Household Dry Food Cooking, Part 2

This is a guest post by Craig Bergland on how to build your own inexpensive solar cooker. His handle is renofreepress here at The Oil Drum.

Craig built his first two solar water heaters at age 18. Now 61, he is a lifelong conservationist whose passion is turning the waste of one process into the resource for another. He is currently saving plastics in hopes to be able to melt them to casting temperatures or for injection molding to replace parts for our toys. Craig hopes to reach our youth to encourage them to get involved in building simple solar devices, including showing them how to easily build a parabolic form. He is looking for help in designing tracking mechanisms for solar devices. Craig worked 35 years in the casino industry, including working on design teams for new equipment, and teaching electronics/slot repair. In 2006 Craig was the Green Party candidate for Nevada Governor. In 2008 he ran for the House of Representatives.

This is to expand on a campfire post I submitted on April 9, 2009, which was primordially inspired by Jason Bradford, so call this part 2. Having learned a lot in the last year, I want to share what has morphed into a pretty nice cooking kit. After Debbie Cook's recent post here about it being time to do Epic Shit, perhaps it's time to continue on with simple solar cooking.

Commercial box ovens run around $300, and homemade cardboard ones do not have a good life span due to weathering, etc. I call this device the square foot solar cooker, and you can make one for under $10 (for the complete kit) if you are willing to do a little scrounging.

For about $12, you can buy a set of six mirrors (you need 3) from your hardware store. These are a foot square, and are often used for tiling bathrooms, and some quirky folks' ceilings above the bed. Don't buy the beveled-edge set, they're twice as expensive.

You can fasten the mirrors together with duct tape, as shown below, and the unit can be either collapsible/portable, or permanent (with the addition of some silicon sealant around the inside corners).




It is a good idea to put a square of duct tape on the bottom (base) mirror, to keep it from hitting cement and breaking. Also, a run of scotch tape along the edges of the mirrors that touch together is a good idea to keep the mirrors from chipping when you fold them up. You could alternatively build reflectors out of cardboard and foil for nearly free, as they perform almost as well. For more on construction details please visit my post on the cooker.

The second component of the cooker is double jars. A large outer gallon jar covering a blackened inner quart sized cooking jar provides double jar insulation, and you can easily reach boiling temperatures. The inner jar should be a high-quality canning jar, painted black, with a stripe down one side for viewing the cooked foods, and to see if it needs more water. Again check the above link.

The outer jars can be purchased from a local bar (olive and cherry containers work well) or tip the barkeeper a dollar to save you a couple of them. They come in glass, #1PET plastic, or #5 PP plastic. Any of them will work well, but the PET types seem superior as they accept all wide mouth quart-sized canning jars, and heat up more rapidly than glass. Glass does last longer if you don't break it. However, I really like the Square Foot Cooker, as it is pretty impervious to weather, and with care will outlast all of us.

By adding a one-quart brown beer bottle, and drilling a one-inch hole in the outer-jar plastic lid, you can make a water purifier that will easily disinfect a quart of water in an afternoon. This one-inch hole, by the way, will allow you to insert a wine-bubbler into the outer jar lid, if and when you decide to make some homemade wine. I would recommend that you have your bartender save you about 4 or 5 of these gallon jars, so that you can simultaneously cook food, purify water, and be brewing a couple of batches of nice raisin sherry.


I will admit that this unit, with the addition of a foot of 3/8 'U' shaped copper tubing and a cork, will distill water. And I can say with good certain-certainty, that it will also distill alcohol, although it is illegal to do that without a permit, in some locales.


While I don't know for certain, let me suggest that a quart of home-made wine could theoretically yield 5 ounces of high octane alcohol fuel in an afternoon. And if I send off for a permit to make my own 'gasohol,' I’ll let you know the results. My 8-year old 100mpg scooter, in theory, could be adapted to run on pure alcohol.

For you math and physics folks, below is a chart of a recent test I did on the heat-capabilities of 2 kinds of outer jars, the plastic ones. It was conducted on April 6, 2010, on a mostly sunny day with an outside temperature of 44 degrees. The one-quart test jars were at 48 degrees.


As shown from left to right are the 5 test units. Measurements were made every 10 minutes, and here are the results in degrees Fahrenheit.


Here are my conclusions. The PET jar heats fastest (faster than glass, a later test...), although it seems any jar with the reflector will reach both disinfecting temperatures (arguably somewhere between 125 and 160 degrees), and each will reach the evaporating temperature to separate alcohol from water which is apparently somewhere around 185 degrees.

If one could intermittently run a small single cylinder engine (moped/scooter, 4 stroke?) on alcohol, then it should be possible to mate the driving wheel up to some kind of mechanical contrivances, for example, the old-timey system of belts and pulleys to run shop machines, sewing machines, etc. Or, one could in theory power a couple of car generators, or water pumps or big-ass fans or a combination of all of the above. I hope there will be some discussion of this here?

The next project is to be my first attempt at making homemade cheese. This requires temperatures of between 110 and 180 degrees, depending upon what kind of cheese you're making, and this cooker should be able to easily accomplish that. I would suspect that the very slow heating system here will provide superior cheese because of its gentleness, but that remains to be seen.

And finally, as stated somewhere else here, I have used this to pressure cook soybeans. That is an awesome feat, as soy is not done until it is very squishy.

One might even be able to use this as a 'waterless' canner…?

I've got a quart of rice we cooked on Earth Day, that still does not give off a nasty decomposition smell, although it's starting to turn just a bit ripe as I keep opening it to check. It was still sweet smelling a week ago.

I hope that some of you will build one or two of these, and let us all know what capabilities you find. It should be able to bake bread, cook meats, and do much low-volume semi-high heat functions.

Also, a last nice thing to know is that you can use this to cook your evening's rice etc., if in the morning you point the mirrors to about the 6:00 PM position where the sun will be then. When you get home from work, your food will be piping toasty hot, absolutely un-burnt, and waiting for you.

For the cost of 2 packs of mirrors ($25) you can build 4 cookers that will give you a gallon of cooked foods or whatever on a good sunny afternoon. This pretty much seriously rivals a domestic $300 solar oven. Admittedly, we only use about 3% of our energy for cooking food, but a BTU saved is a BTU earned in my opinion.

Now clotheslines, they're probably even more efficient, but we’ll save that for another day.

Thanks for your attention, and I eagerly look forward to replies and discussion.

Hi Craig. I have a few boxes of 12" x 12" mirrors in my "collection". Neat design. I may put one together tonight.

You are a tinker after my own heart. I built my PV trackers from old C band (10 -12 foot) sat dish mounts and am planning to build a concentrating solar water heater using an 8 foot dish and mount (and the mirrors mentioned above). I use trackers from this guy: Relatively inexpensive and they work great. I just hook them up to the old sat dish actuators (24vdc) add some power and they track great. I also found an old Zomeworks passive tracker on a junk pile that I use to pump our potable water with PV.

One of four PV trackers I've built from "one man's junk":

I'll let you know how my cooker turns out.

Hi Ghung, et al.

Craig's post went up prior to his being notified. I'm sure he'll be signing in as soon as he reads his email. Hope you'll check back.

Craig, you are the man! A Doer. I love reading stories from inquisitive minds working towards solutions, very refreshing. Been researching various solar cookers and am inspired by the simplicity of this. Going to make one tomorrow and I'll let you know how it goes (Dunedin, NZ, heading into winter). Nick

In my youth, I would wrap up hamburger meat, vegetables, and spices in several layers of foil. Then I would strategically place the package in the engine compartment of my Honda hatchback. I would drive my normal route and when I arrived I had a hot meal waiting for me under my hood. I do not know if I can recommend doing such things today, I am older now and there is a risk of fire.

Reminds me of when we used to put an opened C ration can on the generator manifold, back in the day. Works on slightly popped beanie weanie cans, too.

I'm looking forward to trying the corner cue mirror solar oven. I had a solar cooker long ago, made from a styrofoam cooler lined with aluminum foil, an old piece of window glass and a small cast iron kettle. This really low tech cooker actually worked OK by just setting it on my deck in Seattle. Of course Seattle has a lot of sketchy weather so some days it didn't work at all. And it shredded eventually.

Question: Did you try the clear jar without the interior brown bottle to see how hot it got?

Second: In one of the pictures, you appear to have spray-painted the jar black. Did you try heat tests with just a painted jar? (No inner bottle.)

My interest in part is that I recently transplanted a bunch of seedlings into compost that *wasn't* sterilized. Which meant that tons of weeds sprouted, time consuming to remove. Have been thinking there has to be a way to use solar energy to sterilize soil/compost, strictly for transplanting purposes.

Question one, no, haven't yet.
Question two, that picture (2nd from last was a mistaken post) this was an attempt to measure just how hot a single outer jar got, and/or to see if it would distill (probably not). I lost my notes on that one, but I think it got to about 130 degrees. But then a gallon at 130+ diluted with cold will make nice dishwashing water. Will try more measurements as it looks like we've finally got some good sun in the forcast.

I've finally come across a Fresnel lens out of 40 something inch TV, hat tip to greenish, I think. For some time know I've been kicking around the idea of a solar retort. I'm sure most here are aware of the temps one can achieve with one of these lenses.
I'm thinking of using a double container similar to this only larger, say 120 gal. sealed aquarium inside an 150 gal. water filled aquarium. The focal point of the lens would be focused on biomass inside the 120 gal. tank ( with an exit valve to capture boigass) Does anyone here want to help me parse this out?

I've got a 1 meter parabolic I pull out every so often. It DO get hot. It will discolor big spots on my nice dutch oven, and even put coloration on the pressure cooker. One time I forgot to reposition it and it burned up the plastic handle. It works great, but I think I will move the focus back farther away from the focal point to keep that intense heat from messing with my metal. Total heat gain should be the same but slower.
Been wanting to adjust the focus fine enough to heat up a nice old soldering copper I picked up at antique store.
What kind of temperatures do you want, and what to use it for? It may be that instead of water filled, air filled might give better performance, but I don't know much about physics....
Is your biogass to be from making charcoal, or from other organics like animal wastes?
Check out the site for some of carl's(?) work on biomass heaters. He built one (2X5) that gives out an extraordinary amount of btu's from one filling of grass clippings. He claims enough to heat his house AND make domestic hot water, and it needs recharging every few days as it almost completely decomposes

Good article. We need more ideas like this about how to transition to a low energy lifestyle. I too made a solar cooker and these are simple, effective, and transformative, if we only make the lifestyle shift.

I am very interested in finding some way to run our chainsaw and mower on alcohol. Does anyone think
that straight alcohol will
work without ruining the
engines? Should something
be mixed with the alcohol?

I despair when thinking of
cutting our winter supply
of wood by hand.

A little googling shows that 2 cycle chainsaws , where oil is mixed with the fuel in the tank, are best adapted for running on ethanol. 4 cycles, like the mower and cars will need some adapting.

Ethanol cannot be distilled above 90% by conventional methods, so you have 10% water to cause corrosion. Also, running straight ethanol makes engine starting difficult, but perhaps using a spray of starting fluid (mostly ether) in the carburetor or air cleaner, will get it going.

Ethanol has a higher octane rating than gasoline, meaning that it can be used at higher compression ratios than gasoline and will be more efficient; however, an engine modified to run straight ethanol at high compression cannot use gasoline.

There's a book out called "Alcohol can be a Gas", by David Blume, which is nearly some 600 pages. There is a section in there about 2 strokes, but I'll have to pull it out and look. (like I'll ever have time to finish it...) He says starting on P. 425, that they will work, tho' he uses synthetic oil, and is careful to use alcohol at around 190 proof. One problem he sees, is, "Lack of fouled plugs is often a problem when chainsawing..., since it deprives the woodsman of his best excuse for taking a break." LOL. He also claims it don't smoke much.
I think JE is probably correct.

Thanks JE, Paul and Reno! I found the book on Amazon and have ordered it. We do have a copper
still that we've never used; so I guess it's about time to pull it out and start practicing. :)

I haven't seen this book, and I have never tried to run alcohol in a small engine except once, just to see if it would run.That was an old four stroke Briggs and Stratton garden tiller engine.She fired right up but would not idle, and I had to keep the choke partially closed.We drank the rest of that bottle of John Diesel(190 proof from the ABC store).

I expect existing older carbureted engines will need to be modified to some extent to run on straight alcohol;this could involve resizing the "Jets"in the carburetor, or replacing it.

I do fix a lot of engines, and the carburetors and fuel lines of older engines do NOT give good service with gasohol.Obviously the alcohol causes early deterioration of hoses, gaskets,and especially diaphragms,not to mention corrosion of the metal body of the carburetor.

This problem has pretty much been taken care of in newer engines, the ones less than about five or six years old, and most of the ones built for the last ten years are ok in this respect..

I strongly suspect however that a typical small engine fuel systen designed to handle e10 will go belly up on e85 or e100 in a hurry.

If I ever have to run such an engine on straight alcohol, I will run it bone dry each time I use it, and refuel it only five minutes before I need it again.

By bone dry I mean turned turtle or siphoned and the tank emptied ; the choke set,and the primer bulb if so equipped, both used until the engine will not "hit a single lick" after repeated attempts to start it.

But I don't see any reason the manufacturers can't easily build these engines to give good service on straight alcohol; they will just have to use different materials that are impervious to alcohol in the fuel system.

I am interested in building an insulated, covered parabolic cooker that will be mounted on a post permanently but so arranged that I can easily and quickly aim it toward the sun by hand.

I gather that aluminum foil will work fine for the reflector, and I have everything on hand except for the materials for the cover.

What materials are best suited to making the transparent cover?I doubt if I could cut safety glass but have never tried to do so.

How big will the cooker need to be to bring a gallon size black iron pot full of water to a boil in an hour in full sun on a clear day?

It is way too easy to justify not bothering with a solar cooker when you are busy to save only the amount of juice needed to cook a quart of soup or rice on the electric stove.Of course a time may comw when I don't have the dime, or the juice may be rationed as it is already in some parts of the world.

Being able to do a gallon, or even two or three gallons, opens up all sorts of interesting possibilities on hot summer days when the gardens are at full production and freezing and canning are underway..Not only would I save the electricity, but the kitchen would be cool enough to do the prep work comfortably with the stove off.

The electric dryer is a real juice sucker, but again the convenience argument holds-save a kilowatt hour, or maybe two or three kilowatt hours, still less than fifty cents, or spend ten or fifteen minutes minimum more time per load line drying the laundry?Only one young woman in this immediate nieghborhood will even babysit for six dollars an hour cash ,and that includes free snacks, movies, and bringing along her own toddler, so she is basically already babysitting anyway.

So I intend to build a labor efficient clothes line.

It will consist of a single post which will easily rotate, like a lazy susan,with the lines mounted on an inverted or point down conical framework.The bottom line will be only about three feet or so from the ground,and the next one maybe a foot higher and and somewhat longer, with each line being higher and longer until the last one is about six feet off the ground at the large end of the inverted cone.

A small work table,about two feet by three, made of metal or pressure treated lumber, and also mounted on a single post,will be located close by. .The single post is important, as it enables you to work around the table with a lawn mower quickly.

This arrangement will enable me to hang a load of wet laundry and take down a load of dry laundry without bending over or moving out of my tracks.

No iron work clothes will go directly onto hangers or be folded as they go into the basket.

This is not an original design;I saw it someplace on the web, but my old computer died, and all my bookmarks died with it.

Such a line will allow me to stand in one spot and hang the laundry or take it down;I can even fold our no iron stuff directly into an empty basket.

If anybody here has one of these already, I would like to hear about thier results.

A gallon to boil in an hour. Piece of cake. Get some #8 stainless steel AKA mirror stainless. It is rather pricy @~$5 sq/ft but 22 gage is easy enough to bend into a parabolic. Be carefull because it will get to be a bit warm. Just after Craig showed me his mirror setup, I built a larger 32 X 24 parabolic and used jars that Craige gave me. It is more powerfull. I keep it off sun a bit so it doesn't burn the food. I will get a black gallon pot with black lid and see how long it will take to boil water. At our altitude water boils at 205F.

There are lots of solar projects on the web. Here is one.


There are a number of solar cooker designs that will fit your needs;

For an unattended parabolic, there are placement techniques;

and there are ones that can easily be moved infrequently;

and there are ones that track the sun;

For enclosures, here's one example;

One could easily build their own polycarbonate enclosure using techniques similar to what the main article above shows.

We have a retractable clothesline, can't help you there.

Hi Mac, I'd like to see a picture when you finish your rotating clothesline. Sounds like an interesting 'spin' on the rotary clotheslines that have all the clothesline in a single plane. Your idea might allow three arms instead of four.

It is handy to be able to stand in one place while hanging the laundry. The indoor clothes drying rack that I make is round and rotates for just that purpose.

I wasn't sure from your description, but will the worktable be on an arm that also pivots around the single clothesline post? You may need a deep and sturdy foundation, because eventually somebody will sit (or merry-go-round) on that worktable.

Thanks everybody, especially for the links!

I am going to put the laundry work table on its own post, but very near the clothesline, so there will be no merry go round problem.It will also double as a work table for grilling and so forth.

We used to use an outdoor line exclusively, but got away from it when Momma was bedridden;there just aren't enough hours in a day to get everything done sometimes.

It will take me about a day to fabricate the rotary line and table, and another three or four hours to dig the post holes and set the posts and finish the installation.Total out of pocket costs will be less than fifty dollars, using scrounged materials, except for a couple of bags of redimix concrete.

If this saves me a half an hour a week of laundry chore time, which seems reasonable,I will be very happy and the electric dryer will only be used henceforth in really nasty weather-we get some of that every winter, and sometimes it rains for a week or more in the spring.

Readers who have not yet made the transition to a low cash, low energy lifestyle will be VERY,VERY suprised at just how long it takes to get all the chores done.Anything that can be done within reason to speed up the day to day work NEEDS to be done.

The cooker will not save us very much money in the short term;the electric range isn't all that expensive to operate, especially if just one burner is in use.

But if we need to go back to the wood fired range due to rationed electricity, or a problem arises putting our hands on enough cash to pay for the juice, the day or two it takes to build the cooker will be time very well spent.It will save a substantial amount of time and expense compared to cooking with firewood.

When all is said and done, I doubt if you can cut/haul/ split and carry in the necessary firewood, and tend a wood fired cookstove,in less than ten to fifteen minutes per meal; the time might be somewhat less during the heating season, as the cookstove might be kept hot SOMETIMES.

Firing that sucker up in hot weather turns the kitchen into a furnace in less time than it takes to fry a couple of eggs..My Momma slaved over this very same stove rightstraight thru the fifies and early sixties until we were able to afford an electric stove.

A kitchen range is a great heater, and burns efficiently, but it takes a long time to cut and split the wood as the fire box is very small.

Consequently it is FAR more efficient in terms of time and labor to use a stove designed for space heating for that purpose;such a stove will accept MUCH larger sticks of firewood.

We will use the wood range only in cold weather and on days when we aren't very busy until the day circumstances force us to do otherwise.

That day might not be that far off.

OFM - I use clothes lines so I do not have to wait around for the dryer to do its job. And, if I leave anything on the line a few hours too long, the sun just serves to make them fresher. I do not mind the effort, but then I am only 65, so in ten years or so, it may start to get to me.

My method requires a few extra changes of clothes, so I can have plenty if we have a strek of bad weather, but then I am not dressing for show anyway.

Also, the savings if substantial, expecially if using an electric dryer. Gas dryer, less savings in KWH, but gas is cheaper - but a BTU is still a BTU.

One nice thing about this cooker, is that you can set it up in the morning or afternoon, and by evening it will give you a quart of rice or potatoes, or whatever else you want. Needs no adjusting, only that you line it up to where the sun will be when you want to eat. If you want to eat at 6, point the center of it at about 5 oclock. do some experimenting, and I would guess even 4:30 or 4 oclock setting will cook it and it will still be very very hot at 6. With two of these units you can cook 2-quarts, and with 4 you could cook a gallon of food in a short afternoon.

As far as a parabolic, I once read/saw a short picture/article about a cooker built in the 1890's I think. It was N/S oriented, and focussed onto about a 2 or 3 inch pipe, probably 6 feet long or so, and that pipe was welded/affixed at the top onto a large oil reservoir, which had an oven built in. The oil circulated naturally throughout the day to the hot upper reservoir, and the claims are that once it got up to temp, it would maintain it throughout the night and into the next day. haven't tried it, don't know if it works, but would sure like to build one....
Don't think you need to glaze a parabolic type, as the heat gain is tremendous.

Also, I'm really convinced this little square foot cooker will let you do waterless outdoor canning. My pressurized soybean experiment just scared the crap out of me, it got so hissy hot. But then I've never canned.

Our clothesline system is on a pulley, and can be taken down to get the motorhomes out of the backyard. Just plop the laundry basket on the chair, and move the line on the pulleys. I do like being out in the sun, and it's really no chore to me to hang out clothes. I could use a dryer, but would have to work for someone else to pay for that. I'd rather have my own time. I did see a nice rotating clothesline at homedepot or one of those today, it was about 50 bucks. It rotated, and looks like it could be easily taken down when needed.

Thank you so much Craig, well done. Now I know I can run my Honda Super Cub on homebrew, or make electricity from a car alternator hooked to the Cub run on homebrew.

I particularly like the idea of distilling alcohol, because it essentially allows you to store the solar energy as a liquid fuel for use on demand.

In this regard, I would like to see a lot more information on distilling. Questions needing answers would be:

How can you "grow" and store your own yeast.

Can gas bar-b-que grills run on ethanol? Same for cars, tractors and other devices needed to be self sufficient. How to do it in a practical manner.

Another use for rough and ready distilling is to make stove fuel. A standard boat stove is just a receptacle for the fuel and a burner in a metal case. Boat stoves will burn any combination of ethanol and methanol. In fact, a mix of ethanol with some methanol is ideal. This is exactly toxic bathtub brew. It can be made from anything that will ferment, for example windfall apples or apples attacked by coddling moths or grain damaged by rain.

Alcohol has half the energy density of petroleum based fuels. That may not matter in a lot of applications. If what you want is some hot tea with your solar cooked soup or fried eggs for breakfast, the boat stove is ideal.

deleted as untimely.

Distillation in industry is done in a column with perforated plates or trays. A reboiler is at the bottom and a condenser at the top. The condensing liquid drips down from tray to tray, countercurrent to the up rising vapor. The boiling point decareses going up from tray to tray. This way energy is conserved making the heat do multiple duty and giving a highly enriched product.

A rather complex topic somewhat oversimplified; however you can probably find everything you need to know about building an ethanol distillation tower on the internet without having to consult a chemical engineering text.

I agree, distilled fuel is great for when the sun isn't shining. It's like stored sunlight, just as is oil and gas, but burns clean and doesn't add to CO2 burden like FF's.
I was reading something about making batches of yeast the other day, and will have to try to find that for you.
With my winemaking, while I haven't tried it, I suspect if I took a few ounces of brewing wine and added it to new wine, I'm guessing the yeast from the former would do just great. Tho' maybe just a bit of a slower start. Thanks for the great idea, will try that with my next batch of raisin sherry!

I'm guessing alcohol might work with a bbq grill, but don't know. You might have to make some mods. I recently changed out a kerosene stove to run on vegetable oil, and while it worked was not really thrilled with its heat output. Just won't get as hot, and the wicks are a lot more fussy, but it does work. Tho' it does run much much much longer on oil than kerosene.
I think I would like to try this on alcohol, as certainly it would get nearly as hot as the kerosene would. I bought this unit to help baking bread when the sun isn't shining, and also got at the same time a nice little 12X12 tin oven which will hold 3 to 4 loaves of bread.

Notes on distillation.
While I know it is illegal to distill alcohol without a Federal Permit and permission, I can tell you from experience that this unit will distill water. And since alcohol evaporates at a lower heat it will certainly still it, too. I'm guessing 20 drops a minute on a good sunny day, but that's only an estimate. The nice thing about distilling with this, is that it takes no fossil fuel to heat, and does not require frequent tracking once the liquid gets up to temperature. Just re-focus it every half hour or so, or just let it alone, focussed at a good area of the sky, and do a small batch at a time.
I'm guessing distilled alcohol from this to be in the neighborhood of 170 proof or so, but, again, I haven't yet gotten a license to try this, so I just can't tell you for sure....
While I have looked at some types of stills, they look to be beyond my current capabilities to build. This current system, while possibly not nearly as efficient, only needs a cork, and a foot long piece of "U" shaped inverted copper tubing to work. Very inexpensive, and easily made.
I think it's a good trade-off for folks like me with but little mechanical skill.

Last thoughts -- these glass mirrors are potentially very dangerous, and life threatening were you to fall on one.
PLEASE use a lot of care in handling these, and don't leave them laying around where small folks might be running around.
Please, use caution, and it might be best to put them on a tall table or bench in the yard.
Also, when using the device to pressure cook, make sure you let the glass cooking vessel cool down before you even ever think about handling or opening it.
And NEVER set down a hot glass jar onto a cold surface, it may spontaneously disintigrate.
It's like the GOM spill, very dangerous to life and health.

Using a "pot still" rather than a distillation column requires triple distillation to reach 90% alcohol as I was told by a depression era bootlegger (my great aunt). This is especially important if you want to drink it because you will avoid most of the toxic fermentation products.

Safe to drink does not necessarily mean good tasting. Charcoal filtering will remove some of the remaining toxins (headache producers at this point) and mellow the taste. The charcoal must be made properly or you will get a smoky taste. I recommend buying your drinking alcohol to end up with a better product. Also, the time and cost of ingredients hardly justifies home brew for the novice.

Paul, appreciate your knowledge on all this, certainly you know whereof you speak, as you hit all the stuff I've read on distilling. Someone said distillers generally throw out the first bit of distillate as it contains stuff other than ethanol.
Fortunately for me, I stick to wine and beer, because hard alcohol makes me obnoxious and stupid at best, and God forbid I write anything under the influence, because there is an odd chance I'll post it somewhere, and then have to hide my head for weeks. But then too much beer does the same. Oh well.
Thanks for your expertise...and while I don't distill, it's nice to know this stuff is there if ever a need, and that we can ask you for more info.

All of the headache and hangover toxins are present in wine and beer. They are a long list of aldehyde and ketone compounds, along who knows what else, all present in trace quantities. Many of these compounds are responsible for the taste and aroma, which we appreciate.

Excellent information. Thanks for posting it.

I've heard that when working with parabolic reflectors it's essential to protect your eyes from possible damage to the retinas by wearing strong UV-protective goggles or sunglasses, such is the intensity of light concentration involved, and ditto for Fresnel lenses. Is there any hazard to your eyesight with this kind of cooker? If so, what precautions should one take?

Do I assume correctly that the temperatures given are in degrees Fahrenheit?

Thanks for mentioning that very important topic. Certainly focussing parabolics give of some screaming hot energetic wavelengths, and that should surely be a huge caution to all folks.
I did forget to talk about that, and while I conducted the jar heating tests, it did certainly screw up my eyes for a bit. I ended up closing one eye.
You'll learn to approach this mirror cooker from the side, where you don't get all that glare from either the front or even reaching over the back.
And you should make a conscious effort to do this, because often I forget unless I pay attention to remembering that.
I'd suggest getting some good eye protection, or squinting a whole bunch to protect precious eyes.
Yes, temps are in farenheits.

Just a little more on solar-simple stuff. I put a 100 ft coil of black plastic pipe on my flat roof, over a bit of wall insulation, and covered it with a couple of discarded single pane windows, and I get lots of hot shower water into my bathroom by way of a 20 watt circulating pump. The pump has a timer set to run from mid morning to mid afternoon.

I use it only in non-freezing months, of course. And I am the on-off control for cloudy days. In winter, I have a parallel heat loop going by the wood stove.

My spouse, who can be very annoyed by my many failed attempts at advancing toward the carbon-free future, now takes her baths without complaint or comment, and we save a lot of the propane that used to run thru an instant water heater.

That thing kept loosing its mind, leading to screams from the shower. Now, no screams.

"....we save a lot of the propane that used to run thru an instant water heater.

That thing kept loosing its mind, leading to screams from the shower. Now, no screams."

It sounds like our Bosche 225. Their circuit boards are defective and the flow detectors are cranky. Make sure the little strainer screen on the inlet stays clean. I finally gave up on ours and put our old Bosch 125s back on line to boost the solar/woodstove when needed.

Yeah, I got tired of my wife screaming; "HONEY! Go push the reset button again!"

I did the same thing on the motorhome, coiled a good chunk of that (not as much as you), and covered it with plex.
Man, did it put out some hot stuff. Kinda slowly, but it surely was steamy hot at first.
Of course that's a dangerous thing to use in a shower, but for a bath, it's the ticket. Or mix it into cooler water before using.

Our solar water system gets some ferocious temperatures, so we use a lot of care when showering, especially when first turning on the water. The mixer valve sometimes likes to wander, so as you turn up the hot, it will slowly sometimes cool slightly, and after turning up again, it'll give a dose of ooops, back off. But it's well worth it. I like the 'feel' of solar heated water better than other types. I think it feels less harsh somehow.
Kinder and gentler or something like that.
Ow ow ow ow.

Love your writing, I can just hear your poor wife screaming as the water changes suddenly. Been there.

Nice thread . I built one too :

Colorado Bob's Solar Oven

Reflec Tech Mirror film

I still have about 2/3's of a roll ....... 46.5" X 39 ft roll .

I had to buy the min. of 150 sq. ft. If you're doing small experiments, I'd be happy to sell off this in smaller sizes .

Bob, that's some serious looking stuff. Gonna check it out further when I log off here. Maybe you shoulda done this post....

Reno -
Oh no, the great thing is how we all take different tacks.

Bob, looks like a great webpage, and I'll vid the vids later tonight.
That's one sweet looking oven. I've always wanted to build a neighborhood scale solar oven, and you have encouraged me to put some energy into that.
I grind way more grain than I need, and an oven like that would be an invitation to my neighbors and friends to have a day of solar breadmaking. And party afterwards.
While I haven't explored your stuff yet, do you have a backup for the unit? I was thinking of putting in propane for when the sun suddenly disappears. Been frustrated too many times when baking bread. Perhaps you already have that covered on your page, so I'll look later. Thanks for posting that for all of us to ponder and appreciate.
You're the only fabulous Farrrington freak I know besides myself, and the third person I know who has read "Direct Use of the Sun's Energy", by Mr. Daniels.
This is in my opinion the Granddaddy of solar books, and I guard mine carefully. It is my second favorite book next to the Urantia Book which I also guard religiously (LOL).
I do see Mr. Daniels' book for sale once in awhile on the internet, and anyone who wants a serious source on solar should snap one right up.
Rumour has it he worked on the Manhattan project. Do you know?
I need to read it again, and pay attention to his section on solar refrigerating and freezing.
By the way, anyone here have ideas on modifying refrigerators to use cool night air for cooling food?
I ws thinking a wedge shaped piece on the door with fans to the outside might cut out some energy use.
It is often much cooler out at night than the inside of our fridges, and why not use that instead of turning on the refer's compressor?
It seems so stupid to use electric to cool and freeze our foods when so often it's colder outside.
Actually it really pisses me off to see such gross inefficiency.
By the way, to hustle a great site again, has some outstanding stuff on it if you take the time to search around a bit. Tube transportation systems, house heating(water heating) compost drums, buried pipe water stills, and pipe in ground air conditioning for very cheap. And a really good expose on Global Warming IMHO. Worth your time to check out.
(I have no connection with this other than having corresponded with him briefly)

Send me an email on what the reflec runs...?

Farrington Daniels was one of my mentors. A very kind, very competent scientist, with all the right values. He took me as I was- a wet-behind-the-ears young tech wonk fixated on his one great idea (solar stirlings), and gave me as much wisdom as I was then able to absorb thru my extremely thick skull.

Daniels knew it would take time to make any difference--and he sure was right there!

BTW, with his help and other's, I did get a pretty good and inexpensive solar stirling working- that was long ago. No money guy has ever picked it up, but that might change in the current situation.

Oil is too cheap, so cheap you can just throw it away. Daniels asked me "Just where is this "away"?". We now know, GOM.

Fridges in cold weather. Nutty, isn't it? All you have to do is punch a hole thru the insulation and run a little fan that blows in the cold and out again thru a tube. Or, to be fancy, set up a heat pipe and have it all work automatically from the temp difference.

Or, just put the food out on the porch like my mom used to do. Dang! why didn't I think of that?

So I made one, tested it, and I'm STOKED on it! Three 37x37 inch squares of hard board with foil glued to it. Foldable, transportable.
500ml of water got too hot to touch after 2 hours in full sun - and we're nearing winter solstice (Dunedin, NZ). Got some eggs on the go at the moment!


You are soooo cool. You're the first person of all the folks I've hawked this to who has made one. Wow.
May I say you did a superlative job with the foil. It's clean looking.
Now here in the N. Hemisphere, I would say that your cooker as shown (by shadow) would be trailing the sun (IOW, needs to be moved clockwise). But you're in the South, so is your cooker actually leading the sun?
If so, that's the way to do it.
Please, keep me/us informed of your experiments, and maybe we can share this stuff, if our hosts here will keep this open for comments.
Otherwise, let's email
I love it.
Also, as Kevin so sagely suggested, DO protect your eyes.
PS, how much is 500ml?
(I'm an slow American...duh)
Eggs cooked in it will take you probably over an hour depending on your liking. Be aware that the sun will slightly discolor both the shell and the inner egg. You may find that if you wrap them in foil it'll reduce that?
But still tastes great
Now make a couple more cookers and you can have a full course solar meal. LOL.

Thanks! But seriously no one else has followed you?! Damn, we need more doers in the world.

Lots of doubts from people, until they stuck their finger in the jar! Yep it's leading the sun, left hand wall (right side in photo) pointing to 5pm. With an outside air temp of 10 degrees Celsius, and the sun quite low in the sky, I'm stoked. An egg cooked fully through with no troubles (I checked after an hour), and 1/3 cup dried chic peas hot and soft after 50 minutes. I'm blown away! Want to build a BIG one now :)


500mL is half a litre or roughly a quart.

Keen to email if this thread closes to comments - saltwaterimages[at]gmail[dot]com


Great photo.
One thing to consider before building a BIG one, is the possibility of several smaller ones. This will give you great leeway in timing different length cooking foods, and allow you to have them all done at the same time, or even staged if you wish. Did you move the cooker to follow the sun, or just aim it and let it 'batch' cook? I think the latter is the way to go -- set it, forget it, eat it....
Or, of course, track for longer cooking foods.
Lotsa possibilities.
Right on Nick!

I moved it once, to it's final position of the day. Having trouble with paints on glass.. gloss black with a brush and "hot paint" matte spray, both scratch off the jars, even if etched with sandpaper first. Ideas?

I use a can of flat black spray paint, and then let it bake in for a couple of days, that seems to help solidify it. To touch up, take a small brush, spray some paint in the cap, and then brush out the worn spots.
Don't know how to correct this problem, but just repaint it a little bit when it gets too worn.
Would like to powdercoat one of the jars, black, and see how that works, but don't know how expensive that would be. Powedercoat should last a long while.
Cloudy here today with possible snow tonight, sheesh, it's almost June....

Thanks Craig.
You have solved my problem of how to cook on my yacht without blowing myself to smithereens with Gas.

Craig -

I have some sign cans, sheet metal 24 X 34. Going to give your design a try. I really love simple stuff. I'm toying with a focusing melt furnace for alum.

Greenhouses are my real interest .!/photo.php?pid=5129251&id=663574992!/photo.php?pid=5134164&id=663574992

Bob, also interested in melting aluminum. The mother earth news years ago showed a design for a focusing collector made from conduit and square foot mirrors. I think it was about 10 by 10, tho' I don't remember much about the performance.
Also melting zinc or pot metal might work, I think it has a lower melt point, but higher strength when cast, though I don't know. Yet.
I've built several solar air heaters, and they work fine, but now I am of the mind that it is much more efficient to build greenhouses attached to South of houses. That way you get heat, a nice area to be in, a sun room, more oxygen, and food. Heat boxes may be good for apartments and rentals, etc. My beer can heater is very lightweight, and should be portable when I finally get it done.

Another contraption melts zinc pennies in seconds. The lens is 22".