Solar Stills, often reccomended, never useful?

Well, I can only give you my own limited but recent experience. I can't say that solar stills *never* work. But at the beginning of July, in the Grand Staircase-Esacalante National Wilderness, I and an instructor from BOSS built the best damn solar still we could. We filled the pit with fresh wet willow boughs. After 24 hours there was no water in the cup. We poured a half bucket of water into the ground in the pit. The next day there was a quarter cup of water in the cup. That seems like a damn meager return, especially considering the amount of sweat we poured out digging the thing in the first place.

If I were short on water, I think I would invest my energy in looking for it rather than trying to make it.
 
Ditto Walks Slowly's experience. Some years ago, my brother and I set up a solar still in his yard in Hawai`i -- much nicer than anything we might be able to make in a survival-type situation. We could barely fill a saltshaker. Needless to say, we sweated away more water than we gained.

gmm
 
So what is the consensus here? Forget about solar stills?
Maybe Greg, Ron and Jeff (Randal) could shed light on this.....
Are you guys around?
Thanks in advance,

HM
 
I meant to write...Jeff (Randall)...
My apologies for the typo.

HM
 
I would think that one place they might work is where you have a large supply of salt water. A key for getting good production would be a large difference in daytime and night time temperature. Hot days to heat the pit and cold nights to cool your plastic sheet and get good condensation. This sounds like the desert or mountains. It is dry or thin air that gets you the thermal cycles, but that reduces the moisture you need for condensation.

Maybe with 100% relative humidity on an island with lots of salt water for your pit the method works. The advantage is that once you have built your pit you can use it for weeks.
 
Sorry everyone... I have been gone on a week long training. We had a very diverse group of students but all in all it was a great trip.

To answer your question about solar stills. I don't use them... I waste more fluids constructing them then I get in return... Instead, I use transpiration (preferred since the source is reusable provided you move the bag every 2 to 3 days) or vegetation bags. They are easy to construct and provide a decent amount of water if done properly.

Sorry for the delay in response... have been surviving
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Greg Davenport
Simply Survival's Wilderness Survival Forum
Simply Survival's Web Page
Are You Ready For The Challenge?
Are You Ready To Learn The Art Of Wilderness Survival?
 
I teach folks how to use 'em. After they learn, they know enough not to bother to make one. We sometimes show transpiration stills and those can work under the right conditions.

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Learn Life Extension at:

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I've experimented with these, in the desert area near Grants N.M. I set up three stills, as carefully as possible and managed to extract perhaps a cupful per day per still...not too impressive. Good thing it was a leasure/skills weekend, not a survival situation.
Could someone explain the vegetation bag concept?
 
MDP, Please e-mail me your address again, it has become lost in the cybernightmare called "My Computer" Thanks JJ
 
Desert plants are experts at conserving water and I imagine they lose very little water by transpiration. At any rate, most are C4 plants (they use a special type of photosynthesis) and only open their stomata at night so the bags would probably only be effective at night (of course, I'm guessing here, I have no real experience in this). One other problem I am imagining: if you try to use cacti, wouldn't the thorns poke holes in your bag and defeat your purpose?


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Hoodoo

And so, to all outdoor folks, the knife is the most important item of equipment.

Ellsworth Jaeger - Wildwood Wisdom
 
Originally posted by Greg Davenport:
Instead, I use transpiration (preferred since the source is reusable provided you move the bag every 2 to 3 days) or vegetation bags.
Click to expand...

Is that the method of placing vegetation in a bag and sealing it and waiting for the water to evaporate and collect?
 
Greg's book "Wilderness Survival" describes the transpiration technique. After reading it over for the second time, I'm a little confused at what exactly is occurring--evaporation or transpiration.

The general idea is to cover a plant or branch with a bag and have a low spot in the bag to collect water that comes from the plant.

Now the question is: how does the plant give up its water? It seems to me this is more a transpiration process than one of evaporation although evaporation plays a role.

Anyway, transpiration works something like this: plants take in CO2 from the environment and convert it to carbohydrate by photosynthesis. They get CO2 by diffusion of CO2 through pores in their leaves called stomata. These pores can be open or closed by guard cells that surround the stomata.

When plants open their stomata, CO2 moves in but also, water moves out, also by diffusion. The water is brought into the plant through the roots and moves upward through the stem and into the leaves by a process called transpiration. Upon exit, this water is in the form of water vapor so I guess evaporation is occurring here.

So if a plant wants to do photosynthesis,it has to open its stomata to get CO2 and in the process, it loses water to the environment. This obligatory water loss can be captured using plastic bags which are placed over the vegetation.

I'm guessing that this process would be most effective if you used a clear plastic bag which would allow sunlight to penetrate, enhancing photosynthesis and stomatal opening (but I could be wrong on this).

No doubt there is also some evaporation occuring across the surface of the plant. No plant surface is 100% waterproof but plants have a waxy cuticle which makes them nearly waterproof. However, I'm sure some water loss occurs across the surfaces of the leaves by evaporation but I think it would be tiny compared to water loss through the stomata.


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Hoodoo

And so, to all outdoor folks, the knife is the most important item of equipment.

Ellsworth Jaeger - Wildwood Wisdom
 
I'm not sure we should abandon the idea of a solar still as an option just yet.

I first read about solar stills in Colin Fletcher's book The Complete Walker II. Anyway, there is a fairly detailed discussion of the solar still in The Complete Walker III, including pros and cons and reasons why it might or might not work. Here is a quote: "An Air Force medical colonel has called this still "the most significant breakthrough in survival technique since World War II"--and the colonel headed a team that experimented with the still for twenty-five days in the Arizona desert. Judging by the team's findings, which essentially confirmed those of the original researchers, there seems no reason why this still should not save your life, or mine, if either of us ever gets into water trouble while backpacking in the desert--provided we have a clear understanding of what to do."

He also lists a bibliography that includes an article published in Science, 149, Sept. 17, 1965, pp. 1377-9.

Here is another quote (classic Colin Fletcher): "I am ashamed to say that I have yet to follow my own sage advice and give the rig a trial run. But the idea still sounds to me like a practical proposition. A reader had her Sunday School class of five- to nine-year-olds build a still, guided only by instructions in the earlier edition of this book, reports that the children constructed one, "completely on their own, in 1 hour 15 minutes....And when the first drops of water began to collect and run down into the bucket, they jumped up and down yelling, 'It works! It works! WE DID IT!"

He also points out that the still can be used to purify water. This could be very useful in desert survival as often desert wadios are brackish and unfit for human consumption.

Evidently there are many critical components to building a successful solar still. It kinda reminds me of building a firepiston. I know they work because I have 4 videos on my harddrive showing them in operation but I haven't been able to get mine to work...yet.
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Hoodoo

And so, to all outdoor folks, the knife is the most important item of equipment.

Ellsworth Jaeger - Wildwood Wisdom

[This message has been edited by Hoodoo (edited 08-01-2000).]
 
Tranpiration bags - a clear bag is placed over non-poisonous vegetation that has sun exposure throughout the day. Using a small rock a low area is created for the moisture to pool. If you have sugical tubing (a long piece) tie a small loss knot on one end and place it next to the rock; the other end should run out of the bag so that you can drink the moisture off. Be sure to seal the bag completely and to drink off the moisture before dusk. Move the bag every 2 to 3 days in order to reuse the original spot (needs several days to rejuvinate). I am not a horticulterist but my understanding is the moisture is created through condensation and evaperation, etc.

Vegetation bag - downfall is you have to kill the vegetation. Non-poisonous vegetation is placed inside a clear bag which is place in an area with direct sun exposure. Use a rock and a small indent in the ground to create a low area for the moisture to pool. If you have surgical tubing use as above. The vegetation will die off in several days.

Solar stills - will produce... but one oversight here is... they need to be moved every couple of days. Thus its greatest downfall.... yes there are many factors that come into play as far as the amount of moisture you collect. I have used this method many many times... and it never produces as much as the other two mentioned above. Option yes.... good option... not really.

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Greg Davenport
Simply Survival's Wilderness Survival Forum
Simply Survival's Web Page
Are You Ready For The Challenge?
Are You Ready To Learn The Art Of Wilderness Survival?
 
I guess there are really two different questions here -- do solar stills work at all? and, if they work, are they worth building in a low-water survival situation? The second question involves issues of water loss from the effort of construction, the amount of return on that investment, the time spent waiting around for the return on that investment, and lost opportunity costs -- that is, what you could be doing *instead* of building a solar still and waiting around for it to work.

Thinking about it this way, it seems to me that a solar still is a poor investment. I can't comment on transpiration bags; but I guess my preference right now would be to spend my time and energy looking for water -- for example, trying to gain some elevation and looking for lines of green plants, or looking for damp sand under rock overhangs, or looking for basalt rocks where rainwater might have pooled. But I can certainly be persuaded that this view is inorrect.
 
Perhaps we should treat solar stills like traps and snares? If I set one trap or snare, I'll probibly go hungry, but if I set ten or twenty, I might end up a fat rat!
Since solar stills seem to distill the water from the ground, is it safe to urinate in the still and "recycle" the water?
 
Originally posted by bill clancy:
Since solar stills seem to distill the water from the ground, is it safe to urinate in the still and "recycle" the water?
Click to expand...

That's the claim. And supposedly you can cut up vegetation, etc and put in there too, using it like a vegetation bag.

I guess one of the problems is that the texture of the plastic is important because the condensate could drop off before it reaches the cup. Also, the cup itself is supposed to be important. Supposedly metal cups are a no no because the water will vaporize out of them. I think plastic containers are supposed to be better.

Guess I'm going to have try this myself, just for the fun of it. All in all, it seems like transpiration and vegetation bags are a heck of a lot easier to implement and make work. Still, I wonder about C4 desert plants. These plants only do photosynthesis at night. Therefore, it seems you would only want to bag these plants at night since they close their stomata during the day.

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Hoodoo

And so, to all outdoor folks, the knife is the most important item of equipment.

Ellsworth Jaeger - Wildwood Wisdom

[This message has been edited by Hoodoo (edited 08-02-2000).]
 
We were taught solar still. A US Park Ranger tried it in Big Bend National Park with dismal results. I`d forget it.
 
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