Solar Still [Archive] - Glock Talk

PDA

View Full Version : Solar Still


Bolster
07-25-2011, 12:28
Hi, I'm new here, but thought someone might be interested in my build of a portable Solar Still. I live in Los Angeles, near the coast. Our fresh water supply is "iffy" at best, requires the goodwill of Northern California to send it here, and requires the grid to be up, for pumping. It's one of the more severe vulnerabilities to living in LA if something goes wrong (there are many others, too). However we do have an endless supply of sea water! So I'm now on my third revision of a small solar still. Here's the progress to date.

Goals are: (1) portable (2) easily stored and/or used as its primary components, a storage tub, a cookie sheet (3) food-grade throughout. I'm purposely compromising on size (many stills are 1 square meter in size, this is only .12m in size) realizing I'd need multiples if I were to depend on desalination as a source of drinking water. At least I can work out some of the design issues in miniature if the need arises to build a larger unit.

http://members.cox.net/kspot/interest/solarstill11.jpg

In preparation, I read about a dozen academic articles on solar stills; this one combines an Iranian design with a Jordanian design. It gets the water tray (a teflon coated cookie sheet) up high where it will be directly in the sun (tho would work best if rotated throughout the day), and it lets the distillate fall into the bin below (a busser's tray, available at Sam's Club and the like). It required a wire-frame tray holder that was surprisingly challenging to fabricate, due to a necessary tradeoff of angles. The angles of the wire frame tray holder had to be complimented by the angles of the wooden tub holders. All of this would have been much easier if the tub had 90 degree angles on it, which it doesn't.

So in the photos you see (1) the angled tub holders (which should rest on a piece of plywood rather than directly on the lawn, so it can easily be turned to the sun about 3x per day). (2) the tub in place. You can't see the reflective mylar on the back inside due to the shadows in this shot, but it should help concentrate sunlight. (3) wire-frame tray holder in place. This required several angles, one of which is to not allow the wire frame to actually touch the distillate. Another angle was required to allow the cover to fit. The wire frame is holding me up. I had wanted to try the still today but the paint on the wire frame has not fully dried from two days ago (stupid Rustoleum), so would impart fumes. Must wait another day, or however long it takes. (4) Tray in place. It's medium-dark grey standard cookie sheet, and I will probably add a black cloth to the bottom of it before pouring in the brackish sea water. In the center you see a bubble level, for getting it set up. (5) The glass cover with rubber gasket has been added. Not shown are the clamps used to hold the glass cover in place.

As mentioned, the still is small, .12 meter area, so expectations must be similarly scaled. Most research is done on 1-square meter stills. The tub-still idea is viable only if you'd put out multiples. However they would be easily storable (stacking design) and a failure on one would not bring down the entire still, as on a larger one.

Thanks for looking.

cyrsequipment
07-25-2011, 12:54
Very nice, thank you.

Kieller
07-26-2011, 11:25
You'll have to give us a report on how it did for you Bolster. I'm interested to see how the new design worked out.

Markasaurus
07-26-2011, 11:44
I live here too, have the same opinion on the shakiness of the state.
Anyway, it does have to be food grade but i have an idea, the heating surface should probably be black. If you were to bake on some gunkote gloss black (the pan would have to be without teflon coating) you'd improve the efficiency of the still. If you did it right i think there'd be no worry about the black finish leeching into the water - if it did, it would be visible.
Also you could point some cheap mirrors at the still, or even add them on, and make it even hotter and faster.

Bolster
07-26-2011, 11:58
Update...

Won't call this a dry run, let's call it a wet run. Stupid Rustoleum on the wire frame has had 4 days to dry and isn't very whiffy anymore, so I'm giving the new still a test with tap water. This is my third version of a still; previously I used plastic as the covering material. With the glass top: This sucker gets hot in a hurry (and heat is GOOD for a solar still). It was sheeting distillate in under an hour of morning sun, around 9am. Haven't seen that before!

Here it is under full steam at 10:30 am, with lots of distillate sheeting. NONE OF THE DISTILLATE DROPS BACK INTO THE TRAY! This was bedeviling me in previous designs and robbing me of efficiency. This one improvement by itself should increase efficiency dramatically, so I've learned that glass is vastly superior to plastic. (I read as much in the academic papers.) I think I could relax the angles on this design and still get 100% sheeting.

http://members.cox.net/kspot/interest/solarstill12.jpg

Here's a closeup of the tray (partially obscured by the glass cover). Notice how there are bubbles all across it. It's hot in there! (Would be even hotter if I could have found a black tray and a black tub...D'oh!) I spec'd 1/4" glass (thick) to keep the heat in as much as I could. Wish I had put a thermometer in there to monitor temp. Most efficient time for a still is 12-2pm, so there's lots more to go.

http://members.cox.net/kspot/interest/solarstill13.jpg

My previous attempts in this size tub (abt 14 x 20), using the more traditional method of a plastic top weighted by a stone over a cup, netted me 1 oz (for version 1) and 2 oz (for version 2). I have hopes of at least doubling production with this version 3.

PS: Hey Kieller, didn't know you hung your hat over here too! I just found the place.

Marka: Black is a very good idea. For some reason I couldn't find black pans when I was at Target, just grey. But I know they exist and they'd be superior. Putting a black cloth in the bottom would mostly accomplish the same thing. FYI the back inside of this tub has a layer of reflective mylar, which really helps in the morning. Not so much noontime as the reflections aren't there.

quinnt
07-26-2011, 12:19
Seems to work well. I was more thinking of an alcohol still when I read the thread title though:whistling:

Bolster
07-26-2011, 12:21
Seems to work well. I was more thinking of an alcohol still when I read the thread title though:whistling:

That's next!!! But first I need clean water to rinse out the shot glasses...

:drunk:

Big Bird
07-26-2011, 17:15
The concept of a solar still requires a supply of humidity. If you dig a hole big enough and put a piece of plastic weighted down in the middle so it drips into some cotainer in the bottom of the hole you will do better. The humidity is drawn out of the surrounding earth and condenses more readily because of the temp differential between the cool ground and the greenhouse effect of the still. It depends on where you do this and the moisture content of the air but I've set up solar stills teaching wilderness survival and have gotten more than a quart in a day...

docmark777
07-26-2011, 18:33
So, how much water did you get?

Bolster
07-26-2011, 22:56
I'm pleased to report that today's intake was 24 oz ... that's 3 cups. That's a big improvement over my previous best of 2 oz with plastic sheeting in the same tub. So two of these small stills would just keep you alive, provided the sun cooperated, the temperature was moderate, and your activity was not vigorous. Three would be better.

There are some improvements to be made, and I'd like to make three stills total. They'd pack into a small space. I'll probably make them the same general design but I'd like to source black tubs and pans for the next version. The still gets surprisingly hot in use. I think I see some warpage on the side of the tub that wasn't there earlier. It is uncomfortable to press your hand against the back of the tub for 10 seconds...that's how hot it gets!

http://members.cox.net/kspot/interest/solarstill14.jpg

I'll try this on ocean water next.

You guys didn't get to see my earlier trials, but they were of the commonly seen type in survival books, consisting of a sheet of plastic over a "hole" (the hole being my bin, in this case), weighted with a rock in the center. I filled the basin with brackish water (that would be the necessary moisture) and set a cup to catch the distillate. That's when I got 1oz and 2oz for my efforts. In the real world, you'd want a hole much, much larger than my little basin.

My goal here was to see how efficient I could get a small still. The oft-recommended 4-ft-wide, 3-ft-deep solar still hole can under the best conditions make 4 cups of water. Here we are dealing with a 1-1/2-ft-wide, 1/2-ft-deep "hole" that made 3 cups. You can see how efficient it is! Run the numbers, it's almost 12x as efficient as the hole-type still. I mostly cribbed designs from the middle east, where they are very keen on solar stills. All designs recommend obtaining as much heat as possible. Nobody recommends keeping the brackish water (or other moisture) cool for better evaporative efficiency...just the opposite. Get your brackish water as hot as you can. Some designs pre-heat it before it hits the still.

One inefficiency I haven't dealt with, is that I did not drain out the distillate as it's made. It would be nice to have a hole in the bottom of the tub so the distillate ran out into a bottle, and didn't get re-evaporated, thus reducing efficiency. No need to re-evaporate anything! But I just haven't wanted to punch a hole in the tub.

What still would I like to own? This one...but mine cost $55, and could have cost a LOT less if I'd have cut my own glass (that was $30).

http://www.landfallnavigation.com/memss.html

NOTE: Friend who owns the linked sea survival still says there's no way to disassemble and clean. So as it became corroded with salt, its life would be over.

Syclone538
07-26-2011, 23:08
Very cool thread from a brand new member. Keep us updated.

Kieller
07-27-2011, 11:18
The concept of a solar still requires a supply of humidity. If you dig a hole big enough and put a piece of plastic weighted down in the middle so it drips into some cotainer in the bottom of the hole you will do better. The humidity is drawn out of the surrounding earth and condenses more readily because of the temp differential between the cool ground and the greenhouse effect of the still. It depends on where you do this and the moisture content of the air but I've set up solar stills teaching wilderness survival and have gotten more than a quart in a day...

Potentially, depending on a whole host of variables.

What Bolster is trying to create is a system that can easily be moved and re-used over and over again to provide a constant supply of water. Living right next to the ocean he has access to a lot of brachish water to fill the stills with.

The big problem with using in situ solar stills is that they dry out the surrounding soil quickly and require you to dig another hole. If Bolster used this technique his backyard would look like a muffin pan within a few short days! :rofl:

Oh and yes Bolster, I hang out over here but unfortunately most of the threads are advertisments anymore so I don't post much.

Nice job/writeup on the stills Bolster. Let us know if you make any of your further improvements and whether or not they improved efficiency. :supergrin:

Big Bird
07-27-2011, 19:48
Potentially, depending on a whole host of variables.

What Bolster is trying to create is a system that can easily be moved and re-used over and over again to provide a constant supply of water. Living right next to the ocean he has access to a lot of brachish water to fill the stills with.

The big problem with using in situ solar stills is that they dry out the surrounding soil quickly and require you to dig another hole. If Bolster used this technique his backyard would look like a muffin pan within a few short days! :rofl:

Oh and yes Bolster, I hang out over here but unfortunately most of the threads are advertisments anymore so I don't post much.

Nice job/writeup on the stills Bolster. Let us know if you make any of your further improvements and whether or not they improved efficiency. :supergrin:

Not really. You can pee in the hole. You can cut brush/vegetation and put it in the whole. You can take contaminated water from the sea/swamp/river/creek and prime the still. And I can make a helluva lot bigger still with a lightweight sheet of plastic and a piece of tubing/hose that will weigh next to nothing and pack away in little space.

I don't discount the concept of what he's doing. Just that it can be done on a larger scale with simpler materials and generate quarts of drinkable water (again, depending on where you are). To do this right you need to dig a hole about 4' across and maybe 2-3 feet deep. You'll need maybe 8-10 feet of some form of flexible tubing--garden hose, aquarium air tubing anything...as lomg as it long enough to reach the water container under the plastic. A sheet of plastic maybe 8 square feet. Some form of water container--clean 5 gallon bucket etc. That's it! It takes a lot of drying out to dry out a big hole...and as I said its very easy to prime the hole if you do. What could be easier to pack up and move?

Bolster
07-27-2011, 21:43
Different stills for different uses. I'd never haul my tub and glass still in my backpack. And I'd not dig a 4x3 crater in my lawn. Depending on the location, a 4x3 hole may not be possible (such as a Los Angeles apartment complex), or if it is, can be a major chore. I live in an area where the clay is so dense (almost rock-like) a 4x3 takes a half day to dig with a pick. I know this from planting trees on my property.

What I'm trying to make is a small, portable desalination device (including roof mountable or useable on a boat in calm water) that's efficient for its size and breaks down into useable components when it's not needed as a still. Both my own testing and comparison with various reports shows this still to be approximately 12x more efficient than a hole-in-the-ground by size comparison. Mind you, I didn't come up with all the ideas on my own. I read at least a dozen academic papers on stills before designing this one. My still is crude and toylike by the standards used in the middle east, where they rely on sophisticated distillation desal plants.

The hole-in-a-ground still is expedient, and life-saving, but inefficient compared to what you can fabricate with "advanced" materials such as glass and teflon-coated cookie sheets, rubber gaskets, etc. Plastic sheeting is just not an ideal material for an advanced still, although it's expedient. Neither is it efficient to place the moist material at the bottom of a large hole. Efficiency increases dramatically as you raise that moist material into the sunlight and get the whole still damned hot.

Yes, this still will obtain drinkable water from seawater, pee, poop, blood, roadkill, radiator water (not antifreeze, tho!) brackish water, and plants, just like the hole type will.

FYI, garden hoses are not considered food safe, but again, are expedient. Best to carry clear PVC hose if you're expecting to make a hole still.

I recognize the value of a hole still, but it's not the answer to the problem I'm trying to solve. I wanted something much smaller and more efficient that required no digging. I'm talking Mini Cooper, not Panel Van.

Syclone538
07-27-2011, 21:57
How long would it take 1 person to dig a 4' round hole 3' deep with a shovel?

Bolster
07-27-2011, 22:09
How long would it take 1 person to dig a 4' round hole 3' deep with a shovel?

Totally depends on the soil. On my property, you can't dig a 4x3 with a shovel at all. The shovel won't penetrate. With a pick, takes about 4 hours. I had to dig 4x4 holes to plant my trees, it was a chore. (I eventually purchased a Bosch demolition hammer with a spade bit!)

But in the sand by the ocean? Pretty quick.

If you're talking about a hole type solar still in the boonies, don't forget to pack your shovel...or your Bosch demolition hammer!

Kieller
08-02-2011, 10:52
Sounds like you have a much better AO to be using in ground stills Big Bird. Here is it 50% rock and 50% nasty clay. Tough to dig in and not very moist, especially now with this heat we have been having.

I could see how these in ground stills would be useful in more moisture rich environment with decent soil.