June 5, 2010
My first idea for the glass window on the front of the oven was to use a recycled microwave oven turntable held in the center of the stainless steel mixing bowl with a clip so it would be free to expand and contract. An online seller of replacement turntables mentioned ceramic glass and regular glass, but I imagine this one is regular glass. It is not clear, and has bubbles in it, and probably reflects lots of energy, but I wanted to try it. (I am in the process of making a frame to hold three inch strips of very clear optically good glass from some junked Xerox Copy machines.) Here is a photo of the turntable window:

The oven reached 450 degrees today, and we baked some bread and two meatloaves, plus boiled some water (during the warm up) and dried some wood (after it was shut down.) Here is a photo after shutdown:

I have added more insulation, and just noticed that the oven door gasket melted down, so I’ll replace that with a fiberglass rope made for wood stoves. We also took some photos of the food we cooked today.

It would be nice if this tracked the sun. I’m using a crank-up kitchen timer and set it for ten minutes. When the bell rings, I go to the Helios and crank each wheel (up in the morning, and down after solar noon), and then move the cart under the oven so the light strikes one side of the glass. In the next ten minutes, the "beam" moves diagonally, and when the bell rings, re-adjust. Someone said it reminds them of the LOST television series where the timer needed to be reset every 108 minutes. Poor Desmond! The oven needs to be pre-heated, so baking/roasting things on "impulse" won’t work. Right now, the oven is warming because we are going to bake some Biscotti, and perhaps some herb flavored potato slices. (Yumm!)

Well, the Biscotti is delicious! The weather forecaster "missed" the sky cover estimation by about 15%. (I would estimate 60% sky cover, and the forecast was 45%.) Big thick clouds, and if I got the focus right on the glass when the sun was shining, the extra cast iron I put in the oven helped hold the temperature. When the Biscotti was placed in the oven for the final baking, after slicing, the sun came out in full force, and the temperature climbed toward 400 F. It was done in a flash, so I placed a bowl of small wood chunks in the hot oven, and cranked the mirrors down and went in the house to watch the evening news. Later, we rolled the concentrator into the barn because we are expecting clouds and possible rain showers/thunderstorms for the next three days. During this time, we will be using the Anderson TLUD-ND Wood Gas Cook Stove with these dry chunks that I placed in the oven. Here is a photo of the chunks:

Fuel for gasifiers and wood gas generation needs to be dry. I will now also be able to experiment with torrefied wood, which hopefully won’t stink up my oven.. (I may write another article about using wood gas on those rainy or overcast days when solar won’t work.)

Tidbits and food-for-thought:

My oxy-acetylene welding googles are handy for eye protection when running out to adjust the mirrors, but I’m still getting a headache/eyestrain from looking at the beam of light. The National Weather Service has a graphical forecast and the % sky cover seems to be the one to watch, as well as the wind, of course. The sky cover forecast for the next three hours is about 45%. I threw another piece of cast iron into the oven to help hold the temperature. ..still running with the cracked microwave turntable..and still need to tighten up the focal point of the mirrors. ..Did you see the discoloration of that stainless steel bowl that is holding the glass? Good 316L turns blue at about 1000 C. Well, stainless doesn’t conduct heat, and directly behind that bowl is lots of glass fiber insulation, so I guess there is no place to the heat to move to..thus high localized temperature.. Ding...or "ring"..my Helios calls...