Tuesday, April 7, 2009

Solar Cake with a Windshield Shade Solar Oven

We were encouraged by the yummy s'mores we made in the kid's pizza box solar oven. However, we were hoping to do more cooking than just melting chocolate. We wanted a real oven.

There are many different designs for do-it-yourself solar ovens, we decided to try out the one developed by Kathy Dahl-Bredine, mainly because it looked like it would be simple and fast to make. It calls for very few supplies:

  • A car windshield shade

  • Stick on Velcro tabs (found at a fabric store)

  • A small to medium sized plastic wastebasket or bucket

  • A square cooling rack
  • A black cooking pan or pot

  • An oven bag (like what you use to cook turkey in at Thanksgiving)

The instructions are simple as well.

  • Lay the visor out with the notched side facing you.

  • Stick one side of the Velcro tabs evenly spaced down the top side of the visor to the left of the notch (it takes about three or four tabs).

  • Stick the matching Velcro tabs on the underside of the visor to the right of the notch, so that when you bring the two sides together to form a funnel, the Velcro tabs match up.

  • Bring the two sides together to form a funnel.

  • Place the funnel on top of the wastebasket.

  • Position the cooling rack into the funnel, so that it rests on the edges of the bucket (the bucket is under the funnel, the cooling rack is on top of the funnel).

  • Put the food to be cooked into your pot.

  • Put the pot inside the cooking bag, and close the bag.

  • Place the pot inside the bag on top of the cooling rack in the sun.

We attempted to bake a cake in our oven, using a small cast-iron skillet. After four hours, the top and one side of the cake were done. The other side, and most of the underneath were still doughy. We have read that this type of oven reaches 350 degrees Fahrenheit, but ours did not seem to get above 200 degrees (however our oven thermometer was in the bag, but not in the pan itself).

I am not sure if a cast-iron skillet is a good conductor of heat. We will have to continue to experiment with different pots and different angles into the sun. We cooked our cake from 10 a.m. to 2:00 p.m., so I think we took advantage of the maximum sun energy - but the shape of our oven might not have been quite right. Tonight will be a research night, and if it's sunny tomorrow, we might try again.

I understand that this type of oven has been used in undeveloped areas of the world to help in food preparation and water purification. The children are intrigued by a science project that has real world applications. Besides that, it appeals to my inner Macgyver (I wonder if we could fabricate a solar oven out of chewing gum wrappers?)

It's great to be a homeschooler!


tsponheim said...

Cast iron is a good conductor but has high mass, making cooking take much longer. Use a light-weight, dark pot with a dark lid.

Tom Sponheim
Solar Cookers International

LJohnson said...

Thanks! Our plan for our next try is to use a small, black bread pan, covered in a glass bowl and sitting on top of a black metal bottom of one of our springform pans - all of this will sit on top of the rack. That is if the sun decides to shine again :)