizing ev car chargers (car makers should pay for) instead of high speed railways makes me sad.
Part of my idea is to use desalinated water to build artificial lakes and rivers. Specifically, a river system along interstate highways, especially in the US west and alongside that infra build highspeed railways. These two things along with interstate highway will allow new towns and cities to flourish which will help with economic activity recouping some of the cost but also solve homelessness, climate goals and even social unrest and instability. It passed my poorly done napkin math.
If hitler had plans to dam the mediterranean and turn the sahara into an fertile land and generate crapton of energy wth are we doing today with all the peace, economic health and insane amounts of technical progress? $300B in subsidizing ev car chargers (car makers should pay for) instead of high speed railways makes me sad.
> On a sunny day, total solar energy hitting the top of the atmosphere
Aren't they all sunny at the top of the atmosphere?
> gives about 1360 watts per square meter
I assume that's very much latitude dependent
Aren't they all sunny at the top of the atmosphere?
> gives about 1360 watts per square meter
I assume that's very much latitude dependent
[deleted]
should be the same at all latitude
But only if you point angle it towards the sun, so at 45 degrees latitude a 1x1m panel would take up 1x1.41m of ground area.
There’s also more atmosphere in the way the further you go from the equator which will affect how much solar radiation reaches the earth. Overall only about half of solar radiation reaches the surface.
There’s also more atmosphere in the way the further you go from the equator which will affect how much solar radiation reaches the earth. Overall only about half of solar radiation reaches the surface.
A breakdown like this is why I come to HN.
Thank you.
further down the article:
> if each stage were scaled up to a square meter, it would produce up to 5 liters of drinking water per hour
so 1m², times the number of layers.
> if each stage were scaled up to a square meter, it would produce up to 5 liters of drinking water per hour
so 1m², times the number of layers.
I think the layers are on to of each other
if the total surface is a square meter, it doesn't bring any more solar energy to stack layers, right ?
For most cities, the cost of the water infrastructure (building and maintaining pipes) is much more expensive than the cost of the actual water.
In Melbourne, Australia, since tap water mostly comes from catchments in national parks, water requires very little treatment (some fluoride and chlorine is added), so it works out cheap: ~$25 AUD per million liters. Desalinated water, by contrast, cost about 24 times more (~$600 AUD per million liters).
In Melbourne, Australia, since tap water mostly comes from catchments in national parks, water requires very little treatment (some fluoride and chlorine is added), so it works out cheap: ~$25 AUD per million liters. Desalinated water, by contrast, cost about 24 times more (~$600 AUD per million liters).
$600 AUD per million liters is still dirt cheap. That comes out to about an extra $3.5 per person per month (assumes 50 gallons of water/day/person). Would you be willing to pay an extra $3.5 per month to never have to worry about a drought again?
I know I would.
I know I would.
The desal plant in Sydney cost $2B.
The cost of simply keeping it turned off is $500,000 a day.
Simply building bigger dam walls would be a far better choice.
The cost of simply keeping it turned off is $500,000 a day.
Simply building bigger dam walls would be a far better choice.
That sounds like a 10 year straight-line amortisation rather than an operational expense. Is that the actual operational cost?
$500k a day is the operational, this is without it pumping a single litre of water. Not sure how much it is when operating.
Raising the few dam walls that service Sydney is nowhere near the same cost but people are very angry about it ever happening because it would basically remove entire flood zones from the planning maps and encourage development in their areas.
Raising the few dam walls that service Sydney is nowhere near the same cost but people are very angry about it ever happening because it would basically remove entire flood zones from the planning maps and encourage development in their areas.
> $500k a day is the operational, this is without it pumping a single litre of water.
How? I don't understand what that money is being spent on.
How? I don't understand what that money is being spent on.
Wouldn’t it make the cost of anything using power nearby more expensive too?
> Would you be willing to pay an extra $3.5 per month to never have to worry about a drought again?
Yes, you'll never have to worry about your basic supply of 50 gal/d/person being threatened in a drought, but just think about this for a second: the population of Melbourne is around 5 million people. In the 2020-2021 year, Melbourne Water delivered 439 billion liters (116 billion gallons) of fresh water[1]. That is roughly 318 million gallons of water consumption on an average day. What kind of drought would reduce the available water from 318 million gallons to 25 million gallons per day?
Personal consumption (drinking, showering, household washing) is not the primary driver of water use. In general, it is dominated by agriculture, and to a lesser extent by industry. The economics of these activities would not permit an order of magnitude increase in the cost of fresh water.
[1]: https://www.melbournewater.com.au/media/18976/download
Yes, you'll never have to worry about your basic supply of 50 gal/d/person being threatened in a drought, but just think about this for a second: the population of Melbourne is around 5 million people. In the 2020-2021 year, Melbourne Water delivered 439 billion liters (116 billion gallons) of fresh water[1]. That is roughly 318 million gallons of water consumption on an average day. What kind of drought would reduce the available water from 318 million gallons to 25 million gallons per day?
Personal consumption (drinking, showering, household washing) is not the primary driver of water use. In general, it is dominated by agriculture, and to a lesser extent by industry. The economics of these activities would not permit an order of magnitude increase in the cost of fresh water.
[1]: https://www.melbournewater.com.au/media/18976/download
You missed a zero. 5 million people by 50 gallons/day is 250 million gallons/day. So they only missed by ~25%.
Australia uses a estimated ~16T liters of water per year [1] for all uses including personal and agricultural. That is 16M ML * 600 AUD/ML for a total of ~10B AUD.
Australia has a population of ~25M. So that is ~400 AUD/person to completely replace all water usage in Australia. As Australia is a island, I assume they do most of their own agriculture, so for additional 400 AUD on their food bill a year they never need to worry about a drought ever again.
The Australian government appears to have a budget of ~500B/year which is around 25% of GDP [2]. So, for ~2% of the government budget or ~0.5% of GDP the economics are completely managed.
[1] https://www.worldometers.info/water/
[2] https://www.aph.gov.au/About_Parliament/Parliamentary_Depart...
Australia uses a estimated ~16T liters of water per year [1] for all uses including personal and agricultural. That is 16M ML * 600 AUD/ML for a total of ~10B AUD.
Australia has a population of ~25M. So that is ~400 AUD/person to completely replace all water usage in Australia. As Australia is a island, I assume they do most of their own agriculture, so for additional 400 AUD on their food bill a year they never need to worry about a drought ever again.
The Australian government appears to have a budget of ~500B/year which is around 25% of GDP [2]. So, for ~2% of the government budget or ~0.5% of GDP the economics are completely managed.
[1] https://www.worldometers.info/water/
[2] https://www.aph.gov.au/About_Parliament/Parliamentary_Depart...
You're right, that was sloppy of me. It sounded right, but I think Melbourne Water statistics probably truly are dominated by domestic use, since it's a city.
You can see the numbers don't match up; you're using a figure of 16T liters annually, whereas 25 million people * 50 gallons / day-person * 365 days * 3.785 liters/gallon is 1.727T trillion liters annually.
Anyway, I am suspicious of the 600 AUD/ML figure, or else a lot more Gulf states would be food independent.
You can see the numbers don't match up; you're using a figure of 16T liters annually, whereas 25 million people * 50 gallons / day-person * 365 days * 3.785 liters/gallon is 1.727T trillion liters annually.
Anyway, I am suspicious of the 600 AUD/ML figure, or else a lot more Gulf states would be food independent.
Yes. Domestic use is a tiny fraction of all water usage. However, as you point out it is necessary to incorporate the food water to determine actual water independence.
600 AUD/ML is ~400 USD/ML. The Sorek B plant in Israel is profitably contracted at ~0.40 USD/m^3 [1] which is comparable. That is one of the largest plants with cutting edge technology and one of the cheapest prices I have seen in my research. A quote of 600 AUD/ML for desalinated water right now in Australia seems a tad questionable, but not outside of what is possible. 2-3x that number is almost certainly believable (though they almost certainly do not have bulk scale) and would only increase the costs to 1.5% of GDP.
[1] https://ildesal.org.il/sorek-b-desalination-plant/
600 AUD/ML is ~400 USD/ML. The Sorek B plant in Israel is profitably contracted at ~0.40 USD/m^3 [1] which is comparable. That is one of the largest plants with cutting edge technology and one of the cheapest prices I have seen in my research. A quote of 600 AUD/ML for desalinated water right now in Australia seems a tad questionable, but not outside of what is possible. 2-3x that number is almost certainly believable (though they almost certainly do not have bulk scale) and would only increase the costs to 1.5% of GDP.
[1] https://ildesal.org.il/sorek-b-desalination-plant/
Melbourne is the perfect example of "what are we going to do when the water runs out". Remember when the storage was down to single digits?
do you have a reference handy for this storage time series?
from the historical net loss rate approaching the lows one can estimate the required backup desalination flow rate.
from the historical net loss rate approaching the lows one can estimate the required backup desalination flow rate.
Also here disposal of water cost nearly the same as water itself. 1,5€/m^3(water) vs 1,41€/m^3... And here it is sourced from artificially rained groundwater. So not most expensive way.
Are you saying that the water is so cheap that switching to desalination will be a non-issue OR are you saying that this will make the water a large enough portion of the cost to make it significant?
> Are you saying that the water is so cheap that switching to desalination will be a non-issue
For human consumption: this is pretty much true. Desalinization works just fine for people. The biggest issue is where to put the extra salty waste products.
When people talk about the "water crisis" in the US, for example, it's always about big agribusinesses doing farming.
For human consumption: this is pretty much true. Desalinization works just fine for people. The biggest issue is where to put the extra salty waste products.
When people talk about the "water crisis" in the US, for example, it's always about big agribusinesses doing farming.
> The biggest issue is where to put the extra salty waste products.
The U.S. has "salt farms" where they evaporate water to produce salt. Sounds like colocating near the desalination plant would make those cheaper to operate.
The U.S. has "salt farms" where they evaporate water to produce salt. Sounds like colocating near the desalination plant would make those cheaper to operate.
any time there's a fish storm in the atlantic, just dump the salt in that area?
> The researchers estimate that if the system is scaled up to the size of a small suitcase,
Go on then.
Yet another MIT paper on desalination jumping the gun and announcing a breakthrough, that could be scaled up to modestly useful sizes if only they had the time and the meagre budget to do so.
Here’s[1] a previous announcement from Feb 2022 of a device that could produce water for a small family for only $4 of materials, that they didn’t bother building.
[1] https://news.mit.edu/2022/solar-desalination-system-inexpens...
Go on then.
Yet another MIT paper on desalination jumping the gun and announcing a breakthrough, that could be scaled up to modestly useful sizes if only they had the time and the meagre budget to do so.
Here’s[1] a previous announcement from Feb 2022 of a device that could produce water for a small family for only $4 of materials, that they didn’t bother building.
[1] https://news.mit.edu/2022/solar-desalination-system-inexpens...
I mean they're researchers, not builders. If this all checks out, they've done their part and this should inspire builders to run with it and commercialize or open source a printable design.
Specialization is great, glad someone is focused on continually pushing the research and improving the designs, and this one supposedly improves on last year's design. There are others who are better at scaling & commercializing, and those types are probably a lot worse at basic research.
Every inventor and researcher doesn't need to start a startup.
Specialization is great, glad someone is focused on continually pushing the research and improving the designs, and this one supposedly improves on last year's design. There are others who are better at scaling & commercializing, and those types are probably a lot worse at basic research.
Every inventor and researcher doesn't need to start a startup.
Wouldn’t you consider “validating that it works beyond the chip-sized proof-of-concept” as part of research, especially considering the claims are that it will scale to a modest briefcase-sized unit ? We’re not talking about something that requires mass-manufacturing scale here …
Practical Engineering recently had a video on the topic "Why is desalination so difficult"
https://youtu.be/mxqOPdEUNTs?feature=shared
https://youtu.be/mxqOPdEUNTs?feature=shared
I like the videos posted by Practical Engineering, but I found this one unsatisfying. Both distillation and reverse osmosis are energy expensive, but this doesn't answer whether this is because these are poor techniques or because desalinating water is fundamentally+physically difficult.
Are there thermodynamic limits to how efficiently water can be desalinated?
Doesn't this feel like a problem where a Carnot-like argument can be made?
Are there thermodynamic limits to how efficiently water can be desalinated?
Doesn't this feel like a problem where a Carnot-like argument can be made?
A simple evaporation system without heat recovery would use about 100x the energy of reverse osmosis per unit of fresh water produced (which is somewhere around 5 to 8 kWh per cubic meter of fresh water.)
PV-driven RO, even without energy recovery, is going to produce much more water than this scheme.
PV-driven RO, even without energy recovery, is going to produce much more water than this scheme.
Don't RO systems need regular maintenance, and have consumable parts? It sounds like this was designed to work unmaintained for years. That could balance out the efficiency.
Any system that has saltwater flowing through it is going to need regular maintenance to deal with buildup and corrosion.
More that the important wear component in a RO system is a membrane that depends on access to sophisticated manufacturing, while plumbing is relatively easy to DIY in the field, and the big innovation in this system is 2.5mm perforated polyurethane which can also be remade with simple tools (and access to polyurethane of course but that's simpler to make or salvage than RO membranes).
Kind of analogous to ICE vs electric cars; electric cars are simpler in principle but the most important components require access to advanced semiconductor and battery manufacturing, while all the components, in theory, of an ideal "ICE car" can be recreated with early 20th century machine shop technology
Kind of analogous to ICE vs electric cars; electric cars are simpler in principle but the most important components require access to advanced semiconductor and battery manufacturing, while all the components, in theory, of an ideal "ICE car" can be recreated with early 20th century machine shop technology
I think it's worth remembering that many of the first cars were electric. I'd argue an EV is easier to build than ICE. Neither kind built with primitive tools is going to perform like the modern-day ones.
https://en.wikipedia.org/wiki/History_of_the_electric_vehicl...
https://en.wikipedia.org/wiki/History_of_the_electric_vehicl...
A modern electric car is probably comparably difficult to a modern ICEV. If you want to draw a comparison with early 20th century machine shop technology, then compare with an EV of that era. They existed. Lead acid batteries are much simpler than lithiums.
I also think that seems likely, just reading their announcement though they claim eddies prevent buildup and the thing looks like a glass solar still, so the brine may not contact anything it can corrode. Even normal countertop distillers come out cheaper per gallon than an RO system depending on your electricity prices, though that is not with saltwater for either.
Nowhere in either this article or the paper is an estimate given for cost, nonetheless an analysis justifying the estimate.
Desalination has a fundamental energy cost, and solar energy is fundamentally limited by what is received. The real question is whether it is cheaper to set up a solar-thermal desalinator, or set up solar panels that can power more efficient desalination methods.
Solar panels are cheap and getting cheaper quickly as there is an incredible economy of scale. While desalination systems could likewise be mass produced, there will never be as large a demand for that one specific application of solar power as for general solar power. Further, photovoltaics are reasonably simple solid state devices which are well suited to mass production. I am highly skeptical a priori that a solar thermal system could compete on economic terms. Perhaps in a space confined situation it makes sense, but it's tough to run out of space in the ocean.
Desalination has a fundamental energy cost, and solar energy is fundamentally limited by what is received. The real question is whether it is cheaper to set up a solar-thermal desalinator, or set up solar panels that can power more efficient desalination methods.
Solar panels are cheap and getting cheaper quickly as there is an incredible economy of scale. While desalination systems could likewise be mass produced, there will never be as large a demand for that one specific application of solar power as for general solar power. Further, photovoltaics are reasonably simple solid state devices which are well suited to mass production. I am highly skeptical a priori that a solar thermal system could compete on economic terms. Perhaps in a space confined situation it makes sense, but it's tough to run out of space in the ocean.
A Solar thermal system will definitely out perform using solar panels to produce heat. A typical commercial solar panel is only 23% efficient whereas solar heaters are above 95%. With 4x the energy for the same area and a lot less sophisticated technology there is little doubt heating the water directly is better. But like with all desalination its a relatively slow process that leaks a bunch of material behind that damages everything and the costs will be dominated by all those other aspects not just where it gets its energy from.
You get 4 times the energy per unit area, but if it costs more than 4 times more per unit area, the photovoltaics win. The cost per square meter of solar panels is currently around $40. Is a square meter sized solar thermal desalinator currently less than $160? In 10 years when photovoltaics are $15 per square meter, will the solar thermal desalinator be less than $60?
Sounds interesting.
Seems like it uses energy from the sun, but also requires a location with ocean currents. So finding good installation locations along the shoreline where it is both deep enough to work while being shallow enough to maintain may be a limit on how much capacity you could have.
Hopefully they are able to try a scaled up version in a LESS controlled environment to see if additional problems arise.
Seems like it uses energy from the sun, but also requires a location with ocean currents. So finding good installation locations along the shoreline where it is both deep enough to work while being shallow enough to maintain may be a limit on how much capacity you could have.
Hopefully they are able to try a scaled up version in a LESS controlled environment to see if additional problems arise.
"Cheaper than tap water" is an inane meaningless claim. Cheaper than tap water where? Tap water isn't one price, the price of fresh water is hyper local. I doubt this technology will make water cheaper even for most people living along a coast.
> From these tests, the researchers calculated that if each stage were scaled up to a square meter, it would produce up to 5 liters of drinking water per hour
So 1) They haven't yet tried this at the scale of one square meter. So this is a lab project that is nowhere close to commercialization but that doesn't stop them from making grand vague pronouncements about its potential. Classic MIT tbqh.
2) 5 liters per square meter per hour is trash. An average American uses a bit more than 300 liters of water a day, so you need 60 square meters of this to support one average American. So you'd need more than 5000 square kilometers of this to provide water to NYC. Does this sound like it's going to be cheaper than the tap water they already have?
> From these tests, the researchers calculated that if each stage were scaled up to a square meter, it would produce up to 5 liters of drinking water per hour
So 1) They haven't yet tried this at the scale of one square meter. So this is a lab project that is nowhere close to commercialization but that doesn't stop them from making grand vague pronouncements about its potential. Classic MIT tbqh.
2) 5 liters per square meter per hour is trash. An average American uses a bit more than 300 liters of water a day, so you need 60 square meters of this to support one average American. So you'd need more than 5000 square kilometers of this to provide water to NYC. Does this sound like it's going to be cheaper than the tap water they already have?
> 5 liters per square meter per hour is trash. An average American uses a bit more than 300 liters of water a day, so you need 60 square meters of this to support one average American.
Unit check. 5 liters per hour is 120 liters per day. So you need 2.5 m^2 per American (ignoring whether the hourly rate is sustainable, just correcting units).
This is about a third of the projected area of a typical car, so in terms of surface-area-per-person we're at about half that of cars (given about 2/3 of a car per American).
Unit check. 5 liters per hour is 120 liters per day. So you need 2.5 m^2 per American (ignoring whether the hourly rate is sustainable, just correcting units).
This is about a third of the projected area of a typical car, so in terms of surface-area-per-person we're at about half that of cars (given about 2/3 of a car per American).
you can only account for 6hrs of sun per day, so it's more like 30liters per day. that gives you 10m^2 per American. however serving Americans is not a practical use case. i agree these kinds of systems are not going to be competitive with large scale PV driven RO (i build medium scale solar RO plants in africa and they're pretty good and surprisingly affordable). however having a mobile one you can put on a vehicle or deploy in a small scale distributed manner with little to no expertise would be extremely useful in low population density or nomadic context.
Good catch.
I guess one problem is that by definition, sea water is at sea level, and any desalinated water would have to be pumped to deliver it anywhere. Pumping costs. By contrast, isn't most fresh water delivered by gravity, for free?
How destructive is hot dense brine (the waste from) desalination systems? Seems like it would sink to the floor and create a dead zone.
It's not good, desalination plants have to mitigate this with long diffusers that regulate the rate and concentration of the brine that is being put back into the ocean.
Here is one for sale: https://www.jains.com/Pipefittings/JainPEPipes/spacial%20fit...
Here is one for sale: https://www.jains.com/Pipefittings/JainPEPipes/spacial%20fit...
Desalination: https://en.wikipedia.org/wiki/Desalination
Brine > Uses: https://en.wikipedia.org/wiki/Brine :
> Culinary, Chlorine generation, Refrigerating fluid, Water softening and purification, De-icing, Quenching
Uses for Brine / NaCl not listed on Wikipedia:
Hypochlorite generation. Hypochlorite is the sanitizing primary component of household bleach. Hypochlorite can be made with a 5V USB Hypochlorite generator, salt, water, and watts of electricity.
Salt-based cleaning products; "Non-Toxic Cleaners and EPA Disinfectants" https://saltbased.com/
Energy storage; thermal battery (as heated by concentrated solar, for example)
Energy storage; /? brine NaCl batteries:
Sodium-ion Battery: https://en.wikipedia.org/wiki/Sodium-ion_battery
/? Proton battery brine / sodium
Not brine, but if you're already processing seawater:
Diesel can be made by processing lots of seawater
Hydrolysis and Electrolysis; [Green] Hydrogen production
Nuclear Fusion; to extract D, T, He3, and He4 from (Helion,)
What can be made with Brine and/or NaCl with modern sustainable production processes involving e.g. lasers and fusion heat?
Salt belt: https://en.wikipedia.org/wiki/Salt_Belt :
> The Salt Belt is the U.S. region in which road salt is used in winter to control snow and ice.
Nebraska roadways are treated with brine to pre-treat and de-ice roadways (instead of rock salt, which corrodes many metals).
Though listed as a DIY weed killer ingredient, sodium is a dessicant which dries and prevents plant growth, so salt on the lawn will kill weeds but then leave a dead patch.
Does discharge of fresh water into the ocean by desalination plants, for example, affect the thermal content of the water due to formation of halocines and other thermochemical effects?
Solar pond: https://en.wikipedia.org/wiki/Solar_pond :
> A solar pond is a pool of saltwater which collects and stores solar thermal energy. The saltwater naturally forms a vertical salinity gradient also known as a "halocline", in which low-salinity water floats on top of high-salinity water.
Brine > Uses: https://en.wikipedia.org/wiki/Brine :
> Culinary, Chlorine generation, Refrigerating fluid, Water softening and purification, De-icing, Quenching
Uses for Brine / NaCl not listed on Wikipedia:
Hypochlorite generation. Hypochlorite is the sanitizing primary component of household bleach. Hypochlorite can be made with a 5V USB Hypochlorite generator, salt, water, and watts of electricity.
Salt-based cleaning products; "Non-Toxic Cleaners and EPA Disinfectants" https://saltbased.com/
Energy storage; thermal battery (as heated by concentrated solar, for example)
Energy storage; /? brine NaCl batteries:
Sodium-ion Battery: https://en.wikipedia.org/wiki/Sodium-ion_battery
/? Proton battery brine / sodium
Not brine, but if you're already processing seawater:
Diesel can be made by processing lots of seawater
Hydrolysis and Electrolysis; [Green] Hydrogen production
Nuclear Fusion; to extract D, T, He3, and He4 from (Helion,)
What can be made with Brine and/or NaCl with modern sustainable production processes involving e.g. lasers and fusion heat?
Salt belt: https://en.wikipedia.org/wiki/Salt_Belt :
> The Salt Belt is the U.S. region in which road salt is used in winter to control snow and ice.
Nebraska roadways are treated with brine to pre-treat and de-ice roadways (instead of rock salt, which corrodes many metals).
Though listed as a DIY weed killer ingredient, sodium is a dessicant which dries and prevents plant growth, so salt on the lawn will kill weeds but then leave a dead patch.
Does discharge of fresh water into the ocean by desalination plants, for example, affect the thermal content of the water due to formation of halocines and other thermochemical effects?
Solar pond: https://en.wikipedia.org/wiki/Solar_pond :
> A solar pond is a pool of saltwater which collects and stores solar thermal energy. The saltwater naturally forms a vertical salinity gradient also known as a "halocline", in which low-salinity water floats on top of high-salinity water.
Sounds like it’s easily solved with a diffuser.
It's a very difficult problem to solve at human scale. And getting it wrong can have catastrophic impacts.
Even if 100% of grey water runoff is mixed with the brine, the resulting concentration is still high enough to cause a localized collapse in the ocean if it isn't properly regulated.
Even if 100% of grey water runoff is mixed with the brine, the resulting concentration is still high enough to cause a localized collapse in the ocean if it isn't properly regulated.
So, again, sounds like diffusing it to appropriate levels within the natural salinity variance solves the problem just fine.
If it's discharged with household sewage, it should be close to original salinity, assuming most of the household water usage eventually goes out the sewage pipe.
That's.... remarkably clever. But I think the system loses quite a bit due to evaporation.
and gains quite a bit due to rainfall
Title makes no sense. It says tap water is cheaper than tap water
Not a water expert here but surely all tap water is not desalinated.. That would be just outrageous expensive with current pricing and technologies.
Once desalinated, it becomes what is known as tap water. (Except only a few liters per day per unit)
But yes. You’ve hit on the one of the absurdities of the headline: drinking water costs vary wildly based on a large number of factors including the source and treatments.
But yes. You’ve hit on the one of the absurdities of the headline: drinking water costs vary wildly based on a large number of factors including the source and treatments.
The researchers estimate that if the system is scaled up to the size of a small suitcase, it could produce about 4 to 6 liters of drinking water per hour and last several years before requiring replacement parts. At this scale and performance, the system could produce drinking water at a rate and price that is cheaper than tap water.
This seems like it would be extremely useful if it pans out.
This seems like it would be extremely useful if it pans out.
scale up to a small suitcase...how small is it now?
… and what is preventing them from scaling up to a small suitcase?
That's a very good question.
We see these articles all the time, and they somehow don't get scaled up. You'd think they'd at least scale this up to the size of a typical rooftop solar panel before issuing a press release. So what's the problem? Uses some expensive material? Hard to fabricate at scale? Doesn't actually hold up in bright sunlight?
Go back and read their previous "breakthrough announcement" from 2020.[1] That has more useful info. That system used some expensive aerogel. The process is a bit clearer, During the daytime it evaporates salt water and condenses the vapor. During the night it back-washes the wicking material. Whether this can actually work with some simple device floating in a pool of salt water is not clear. The experimental systems all have plumbing, pumps, and instrumentation.
If this is for real, please scale it up to at least kiddie-pool size before turning on the PR department.
[1] https://news.mit.edu/2020/passive-solar-powered-water-desali...
We see these articles all the time, and they somehow don't get scaled up. You'd think they'd at least scale this up to the size of a typical rooftop solar panel before issuing a press release. So what's the problem? Uses some expensive material? Hard to fabricate at scale? Doesn't actually hold up in bright sunlight?
Go back and read their previous "breakthrough announcement" from 2020.[1] That has more useful info. That system used some expensive aerogel. The process is a bit clearer, During the daytime it evaporates salt water and condenses the vapor. During the night it back-washes the wicking material. Whether this can actually work with some simple device floating in a pool of salt water is not clear. The experimental systems all have plumbing, pumps, and instrumentation.
If this is for real, please scale it up to at least kiddie-pool size before turning on the PR department.
[1] https://news.mit.edu/2020/passive-solar-powered-water-desali...
these premature announcements always make me think of a little kid desperate for attention to have mom/dad hang their drawing on the fridge. it's cute from a developing child, but as grown as adults, it's just sad really.
oh, you had a clever idea, but can't do anything practical with it? here's your gold star. now go have some milk and cookies and get ready for your nap.
oh, you had a clever idea, but can't do anything practical with it? here's your gold star. now go have some milk and cookies and get ready for your nap.
It's a wicked and pervasive problem in academia. Put otherwise capable people in a pathological incentive matrix and this is what happens.
In an ideal world, wouldn't we want people to be showing their work earlier in the process? Inspiring others to join in on the action?
We saw with LK99 the world rally around a promising lead and discover some interesting things very quickly. Why not run these kinds of science/eng research problems like we do open source projects?
Having good desal is an incredibly important problem that should inspire this kind of collective action. It's not super esoteric research.
We saw with LK99 the world rally around a promising lead and discover some interesting things very quickly. Why not run these kinds of science/eng research problems like we do open source projects?
Having good desal is an incredibly important problem that should inspire this kind of collective action. It's not super esoteric research.
Show work, fine. Use an article title "Desalination system could produce freshwater that is cheaper than tap water" and say nothing about the problems, clickbait.
Instead of a gold star, they probably would like to have some funding.
I'm sure MIT is fine - just looked, they have at least 50 million in leftover revenue from fy2022, and they have ~60 billion in assets.
Or a large suitcase? Or a thousand large suitcases?
A naïve question but genuine. Reducing atmospheric pressure reduces boiling point, so would a pressure pump mixed in with heating be beneficial?
Relatedly, Howard energy efficiency be affected if you didn't heat the water to be desalinated, but just evaporated it using low pressure? Would it be less, more, or equally efficient than using heat alone?
Relatedly, Howard energy efficiency be affected if you didn't heat the water to be desalinated, but just evaporated it using low pressure? Would it be less, more, or equally efficient than using heat alone?
I think the energy needed to vaporize water goes up slightly as you reduce the pressure. To condense the vapor you need to remove energy and that represents a loss in a single stage system. You can use multiple stages each at a lower and lower pressure to increase the efficiency. Using the heat of condensation to vaporize the water in the next stage.
You underestimate how cheap tapwater is. I'm paying €1.21 for 1m³ and that includes taxes.
Maybe where you are, but the true cost of water in many important regions is very high and running out. The Colorado river basin is on the brink of drying out completely and that's the best agricultural land in North America as well as the source of tens of millions of people's water.
> The resulting water vapor can then be condensed and collected as pure, drinkable water.
Article doesn't mention how this part would work. Peltier cooler? Heat pump? Is that included in the "suitcase sized" concept? What powers it?
Article doesn't mention how this part would work. Peltier cooler? Heat pump? Is that included in the "suitcase sized" concept? What powers it?
So 1 suitcase-sized device can generate about 1-1.5 gallons of water an hour. (A gallon is a little less than 4 liters.)
The average American uses 82 gallons of water a day.
Assuming 10 hours of sunlight, that requires 8-12 of these per American.
I wonder how practical that is?
The average American uses 82 gallons of water a day.
Assuming 10 hours of sunlight, that requires 8-12 of these per American.
I wonder how practical that is?
How much of that is shower water though? Drinking water, I think is probably closer to 2-3 gallons (on the high end) per day for most Americans.
We also shouldn’t forget that after disposing of the water, the local municipality can recycle it! For island nations, a few strategic water reserves could be cleaned and stored for future use.
And then obviously, for more developing nations, they already use a lot of grey water for daily activities, so this becomes a source of consistent clean drinking water.
We also shouldn’t forget that after disposing of the water, the local municipality can recycle it! For island nations, a few strategic water reserves could be cleaned and stored for future use.
And then obviously, for more developing nations, they already use a lot of grey water for daily activities, so this becomes a source of consistent clean drinking water.
This reminds me of the first ever solar desalination system, which was built by a Swedish engineer, for the saltpeter mines in Chile, over 100 years ago
It would be great if they can scale it up and make it widely available
It would be great if they can scale it up and make it widely available
Awesome! It should even be cleaner than tap water with heavy metals and other contaminants removed by the evaporation. Just need to add some minerals back into it afterward.
there's one big problem. It looks like they're creating distilled water. The WHO has stated that distilled water without the minerals that they normally contain puts people at increased risk of health problems. and you can't just get minerals from another source: that's not the problem. the problem is the water itself lacking in minerals creates problems for the body.
Citation needed. The best source I could find (in 30s) suggests the WHO neither recommends no discourages drinking distilled water.
https://svalbardi.com/blogs/water/distilled-safety
A casual application of math to the concentrations of minerals in tap water would show you that simply eating vegetables would provide much more in the way of minerals (namely calcium and magnesium). If you drink 2L of 60mg/L Ca and 25mg/L Mg, that's only 12% daily value.
"Unsafe to drink DI water" is a myth. If your diet is that marginal that +/-12% matters, take a supplement.
https://svalbardi.com/blogs/water/distilled-safety
A casual application of math to the concentrations of minerals in tap water would show you that simply eating vegetables would provide much more in the way of minerals (namely calcium and magnesium). If you drink 2L of 60mg/L Ca and 25mg/L Mg, that's only 12% daily value.
"Unsafe to drink DI water" is a myth. If your diet is that marginal that +/-12% matters, take a supplement.
here's the citation:
https://timesofindia.indiatimes.com/readersblog/ezhil/danger...
Distilled water has been used in many parts of the world extensively without major issues. My wife drank it for years in Hong Kong without any issues.
If you eat a normal diet, the minerals lost in distilled water are a faction of what you consume with your food.
If you eat a normal diet, the minerals lost in distilled water are a faction of what you consume with your food.
Perhaps stir in some mineral powder before serving?
> there's one big problem.
Bombastic.
> It looks like they're creating distilled water.
"distilled water" can mean many similar things. It is not a binary property of water:
Consider a water still that has 3 ports: one intake port of seawater, an output port of brine and an output port of water with a lower salt concentration than seawater.
Distilled can in this case refer to the water exiting the third port, even though it still contains some salts.
Distillation and purification in general is a process with diminishing returns: to get ever lower ppm's of mineral content requires ever more patience or energy.
In the context of seawater desalination, "distilled water" typically means water with sufficient salt removed to be now potable. Either way even if the third port was effectively Sigma-Aldrich 100% pure H20, the simple fix would be to dilute a tiny amount of the brine into the distilled water to restore the mineral content to potable levels.
You did not reference the study or page of the supposed WHO conclusion.
When I was studying at university I recalled the concensus basically being that the adverse health effects are a myth, since 95% of our salt intake comes from food.
Remember sailors have been drinking distilled water for over a hundred years.
Steamboats needed the ability to desalinate water anyway.
It is quite conceivable, that this myth starts as a counter-myth for a prior myth.
Scientifically different types of desalinated, deionized and distilled waters are closer to pure H2O than normal waters.
Linguistically pure is the antonym of impure.
The mere existence of distilled or pure water in the scientific literature conceivably caused purity zealots to opt for drinking distilled waters, falsely claiming health benefits.
Just like taking 10x vitamin C doses will not make you 10x healthier, neither would drinking distilled water. But it "sounds" purer.
In order to counteract obsessions about drinking distilled water, and to counter the false and disinformative claims of health benefits, some started opting to use the same tactics and weapons to stop the "pure water zealots", and the countery-myth is born.
That was my interpretation at university. So it surprises me to learn that WHO would recommend against drinking distilled water.
Of course only drinking distilled water would not be healthy indeed: you also need to eat, breathe, etc.
So I first did the easy check: wikipedia.
On wikipedia the same vague statement of the WHO concluding something along the lines of it being unhealthy is reiterated, but with a [citation needed] appended. Recall anyone can edit wikipedia. Such citation was never provided.
So next I tried to find the source myself, and downloaded the 312 page Drinking Water and Health: Volume 4 1982.
What page am I supposed to be looking at?
As I said at the start, its a non problem, because adding back in some mineral salts to the desired ppm is easy to do.
Bombastic.
> It looks like they're creating distilled water.
"distilled water" can mean many similar things. It is not a binary property of water:
Consider a water still that has 3 ports: one intake port of seawater, an output port of brine and an output port of water with a lower salt concentration than seawater.
Distilled can in this case refer to the water exiting the third port, even though it still contains some salts.
Distillation and purification in general is a process with diminishing returns: to get ever lower ppm's of mineral content requires ever more patience or energy.
In the context of seawater desalination, "distilled water" typically means water with sufficient salt removed to be now potable. Either way even if the third port was effectively Sigma-Aldrich 100% pure H20, the simple fix would be to dilute a tiny amount of the brine into the distilled water to restore the mineral content to potable levels.
You did not reference the study or page of the supposed WHO conclusion.
When I was studying at university I recalled the concensus basically being that the adverse health effects are a myth, since 95% of our salt intake comes from food.
Remember sailors have been drinking distilled water for over a hundred years.
Steamboats needed the ability to desalinate water anyway.
It is quite conceivable, that this myth starts as a counter-myth for a prior myth.
Scientifically different types of desalinated, deionized and distilled waters are closer to pure H2O than normal waters.
Linguistically pure is the antonym of impure.
The mere existence of distilled or pure water in the scientific literature conceivably caused purity zealots to opt for drinking distilled waters, falsely claiming health benefits.
Just like taking 10x vitamin C doses will not make you 10x healthier, neither would drinking distilled water. But it "sounds" purer.
In order to counteract obsessions about drinking distilled water, and to counter the false and disinformative claims of health benefits, some started opting to use the same tactics and weapons to stop the "pure water zealots", and the countery-myth is born.
That was my interpretation at university. So it surprises me to learn that WHO would recommend against drinking distilled water.
Of course only drinking distilled water would not be healthy indeed: you also need to eat, breathe, etc.
So I first did the easy check: wikipedia.
On wikipedia the same vague statement of the WHO concluding something along the lines of it being unhealthy is reiterated, but with a [citation needed] appended. Recall anyone can edit wikipedia. Such citation was never provided.
So next I tried to find the source myself, and downloaded the 312 page Drinking Water and Health: Volume 4 1982.
What page am I supposed to be looking at?
As I said at the start, its a non problem, because adding back in some mineral salts to the desired ppm is easy to do.
You’d think for such a breakthrough they’d at least provide a video. I couldn’t find one elsewhere, has anyone else?
New Orleans could use this right about now.
Usually the problem with Desal is not the energy, it's the fact that there just isn't enough coastline. California could cover every inch of coastline in Desal plants and not have enough fresh water.
If they could build platforms in the ocean with some way to get the water to land, maybe this could work, but the Western US is screwed unless we can find other ways to save water, even if this tech were totally free.
If they could build platforms in the ocean with some way to get the water to land, maybe this could work, but the Western US is screwed unless we can find other ways to save water, even if this tech were totally free.
Show your work? Urban Californians use 6.6e6 acre-feet/year and that implies we would need about 100 of these tiny little facilities.
https://www.google.com/maps/place/Claude+%22Bud%22+Lewis+Car...
That's only if you intend to supply 100% of water from desal, which nobody is suggesting.
https://www.google.com/maps/place/Claude+%22Bud%22+Lewis+Car...
That's only if you intend to supply 100% of water from desal, which nobody is suggesting.
On a sunny day, total solar energy hitting the top of the atmosphere gives about 1360 watts per square meter (source - top result from google, something something NASA). It takes about 4.184 joules to raise one ml of water by 1 degree celsius. Let's suppose that the "suitcase" proposed in the article has 1 square meter of space (a pretty large suitcase) and is able to capture 100 percent of solar energy (unreasonably effective). Then pure solar energy-wise, there is enough energy to raise 325 ml of water by one degree of celsius per second in a square meter. If the water is, say, at 16 degrees (the temperature of the ocean near me), in would take 84 seconds to bring 325 ml of water to boiling temperature. To transform boiling water to steam, each ml of water takes an additional 2257 joules. In 540 seconds, the 325 ml of water is now converted to steam.
In total, it has taken 624 seconds to steamify 325 ml of water (under very optimistic circumstances). Morally one could do this almost 6 times in an hour, giving approximately 2 litres of water per hour.
(Edit): Looking a bit closer, I see that the article's description of their work suggests that they recapture some of the energy from condensing the steam back into water. I didn't account for this. Even a moderate amount of recapture changes the math very favorably.
This makes me suspect that their claim of 4-6 liters per hour would require a rather large "suitcase"-sized device, but is within the ballpark of reason.