It’s easy to use electricity — solar-generated or otherwise — to desalinate water. However, traditional systems require a steady source of power. Since solar panels don’t always produce electricity, these methods require some way to store or acquire power when the solar cells are in the dark or shaded. But MIT engineers have a fresh idea for solar-powered desalination plants: modify the workload to account for the amount of solar energy available.
This isn’t just a theory. They’ve tested community-sized prototypes in New Mexico for six months. The systems are made especially for desalinating brackish groundwater, which is accessible to more people than seawater. The goal is to bring potable water to areas where water supplies are challenging without requiring external power or batteries.
The process used is known as “flexible batch electrodialysis” and differs from the more common reverse osmosis method. Reverse osmosis, however, requires a steady power source as it uses pressure to pump water through a membrane. Electrodialysis is amenable to power fluctuations, and a model-based controller determines the optimal settings for the amount of energy available.
There are other ways to use the sun to remove salt from water. MIT has dabbled in that process, too, at a variety of different scales.
desalinate during the day enough water to last during the night.
I’ll take “Tell us that you haven’t read the article, without telling us you haven’t read the article.” for 1000, Alex!
To save you a click and some precious time, this is from the first few paragraphs:
“As sunlight increases through the day, the system ramps up its desalting process and automatically adjusts to any sudden variation in sunlight, for example by dialing down in response to a passing cloud or revving up as the skies clear.
Because the system can quickly react to subtle changes in sunlight, it maximizes the utility of solar energy, producing large quantities of clean water despite variations in sunlight throughout the day.”
Who wants to read articles or watch videos? I absorb a gestalt directly from the etheric aura of the headline, which is the one true message and soul of any online post
It sounds kinda like MPPT but the load is a desaliniser not a battery. Neat!
Electrodialysis has the advantage of being throttleable like this. But, by incorporating no storage, and sizing the system to accommodate the peak power output available, you need to make your desalination plant 5 times bigger than your actual needs.
If you put in a bit of storage you could run a much smaller and cheaper desalinator for a much larger fraction of the time.
They are really just trading off cost of “expensive” storage for cost of the much bigger desalination plant.
Instead, you could pump the water up a hill or a water tower when you have power, store it in a tank, and let the pressure feed a conventional, appropriately-sized RO system 24×7. (If you don’t have a tall enough hill or tower, you could even use a hydraulic pressure intensifier and use the water itself as the energy storage.)
In 1969 the cost of a 1 million gallon per day plant was estimated between $798k and $1.05M of which $96-172k was attributed to stack cost, whereas a 10 million gallon per day plant was estimated between $3.65-5.4M with $887k-1.925m in stack cost. However the 1Mgpd plant occupied a space of 2 acres while the 10Mgpd plant only required 4 acres of land. with the stacks themselves only occupying a minor portion of each plant.
Given that any such plant would likely co-locate solar panels and facilities the difference in scale is negligible.
https://digital.library.unt.edu/ark:/67531/metadc11731/m2/1/high_res_d/Bulletin0470.pdf
The expense of buying maintaining and replacing batteries would likely exceed the cost of increased electrodialysis capacity. In addition, running a larger stack array at a reduced capacity should extend stack life proportionally, resulting in a lowered cost of operation and maintenance.
Building the plant to fit the solar power available would also allow, at an elevated expense, grid feeding for additional capacity when the plants capacity had been exceeded either by peak demand or by population growth.
The expense of a suitable high altitude water store and pumping, or the implementation of alternative means of pressurization would certainly be more capital and energy intensive as well.
Running a hydraulic intensifier means you need to upsize your feed storage anyway as you need a much larger water supply to increase the pressure of a much smaller flow.
And yeah, there’s lot’s of communities that could afford to build a large feed and storage area (its just a cement-lined pond at the cheap end that can be done with local labor) that couldn’t afford to purchase a generator/fuel or batteries and couldn’t afford the maintenance costs associated with ‘high-tech’ and RO.
There’s lots of communities where this is irrelevant, there’s lots where this is a better solution. A solar desal plant working brackish water can be pretty darn low maintenance, especially compared to RO systems.
I keep wondering, if they have ample space available in a desert region, why don’t they just make a field of trenches with black tarps on the bottom and plexiglass on top, then draw the humid air out as the water keeps evaporating. Condensing the humidity then gives you clean water – and a lot of heat that you can use to pre-heat the water going into the trenches.
A heat absorbing surface gives you about five times the energy input per area from the sun compared to a solar PV panel, and it’s cheaper to build.
A good survival technique is to simply wrap an appropriately-sized sapling or shrub in a plastic garbage bag or tarp. Do this correctly and in the mornings it will have quite a bit of condensation inside. You just have to strain out the bugs.
Only if they taste bad.
Its a tradeoff of costs. There’s a plant size where your idea is optimal, there’s a plantsize where this is optimal. I suspect this one is optimal at larger capacities than the evaporation-trench one. Land is cheap but its still going to get expensive if you need enough of it.
The process must be extremely efficient, because on the point of land use you’d use much more land on solar PV than direct solar thermal – unless the electricity actually comes from somewhere else and you pay a subsidized price for it.
That is, the case can be economical as well: if you produce and use your own solar electricity, then you get no rate subsidies from the state, but if someone else makes it and puts it on the grid, then the taxpayers pay first and then you pay whatever cost remains (may be negative cost).
Inevitably you make brine , so what do you with it ?
Saltwater batteries? Pickles? Foot spa?
Put it in an evap trench, let the water evaporate out, sell it as ‘Himalayan’ salt.
You could add the rust that is a byproduct of steel pickling process in steel plants to add to the salt. The iron is the only thing that make Himalayan salt “special”, giving it it’s pink color.
This. Since you can’t store it locally (else the concentration of salt wlll increase and make the system less an less efficient), you have to dry it and transport it to somewhere else (like… the sea ?) So in the end, you’ll have to pay for removing the salts twice.
Sprinkle the salt on glaciers near the sea. That way the salt will be mixed in before being introduced into the seawater.
B^)
Nothing:
https://en.wikipedia.org/wiki/Monte_Kali
Nothing is not an option
The Werra river has become salty (≥500 mg/L chloride at Gerstungen, and 65 mg/L chloride at Bad Salzungen (measurement of June 2003). The legal limit is at 2,500 mg/L chloride, which is saltier than parts of the Baltic Sea. The groundwater has become salty as well.[5] The invertebrate fauna was reduced from 60–100 species to 3.[6] K+S are licensed to keep dumping salt at the facility until 2030
Personally, I’ve always thought that a solar still made of rock and glass should be a viable way to make barren islands habitable. Build small rock levees to trap sediment and a solar still to supply fresh water. It would take centuries to work, but if there is fresh water and sediment to trap it, plants will grow.
For the goals stated in this article a solar still seems a rather lower cost option. Especially if you don’t seek system lifetimes of centuries. That allows plastic film instead of glass. The people who have the greatest need for this don’t have a lot of money. Designing technology that the primary user can afford is critical to success. Otherwise it’s just a solution in search of a problem.
In remote parts of Myanmar they drill oil wells using a tripod, pulley, rope and a section of steel pipe with the edge beveled. They pull the rope to raise the pipe, drop it and repeat until it’s full. They pull it up, knock out the mud and repeat until they reach the oil. They drop baggies of water down the hole to make the formation they are drilling through stick in the pipe. They drill 30-50 ft. Even “offshore” on bamboo platforms. The oil is distilled into kerosene using 55 gallon drum stills that are heated by burning the heavy fractions. Obviously, this is so remote that it’s more cost effective for the end user. The “pipeline” is young women with containers they carry from the well to the refinery. All this appeared in a front cover article in “The Oil and gas Journal”. I was blown away when I saw it and made a photocopy which I still have. There is nothing as compelling as hunger to make humans inventive. The wells decline quickly. So they just move over 50 ft and spud another well.
The same technology can be used to drill water wells. But you can’t get a government grant and public acclaim for it. So instead we get “solutions” that the intended beneficiaries can’t afford and will only get if someone gives it to them. I hope this is better than that, but I’m very skeptical. It looks too expensive to be of practical use to those who need it most.
Just build freaking rivers.
Why not use a windmill to pump the water up to a header tank, as you only need around 2 atmospheres for reverse osmosis? Which you can then run continually, and at nighttime too.
Pressure-retarded osmosis (PRO) or “blue energy” is an interesting counterpart to desalination – it generates electricity from the osmotic pressure difference between fresh and salt water using similar membrane technology. A semi-permeable membrane allows water to naturally flow from fresh to salty side, driving a turbine. The theoretical maximum power density is about 25 W/m² (at ~0.019 L/s/m² flow), though practical systems achieve less. While Norway’s Statkraft built a prototype plant in 2009, membrane fouling and cost remain challenges. Research continues at several institutions, focusing on new membrane materials and hybrid systems.