Well. In my vast experience 1 square meter of evaporator produces about 1 liter per day. On the other hand 1 square meter of solar panel makes 200 watts and you need 20 watts/liter/hour on the osmosis machine. So the panel is 10*200/20 = 100 times more "efficient", if the use of land area is the issue here (and if the sun shines 10 hours)
Yes, it is much more efficient. It takes a lot more energy to transition water from gas to liquid state (energy which is mostly wasted when the water vapor is converted back to liquid) than is needed just to work against osmotic pressure.
Unless the condensing coils transferred heat efficiently enough to boil the incoming water, that would barely make a dent in efficiency.
> [water's] enthalpy of vaporization, 40.65 kJ/mol, is more than five times the energy required to heat the same quantity of water from 0 °C to 100 °C (cp = 75.3 J/(K mol))
Efficient heat transfer just means using a big exchange surface versus a small material thickness and/or good heat conductivity of the material. But the problem you probably have in mind is that the vapor can't drive the boiling as for the vapor to transfer its energy it has to be condensed, at which point the question becomes why would the vapor condense and boil the water on the other side versus simply boil itself. The answer here should be a pump, so as to make the pressure on the condensation side higher than the pressure on the boiling side. The pump will need energy to maintain the cycle, but it will be (much) less than the energy needed to boil off water in the absence of the pump and condenser. The question becomes open again, I think, why would this be less efficient than reverse osmosis?
Sufficient pressure is actually exactly the problem, but it shouldn't be necessary to think about that. I'm just saying, intuitively, could you imagine pumping steam through condensing coils and the water around it boiling as a result? Like say you're boiling some water on the stove and steam is rising out of it. If you held a cup of water in that steam, how much steam would it take to boil that cup of water?
Keep in mind water vapor is lighter than dry air of the same temperature; it takes up about 2000x as much volume as the same mass of liquid water. The vast majority of the steam that goes into a practical condensing coil will come right out the other side, only a tiny amount of the steam that's in very close proximity to the surface of the coil will actually condense, which like, if you imagine steam going into a curly metal pipe immersed in water, I'd hope it's intuitive that tons of steam would make it out.
You'd need crazy long and thin pipes, crazy high pressure, and crazy pipe configurations so there's way more steam surface area than water being heated, in order to boil water with the equivalent amount of steam.
There's other tradeoffs here, of course. Both solar panels and reverse osmosis machines are expensive, they're like fancy machined semiconductors and ceramics and stuff, whereas an evaporator is some metal pipes and tanks and maybe some glass or mirrors, so depending on application they may be much more cost effective. But in terms of efficiency, there's no comparison.
This is really fantastic. I hope they can scale out to more villages in Mexico and around the world.
In such remote places, there are regular outbreaks of serious waterborne diseases like cholera and dysentary, hepatitis A is widespread, and amoebas, giardia, schistosoma, various parasitic worms, etc. are endemic.
The hard part is setting up the social/institutional structures to maintain the equipment. The technological problems per se are relatively straightforward at this point.
Rural peasants typically don’t have the technical knowledge, connections, or capital to set up their own water treatment facilities, and often communities are too remote and sparsely populated to be worth piping fresh water in from a long distance.
I particularly appreciated how the MIT engineers trained local residents to operate and maintain the system, and they set up enough payment structure for the plant to pay for its ongoing costs. If that can be sustained indefinitely without too much need for additional external help, then the project should hopefully keep people healthy for decades, on only a small up-front investment.
I'm genuinely interested to know if the altruistic/community driven ethos of these efforts ever last? Once the NGO leaves town and the local federalè or whoever notices a nice little income stream?
'At this price, the community reaps a profit of about 49,000 pesos, or $3,600, per year. The community has appointed a committee to manage the incoming funds, setting aside some money for maintenance and repair of the system, and investing the rest back into the community.'
Nothing of value has happened in last 30 years, since the introduction of low-powered osmosis with feedback loop. I recall hand-cranked devices came about 1985 and I also remember I bought 6 watts solar panel for 80 Australian dollars.
So this is not an important piece of news at all. Sorry.
I would like some more details on the deployment and maintenance costs of this system. Maintenance costs play a huge role in long-term sustainability and if the initial costs are too high, many people in need of clean water might not get the system in the first place.
'She adds that the residents in La Mancalona have taken ownership of the technology, having been trained to operate it on a day-to-day basis, from changing out ultraviolet lights and filters to testing the water quality and replacing batteries. They also have a list of local suppliers for replacement parts.'
There are abundant small-scale wind turbines available, but there are rarely opportunities for them to perform nearly as well per installation effort & cost, as large 1MW+ turbines mounted on massive towers. A town of 100 households who each set up wind turbines in their backyards are paying >10x what a town of 100 households who buy a share in a wind farm coop for the same amount of electricity are paying. Wind has gotten very cheap very quickly over the years since Altamont Pass was put in with 100kW turbines, and a lot of it is down to bigger turbines and towers.
Solar photovoltaic power, on the other hand, scales down fairly well. It doesn't deal with altitude-dependent winds. The economies of scale, while still considerable, are smaller because no matter the scale, all solar photovoltaic facilities involve parts that fit on a shipping pallet.
At this scale, two solar panels, so something like 1200 watt hours of energy per day I don't think you'll find a wind generator and tower to beat the price.
24 hour operation may not be requirement. Clean water stores just fine.
I was going to list a counter example of a place where wind would be a better idea, but all the cloudy places I can think of have rain, so they probably get water from that. It's a big world though, I'm sure lots of places have bad enough sun that the number of panels would make the cost tip in favor of wind.
> At this scale, two solar panels, so something like 1200 watt hours of energy per day I don't think you'll find a wind generator and tower to beat the price.
There are many small scale wind generators that produce more than enough energy to run watermakers on yachts, much more cheaply solar panels for the energy output.
This has been a solved problem for quite a few years.
I was also contemplating windshield wiper motor and solar panel. My tests showed I needed at least 30 watt panel, which was too cumbersome in a kayak. So my collapsible windmill equals 24*30 = 720 Watt hours of solar energy.
I had 10 liter can and I needed 3 liters/day, so I started the windmill only twice per week.
