The most important and difficult item to find is the umbrella.  It should be an umbrella with sixteen ribs of 1 – 1.2 cm in diameter, which are not easy to find as most umbrellas have only 8 or 10 ribs.  I located one of these in an online store at http://www.bazarfrancia.com/ .  It cost me 15 € with shipping costs.

Using the same procedure as that for the paracocina   I cut off the shaft of the umbrella but I don’t use it for closing; instead I fold it so that it is easier to carry.  In order to position the structure I use a screw that fits into the drilled hole on the shaft.  I left a part of the closing strap for storing it as you can see in the central photo.  In addition, I had to attach a couple of tension cords to stabilize the cooker in the wind.   

As for reflective material, I thought over various possibilities. I think I found something ideal but I didn’t use it since I live in the Canary Islands (Spain) and it would have to be shipped from Barcelona, which didn’t seem to be worth it.  If you have better access to this material and want to test it out I would recommend mirror polished aluminium:  http://www.alucenter.es/esp/productos_familia.php?familia=5       

This material is used for lighting.   A sheet of 2000x1000x0.4m/m weighs about 2.20Kg and costs between  4.85€/Kg. to 5.55€/Kg. The quantity needed depends on the size of the umbrella used. 

Apart from this, I went back and forth between various possibilities because aluminium foil has the disadvantages of wrinkling easily, and it won’t stand up to all the repeated opening and closing of the umbrella.  In my opinion, the more polished, shiny and mirror-like a material is the better.  I came across various:  aluminium tape that is used for heating systems, aluminized cardboard, and adhesive plastic that can be easily found in fabric or stationary stores, which is what I finally used.

The stand and grill

I used a compact camera tripod because I was not able to find a plant stand of the right size, though I know they do exist.  With this tripod I gained in portability and precision because you can adjust the height in order to find the exact focal point.   The umbrella with 16 ribs provides a very precise focal point in the direction of the shaft.  Its disadvantage is that it is more fragile and more expensive, about 20€.

For the grill I glued a small barbecue grill with high-temperature resistant silicon.  This is the weakest point of my model because if you’re not careful the grill can fall off the tripod.  I think that ideally the grill should be soldered onto the tripod

I positioned the silicon glue such that it maximizes the stability of the cooking pot.  The pot doesn’t move at all. 

The cooking pot

            The cooking pot gave me plenty to mull over:  what would be the best type?  If I let my imagination run wild, I thought that the ideal solar pot would be a Pyrex pressure cooker in which one could place various black pots of different forms and sizes.  But let’s stop dreaming.  In order to select the type of pot, I read practically all of the reports on every type of solar cooker that I could find, these are the conclusions that I came to:

·         Material: aluminium or thin steel.   

·         Type: lower is better than high, but with enough height for cooking.  A low pot or a high frying pan is best. 

·         Color: black.

·         Lid: black is better than glass.

·         Size: 20 cm in diameter.  About 1.5-2 litros. At first I thought that the smaller the pot the more quickly it would heat up, but then I realized that a small pot is less efficient because it captures fewer rays..

Personally I like frying pans or casserole dishes because they have most of these characteristics and they may come with pressure lids that maintain the heat.  Steel ones are stronger than aluminium.  Unfortunately I haven´t seen any that are black.  They are all the colour of metal.  One solution is to paint them with a black matte heat-resistant spray paint that is used for barbecues.   It is not expensive and with practice good results can be achieved.   .

In addition, I used a second frying pan made of glass in order to insulate the first one.  It is a bit bigger so I stuck on bits of cardboard for a better fit. 

Recommendations

Don’t take it lightly.  It really heats up.  In order to prevent any type of risk, it’s best to use gloves and sunglasses. Also it’s better to cook while standing behind the cooker.  That way you also don’t create shadows on the reflector. 

In order to capture the maximum solar radiation it’s necessary to turn the cooker at least twice an hour so it faces the sun.  Turn it very slowly and carefully holding the stand and the pot or else removing them for a moment. 

For transporting the pots it’s a good idea to use a basket in which they fit well.  The basket will protect them as well as help conserve the heat. 

I carried out this Project with lots of interest and a fair bit of effort.  I hope that it helps in some way.  If you decide to try it out, please, I would love to hear about your experiences.  If you wish, send me an email.  I think that vegetables cooked in their own juices, and new potatoes cooked in their skins would be delicious.  Why not try them?

Juan Francisco
September 16, 2006

Email: juanfranciscoparedes@gmail.com