Willow Basket Parabolic Solar Cooker
Created by Elizabeth Titus, Elle Parks, Simon Walter-Hansen and Bart Orlando for the Lost Valley Education and Event Center. Above - Kim Goulet displays Challah Bread she prepared and baked using the Willow Basket Solar Oven at the Lost Valley Education and Event Center in August of 2016.
(Please click on this url to watch the video. https://www.youtube.com/watch?v=_PmX6JB7cOs)
(Advance the video to 15:29 if you wish to skip ahead of the dough making details to the solar baking and grand finale.)
Testing Research Results For 2015 - 2016[edit | edit source]
'RESEARCH UPDATE 6-6-2015 The basket boils 2 gallons within 2 hours from 11am to 1pm on a sunny 82o f day at Lost Valley. '
'RESEARCH UPDATE 6-12-2015 The basket boils 2 gallons within 2 hours from 11am to 1pm on 5 warm sunny days in a row at Lost Valley. '
'RESEARCH UPDATE 6-13-2015 The basket heats solar oven to 325of within 2.5 hours from 11am to 1:30pm on a 75of sunny day at Lost Valley. '
'RESEARCH UPDATE 6-25-2015 The basket heats solar oven to 335of within 2.5 hours from 11am to 1:30pm on a 90of sunny day at Lost Valley. '
'RESEARCH UPDATE 6-26-2015 The basket solar oven bakes bread within 1.5 hours from 11:30am to 1pm on a 90of sunny day at Lost Valley. '
'RESEARCH UPDATE 6-29-2015 The basket solar oven bakes bread within 1.5 hours from 12am to 1:30pm on a 89of sunny day at Lost Valley. '
'RESEARCH UPDATE 7-1-2015 The basket solar oven bakes a batch of 30 cookies within 1.5 hours from 12am to 1:30pm on a 90of sunny day at Lost Valley. '
'RESEARCH UPDATE 8-3-2016 The Parabolic Willow Basket Solar Oven Temperature Reaches 350of for the first time on a 90of sunny afternoon at 2pm in the testing meadow at Lost Valley. '
'RESEARCH UPDATE 8-4-2015 The Parabolic Willow Basket Solar Oven Bakes a perfect carrot cake within 2.5 hours from 11:30am to 2:00pm on a 94of sunny day at Lost Valley. '
'RESEARCH UPDATE 8-10-2016 The Parabolic Willow Basket Solar Oven bakes perfect Challah Bread for the first time on an 85of sunny afternoon from 12 noon to 2pm in the testing meadow at Lost Valley. '
'RESEARCH UPDATE 8-18-2016 The Parabolic Willow Basket Solar Oven bakes a perfect vegan lemon cake at 375of for the first time, on a 96of sunny afternoon in 1.5 hours from 12 noon to 1:30 pm in the testing meadow at Lost Valley. A 2nd baking session yielded one large batch of oatmeal cookies topped with dark chocolate and coconut on the same afternoon. '
'RESEARCH UPDATE 8-19-2016 The Parabolic Willow Basket Solar Oven bakes a perfect Veggie Pizza at 400of for the first time, on a 104of sunny afternoon in 2 hours from 1:30 pm to 3:30 pm in the testing meadow at Lost Valley. Note - A prior first attempt at 11 am was slowed and delayed for lunch by 9 simultaneously occurring jet contrails that expanded and converged into 6/10 cirro-stratus artificial cloud cover, reducing the intensity of the sunlight which intern reduced the oven temperature. A batch of solar french fries was ruined by lower deep fry oil temperatures on 2 separate parabolic cookers as the first pizza was baking. '
'RESEARCH UPDATE 8-22-2016 The Parabolic Willow Basket Solar Oven bakes gluten free oatmeal cookies at 350of on a 78of sunny afternoon in 1 hour from 11:30 am to 12:30pm in the testing meadow at Lost Valley. A 2nd baking session yielded another batch of oatmeal cookies topped with dark chocolate and coconut on the same afternoon. '
8-12-2016 - Lost Valley: Parabolic Willow Basket Solar Oven Temperature Reaches 425of for the first time on a 95of sunny afternoon at 2pm in the testing meadow. [edit | edit source]
Reasons for using a basket as a model for solar cookers[edit | edit source]
by Bart Orlando
We wish to empower the people of non-industrialized nations, using a method of parabolic solar cooker construction that can employ the skills of traditional basket weavers, using indigenous plant materials. The instructions for making parabolic basket solar cookers, should be embossed or etched into the convex surface of solid aluminum or stainless steel parabolic parabolic solar cookers of similar shape, fabricated (out of salvaged metals) by factories capable of spin-forming or stamping out soccer stadium light reflectors. These durable, metallic paraboloids can then be airdropped to remote villages and refugee camps from C-130 cargo planes for use in educational demonstrations and as templates with instructions in universal stick figure language for weaving parabolic baskets.
Mirror finished reflectors should be provided from food grade stainless steel mirror finished lids from canned vegetables, (made without BPA liners), airdropped to remote villages and refugee camps, in order to feed malnourished/stunted children, while the rest of the can is used as a cooking pot after being initially blackened over a cook fire prior to use. By distributing thousands of metallic paraboloid templates, millions of parabolic basket solar ovens can be created by the very people who need them most.
Two billion women spend most of each day walking many miles from their villages to locate firewood for their cook fires, which is then carried back in large heavy bundles. Women tending the cook fires, breath in the smoke and contract emphysema. This type of deep focus-parabolic solar cooker can also pasteurize drinking water that would otherwise have to be heated with firewood or carried long distances from safe deep water wells. Parabolic basket solar cookers require about 100 times less work to use than what has traditionally been the norm for more than half of the women of Earth. This provides for more leisure time which could be spent participating in such things as literacy programs and building local cottage industries (such as solar oven basket weaving) to provide cash income.
Initial testing has demonstrated that this prototype can repeatedly boil 2.5 gallons of water and heat a small oven chamber to 330 degrees Fahrenheit in 1.5 hours, in direct sunlight at midday in the summer (and every sunny day in equatorial regions). In recent testing, following modifications to the design and the positioning of the oven chamber, it routinely reaches temperatures of 350 degrees f. and has reached 425 degrees f. on three separate occasions. It bakes cookies, cakes, bread, and even veggie pizzas!
Potential uses and applications[edit | edit source]
Parabolic basket solar cookers can be used for the follow purposes:
Pasteurizing drinking water
Preparing cooked meals
Satellite telecommunication dishes for internet up links, to be used for educational purposes in village schools. (antenna included in airdrop)
How Parabolic Solar Cookers Work[edit | edit source]
by Bart Orlando
Parabolic solar cookers are powered by VISIBLE LIGHT radiating from an immense hydrogen fueled
thermo-nuclear fusion reaction located 93 million miles from Earth, within the core of a star, we know as our Sun. Solar cookers convert visible sunlight into thermal energy (i.e. heat).
The word parabolic refers to the precise mathematical curvature of the reflective mirror which creates a reflecting lens that concentrates direct sunlight to a focal point when aimed directly at the sun. If a black kettle is filled with water and positioned at that focal point, it will receive and absorb more sunlight then if it were simply set out in direct sunlight on its own. As the concentrated sunlight is absorbed by the kettle it is converted into thermal energy which causes the temperature of the water in the kettle to rise as high as 100o C. In contrast, the light striking the mirror is not absorbed but is reflected and so the surface of the mirror remains close to ambient temperatures.(In climates where mid-day ambient temperatures are sub freezing i.e. at high latitudes or at high altitudes, any boiling water that spills from the kettle, down upon the surface of the cold mirror below, will readily freeze.)
In this way, the energy of sunlight can be directly converted into thermal energy for cooking, water pasteurization and for solar flame ignition all around the world. The mirrored surface can also focus a microwave signal for satellite telecommunications if an antenna is positioned at the focal point in place of the kettle and the parabolic basket, now a satellite dish, is aimed at a communications satellite instead of the sun and used for educational purposes, relaying news, emergency communications and internet uplinks.
Discussion of choices around construction[edit | edit source]
by Elizabeth Titus
This basket is meant to inspire indigenous crafters to use their local materials. Willow is a very commonly available weaving material, and relatively easy to use.
We looked at several online resources for weaving and willow treatment.
I used the weaving techniques shared on the site Jon's Bushcraft  for the base. Once I got to the sides, I decided to simplify to one weaver to enable the exact dimensions and shape we were going for.
The Math[edit | edit source]
by Elizabeth Titus
Before we began construction, we graphed 3 parabolas; y = .4x2 , y = .5x2, and y = .6x2. Bart chose y = .4x2 because it was just shallow enough to aim by tilting while remaining a deep focus paraboloid. We decided to create one that was 5 feet wide in diameter. I calculated the heights of different diameters accordingly.
For this basket, I created a chart of values corresponding to y = .4x2 for x and y up to 2.5, since our diameter would be 5 feet, so the radius would be 2.5. This happened to be the height as well. We decided to truncate the base at a diameter of 1 foot so it would have a level base (in addition to simplifying the weaving process). This was at a height of .1 foot, so I subtracted .1 foot from all the other heights.
Step by step procedure (best practices)[edit | edit source]
by Elizabeth Titus
Please click on the blue numbered hyper-links to view illustrative photo images.
Soak the straight willow pieces  for one day per foot of height. You want mostly 3-6 foot long pieces.
Here is a chart of values we generated for height and diameter.
|2||about 3 2/3 inches|
|3||about 9 2/3 inches|
|4||1 foot 6 inches|
|5||2 feet and 5 inches|
This site was the main inspiration for technique: []
Select 12 - 16 willow pieces to be original stakes. We used only 6, and got the feedback that it would be stronger with more, but it may be more difficult to begin.
Slice with a knife into the middle of half of the stakes , threading the other stakes through all the split ones . You might alternate thicker ends for more symmetry (hence stability) throughout the basket.
Take two smaller weavers. Trim to points, and tuck them into the same slot in a split stake, take them around the closest stake, twist them on the other side , and continue crossing over each stake and twisting once on the opposite side. As you do this, work to spread apart the stakes so they fan out from the center. A helper friend might be useful here. When one weaver runs out, overlap a new one in to splice it. Weave in this fashion until you have a circle with a foot diameter, filling in gaps if need be.
Once you have your circle base, notice how strong, flexible, and long your stakes are at the circumference. Select some new stakes to trim to a point and insert to the right of selected stakes you want to replace before you continue. Any replaced stake should be cut off at the edge of the circle. 
Now you will create the rim of the bottom of the basket. Warm up the base of the stakes by rubbing them and bending them gently, then bend one to the left, behind two stakes and then straight up. Do this with each stake in succession, to the left, tying stakes upright to get them out of the way. A friend can be helpful here, too. The last two you will need to tuck in and up, so the pattern continues all the way around, and creates a self-contained rim. 
Stake the 2 foot hoop up about 4.5 inches off the ground. I added a bit of height to account for the basket bottom. You might use solid willow pieces, sharpened at both ends in order to be driven into the ground and stuck into the hoop.
Stake the basket to the ground in the center of the two foot hoop. Tie the stakes to the hoop, letting them spiral a bit but trying to get the center stable  . Weave in and out with one weaver at a time until you reach the hoop.
Set up the 3 foot hoop so it is about 10.5 inches off the ground. Set the basket up inside it, without the previous hoop, and weave until you reach that one  . Continue with the 4 foot hoop, which is about 1 foot and 7 inches high , and the 5 foot hoop , which is 2 feet and 6 inches high. You might decide to use other wood for stakes, sharpening the end to drive into the ground and adding a nail to the top with its head clipped off so it can attach to the hoops . 
As you weave new ones in, you might use them to stabilize previous weavers by weaving in and out toward the base, then turning to weave sideways. Push down your weavers as you go and work to tuck away ends neatly for more stability. When you are done, trim ends that stick out too much. You also might add new stakes in as you go by pushing them into the weave, and preferably base.
Once you reach the top, leave some of the stakes sticking out to hold the weavers, trimming them up. The top would be easy to pull off, so select some good pieces to make handles that also hold the top on. Shave each end to flat wedges, and for extra grip carve several upward facing notches on each side. Warm up the willow by gentle bending and rubbing for warmth. Bend each piece and insert ends at a chosen distance apart around the top. Place two together for stronger handles. Be conscious of how much of a gap you are creating; too big a space will make it easier to accidentally pull them out.
Debrief (what worked , what did not)[edit | edit source]
by Elizabeth Titus
Willow is much easier to work with when properly soaked. Harvest in the winter, let sit and dry for many months, then soak for a day per foot of length. Take it out to mellow a day before you use it. Try to use it for the base within 4 days of soaking. This is the trickiest part, with the tightest turns. Once you get up to the 2 or 3 foot diameter hoop, the turns are much more forgiving and you can be less selective about the state your willow is in. If your willow is breaking or creasing, check your soaking methods and maybe spend more time warming it up where you want it to bend.
We tried a lot of methods for measuring the dimensions of the basket as we worked, including trying to make an internal guide with a stick as the axis and strings attached, an external hanging basket with the hoops tied together in order to cradle the basket, and measuring and re-measuring as we went. The best technique by the end seemed to be staking up one hoop at a time, and centering then staking the basket inside. I did a lot of number crunching to try to calculate other relationships between points and diameters, but the simple height:diameter relationship was definitely the most helpful.
Staking worked okay with sharpened willow stakes, but we needed something taller and more uniform for the higher hoops.
We decided that storing the basket upside down might be the best to maintain integrity.
Additional Note From Bart: After one year, the basket began to loose its true paraboloid shape and began to sag along the side closest to the ground (when aimed at low declination angles) as shown in the linked photos.  I think this is because it was agreed not to use the hoops as permanent-attached constraints that would have been evenly spaced from the base or vertex up to the rim as originally intended and indicated by the results of a previous attempt at weaving a parabolic basket solar cooker in 2007.  However the sagged shape turned out to be almost perfect for baking cakes and cookies in late summer when the midday sun was at a lower declination.  This shape would not be suitable for mid-day solar cooking in equatorial regions when the sun is near zenith but would be suitable for use in the morning and late afternoon in those regions. Perhaps both styles should be made for use during the two extremes of declination angles.
The maximum oven temperature observed was 335 degrees Fahrenheit on a 90 degrees Fahrenheit day. Higher oven temperatures were probably achieved on days over 100 degrees though no measurements were made on those days. 325 degrees Fahrenheit on a 75 degree day was the maximum photographically documented temperature.  
I feel that a stronger skeletal structure for such large baskets should be made of rattan or bamboo in a way that allows for materials such as willow to be woven in to fill out the shape of the basket. Papasan chair frames provide an example upon which to base such a design.
I feel that the next attempt at a basket solar cooker should use circular 10" diameter aluminum mirrors that mimmick the use of mirror finished vegetable can lids.
The Willow Basket Solar Cooker Boils Water[edit | edit source]
Please Click Start The Black/Red Video Arrow Icon And Then Click Full Screen.
Parabolic Template[edit | edit source]
by Bart Orlando and Simon Walter-Hansen
A parabolic curve, of the equation y = .4x2 was plotted using a Cartesian plane with x and y axis drawn on the surface of a large section of 3/8" thick scrap plywood. The curve was cut out using a jig saw. This parabolic template was suspended within the basket periodically to check that a precise parabolic curve was being woven.   
The Aluminum Mirrors[edit | edit source]
by Bart Orlando and Simon Walter-Hansen
Mirror finished aluminum was purchased from the Alumet aluminum supply company. 
Two 4 x 8' sheets were cut into wedge shaped facets, technically referred to as gores, using a plasma cutter. 
A facet shaped wooden guide was made for the plasma cutter to trace along.  The facet width was approximately 7" and the facet length was chosen to extend from the basket rim down to the edge of the outer circumference of the flat 1' diameter base of the basket which is shaded by the suspended cooking pot.
The facets were attached to the basket using zip ties threaded though three small holes, drilled near each corner of each facet.
These mirror finished aluminum facets will be replaced with mirror finished, food grade stainless steel can lids as soon as possible in order to demonstrate the feasibility of using them as solar reflectors (and solar-cooking kettles), as would be the case in remote villages and refugee camps receiving airlifts or airdrops of such custom-canned vegetables.  
Special Thanks To[edit | edit source]
Colin Doyle - Director of Permaculture Projects Lost Valley Education and Event Center
Justin Michelson - Executive Director - Lost Valley Education and Event Center
Simon Walter-Hansen - Engineer/Mentor - Lost Valley Education and Event Center
The Lost Valley Education and Event Center [www.lostvalley.org]