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Solar Cooking Project :

We first started with solar coolers in 2001. We had some experience in a CYTED proyect, but along came an excellent opportunity to apply them in San José de Maipo thanks to FOSIS. This is a fund that our government has for projects to help needy families. In this project we worked with about two dozen families in San José in solar cooking, fruit drying and solar water heating.

When we had to choose a type of cooker, we decided to use the box type, since they're very reliable and simple to operate.

Now we've expanded our original experience to numerous other places. Our original design has been simplified and improved along the years. Now we have cookers in operation in San Pedro de Atacama, Ovalle, Coltauco, Mincha and now in Putaendo. Besides this, at least a dozen other cookers have been built by our readers.

First we built one with 50 mm insulation and a second one with 100 mm. Because thermal results of the second one were much better, all the following units have been made with the higher insulation. Temperature tests have shown that the unit with the smaller insulation maintains about 130ºC in the central hours of the day, while the better insulated model surpasses 170ºC, with better heat retention.

But now we've gone back to the original 50 mm. This is because stagnation temperatures that are too high can easily crack the glazing. Also because at first we expected that here in San José one could cook on a clear winter day. But in winter beam radiation landing on the glazing is not much more than 600 [W/m2], and with the low ambient temperatures, the oven does cook, albeit very slowly. So in fact one can use it here from spring until late autumm. However in the northern part of Chile (from 30° Latitude or less), they can be used year around.
 

According to our plan, we first started with solar cookers. This is because it was the technology we were less acquainted with and also because it demanded the most work to build. The type of solar cookers we built are of the solar oven type, similar to those used in the Villaseca project in the north of Chile. However, there were important imporvements to better adapt them to the climate and solar conditions that exist in el Cajón del Maipo:

• The size was increased so as to permit one to cook a typical oven pan or else two pots of smaller size.

• For thermal insulation we used fiberglass mat instead of expanded poliestirene, because it resists higher temperatures much better.

• We used almost 100 mm of insulation instead of the typical 50 mm so as to permit cooking in colder periods.

• Special attention was given to the placement of the insulation as well as proper sealing so as to better retain heat. 

Now we've again simplified the design. We found that one doesn't need more than 50 mm of insulation (this was studied both by theory and testing). This is enough for the cooking temperatures one has, and also leads to lighter cookers. Also now we use a glass tilt of either 20° or horizontal, according to where we expect them being used. It's much simpler to build a box cooker with horizontal glasses. Now we opt also for a model that's much wider than deep. All of these modifications mean that the sun reaches the bottom of the cooker more easily and also that one has less shadows on the sides.

We've kept the loading from the back, since these is much safer than top loading and improves the overall sealing.

See an article (in spanish) on solar cookers in documents

The operation of the solar cooker proved to be much better than we expected. It permits the preparation of a wide variety of dishes. We've made: cakes, muffins, chicken, meat stew, beans, roast meat (pork, beef and rabbit), rice, bread and many other dishes. Water can be boiled and the high insulation permits keeping dishes warm for several hours after the sun sets.

Operation has proven to be simpler than expected. One only has to readjust orientation once an hour or less. Very even temperature inside keeps the dishes from burning or sticking, so one doesn't need to stir the pots. This makes cleaning pots a breeze. One can use almost any type of pot, even though the ideal are covered pans made of pyrex. With just some experience, one can prepare the food, preorient the cooker and let it cook totally unattended, returning only when dinner's ready! (typical cooking times range from 45 minutes to about an hour and a half).

Because cooking is very simple, this means that the person that does the cooking doesn't have to oversee the process. This means he can do other things or simply rest. A few days ago we discovered an additional advantage we hadn't considered: this type of cooker is very safe for children to operate either to warm their food or cook it.They need only minimal instruction. There's no chance of them starting a fire, burning their food and the probabilities of them being burned are also much less.

The chance of being burned is minimal, but not zero. When the oven is in full operation, inside temperatures can surpass 170ºC and there's superheated steam in the interior. So one has to open the oven carefully, letting steam out slowly and wait several seconds before putting your hands inside (covered with gloves!) to remove the pot.

Si llegó aquí desde un enlace externo, nuestro "homepage" está en www.ecomaipo.cl.

If you arrived here from an external link, please visit our homepages at www.ecomaipo.cl.