December 16, 2002, Video Script, Kerr- Cole Sustainable Living Center, Rev.5


Audio Transcription For The Video:  

A visit with Barbara Prosser Kerr and Sherry Cole, At the Kerr-Cole Sustainable Living Center  


(Text appearing on the screen at the beginning of the video.)

Solar power for cooking, heating (and) living.  

Since Ms. Kerr retired in 1982, she and her neighbor and friend, Ms. Cole, have worked on developing a sustaining life style through the use combustion-free energy sources. Kerr invented the (cardboard) solar box cooker to cook food, distill water and sterilize medical equipment.  Kerr lives comfortably in a passive solar home partially dug into a hillside, with a greenhouse, solar cooker oven, windmill, a well, solar water heaters and food dryer in Taylor, Arizona. ________________________________________________________________

  Note: all text included within parentheses denotes changes from the actual spoken or displayed words. These revisions have been made to correct or re-word certain errors, omissions or unclear meanings - or to amplify what was said. It is expected that occasionally the viewer will have to pause the videotape to have sufficient time to read the parenthetical material. For a group, the presenter may from time to time stop the showing to read aloud from the edited version.   





07:30   THE HOUSE  


11:30   THE INVERTER  













49:30   END



It was exciting developing (these solar cookers). In 1973, I had turned my backyard over to … fun!  I was going to make every kind of solar thing that I could get hands-on plans (for) that I (could) do.  So, I made lots of stuff: I made reflective cookers, and parabolic cookers, and slant-faced cookers, and a distiller, and a food dryer and a “doghouse” food dryer … So lots of stuff.

I was still looking for all kinds of plans that I could build. And I heard just a sentence that said there was “a box that cooked. “  And I kept trying to find the plans for that and couldn’t find them.  (It was just as well because until then all cookers had been made from metal or wood.)  But one dull day I had a (cardboard) box and I had a piece of glass in the garage and so I started to try to put a box together. I put it together. And it cooked! 

It turned out to be a very generic design.  They are very simple. You can see here that (as it was refined), it is a (cardboard) box that is insulated. It has a double pane of glass to let the sun in and hold the heat.  And it has a reflector (as the lid). You put the food in by taking the lid off.  And inside is something dark that converts the sunlight to heat.  This is raised up a little bit off the bottom of the box (on narrow strips of cardboard)  because they found at the University of Washington that you get to 15 to 20 degrees (Fahrenheit) better temperature if you take the hot black surface off the bottom so it can’t drain heat that way (into the insulation) and it all has to come into the box. 

We made them a lot of ways.  We made them in cardboard, we made them in wood, we cut flat stuff, and used stuff that was already in shape.  This is a fairly late way to make them. 

A man from Cambodia walked in to Solar Box Cookers International one day and said “You know, you could have made these simpler.”  He showed how to make it simpler (by put one box inside another) … And he was right.  (That became our generic plan.) 

(The following paragraph has been heavily edited to clarify the meaning.)  

There are innumerable ways (to make a box cooker), This is only one, and it doesn’t matter how they are made, as long as they have (glazing to let in the sunlight, blackened surfaces to convert sunlight to heat, insulation to hold the heat in cooking vessels , and reflectors to amplify sunlight. 

The thing that makes heat is the sun rays striking (something) dark.  If (sunshine strikes) a living substance like a tree (green leaves), it makes photosynthesis and the tree grows.  If it is a black thing like a black wall, a black coat or a black pot, it makes heat.  When it is a black pot with food in it, if you keep the heat from escaping, it will build up to cooking temperatures. 

One of things that we had to realize was that you don’t have to have 400 to 450 degrees F. (to cook)   Food starts to cook at about 185 F....fruits and meat. (Cardboard does not catch fire until slightly above 400 F.) When we became aware that the lower temperatures we could reach with these simple systems cooked well, (it eliminated the need for making cookers out of metal) then we had a whole line of development (of inexpensive solar cookers). 

Actually foods cooked at those lower temperatures are known to taste better, it makes tender meat, it brings out the flavor in vegetables and in grains. (Also, the lower temperatures avoid certain harmful substances that are formed at the higher temperatures.)  And so we not only were able reach those (lower) temperatures with simple systems, those (lower) temperatures work better. 

Sherry, you were a critical component because I was playing.  I was literally playing with all these things in my back yard. 

Sherry:  It was fascinating. 

You were the one that said, “That’s a stove that needs to be told about.  That is cooking!”. You  and Georgia identified it as really a (functional solar) oven … that it was not a play toy. 

And further, any time I would do something (crazy) with the designs (Sherry would speak up).  Now with the wooden design, I remember very clearly trying to make something that would lift the glass (lid without getting hands in the steam).  I put up a flagpole and a block and tackle to the glazing and I pulled it up and I fastened it on cleat.  Well, I had been in a boat for a while … In fact, I lived for a year (on a boat) … with my little baby. 

And so I was thinking boats but she looked at it, (and said)   “You can’t do that. No one would ever do that!”  I said, “But we can’t burn our hands.  We would burn our hands when we open the lid and all this hot steam comes out.”   “Well, you can’t do that.”  So we fussed around and fussed around and finally …you will see it later … we found out that you can just take a stick from the front of the glazing  … your hand is down here, the heat is going to come out (up) here if this is the glazing. And you can just prop it up like that and your hand is all out of the way, you see.  Now that was a lot simpler than my block and tackle, and cleat, and line.  And that’s the kind of thing that she has been priceless at. Without you (Sherry) it would never have happened.


07:30   THE HOUSE

This is a 960 square foot house.  It is dug into the hill as far as we could go until we hit solid rock.  We thought we would go deeper but it didn’t turn out that way.  It is built of cinder block (filled with rebar and concrete),  with  2 inches of (rigid) insulation around the outside, a heavily insulated roof, double paned windows to the south which heat (the house) as well as giving light and a beautiful view.  On the front, you can see the outside of the solar wall cooker, the kitchen water heater, a  free standing Paul Funk concentrating parabolic cooker, and the greenhouse windows.  The greenhouse windows in this (locality) can be perpendicular.  They do as well as the slant-face, maybe a little better, because the slanted greenhouse windows tend to burn out plants that are under them.   And so this gives us a lot of light, plenty for the sun (in) this area. 

On the roof, you see two solar chimneys, the little rectangles, one of which has the stove pipe in it (but still works as a ventilator).  These are just (air) shafts that are glazed on the south side and painted black inside.  When the sun hits them the air rises and draws air through the house or through the greenhouse (and out the top of the shaft to the outside) … a very simple, natural, system, passive, that (quietly) provides really good ventilation. 

In front of those you see two kinds of solar panel (arrays).  You may need to look a little carefully to the left up on the post. That is a self-focusing array of four panels that follows the sun. It is not following the sun right now because it is a gray, bad day.  So, it is stuck out of focus.  But meanwhile the fixed array, which is the six that are in the center of the roof, will charge any day even (with weak sun).  They don’t make as much (electricity), but they are more reliable.  So I have both systems.  One that will track for maximum efficiency and one that (will charge with any sun available on both) good and bad days.

Now, this ten panel system is much bigger than needed for a basic simple house. I started out with two panels and a set of (two 6 volt batteries making a 12 volt system).  I worked that for about four or five years. Then I decided I wanted to get a computer, get a refrigerator, and do some things that I couldn’t do when I had the small system, which was plenty adequate for a radio, and lights, and (a recharger for small batteries).



This is the battery bank for storage of the electricity that is formed by the (solar) panels.  It comes down (through the wires) from the panels into (the batteries). Each of these is a  6-volt, golf cart or  wheel chair type battery … they give a long slow deep draw as opposed to automobile batteries which are built to give a quick start but they do not have the duration.  So you need deep (cycle) batteries.   You can get more expensive (batteries) that last better. (My batteries) have to be replaced every seven or eight years, but they work quite well.  There is a governor to keep them from overcharging.  From here the electricity goes into an inverter than changes (the electricity from 12 volt dc) into regular (120 volts ac.) alternating current.   (The whole house is on alternating current and uses standard equipment) except for a direct draw of the 12 volt system into refrigerator (which uses 12 volt dc for higher efficiency compared to ac refrigerators).



Leading in from the battery bank outside, the heavy cables come in to the inverter. This is a (Model) 2012 Trace (inverter) which changes the 12 volt dc to 115 volt ac.  And then (the electricity) leads back out into the master panel and into the various (regular) circuits in the house. 

This is a digital volt meter which tells me how much charge I have. It will give a ring if (the batteries get) over charged or under charged. (Essential equipment is near the volt meter). I keep my keys to the battery box here. I keep a pair of (wire) cutters (here) in case I have to break some (line).  Anyway, these (have) insulated handles (to protect from shock). There is a note pad that periodically I keep the records of what is happening with my whole system.  (I consider the on-going record to be essential to equipment maintenance.)



This started out to be a passive solar greenhouse which means glazing, (and mass), and black stuff and plants. And as it grew … it was originally brown at the top and gray on the sides because that makes it hot, you see.  And then after some years I thought, well, it is always overheating.  I am having to dump heat. And since solar energy can either make heat or photosynthesis, (I thought) why don’t I cut down on the heat by increasing the photosynthesis?  So I painted the whole thing white!   The plants love it. 

And I designed this (area) to be a place that I could do a mural. I could draw in (dark) greens and reds and browns. I could make a pretty mural. We don’t have to do black (to add heat). But it turns out I don’t need (the extra heat) so I just put a geranium there instead. 

You understand that this foundation is a regular house foundation.  Outside has 2 inches of insulation going down 24 inches, so that when the heat is in this earth (in the floor of the greenhouse), it can’t dissipate easily out. It is insulated in here. The cinderblock wall is insulated outside.  The roof is well insulated.  It is double-paned glass.  So it is a solar box. 

One of the problems at our latitude is that you can’t have the back of a greenhouse too deep (or the back plants) don’t get enough light (and reach for the windows). So I had the ceiling left open (for a little less than half of the depth of the room giving room for shutters to slide) so that I can have a lot of sun and then at night I have the shutter(s) here that I can close.  Now that protects from chilling out in the winter time.  It also protects from overheating if I am away and can’t take care of (extra ventilation if it is needed). 

I have had a number of different shutters. I started out with plywood shutters, masonite shutters, (paneling), Styrofoam. (Some of them were very heavy and awkward.)  And then one day things were falling apart and I thought well, I’ve got to get something up there for a little while until I can get it fixed.  So I took 1 x 2 (inch frames) and wrapped them with regular poly (sheeting and slipped them in place … temporarily) … and they lasted three years.  Besides, they are real light weight and easy to run back and forth on what is roof edging.  Just that little trim that goes over the top of roofs, turned upside down, makes the runners … very cheap. (Overhead glazing must be opaque, like fiberglass, or plastic.  Overhead clear glass will overheat a greenhouse, even burn out the plants.) 

Now, one of the things you have to have with any greenhouse is good ventilation (so I put in a west window opposite the door). This greenhouse is facing south with (only) a west window (it has no East exposure) – not ideal.  I should have an east window – but it didn’t fit it into (the rectangular shape of) my plans (because that is most economical).   So I (put in a) west window.  I thought I would ventilate with that and give myself a little bit of space up here to let the air out.
We put a solar chimney out there, which is simply an (open-ended shaft), glazed on the south, painted black inside.  It just sits there and faces south and that is right over the top of this vent.   As it turns out it draws the air so well I don’t open my window very often. (The window only provides light from that direction.)  (The vent cover is opened and shut with a simple rope system.) If it is a bad day, and I do not want to put too much cold in here, I do it half-way, and at night in the winter I close it back completely. 

I did not chemicalize this soil when I started.  Now, (with) most modern buildings, the first thing that they do after they have done the excavation is chemicalize all the soil so that things won’t grow and insects won’t bother you.  But I did not have that done because I wanted clean soil for my garden.  (It has worked fine except I absolutely must not put wood down on the ground as that does bait termites in.) 

This (was) sub-soil.  I brought in potting soil and I brought in load after load of (horse) manure, along with a lot of insects, (beetles and bugs) which I had to (catch and put out) until they finally died out. But this then is a garden. And in it are buried soaker hoses.  And I keep the soaker hoses going so it takes care of itself largely, except for the potted things.  (It takes) maybe five minutes a day just to come in and look, and check if anything needs anything. 

I grow seedlings of course in the spring … flowers year round.  I also grow “boosters” for my salads. There is an herb, I think it is savory, but there is some question about what it is … it is a good salad taste. Collards, which give me a cabbage-type leaf by just using (unintelligible) leaf.  There are cayenne peppers over there, but (they) are more decorative than anything because I can only get 4 or 5 a year. Aloe vera.  And then there are beets.  The beets put up a lot of greens. I just pick the big (leaves) at the outside. There’s parsley, and lamb’s quarter, which around here is a weed (but) it is a highly nutritious weed and very tasty and so I use it for cooked greens and use it for salad greens.  And there is turnip over here. (I use turnip greens in salads.)

Now that is not a big salad (but it is nutritious and) it is big enough for one person.  When I have (company), I have four tonight, I (add) lettuce from the store.  But this is where I will get my taste. 

We also have a tomato (plant) which doesn’t put out a lot of tomatoes, but we get a little pickings (unintelligible) for taste, and that will go in the salad. 

Now, this (greenhouse) is more than (for) nutrition.  This is a quiet place to just really thank God for nature and be happy.  I often just do that. I just come in here. I use it for my prayer space, meditation space, or just sitting down.



There is an inverter that converts to 115 volts (ac) for the microwave, the blender, the lights, and the food mill for grains.  This is the refrigerator. It runs on photovoltaic electricity too, but it is tied in directly to (the) 12 volt (battery bank). So I have no hook up with the (utility grid).



This is the solar (wall) oven.  It has got an inner insulated (oven) door and an (insulated) kitchen cabinet door.  This is the opening that goes through the wall.  There is a little throat there to put (the oven) farther out so that it (extends beyond) the shadow of the eaves.  And the insulated door allows me to put whatever I want in there. And it is wonderful!  It is like the top of the range, the wood range we used to have, where you can put anything you want to cook gently and long term.  And I use it for other things too (that otherwise might be boiled or treated with chorine bleach). I put my dishrags and pots (and things that need sanitizing, like dishes if someone has a cold).  I put them in there and they steam and clean up.   I do teas, and brew broths, and all my (beans and) grains ... when I am not playing around with other (solar cooker) designs that are in the yard. (It will do fine meats and fish.) 

This (solar wall oven) is very handy.  It withstands winds and (during) intermittent snow storms and rains storms, it may still hold enough temperature to keep cooking.

Martha Port: Then I presume some of your solar boxes have been shipped all over the world. (Correction: We shipped plans, not cookers.) 

Sherry: I believe so.  Yes. Yes. And the do-it-yourself plans for people to make their own have gone many, many places…thousands of them. 

Barbara: Many people now make cardboard (solar cookers from) plans. (I believe we were the first to make cardboard solar box cookers.)  We have cardboard plans. We also have plans for a wooden oven. 

Remember that, when we got into trouble talking about plans (for) two stoves? This was in the early days.  We had not realized that (we did not have to provide plans for stands).  I cook on the floor, on the ground.   But if you want to, (you can) put it on a table, or if you want to, put it on a push cart. Sherry likes hers on a wheel barrow …although now she has sort of a doggy cart. 

We had not realized we did not have to (build the stands either). So we had these two big wooden (solar) ovens up on pillars with rollers.  Oh, it was a lot of work. I am not a builder.  I just put things together and see if they will hold. So it was difficult. 

But we got them, and took them to Yuma. Because they wanted us to talk to the Council of Governments down there and they were doing an energy program and they wanted us to tell about it. So we took them down there. It was a bad day (solar-wise)… Sort of a semi-overcast day.  We were doing chicken and rice.  We put it outside, (then) we went inside and did the talking … the program.  And then we had (an interview with a) news reporter lady. We took her outside and said “These are the stoves.”  She wanted pictures so we took her out to take a picture.  We looked in.  The chicken was done … smelled good … the rice was done.  She was oohing and ahhing, because it is sort of amazing. 

I was blabbing on…I talk a lot.  I said we have got plans for another cooker.  I described the plans for a different one.  I wanted to make one where I could pull the glass (to one side) … instead of raising the glass up this way … because we had a friend who was … there were really three of us to start with … I wanted to pull the glass because she had arthritis so bad she could not lift (the lid.)  So I had plans for that. 

The lady puts it out in the paper that we had plans for sale.  (She set the price at $1).  We got 110 requests (with $1. bills enclosed). 

Sherry: 125. 

Barbara : 125 requests, and not a word on paper. Not (even) a sketch of anything. 

Sherry: Not the slighted idea how you would make plans. 

Martha: I bet your got them put together real quick, huh? 

Sherry: Yeah, but we did it. 

Barbara: We really felt with that response that we had to (because they had sent money and the reporter’s reputation and ours was at risk.)



This is the house water (heating) tank, the one with a slant face. You can see that this is a similar design to the (kitchen sink heater) that is in the front (of the house). This is a very low tech water heater. Passive solar.  (People often use one) as a pre-heater so that the water from (a solar heater) goes into a propane or an electric heater.  If you have to raise the water temperature from 90 F to 120 F, it takes a lot less fuel than if you raise it from 35 F to 120 F.  So as a pre-heater it is a great energy saver.  But I choose to use it as a stand alone, which means I do not boost it.  I use whatever I get. 

Now, this is a heavily overcast day.  We are still in the morning and it has snowed already today …  so not good. Yet when we opened it you could feel a puff of heat. (The tank) is warm to (the) touch.  I would say it is 75 F to 80 degrees F temperature there.  Even in mid-winter, (I get up in the morning and take a) shower with not a chill.  It is just a neutral (temperature) kind of water. 

Simple.  This is an old electric water (heater) tank - stripped of its insulation and painted black. The water from the well comes by gravity feed into the bottom (of the tank). There is a pipe that leads that water down to this end…that is the refill.  It gets hot, comes up and the water is drawn off into the house from this top location.  So even if I draw a lot of water it mixes in, rather than cold coming immediately out of here.  It mixes nicely.

(Clarification: Actually the water in the tank stratifies rather than mixes. The less dense hot water floats on top. As the cold water, which is heavier, comes in at the bottom oft the tank to replace the water exiting the top, it forms a distinct layer beneath the heated upper layer. Thus only hot water is withdrawn from the top until it is pretty much depleted.) 

This is a needle valve that I had drilled and put in because there is always gas in water. As it heats up, it comes off (and) you get a pocket of air up here.  Eventually ... if I feel it is not heating the water as well as it might, I open this (valve) and let the air out so the hot water comes all the way up to the top. 

The box around this (tank) is a simple basic (box), insulated sides, (45 degree) slant face for our latitude.   You see, I am at 34 degrees North latitude and that means a 45 degree angle is very functional here.  (The slant face of a cabinet-type water heater, in temperate latitudes, should be angled above the horizontal by an amount equal to the geographical latitude of the location plus 10 or 15 degrees. Our choice of 45 degrees equals our 34 degree latitude plus 11 degrees.) 

My slant face has two layers of fiberglass glazing, and that is it.  I did have an (insulated), reflective cover. Never used it. I thought I would use it to keep blizzards (snow) off. But I find I don’t (need it).  I just ride out blizzards.  Maybe the water is cool for a while but its O.K. 

This is so far from the kitchen … maybe 40 feet  … maybe less … (that) I was drawing close to a gallon of water to get hot water.  Then, I would turn it off and (it would) cool down (in the pipe) and I had to draw that again.  So for that reason I put in (another heater) very close to the kitchen sink.

I would think anyone using passive solar (water heating) might plan to have a tank above each sink.  A sink in the garage could be done, or the shop, kitchen, basement, (barns) could have their own direct draw. They are quite inexpensive.  You have to have the shell of course.  You can get these (tanks) …  this (recycled) tank cost me $15 … I think the other one was $10 … and labor. 

It is real easy to set it up. This back panel, insulated, simply fits into a (recess) here (and fastens with turn keys). 

The (main) water heater at the back is too far to bring (hot) water to the kitchen.  I (hate to) waste water. So I made this one very close.  It is made of a (used) 20 gallon RV water tank – ($10, stripped and) painted black, and inside an insulated box, with a glazed face. If I were doing this not for display I would put it right above a sink (on the roof properly reinforced to carry the weight – perhaps 1000 pounds) and then with less that a pint of water (drawn) I get as warm as I have.  It is very comfortable.  In the winter, (the air) can be really cold, and yet in the morning I may have 70 degree water. Even 50 degree water beats 35. (These are sunrise temperatures. It heats up higher during every sunny day.)  And when the sun is out (in the summer time) I have (water) too hot to touch.



That was when we realized there is a need … a recognizable need (for solar equipment) beyond the curiosity (stage), beyond just showing (and telling), (beyond) the fact that the sun will do these things is very interesting. These were made in the early days of the solar age. 

I consider that we are making slow progress.  There has been an awful lot of talk for decades (that)  “The sun will do these things.”    “Good potential here.”  “It will do this, it will do that, it will do the other.”  But what we did was we made a thing that (really) would do (something useful) … (one that would cook.) Therefore we made a step from theory to practicality.  And at the moment we made that step, we got this outpouring of interest.

Martha: It was a step from playing to a beginning of helping. 

Barbara: A step in the growth of solar that here was an accessible thing that would (use) the sun (…economically).  (With our designs, we moved solar cooking out of laboratories, away from high tech, into the home.  Therefore we were helping break down the barrier to the use of solar energy.)



In fact, Dr. Robert Metcalf in (Sacramento,) California ordered one of our big wooden models.  That was almost mistake.  It weighed 80 pounds and we didn’t know how to wrap it.  We got three or four big cardboard boxes, and we wrapped them over and held them with tape. And we couldn’t pick it up!   We got clothes line and tied around it in four directions.  We were really working even to get it to the bus station to ship it.  We stopped several times and thought, “This is nonsense.  We can’t do this. I mean this is crazy.  We’ll never do this again. But we have got the commitment now, we’ve got his check here.  And we will do this one.  No more!” 

So we got this down to the Greyhound (bus) station and they took it over to Sacramento.  And he opened it up.  He is expecting a toy.  Here is this full sized cooker … this was in 1978, I believe.  He put four big pots in there. He looks at that and takes out his first (cooked) pot  and he realizes that this is really something he wanted to devote his life to.  And as a microbiologist he could see the need for the ability to sterilize and pasteurize as well as cook.  And every summer for 17 years now their family has been fed out of that same cooker. When I go over there to visit, there is Ye Olde Solar Box Cooker. 

Sherry: It is still there. 

Barbara: It was a miracle that we ever got it shipped.  . And Bob is still (cooking in) it.  That (cooker) went where it was supposed to go. 



This is a water supply from a home well which is 250 feet deep.  It is pumped by wind.  See the wind mill turning circles.  It works rather like a bicycle but it goes up and down and there is a long 250 foot rod that goes down to the bottom and runs a plunger.  The water is pulled up and it goes either into the 1000 gallon irrigation tank or (by) underground lines to this 500 gallon house tank.  And that is the total source of water supply for this area. 

This 500 gallon house supply feeds into the house plumbing: kitchen, sink, bathroom, shower.  It also goes into both of the hot water (heaters and waters the greenhouse).  And it feeds through a valve periodically into this (solar) distiller. 

The distiller removes the salts from the water.  It is extremely hard water and salts sbuild up in the water that is (left) inside (the distiller), so you have to flush through 5 gallons (or) a little more every time it (has been) distilling, which is every day that it is (sunny). It gets (the water) hot, (vapor goes) up and condenses on the bottom side of the glass, runs down to a trough here.  A slight gradient puts it into (the tube). Can you see it running now?  From there it goes into a 20 gallon reservoir inside the house where I pull off the drinking water into gallon (jugs) and take it to the kitchen (for consumption and cooking). 

The distiller (spent water), which contains concentrated salts, is still not too salty to be used for growing things.  And so I put it on this whole side garden (to grow) flowers, salad stuff, herbs, this whole area ….




Sherry: Oh, he has been incredible.  

Martha: Dr. Metcalf is the gentleman who has done so much of the research for water pasteurization which is (a) critical (contribution). 

Barbara: Yes. He is a professor of physical sciences.  But his major (interest) is microbiology. He had a master’s student (who) did a series of pasteurization (tests using solar) boxes … gallon (jugs) … (heating) times … and laboratory studies of water at certain points.  (They) established (definitively) what was needed in order to kill viruses, rotoviruses, bacteria, eggs, cysts, worms (in solar cookers) … the whole spectrum. 

In fact, if you bring anything to cooking temperature, it is dead.  (Insert: But it does not kill the heat resistant spores.) So you can (heat water) beyond the (pasteurization) temperature he recommends, (but it is time wasted).  (Water) does not actually have to boil (even to pasteurize).  If it is 15 minutes at (170 degrees F), an hour at (certain lower) temperatures.  (Detailed information and reprints of Bob’s publications are available through Solar Cookers International, 1919 21st St., Suite 101, Sacramento, CA   95814; Phone number: 916 455-4499).  (Using solar energy is a) very simple, cheap way to pasteurize very effectively.  (There is now a Water Pasteurization Indicator dubbed the “WAPI” developed by and available from Solar Cookers International, which eliminates the need for a thermometer.)



These are all variations on solar boxes.  This is the Kerr-Cole EcoCooker, which is our original (manufactured) one, which is (no longer available.) We just lift lid back and put your food in.  It is a very good cooker.  Solar Box Cookers International arranged to (make) one that would collapse down and it will go into this size box (could be carried on an airplane) … whereas that one does not collapse. This one is a version of (the Eco Cooker) made from home construction plans.  And they all cook. Some better … nobody has beaten our Kerr-Cole EcoCooker yet with (simple solar) boxes. 

(Since the production of this video, we participated in the identification and development of a whole new line of solar cooker design … solar panel cookers.  These very simple units have been so successful that Solar Box Cookers International changed its name to Solar Cookers International so as not to limit itself to box designs.  The main effort of SCI today is in the promotion of panel cooker technology in refugee camps and underdeveloped parts of the world.) 

I like the flat top because they stack better. Plus, they look more down-home. 

But there are advantages at our latitudes in having a slant face. Dr. Paul Funk, an engineer(ing) (graduate of) the University of Arizona, has designed this very nice concentrating parabolic (cooker), which internalizes the reflectors. It has (reflectors) inside.  In certain locations, like here, it is wonderful because it is wind resistant.  This thing is heavy on the bottom and if the wind comes, it just scoots around like that (without turning over). (External) reflectors tend eventually to turn (cookers) over (in gusty wind). They are (all) pretty durable, (yet ) nice and light weight.  They are all light weight. When you get to the wooden ones … those are heavy. 

Barbara, pointing out models: Original … Portable …. Home-crafted ... Slant-faced with internal reflector(s). 

Ye olde push stick.  This is like (the oven) we sent to Bob Metcalf, made (with) our wooden (Patio Solar Cooker) plans, (which we still sell).  It is a very basic (solar box).  It was designed so you can take the kind of wood that is produced in our lumber industry, and cut square cuts, and put it together.  So it avoids having to rabbit and it avoids having to cut angles.  (It is an) insulated box (with) double glazing.  I glue a little (lift) tab on the top glazing and just set it in there because I don’t want to trap moisture in there I can’t get out.. It does very well. (I can lift the top piece of glass to clean since it is) not sealed in. (Home-crafted wooden framed double panes always seem to trap moisture.) This thing never tips up.  (The glass is) perfectly safe and can last for years there. 

In the bottom is again a black tray.  It is (placed) up on some (spacers) so it is lifted off the bottom of the oven.  The temperature that this one gets … it has maximized at 354 F … but more or less in the 300 F range.  The others … 275 F to 300 F for the hand crafted ones.  Slightly lower for the portable, but it is nice to be able to carry one on an airplane.  The Eco we know it is going to hit  300 F on any good day.



This (solar food dryer) was built as a prototype in 1985 and I have used it every year since.  You can see how the air flows through the intake where it drops the sand and silt, (flows) up through the (heat) collectors, into the top of the cabinet (where the trays are arranged in two stacks). (The warm air) heats a metal plate (forming) the top third perhaps of this wall.  Which, on the other side, (of the metal) heats air (in the exhaust chimney) which causes a rising column.  This (exhaust chimney) is air tight except for an intake at the bottom, (between the cabinet and the exhaust chimney).  So the only place when this exhausts that it can get refilled is from the bottom.  You get a little vacuum there.  (Since the cabinet box is air tight, the only way the air can be replaced is through the solar heaters.) 

This pocket of hot air has heated the chimney and it also begins to draw down through the food, picking up moisture, getting heavier, cooling a bit. And as it reaches the bottom, the exhaust chimney takes it out. That is a real advantage because in your updraft dryers, your heat flows up through your food and out an exit (at the top).  (Heat) can go up into the food down a number of times during a cloudy/sunny, “on again -  off again” day (without ever exiting at the top).  (This encourages spoilage.) 

In your down draft dryer, if it is sunny, you have your exhaust vent working and your (warm air) flow(ing).  If (there) is not enough heat here to start the exhaust (flow), your heat (pockets at the top of the cabinet and) does not get into your food.  And therefore, you have reduced spoilage.  And (the safe drying) is also based, I think, in part on the fact that there is no stagnant portion (in the drying cabinet) here. (So there is practically never a problem with mold.) So you have better food preservation. 

(An alternative theory on why a down draft dryer works so much better holds that when warm air is introduced at the top of the cabinet and is forced to pass downward through the cabinet, it necessarily does so very evenly. As a result all the food on the trays receives a fair share of the drying action. An updraft dryer, on the other hand, introduces the warmer, dryer, lighter air at the bottom, which allows it to rise in an uneven fashion. There is nothing to prevent the air from forming vertical rising channel which favors a column within the cabinet, bypassing much of the food. This causes uneven drying in which some food may spoil from being held warm but still moist for too long a time.) 

Going down to the lower drawing: this is a schematic of the floor.  It is based on a 4 x 8 sheet of quarter inch plywood.  Could be harder; could be something else. Whatever you want.   It has the exhaust vent, the area for the trays, the area for the collectors. 

It is important to see these collectors not as the big block but (each) as a shallow tray coming up this way, independent of each other.  This one takes in air (and) gives it out to the cabinet. This (east) one starts with the early morning sun … takes in air and gives it out warmed into the cabinet.  And then in the forenoon, you get both of these (east and south) working.  This one (the east collector) drops off and you get these (the south and west collectors) in the afternoon, and this (west one works alone during) the final part of the day.  It won’t work if (the collectors) are not separated because if they are all in one cluster, your heat will migrate from the heating side and chill out on the cold side and never get into your cabinet. 

This is the air intake (coming) from the (solar) collectors.  I can feel the warm air moving through my fingers coming into the cabinet. If the doors were closed, it would make a pocket of air that would heat this metal sheet and cause a rising column on the outer side. 

If you see a black cage back there, that is an additional exhaust chimney that I put in when I realized I had made (the original exhaust ) too narrow.  So it is a retrofit.  Doesn’t change the theory. 

The doors are plug doors.  They are framed in such a way that they fit tightly into here because you want this cabinet to be air tight.  Otherwise, you are not drawing the hot air down and out.  You draw through the door. So you need a plug door that is rather tightly fit. 

This (food) has been (in) about 36 hours.  This, of course, is my hottest tray and it is cracking.  This is the tray on the bottom.  And it is not quite crackling but very close to it.    I like them to be brittle … I like chilies to be brittle dry. The tomatoes are finished.  Those will be used chopped up in salads or put into casseroles or soups.  Or just eaten like fruit.  They are delicious.  And they are done.



This is a collection of the food that has been processed for preservation here.  Much of it has been done in that (downdraft) dryer.  This (tray) is all solid vegetables: corn, okra, carrots, tomatillos, squash, broccoli. They go into soups.  They are great soups.  There are tomatos and peaches in here.  This was dried in 1991.  It still (has) vivid color and is in good condition in the February of 1994.  I am keeping it just to see how long it will stays in good condition. This has been kept (in the dark) at room temperature … (70 to 75 degrees F). 

For my soup I also have tomatoes that are canned in the solar box oven.  Tomatoes and fruits (sour foods) can be done by just putting them in (canning) jars tightening (the lid) and putting them in a solar box.  Things like meats, (this is elk meat) and green beans have to be done by pressure canner.  (Use any fuel you can) to make the pressure.  Solar energy (can) do pressure canning and that is how those were preserved. 

A lot of the preservation is fruit.  This is fruit roll.  Apples, raisins, peaches, apricots…any kind of juicy fruit dries beautifully in there. Or dried fish.  They work excellently. This is a whole set of greens: chard, beet greens, green beans, onion greens, turnip greens, kale, and beets. I use them all winter long.  I put them in a pot with a lot of water, put them in a solar oven (until they are cooked).  Then I pour the water off and that is a vegetable drink or water (to cook) rice, or water for soup. And then I serve the greens over toast. And they are good. (I use them to) keep a well rounded diet going (in the winter), in addition to the (food from the) greenhouse all year.



When you (use) the standard size (EcoCooker),  you can take a case of quart jars, fill them full of water, put dome (canning) lids on (tight and) put them in (the oven.) And, if you don’t paint the quarts dark, it takes 6 to 7 hours in Arizona sun to bring (the twelve quarts) up to pasteurization temperature.  (Darkened quarts take 4 or 5 hours to bring it up to pasteurization temperature.) But then you have got three gallons of water (sealed  in pasteurized) containers with lids on.  You can take them anywhere you want to. You can carry them in your back pack. You can put them in your truck.  You can put them on the shelf and keep them.  For the United States people,  pasteurizing in quart jars seems like a very good way to go. 

Some people build a deeper oven so that they can put gallon (jugs) in there. You always cook better if you paint (the containers) black. If you don’t want to (paint the jars) black, you have to take longer. 

Dr. Metcalf has figures on how long it takes to do the gallons.  I have never built one of those big ones.  I have just seen the pictures and I know that it happens.

There are other ways of pasteurizing (without using sealed quart jars).  The tricky point is that once you get it pasteurized, (the water) has to be kept clean.  You can’t get your finger over the edge, or stir with a dirty something, or let the flies crawl in it.  And you have to drink it from a clean container.  So if you have it in a jar that is already sanitized, then it is easy.  (Each person has their own jar and drinks from it replacing their own lid.) But otherwise, you might put cups in your solar (cooker) until they get too hot to touch, and knock down the microbiological growth that way. Or in some way have (only) clean things touch the water from the point of pasteurization to the point of (using it.)


49:30   END