Solar magnification/concentration for H2O distillation

Aloha permies! My 1st visit and 1st post.

Any simple success out there with boiling water via concentration of the suns rays?

We have tried but failed and never went back to revise our attempts.

In fact, it was a science project for my sons 5th grade science fair project last year.
Using the lens out of a rear projection TV as Grant Thompson does in this video..

I think the failure had to do more so with our patience and lack of planning than anything else. Clearly we heated the water, could see the condensation on the inside of the gallon pickle jar we used, and given the debris we added to the water we could see the convection currents within the liquid.. (I think our max Temp was ~197F) Given more time I'm sure we would have eventually reached a rolling boil but clouds set in and my son lost interest after the first day.

Also, we used a glass jar, on a pizza stone.. Both materials transfer heat really well so i'm thinking the pizza stone actually acted as a heat sink given the narrowly focused beam of sunlight it never warmed up enough to actually HOLD the heat. (Large Surface area, small focused beam) Even when I used an unfocused beam the pizza stone didn't heat up as much as I would have expected it to.

Thinking back we could have had better results from our cast iron Dutch Oven. (Being Opaque, Black, and Cast Iron)

If you could avoid using heat sinks as containers/platforms I think it's totally practical in a pinch..

There was also a kid (I know others have too, he just stuck in my mind) that made a solar reflector out of an old satellite TV dish by gluing a bunch of mirrors to it..


PLEASE DO be careful.. The sun is NO JOKE If you forget what you're dealing with in a split second you're either on fire or you've melted your arm off.. or worse someone else's!
Also, wear eye protection (welding goggles) ! Leather gloves and long sleeves aren't a bad idea either but neither will save you from contact with focused sunlight.

Edited to remove emoticons..

Max Treeboat :Top right of this page below the Permies Banner, and above the Permies Video of the week, is the Permies Toolbox! On the upper left of the Toolbox is the
[Search] Tab. Going there from this forum thread automaticly sets you up for primary results from the Solar Forum threads, or you can select the All Forums function
then just type in a word praise in the 'Search Field' !

Another good topic to search under is Fresnel lenses, this can be salvage from large screen TVs,the quality of the lens, and how tightly the light field can be focused down
to varies from model to model, and seemingly from TV to TV !

Good luck , Good hunting ! Big AL

Max : Your personal search may have found this link, but it came to hand while searching for something else !

after your water reaches, and can be held at 150ºF, Only a small amount of additional UV exposure is necessary !

The Link:


https://permies.com/t/873/energy/uv-light-water-treatment

For the Good of the Crafts Big AL

James A. : I believe you were right about your personal Experiment and Loosing the heat as fast as you were able to make it! I am a little perplexed by the fact when

you added dirt you were able to see convection currents though! i've made a link related to making a solar shower work at its best ! Big AL

Link:

https://permies.com/t/41153/solar/Quick-passive-solar-water-heater

Hope this is useful ! Big AL

To clarify by "seeing" the convection currents we could see the particulates riding them. They would rise to the top in the middle where the water was warmer, transfer to the outside of the jar where the heat would dissipate through the jar and sink back too the bottom.

I also attempted to make a small batch of bio char like this but the jar would fill with smoke and the glass covered with resin.. Eventually it heated up so much on one side it shattered. It would be awesome to make bio char without burning sacrificial wood for fuel.

allen lumley wrote:after your water reaches, and can be held at 150ºF, Only a small amount of additional UV exposure is necessary !

That's good for killing pathogens, but distillation will remove (or rather, leave behind in the dirty water container) other contaminants that can't be filtered easily.

James and Joe : I had previously 'set on' this article from National Public radio because I did not think it came up to their usual high standards of accuracy !

I mention what I believe is a transcribing error that snuck into the reporters story, The important thing is that this was a working model and we should hear
more about this !


https://permies.com/t/39343/energy/Solar-water-desalination-breakthrough

For the Good of the Crafts ! Big AL

allen lumley wrote:I mention what I believe is a transcribing error that snuck into the reporters story, The important thing is that this was a working model and we should hear
more about this !

https://permies.com/t/39343/energy/Solar-water-desalination-breakthrough

While I'd have to drive about 4 hours to anywhere desalination would be an issue, simple solar stills are pretty much the best way to purify small amounts of drinking water in an emergency. (Or extract it from otherwise unusable sources like inedible plants.) Once it's set up, you just walk away and deal with other matters until it fills up, rather than having to feed a fire or other heat source, and there's not a consumed sterilant like iodine or chlorine. The small yield is mainly a function of the collector area; more small stills or a few big ones will produce plenty of water to keep you going. There are a couple of the clear 9x12' plastic drop cloths in my emergency kit for just that reason; I also keep black trash bags in there for the solar collecting surface and Shoe Goo (among other obvious reasons) to seal the two together. Around here, there's non-potable groundwater at about 25-35 feet; the good stuff is at 400+, so no way to get it with a field expedient pump. (Given the layer of rock between the water tables, it's not easy to get to without a lot of equipment.)

Dear Permies,

Many Thanks, for all of your responses.

So far; the answer to the original question, appears to be no.

I do urge you all to keep at it. Because; as of now, the Sun is still our friend.

Yesterday the "Third World" wanted our fresh water and always will.

Today; demand from "The Second World", outstrips a supply that doesn't exist.

Tomorrow; when the "First World" comes knocking and willing to pay ANY PRICE for a thimble full?

IS IT TRUE; that we can't even figure out how to inexpensively, boil water using Solar Radiation/The Sun? And make it portable by a tribe if not a man?

Happy Trails,
Max Treeboat

The fundamental problem here is the huge amount of energy needed to evaporate water, not simply bring it to the boil. Some rough calculations...

It takes 2.3MJ to evaporate 1kg of water.
Solar flux is approximately 1000W in good conditions (perfect alignment, clear sky's etc...).
1 square meter of collector would take over 6 hours to evaporate 1kg of water in perfect conditions.

Assuming you can get 50% efficiency of your collector (unlikely) and that you can get a consistent 3 hours of good conditions per day (depends on environment obviously), you would need 4 square meters of collector to produce 1kg of distilled water. For a typical family wanting only drinking water you might aim for around 10kg of water.... 40 square meters of collector. This puts solar distillation squarely outside cost effective/practical approaches.

An alternative solar approach:

Clarify the water to remove turbidity... Settling tanks etc... Filter through a biological sand system... Use solar to raise the temperature to kill remaining pathogens. It won't remove toxins like heavy metals/arsenic but should handle most everything else.

Solar distillation is relatively easy, but not with a Fresnel lens.

A google search will get you a ton of resources to get this done. Here's one:

http://www.offthegridnews.com/2013/09/16/how-to-build-a-solar-powered-still-to-purify-drinking-water/




My son and I built a "Giant Solar Death Ray" from a dead projection screen tv. While the giant fresnel lens was fun and awesome for melting things, it would be a poor tool for evaporation/distillation. There are a number of reasons why this is so, but I will mention three:

1. Because of the small size of the focal point, a Fresnel lens requires constant attention so it can track the sun to keep the focal point on whatever it is you're trying to heat.

2. To evaporate water in a solar still, you want temperatures that are in the neighborhood of boiling. A giant solar death ray produces very high temperatures (we measured in excess of 2,000F on some samples) in a tiny spot. Because of the very high localized temperatures, this causes very high losses to the adjoining material because of the delta or difference.

Stated differently, you will have much lower heat loss if you try to heat the whole gallon of water to 185F with diffuse solar, than you will trying to heat one tiny spot of water to 500F with the giant solar death ray.

3. There are only so many BTU's or joules coming into an area of one square meter, about 3,400 BTU's. Just because the Fresnel lens concentrates those 3,400 BTUs into one tiny spot doesn't make more BTU's. A one square meter piece of cheap plastic or glass can collect and trap those same 3,400 BTU's in a diffuse way. If you want faster distillation and more pure water output per hour, you need more surface area, not more concentration.

Finest regards,

troy

Michael Cox wrote:Assuming you can get 50% efficiency of your collector (unlikely) and that you can get a consistent 3 hours of good conditions per day (depends on environment obviously), you would need 4 square meters of collector to produce 1kg of distilled water. For a typical family wanting only drinking water you might aim for around 10kg of water.... 40 square meters of collector. This puts solar distillation squarely outside cost effective/practical approaches.

There's a fairly common item that just happens to be almost the same thing as a solar still with hundreds of meters of collector area, though; a cheap greenhouse. Not as dramatic as a concentrating approach, but maybe we should be looking into what it would take to modify the standard hoop house into a giant solar still for unindustrialized areas.

With a distillation still you need to prevent vapour leaks (both cold external air into the system and your humid moisture rich air from getting out and being lost). Vapour leaks make it harder to reclaim the moisture from the "cold" side of your system where you want it to re-condense. I can't see an obvious way to achieve that with a cheap hoop house system - remember that in most environments these end up being irrigated because they lose moisture to the atmosphere so quickly.

I also fail to see the benefit of a full on distillation system which requires at an absolute minimum 10 times the collector area of a heat sterilisation approach.

I remember reading about a system for use in hot countries where plastic bottles were painted black and left in the sun. After 30 minutes above a specific temperature they were sterile. To tell whether your water had been heated sufficiently they had a wax that melted above a specific temperature and dropped a pellet into the bottle in a little plastic case of it's own. Infinitely reusable, cost about 10p per litre bottle to make. No need for fancy collectors.

Note that for a solar still to work, the water doesn't have to boil, it just has to evaporate.

Heating the water to any degree causes the evaporation process to happen faster.

Note that boiling, Pasteurizing, sterilizing and distilling are all different things, used for different purposes. eg, boiling kills virtually all microorganisms, but won't remove arsenic. Distilling removes arsenic, but won't necessarily kill all microorganisms unless combined with boiling and good still design. Distilling won't remove some volatile contaminants, like benzene or gasoline, that usually takes carbon filtration.



There are some very inexpensive designs that use plastic film, so cost doesn't have to be a show stopper except for the very poorest folks.

Troy Rhodes wrote:Distilling removes arsenic, but won't necessarily kill all microorganisms

Assuming no direct cross-contamination, (dirty water coming into direct contact with clean) how would the microorganism get from the dirty water to the clean?

Of course, solar distillation with a cover that doesn't significantly block UV should also UV sterilize the dirty water to some extent.

Distilling won't remove some volatile contaminants, like benzene or gasoline, that usually takes carbon filtration.

Given that gasoline (and other oils) and water aren't easily miscible, and assuming no other contaminant that helps with the mixing process, how much of any common fuel oil wouldn't be removed by settling and skimming?

"Assuming no direct cross-contamination, (dirty water coming into direct contact with clean) "

That's trickier than it sounds. Not really difficult, but I was just pointing out that distillation won't necessarily achieve reliable killing temperatures, and some glazing removes enough UV that that might not get it done either.

Distilling won't remove some volatile contaminants, like benzene or gasoline, that usually takes carbon filtration.

Given that gasoline (and other oils) and water aren't easily miscible, and assuming no other contaminant that helps with the mixing process, how much of any common fuel oil wouldn't be removed by settling and skimming?



In bulk amounts, your method will work to remove the majority of the oily contaminant. But in ppm amounts, which can have health ramifications, the volatile contaminants won't necessarily rise to the top due to brownian motion/mixing. Mostly I was pointing out that distillation doesn't fix everything.

Troy Rhodes wrote:"Assuming no direct cross-contamination, (dirty water coming into direct contact with clean) "

That's trickier than it sounds. Not really difficult, but I was just pointing out that distillation won't necessarily achieve reliable killing temperatures, and some glazing removes enough UV that that might not get it done either.

They're both exposed at the top, but it doesn't seem like sufficient separation would be much of a challenge at all; if we're talking about a 30' wide hoop house, a 1' channel at each edge for clean and a 24' wide shallow channel (maximizing surface area relative to volume to maximize evaporation) down the middle for dirty could be separated by a 2' dry zone on each side, and the clean channels raised a foot or two (or dirty channel lowered) to guarantee any leakage can only go clean-to-dirty.

Given that gasoline (and other oils) and water aren't easily miscible, and assuming no other contaminant that helps with the mixing process, how much of any common fuel oil wouldn't be removed by settling and skimming?

In bulk amounts, your method will work to remove the majority of the oily contaminant. But in ppm amounts, which can have health ramifications, the volatile contaminants won't necessarily rise to the top due to brownian motion/mixing.

Health ramifications long-term, or is this level also a serious concern for sub-week survival type usage? What about using the water long-term in a non-drinking manner? (Washing, dishwashing, etc., while treating smaller quantities for drinking?)

What happens if we go beyond simple "uncontrolled" distillation for the drinking water? (i.e. would it be possible/practical to build a simplified fractional distillation system specifically to remove a single contaminant with a relatively low evaporation point, after the large scale solar still?)

Of course, I'm assuming our theoretical artificial contamination here is a one-time or other correctable event, and the contaminant is known and reasonably pure. (i.e. refined gasoline or diesel spill rather than the Orkin truck crashing into the river upstream with a full loadout of gasoline, engine oil, brake fluid, antifreeze, Orthene, Deltamethrin and others.) Thus the "can we drink it for a week until we clear the source and the rest washes downstream?" question.

I'm pretty sure that hydrocarbon pollutants are broken down fairly well in biological sand filter systems... Rings a bell from some technical paper I saw a few years ago.

Pretty much the only dirty water source that needs a distillation approach is one with heavy metal or salt contaminants. Seems like a perverse design criteria to use solar when other systems are more reliable (they work 24/7 and don't depend on weather), cheaper (sand and a couple of old oil drums) and scale up more easily ( need to double your capacity? Get a second drum in parallel vrs adding an acre of poly tunnel.)

There are a few misconceptions in this thread about energy.

1. The energy needed to bring water to the boil is only a small fraction of that needed to make that volume evaporate - think a ten fold difference
2. The energy needed to evaporate the water is the same regardless of temperature - it takes longer at lower temperatures but the same total energy is needed, you can't get around it by saying it doesn't need to boil

"1. The energy needed to bring water to the boil is only a small fraction of that needed to make that volume evaporate - think a ten fold difference
2. The energy needed to evaporate the water is the same regardless of temperature - it takes longer at lower temperatures but the same total energy is needed, you can't get around it by saying it doesn't need to boil "


All true.

Michael Cox wrote:I'm pretty sure that hydrocarbon pollutants are broken down fairly well in biological sand filter systems... Rings a bell from some technical paper I saw a few years ago.

A well and a recharge zone is really just a gigantic natural slow sand filter, and the 300+ foot wells around here are pretty darn clean, so I'd say it works well when the filter is big enough. The trick would be figuring out how big is big enough.

Pretty much the only dirty water source that needs a distillation approach is one with heavy metal or salt contaminants. Seems like a perverse design criteria to use solar when other systems are more reliable (they work 24/7 and don't depend on weather), cheaper (sand and a couple of old oil drums) and scale up more easily ( need to double your capacity? Get a second drum in parallel vrs adding an acre of poly tunnel.)

The tricky bit with filters, particularly sand filters, is that eventually most contaminants will make their way through. Without a field expedient test, it's going to be hard to know when your filter needs to be cleaned or rebuilt.

2. The energy needed to evaporate the water is the same regardless of temperature - it takes longer at lower temperatures but the same total energy is needed, you can't get around it by saying it doesn't need to boil

I think the disconnect here may be people confusing pasteurization (longer time at considerably lower temp) with boiling. Of course, boiling is preferred in the field because it is immediately obvious that water is boiling and it stirs itself pretty effectively, whereas even with a thermometer, one could be reading a hot spot in a large, still container and not fully pasteurizing all the water. Large volume pasteurization is best used in a system where you have a heat exchanger or similar that takes a while for the water to get through, and has the ability to hold it over the safe temperature during that transit. Bit more complex than a solar still or a bucket of sand/charcoal.