Tracking Solar Cooker Project 2023 and 2024. Solar Cooked Soil, Mulch, Weed Soup, a New Approach in Gardening! (Now With Image Notes!)

Imagine a world where you could make and sterilize your own potting soil and you could process weeds and vegetation in a big garden straight to good mulch in a single day without needing a compost heap! And do all this with the power of the sun! In October 2006, I was off work after surgery and I made a solar cooker. It was fun, the weather was freezing but sunny and each time it cooked a mason jar of food I marveled that it could do that! Not exactly useful but I soon got hooked on the challenge of making a low tech tracking solar cooker! Something that might be really useful for the poorest of the poor so they could solar cook their food without damaging their eyes or getting heat stroke. The king of solar cooking devices at the time was the Scheffler Solar Kitchen but although a nice concept, (only one small motor was needed to work it), it had complex engineering. I wanted to make something simpler (a kind of Scheffler light version) that might bridge the gap between the necessarily large complicated high end devices Scheffler made and something that people could afford, and maybe even make themselves. I made a proof of concept device way back in April 2008. I didn't know how to time it to make it turn at the right speed (15 degrees per hour) but it did much of what I intended. I uploaded details of the concept to a solar cooking website and I thought others might have funding and they would see the value and complete my idea, but nobody ever did. The years went by but I never had enough time to advance the project. I couldn't work in late 2023 due to health issues so I had enough time (but little energy). I began the project again!

For the fork mount and reflector. Metal fence tubing for the axle, a pair of ball bearings, reflective aluminumized plastic, pallet wood, (some in the 6 by 8 size) chloroplast, wood screws, aluminumized plastic

For the timing device, a slow syndronous motor, 1 rpm or slower, an old oscillating fan, (to gear down the rotation from the slow motor), a programable timer (to start and stop the slow motor power at the right times of the day, and to (throughout the day) turn on and off the slow motor again and again so that the gearing down is exactly right to move the reflector at 15 degrees per hour. Some fishing line. A small aquarium bubble pump. This provides air to give you the gradually increasing air pressure that you need to control the speed of rotation of the reflector and air to run the airlift pump that lifts water to turn the waterwheel that powers the winch that turns the reflector. Tubes and garden hose to bring the air to the solar cooker and to make the airlift pump. A one ft square piece of 3/4 inch plywood to make the waterwheel, an old oscillating fan to use as the axle for the waterwheel and the winch. 18 plastic cups to make buckets for the waterwheel and 18 short wood screws to hold the buckets in place. For the water pressure controllers about 18 inches of light rubber tubing , and one length (10 ft of 4inch white pvc drainage pipe. I cut up old ties for concrete forms to make the little levers that clamped the rubber tubing that controlled how fast the air went to the airlift pump.

Wolfgang Scheffler is an Austrian Physicist who trained in Germany. He could probably got any job he wanted but instead he wanted to build a tracking solar cooker that he had come up with. It required some fairly complex welding, etc. and he couldn't get it done cheaply enough in Germany. So he went volunteering in Kenya, and using cheap local labor, he was able to get the thing made to his specifications. He built the solar kitchen that he wanted to build. It wasn't perfect of course so he worked to fix its teething problems for about a year. People in India were interested, so he went there and build more and bigger Solar kitchens. This was a success too. Scheffler solar kitchens have a big mirror that is well balanced and that uses a clockwork to make it rotate at 15 degrees per hour, and maintain the sunlight on one spot all day, and every day. this is usually a hole in a wall where the light heats up the underneath of a cooking surface. This saves the cook from being blinded by the light, or getting heat stroke from the hot sun beating down on his or her head or back. It is great! So what is the problem? Scheffler's solar kitchen has a big reflector that rotate slowly, and every few days it must be adjusted to maintain its focus on the heat window into the kitchen. Other tracking solar cookers are more like big guns on gun turrets, they have to raise and lower to the right angle and turn at each adjustment. Minimum 2 motors and usually a solar tracker to to point at the sun. Scheffler's is way simpler to use. One motor, one speed all day. But the suns path is a little higher or a little lower in the sky every day, so after a few days, you have to readjust the elevation. Every time you redirect it, it automatically changes the angles of each of the individual small mirrors that make up the Scheffler reflector. All 200 of them in the case of the photo! The lens shape itself is adjustable! Even though the change is automatic, and it is done this way to maintain the balance of the device, the cost of Scheffler devices is much greater due to this feature. I have seen university studies of Scheffler solar kitchens from the USA. It can take an entire semester to make one! An ideal tracking solar cooker should be possible to make in your shop in part of a day and whether you make it or buy it, almost every other reflector in the world are fixed focus. So really the task is to make a rigid reflector work a bit like a Scheffler system. One rigid reflector to replace 200 on a deformable metal grid.

Back in 2007, a solar cooking site said that simple solar tracking is the key to getting solar cooking used all over the world. Because Scheffler's method was the best in the world, I studied it, and I used David Delaney's website to understand how and why he did what he did. Maybe there was a way to do something akin to Scheffler that avoided making a flexible reflector? I think people are intimidated by the completeness of Scheffler's solution and nobody ever tried to tweak it! It only took a few days of thinking and understanding to come up with an alternative solution. Scheffler rotates his parabolic dish on the "Equatorial axis" that also passes through the focal point of the hot spot. My solution is to that the entire parabolic dish also rotate with the heat's focal point along the axis of its rotation You adjust up and down on that second axis for seasonal adjustment. And all you need to do that is a fixed size dish and a "fork mount". You do have to do something about Center of gravity issues as you do seasonal adjustment but it isn't an insurmountable problem.

I sometimes had a lull in work over the summer, and would try to arrange my thoughts in a coherent way. And perhaps I even got close to a working solution but I never actually cooked things with those attempts. The part that I never came close to figuring was an accurate timing mechanism. Good clocks were made about 200 years ago, by the British Navy but I couldn't come close to making a decent timing mechanism. I tried to adapt various analogue clocks and timers over several years and nothing worked. I did figure out something that would work, with a little electronic timing system inside but I didn't know how to make it.

Note, this is clunky, it is not what I wanted to do but it works. I had the spare time in 2023 and decided to make a clunky workaround for the timing problem. I couldn't make a little electronic device to time the rotating of my reflector and I had spent years trying. I just don't know how. BUT! I had continuous low pressure air (roughly 3 ft of water pressure) for my pond aeration and for mini airlift pumps in the greenhouse so I made a system that would let that air from the air pump into another pipe. This was very clunky! When you buy a synchronous motor it must be either CW (clockwise) or CCW, (counterclockwise) the first one I bought was CCW/CW which means it can rotate either way every time it gets switched on! (Which is useless!) I bought a cheap synchronous motor that turned at about 1 rpm (much too fast for timing) and I had it attached on an old oscillating fan where the fan blades should be, it turned the fan shaft which geared everything down to turn the oscillating part, to which I attached a wheel and I attached fishing line to the wheel, the fishing line lifted a float that controlled the air pressure in the system. The air pressure was the same everywhere in that little closed system and gradually increasing. So whatever I produced in the shed could be replicated anywhere in the system. (I only did 2 equatorial mounts, but they both replicated what my timer at a distance did.) The gearing isn't perfectly synchronized to turn the reflector at 15% per hour, in my case, it was turning it almost twice as fast as needed. You would have to be a great engineer to calculate and cut gears to get it exactly right. And that is why I have a programmable timer, I have it turn on for a minute or two, then off for a minute or 2 and do it continuously. I only needed it to work for about 10 hours per day, so I had it turn on to do that cycling about 8.30 and then off again at about 6.30 pm. And then I would just unwind the fishing line a few turns ready to start again in the morning. This would work perfectly if my system did an exact number of turns of the blue plastic wheel in 10 hours, but it didn't do an exact number, so my reflector would have to be adjusted in the morning to point at the sun. So, I began tweeking the length that the timer ran. After a few days, I found the spot, I just left it run till something like 7.15 pm and it did an exact number of turns, and I could reset it for the morning, and it would restart automatically at the right time.

My first working equatorial mount was for a solar panel. There were 2 reasons, number 1, isolar panels don't need to be perfectly pointed at the sun, so I if things were not perfect, they were still good, and number 2. It is very easy to know where a solar panel is pointed. It often isn't so clear with a parabolic dish how accurately it is aimed. A 3rd reason is because I was asking others what material to make the reflector from. And the answers I was getting were not making sense.

People were insisting that aluminum foil was a good reflector, but I was worried about getting the foil flat enough and my concern was about losses due to crinkling. So I shone a laser on aluminum foil (different brands of kitchen foil), aluminum sheet and other materials. (plastic coated with aluminum from various chip bags, chocolate wrappers etc.). The reflection was really strange from aluminum foil and aluminum sheet. In one direction, the reflection was a line, and in the direction at right angles to that the reflection was a semicircle! I proved (with a microscope) that the aluminum foil and aluminum sheet has little ridges on it (just like the corrugations on a metal roof on a farm building) and these tiny corrugations explain how we get a semicircle reflection in one direction and a line reflection in the other. (if the surface was flat, the reflection would have been a dot. The aluminum chocolate and chip bag wrapper did have dot reflections. Many people refused to believe my explanation or my results. They got so heated about it that people (en masse) refused to point a laser pointer at any reflective material in one solar cooking group. Unbelievable! Anyway, what is needed for a good concentrating solar cooker reflector is a "mirror like" or specular reflection. And it turns out that there is a simple test we can do! If you get a mirror, and put a little square of the material on the mirror, that you are testing, put a drop of water under the material, it will stick to the mirror and become flat. Shine a light on the mirror, and let it reflect onto something white. If there is a dark patch reflection of the material, it is not specular. if it is hard to tell it from the mirror reflection, then it is a potentially good material. Another thing. If you shine a laser on the material, it should not be able to shine straight through it. That's a pretty obvious one. Unfortunately most aluminum coated plastic lets light get through. Plastic aluminum colored plates from the dollar store were best! Hopefully that means that People can make great paraboloid dishes using the same technique! I had not received any strong recommendations for the "best" reflector material. (Several people insisted aluminum foil was the way to go, and some simply denied its weird reflecting properties) My problem with something that "weird" is that results would not be reproducible from one hour to the next and that the reflections would be different depending on in what direction the material was applied. I ordered a random aluminum coated vinyl wrap. I was hopeful. Unfortunately, it wasn't fully opaque and also it started to fade a bit even after the first week, but still, it was still cooking pots of soil and weeds into October. So, it wasn't terrible, but also not suitable because it was fading fast. I left it out over the winter to continue the fade test.

I wanted to make a partial parabolic dish (somewhat similar to what Scheffler did) but I thought that people would think it too weird. They expect something looking like a parabolic dish, so I should give them a dish. Also, I still wasn't sure how accurate my solar tracking method was. So I made a dish that was "tighter" that a parabolic dish. What that means is that a parabolic dish has a focal point ( a tiny spot where all the light will be concentrated if it is pointed straight at the sun) but if it is not pointed exactly at the sun, a lot of light will miss the target completely. The plan was for the light from my dish to form a focal "ball" that was the size of a large cooking pot. Even if the dish was inaccurately pointed at the sun, the reflection would still form a "ball" and would still heat whatever was in the pot. I made a "deep dish" to prevent stray light exiting the dish and igniting fires somewhere else in my back yard. (That is actually a thing) Looking back, I wish that I had done the partial dish. Because the tracking was more accurate than I had hoped and I used too big of a pot size when I designed the "focal ball". I couldn't fit a turkey bag over the original pot (meaning I couldn't insulate it well) and when I used a smaller pot, much of the light of the ball missed it.

I had something like 6 months of testing and looking at the solar panel mount before I built the reflector mount. Originally, I was going to use the same size axis bars and bearings. But then the idea of using the axis to deliver material to and from the cooking pot appealed to me. Maybe I could have a cooking pot on top of the mount sometimes, and other times, I could swap out something where I could suck air through a pot with holes in it, and down through a mounting pipe and use the solar heat for dehydration! I made a mistake initially and had the dish rotating around the top of the focal area instead of the center of it, but that was fairly easily corrected.

I had a big container of water with a float in it and another closed container which I could fill air into to push water into the float container. I reasoned that this was so overbuilt and powerful that it would keep the reflector accurately pointed at the sun. It didn't because the center of gravity changed during the day, so I set it up in a different way. The air pressure in the timing part lifted a float that was attached by string to the rotating wheel of the fork mount. If it lifted it high enough an air valve (connected directly to the normal air pressure system) opened. Then air pushed into the closed barrel, forced water into the float container and lifted the float until the fork mount moved enough to close the valve. This worked great. Also at the end of the day, when the air pump stopped, pressure dropped due to a small leak in the system, and the reflector returned to its start position! It was now totally automatic!

First cooking stand was too weak and the pot leaned, etc. I made a stronger one and things went well. I made it on a wider pipe that I could quickly swap off if I wanted to try a drying experiment. Or if I wanted to make a better cooking stand. For my first tests, I set up the reflector in the morning and about 9 or 9.30 am, I poured in water and filled the pot to the top, placed it on the stand , put on the lid and let it cook. It became apparent that I needed a cover because at about 80C it didn't get hotter anymore. Then, I bought a turkey bag and realized my mistake. The pot was too big! And the focal ball was too big, because I had designed the reflector for that pot. With a smaller pot, covered with a turkey bag, I had no problem bringing stuff to the boil, but an unknown quantity of light and heat was missing the target. It was very disappointing but at least the thing still worked. I wasn't going to be able to test its limits, but at least I could do some useful stuff.

This part went well! I was using my 7 liter pot (instead of the 11 liter pot I had intended to use), but it wasn't all bad. It was easier to lift 7 liters. The routine was to put the pot on at about 8 pm, at night, put on the lid, put the turkey bag over it. Then the solar cooker would start tracking about 8.30 am, and get pretty hot at about 10 am, and potentially stay up at around 85 to 100 degrees C all day. Steamed soil was made by sieving dry soil, adding about 2 liters of water, letting it steam all day, and emptying it in the evening. Some days it was cloudy, and I would just leave it in the pot for another day. Perhaps a thermometer that records temperature all day would be useful. Weed soup was different. In that case, I would weed the garden, or clip the tomatoes back, or clip back some blackberry bushes, or mow the lawn, or take diseased stuff off the squash plants, chop it up and pack it really tightly into the 7 liter pot. Then pour water over it, put on the lid, put it on the stand on the solar cooker, put on the turkey bag and let it cook. Again, I usually did that in the evening so the cooking could start in the morning. Some days, it would be soil steaming, some days it was weed soup. Depending on my mood, what was available and what needed to be done.

I swapped on another pot, this one had a hole in the bottom, and the lid was loose with holes in it and I had the wider pipe epoxied onto it to fit onto the axle pipe. This worked really well, and I put a fan down below to suck the hot air through the axle pipe and the plan was to suck it into an old dehydrator. BUT, the axle pipe lost a lot of heat. I insulated the pipe and even so, it was still not producing or moving as much heat as I had hoped. It had to heat the whole axis pipe before the heat of the air at the end rose significantly. All in all, delivering hot air through the axis pipe was not a success. Plus the fan that I used was a computer fan. When the exhaust air got to something like 50C, how long might it continue to work? And it wasn't an option for me to put the fan at the start near the pot because the heat there rose to over 100C! So, I guess it is a fail as a dehydration device.

I don't like spending money on "potting Soil" or any inputs for the garden for that matter. Because the garden already had soil! But garden soil has weed seeds and pests in it. If you cook the soil, it is reasonable to think that the weeds will be killed and many of the pests too. Indeed, they steamed soil in Carlow Ireland in an agricultural research center when I briefly worked there a long time ago. I started to use the soil on my vegetables in pots and containers and weeding was greatly diminished. Plus, I think the plants grew better. Weed soup was a bit different, At the end of the day, I poured the soup out into a container with a hole in the bottom, it was on top of another container that collected the liquid. I used the liquid like compost tea diluted at about 1 in 20 in the watering can when I watered the garden. I used the dry cooked weeds as mulch. The mulch rotted far quicker than uncooked weeds. Oftentimes, weed soup smelled delicious. Rose clippings and blackberry shoots and leaves and the water from them, smelled like strong perfume, wild fennel smelled like licorice, and ordinary weeds might have a sweet smell that wasn't bad. I don't know if dilution was necessary but I did it due to an abundance of caution. I believe the carbohydrates and sugars, minerals, etc. dissolved in the soup water probably gave soil bacteria a big boost. After a couple of months at most of mulching and watering with weed soup, there were various "flushes" of mushrooms in my garden. They seemed to happen more in the areas where I had mulched and where I had watered a lot with the weed soup. (I went looking for photo's and videos of the mushrooms, but I couldn't find them. I like the weed soup, mulch idea, because it gets the material and nutrients back into and on top of the soil, as little as 24 hours after the plant material left the garden. The best compost will take maybe 3 months to mature, and at the end of the season, it won't return to the soil till the next spring, instant return to the soil beats that by a long distance!

I was making a little planter on top of a wall, I filled it with plant material from weed soup underneath, and solar steamed soil on top. But there was a problem! I ran out of solar steamed soil half way. So for the rest of the planter, rather than wait for steamed soil, I just used ordinary soil from the pile that I used to make steamed soil. Then I transplanted lettuce into the soil and did a comparison test. I expected a slight difference. Maybe steamed soil being about 5% more productive was my guess. But the result, within a month was that the solar steamed lettuce had grown roughly 20% heavier than the lettuce in ordinary soil! This was far better than I expected. I believe that not only were the weeds killed in the steaming, but a whole bunch of soil bacteria and fungi died too, and they and the dead seeds provided food for the new colonization of the material, just as the lettuce needed nutrients. I did see some red fungal like growth on the cooked soil that did not appear on the uncooked soil. In any case, the difference in growth rate of lettuce was very clear. I don't know if lettuce is a special case. I am sure many people have done comparisons of steamed and unsteamed soils and I am sure my findings have already been proved in the past. (That is why composting facilities and potting soil makers heat the compost to a high temperature). I did see a report that an organic gardening group in the UK does not approve of steaming soil. But only because the steaming uses a significant amount of fossil fuels! Solar steaming on the other hand might use a negative amount of fossil fuel (because it substitutes for transported steamed soil). Both pictures show the same lettuce. In the pictures, taken a few days apart, the lettuce on the right grew in steamed soil, that in the left grew in non steamed soil. You can see weeds in the unsteamed soil. Color on the right is also darker green, meaning it is getting more nitrogen from the soil. You can probably see the size difference too. So, imagine a world where almost every back garden has an automatic tracking solar cooker! (See the end of the instructable for details) Mine only cooked 7 liters at a time, but these are optimized. They take 5 US gallon buckets (approximately 18 liters) at a time. The sit on a hotplate and the rest of the can resides in a heavily insulated oven. A little alarm goes off or a flag drops down when your soil or weed soup, or mixed vegetable soup is cooked! And this oven has a little fan too, so it can crisp up your herbs or dry your fruit on a sunny day if you need drying done!

The water barrel, and the half waterbarrel and the float took up a significant chunk of my backyard. Sure they could rotate the solar reflector, but the whole thing was just too bulky. I needed to find something much smaller. So I looked online. Daniel Connell's sunflower used something internal to the device that was slightly akin to a waterwheel to move the thing. I had success making the first part of my timing mechanism using an old fan, so maybe I could use an old fan to somehow modify what he did and successfully rotate my much bigger reflector? This quickly became a no no, because every second-hand oscillating fan I took apart had plastic parts for the worm gear and I couldn't see them lasting in a gusty wind without significant damage. Next I found out about capstan drives and went to hook up twines like a winch directly to the shaft of the fan axis. I set up my waterwheel and this had no problem producing enough power to move the solar cooker. I was surprised, but happy. This was much smaller than the other solution, and I think it is more likely that people will try it and use it. Note that the waterwheel did not automatically reset in the evening, you had to wait till the airlift pump stopped then wind the waterwheel back a turn to let the buckets empty, and then it spins itself back to the starting position.

To me, 2023 and 2024 were a great success but a little too slow. I wish to go straight to the "right stuff" this year. Here is the new design idea, I will marry what I did way back when, with a fork mount. Essentially, I am going to have a fork mount, and a section of a dish on it (like in the photo). The fork mount will come all the way up to alongside the cooking pot, and the section will tilt on that axis for the seasons. The "section" will be in 3 parts. A middle and 2 outer parts. Only the middle and one of the outer parts will be used at any given time. I will do a drawing later to show what I mean. (It is to prevent the center of gravity straying too far.!

No need for bringing the stand for the cook pot through the reflector, because having a slice in the reflector damages its structural integrity. I will have a separate cook stand coming down from the north, made more like a stationary solar oven and it will have a "shield" so the user doesn't get stray rays in their eyes.. (here at 48 degrees north). Light will come in under the cook pot focused to a point as much as possible. We will try to focus all the light on the bottom of the cook pot and have the rest of it as insulated as possible, so when the heat goes into the . So I will have to build a proper parabolic dish this time. I'm trying a different plastic material to cover the dish, it has thicker aluminum on it so I'm hopeful to do meaningful experiments. I'll continue to use the waterwheel winch, and hopefully improve it. It would be great if it worked forwards and backwards. Probably have a bigger "gearwheel" on the reflector and at some point it would be nice to do photodiodes to open and close the air valves that work the airlift pump. Another fun thing might be a low tech heliostat to send light from the north, east or west to greenhouses for extra illumination.

Almost all solar cooking has eye safety issues. Nobody wants concentrated sunlight to flash in their eyes. And I think if people make designs based on the model this problem can be mitigated. The model is for my latitude (48 degrees north) so the tilt on my equatorial mount is 48 degrees and it is facing north. If you live in Los Angeles, the mount tilt would be 34 degrees. (That probably makes things easier for you). For instance, my stand for the cook pot would be about 4 ft 4 inches high, so I would probably need a step up to it or build the thing on sloping ground. No step needed in Los Angeles for a similar sized reflector! because of the shallower angle. I don't have a parabolic half dish in my model because I have not decided on the length of focus, etc. yet. This model is of something I can make. If you have welding and metalwork skills, you have options to simplify the design. (attaching the reflector to a sturdy stand, instead of separately to the ground like I did). If anyone wants to help this project get to the next level, I thing the best way is to make a version of the little blue gear wheel motor thing in the picture above. It must be possible to program its speed, so it can work with any size equatorial mount wheels or gears. If gardeners have access to large standard reliable tracking solar cookers, they can mulch a lot more, re-use horrible weeds like bindweed and morning glory and various diseased plants (without putting them in the garbage). Plus being able to steam their own soil will save enormously on transport of soil around the country every year to fill greenhouses and people's pots with sterilized soil. Anyway, that's it, till I revise it some more. Thanks Brian