Butterfly Expo

March 31^st 2008

Today AMADER (the Malian Agency for Domestic Energy and Rural Electrification), the group who financed the development of the Butterfly so far, had a demonstration for a department of the Ministry for the Promotion of the Woman, Child and Family. The object of the demo was to highlight the link between energy and the family. AMADER asked that I bring the Butterfly and Helios and do some cooking.

Here we are setting up the Helios on the edge of a soccer field. Once the mirrors started going up their curiosity got the better of them and they put the game on hold to come hang out while we set up the machine.

Some of the adults were concerned that the children would burn themselves with the Solar Fire, but teaching the kids some solar safety was easy, even if we didn’t speak the same language. The trick is to get them to put their hand in the focal point, but not at the point of most concentration. They exclaim and withdraw their hand, surprised by the heat. Then you get them to put their hand back in and slowly move towards the point of maximum concentration… they don’t get very close. Then you burn a stick and the message is clear.

Unfortunately we didn’t have time to organize any baking of cake, but gathering the ingredients to make a nice pot of rice wasn’t hard. Note the rolling boil we’ve got going on. That’s about 5L of liquid and 1.5kg of rice, plus some veggies and beef.

The ladies from the ministry were mightily pleased. Two of the biggest advantages they see are time saved gathering wood out in the bush and improved cleanliness. Cooking on a fire leaves the pot all black and sooty, which dirties hands, clothes and dishwater while solar cooking leaves the pot as clean as when you started (except if you burn the rice, which we almost did…)

Now granted I’m a little bit taller than the average Malian woman, but the ergonomics of the machine are still quite acceptable for women here. Traditionally, cooking is done on the ground over a fire, and overcoming cultural inertia is never easy, but a number of the women we’ve talked to have said the equivalent of ‘so what if I can’t cook on the ground if I don’t have to go gathering/buying as much wood?’

Now we’re going to embark upon more expensive testing and fine tuning of the Helios bread oven as well as the Iron Butterfly designs.

Meanwhile, administratively things have stalled a little bit. I had left the association to do its thing while I do tech development but their follow-up on the contacts we’ve made has been less than satisfactory. I’ve put my hand back in the mix and we’ll see how things progress over the next couple of weeks, at which point important decisions will have to be made.

High hopes, as usual.

Boiled water

The first step to forcusing is determining where we'l place the mirrors. Since we're talking about inclined mirrors arranged on a flat surface there is bound to be some shading/blocking issues. Here, Djadje moves two mirrors around the wing and draws a rough guide to mirror placement so that we can space the mirrors effectively.


To space the mirrors effectively we--
Wait! Stop everything! Emergency! The teapot is broken! All work ceases and Michel heroically breaks out the oxy-acetylene torch and welds it back together. Phew. OK back to work, nothing to see here.


Using the mirror map we drill holes and place three screws in a broad triangle beneath each mirror. By placing a mirror on the screw-tripod and by varying the height of the screws we can incline the mirror such that it reflects onto the pot. You can see one mirror is on target while another is hitting the building.


Once we have all the screws properly adjusted (it's not enough to do it for one time of day, it has to work all day, so once you do the initial focusing you have to keep it on target for a day or two and observe how the mirrors react to different insolation (INcoming SOLar radiATION) angles and adjust accordingly.) we can proceed to backing the mirrors. I'd settled on styrofoam/glue mix. We bought a large quantity of styrofoam for next to nothing and got to work busting it down.


It wasn't the easiest process:


But it did the trick. The problem was how to weigh down the mirrors so they would stay in contact with the screws. For our first try we makeshifted a fast solution because the glue was drying fast:


Afterwards we reflected and determined that we could glue the mirrors and then tie them down using wire. We found out that wire worked so well we didn't even have to glue them.


That means that we could mount the wing and adjust the mirrors a little bit while we saw how they behaved on the machine. They behaved pretty well! We managed to boil some water, and we're at only half power! I assume we're at around half power, but you never know what ol' bucket-o-rocks is up to.


This bodes well for the final product, but the hardest part is yet to come.

The next step is to build the mold, and then use that mold to stamp out copies of our original. It will not be easy. Again, if anyone has any ideas about how to effectively make a very large mold of these mirrors let me know.

Geometry Achieved

Today was a wicked day.

Not only did I get a drive to work (instead of spending an hour walking and taking a packed van) but we basically finished the frame for the Butterfly (my variation on the Papillon) and proved the geometry is sound).

There were a number of problems that I had foreseen (weight distribution, pot placement, spaces between mirrors, mirror shading etc) and had assumed that we would be able to solve with a certain amount of elegance. Kudos to us for actually being able to.

Also, the butterfly is a test of construction precision, because unlike the other Solar Fire technologies, this one is pretty rigid. The Vesta, Apollo and Helios, however, all have movable mirrors and can be modified fairly easily. The butterfly is a one-piece reflector that must follow a pretty precise line of movement to track and reflect the sun easily. Initial indications… indicate… that we achieved an acceptable level of precision. Must be due to all the vicegrips:


And our counterweight (speaking of elegant solutions, note the paintbucket filled with rocks tied opposite the wing):

The butterfly works like this: the two wings face the sun directly, and will eventually be covered with 10cm by 10cm mirrors (like the one I'm holding)
which will reflect the sun onto the pot at the center. The paintbucket-counterweight will eventually be replaced by another wing, so the weight will be balanced. We've substituted that wing for a counterweight because I didn't know how this experiment would turn out and didn't want to make two wings if their shape/construction weren't for certain. I reverse engineered this design by looking at some pictures of the papillon, and so nothing was for sure.

The mirror angles at the edges of the wings are pretty acute, which means that we'll have to fill fairly large spaces with the woodglue/sawdust or Styrofoam mix, but luckily I happened across another type of plastic foam with better cohesion than Styrofoam, so we'll be able to cut it to fill the majority of the space without using large quantities of glue:
However well things went today, the process is nowhere near finished. Once the geometry is finalized, we move on to calibrating the mirrors. There are 100 mirrors to calibrate, which will take a solid amount of time (especially with the heat of the sun these days!). After the configuration, we'll have what we call a master mold. That is, we'll have glued all the mirrors at the proper angle, but in order to avoid having to calibrate 100 mirrors each time we want to make a wing we're going to make a mold of the original wing.

That's a pretty big mold. The parallelogram that makes the wing is short side: 70cm, long side 150cm and width 100cm. We're probably going to go for rebar reinforced plaster or cement (plaster is way easier to work with since it doesn't bond to mirrors too fiercely) but I don't know yet. If you've got suggestions on how to avoid breakage, let me know. I'm slightly worried, but have faith in the guys I'm working with. I don't have extensive materials experience, but they sure know their stuff. I'll let you know how we solve the problem (and the various ways we might fail).

Consider protocol disregarded (surprise surprise)

Monday morning and I 'passed by AMADER to say hello' and incidentally wondered aloud about the state of the financing 'because the SAHABA 2008 is only three weeks away'. There had been some motion, but still no money. They had received tacit approval to include the creation of the domestic solar cooker in their 'global budget' for SAHABA, but had not yet compiled the global budget etc. I said look, if I buy materials now will I be paid back? She said she couldn't guarantee anything, since it's not in her power, but given the tacit approval and the general enthusiasm of the department, I could pretty much count on getting paid back.

Good enough for me. To the truck! To the store! To action!

And by action I mean careful contemplation of the task at hand:
Here is the first little science experiment to determine how we are going to back the mirrors on the papillon. If you check a previous post, there's a picture of a papillon made with curved polished aluminum. My idea is to use mirrors attached to plywood. The question is how to support the mirrors at the appropriate angle. Here I'm mixing various quantities of wood glue and sawdust, or crumbled styrofoam with wood glue. The goal is to have something rigid, lightweight and cheap.

During the long lonely nights while the cyber is closed I amuse myself by contemplating the geometry of the papillon by drawing it out to scale on my bedroom floor:


The results are in! Styrofoam is much lighter and more waterproof, but sawdust is more rigid. More tests to follow, including other materials etc, but already we've got something workable for the demonstration.


Have you ever heard the saying that you can learn a lot about a workshop by the size of it's drill-press?


Basic geometry and initial structural problems overcome. Tomorrow we should start with the mirror focusing to make the master mirror mold. In an upcoming post I explain the process in detail...


Here's a picture of the Malian Minister of the Environment lighting a stick with Solar Fire:


And this evening the association Tile Tasuma (Solar Fire in Bambara) had it's first meeting. From left, President Ibrahim C Tomota, Secretary General Faguimba Tounkara, Assistant Vice-President in Charge of Training and Technology Djadje Samake, Vice President in Charge of Training and Technology Lorin Symington, General Treasurer Lalla Samake, Responsable de la sensibilisation (responsible for public relations, more or less) Boubacar Sidibe. Not pictured are Karim Sanogo who is Secretary in Charge of External Relations and The Accountant):


In summary: tech development is in full swing, hooray!

Le Blog en Francais... encore!

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Merci Olivier!