Intro: 4 Solar Bubble Ovens
It all began with an old drawer in the garage. I was entertaining the grandchildren and thought a solar experiment would be fun. We lined the drawer in aluminum foil and covered it with clear plastic wrap. We put some cheese on tortillas in a bread pan and made a quick delicious snack at 155 degrees. It helped we were in Eastern Washington and the temperature was 105 degrees in the shade. This was the start of our interest in solar cooking.
Step 1: Bubble Wrap Insulation
I stopped at the lumber yard on the way back to Oregon and began searching for something shiny. I found Mylar Bubble Wrap in the insulation area. I purchased a few yards and began experimenting and reading the internet.
Lots of ideas about how to shape the reflector. Parabolic was described as the hottest but most difficult to cook with. It gets very hot and needs constant focusing. The solar trough was clever (it is less critical on the focus) but worked best with an evacuated tube. And cooking was in a strange shaped long skinny pan. I loved the idea but the technology was above my pay grade.
Oh right I don't get paid for this anyway. Except for those cute smiles from the grandchildren.
The solar funnel sounded like a good simple idea. I lashed together a tripod from some branches I had pruned off the cherry tree. I used some spring clamps to attach the bubble wrap to the tripod. I tied the legs together and used the ropes to secure the bottom of the funnel.
At a thrift store I found a glass casserole dish and black pan with a lid. The handle on the lid was 1/4 inch too tall for the casserole dish to close. I removed the factory handle and made a shorter one of wood.
In order to make the pan be at the hottest spot I used copper wire to form a hanger for the dish. It was easy to form a hook at the best height by bending the wire.
I used an electronic thermometer to find the hot spot. It did not work very well on the glass. We also had to move the tripod as the sun moved. It worked to put the shadow of the center leg on the dish to center the focus of the sun. This worked well making grilled cheese.
Step 2: Third Prototype Simplify.
The next step was to change it. We wanted a smaller one that did not require a tripod. To see if we could get similar temperatures we put a reflector in front and raising the pan to get light on the front and sides.
This was hot enough to cook eggs and a cake.
Step 3: Fourth Prototype Movable Wings.
It seems it is complicated to simplify. I complicated this simple idea of a box that opens up to form an oven. The idea was to get the approximate angle of the suns latitude by shaping the bottom of the box. I live in Oregon about half way to the north pole so a 45 degree angle is close. First I put a brick in the base to hold it at the correct angle and support the grill. The grill is to get some light reflected under the dish and pan. The hinged lids are tied to weights so moving the anchors pulls both wings the same amount to make it easy to align with the changing sun angle.
My biggest problem is huge fir tree that stops the sun from shining in the back yard around 3:00P.M.
I had to finish cooking my tofu in the front yard. I was worried it would be found by the neighbors dogs and cats. Fortunately pepper onion tofu is not on their favorite list.
Step 4: Afternoon Cooking.
As the sun gets lower in the sky the power decreases a lot. It really helps to have wings that track it.
It helps to watch the shadow as the sun gets lower in the sky the angle moves faster. It the shadow is centered then the sun should be in the middle of the solar oven.
Their is something special about slicing a squash from your garden and cooking it with the same solar power that grew it.