Saturday School: Funnel Solar Oven

Saturday School:  How to make a funnel solar oven

Items needed:  car windshield reflector screen, tape, box or bucket, oven bag, dark pot with dark lid, cookie rack, weight, food to cook

Put something to weigh down the box or bucket in the bottom of it.  Make a funnel shape out of the windshield reflector, overlap enough for no gaps and adhere with tape, velcro or some other method to hold shape along the sides, place in box or bucket, in the sun facing south (face it to towards the sun). Using some aluminum foil shiny-side-up, cover any holes or seams along bottom.  Place rack to hold pot onto box/bucket edges.  Put pot with food in oven bag and close off with twist tie.  Place on rack.

Your optimal time to cook using this method:  10 am to 2 pm, as that is when the sun is highest in the sky.  This method of cooking will not work if there isn’t enough sunshine to cast a shadow during most, if not all, of the cooking time.  Temperatures reached with this method--based on my experience--up to 200 degrees.


Also:  by using velcro instead of tape, you can undo the screen and fold it up for easy storage or to use in your car as its original intended purpose.

My experiments:  I chose to just warm water, so I could get a in the pot temperature reading too.  I also chose water so that each try would be able to have the same interior conditions (food, moisture, etc.)

First try:  I used a cheap-o dollar store window reflector with no reinforcement, the oven bag temp got up to 150* along with the 3 cups of water I had put into the pot.  I don’t know if it got above that temp at any time or not, but after the 2 hours of being in the same spot, that was the temperature  (I used a oven temp gauge to measure the air temp in the bag, and a candy thermometer to measure the water temp).  I did not rotate the solar oven to face the sun, it was in the same position the whole time from about 12:30 pm to 2:30 pm.  I did notice that with the breeze the screen moved around some and may not have provided the best angles and such for reflecting heat onto the pot.

Second try:  I used the cheap-o dollar store window screen again, but this time I reinforced the back with some sturdy cardboard.  The bag temp got up to 200* and the 3 cups of water got up to 150* after 1 hour of no rotating.

Third try:  I reinforced it even better than the 2nd time--because some of my reinforcing didn’t work as I had hoped, I also added some green plastic garden stakes to help.  The results--including rotating it to face the sun every 30 minutes---the bag temp never got over 200*, and the water temp only got up to 150*.  At least the wind wasn’t able to move the reflector much-as with try 1 and even try 2 a little, the wind was able to move the reflector and make it fold in on itself slightly.

In the future:  maybe try a more sturdy window reflector from Walmart or something.  What is the something:  make one out of cardboard covered with aluminum foil--as a side note:  the solar oven cookbook “Cooking with Sunshine” has directions on how to make one.  Check to see if your library has a copy--it has great recipes and instructions on making 2 or 3 different types of solar ovens.

I hope this tutorial was helpful to you.  This type of solar oven doesn’t have the temperature range of a Sun Oven, but it does get the food warmed up to 200 degrees, so still better than nothing.  See below for more pics.

Try 1:  You can see that the dollar store reflector is no match for a breeze or two.  But even with the flimsiness and flapping in the wind, the temp still got up to 150*!  

Tries 2-3:  Bag temperature got up to 200*, water temp to 150*.  The little inset picture shows the steam coming from the water.  You can also see my not-so fancy cardboard and Christmas tape job (and a garden stake sticking out of the top).  I taped a second piece of cardboard to the box holding the reflector and to the cardboard on the reflector to help reinforce it some more.  There are also two garden stakes going from the bottom to the wings of the funnel, as I found cardboard by itself wasn't holding them up and out.

Please note:  the picture showing the back of the solar oven shows the shadow being close to centered.  To rotate the oven towards the sun, you try to get the shadow to be the same on both sides like below, if the shadow is cast more to one side than the other, it is not directly facing the sun.