This project could be considered green for several reasons.
First it is made from stuff that was probably going to be thrown away. Second, it works completely off-grid. And finally, it is used to roast 'green' coffee beans.
Step 1: The Heat Source
I rescued an old satellite TV dish that was on its way to the dumps, and after adding some mylar with spray glue, and reworking the mounting system, it became the heat source. The mount system has also an old swivel chair turntable underneath that allows me to track the sun East to West. I can raise and lower the dish by titening the nuts on the angle adjust, both behind the parabolic, and at the bottom of the mounting post.
Step 2: The Roaster
2. The roaster.
The roasting cage is an old Bundt pan, mounted on a 24V slot machine hopper motor and affixed to a piece of wood that slides into the parabolic focal point. The motor is a 24V old slot machine motor, scrounged up, although a car electric window motor might work well, too as the turner.
Step 3: The Power Source
The power for turning the cage is an old 25W, 12V solar panel which was donated. Since the slot machine motor is rated at 24V, it seems to run great on 12V and will do it all day long without getting too hot. I have tried several ways to get the motor to slow down, to more accurately control the heating rate of the beans, but the first few methods don't seem to work. Instead I find that by draping a cloth, or some cardboard over part of the solar panel, that allows the panel to produce less energy, and slows down the turn rate significantly. One can actually stop the motor completely by blocking out the sunlight, however in this case the beans start to burn right away. This picture shows the panel with an orange cone, and a piece of wood on it, which is lowering the turn rate of the motor.
Step 4: Loaded and Pointed
The beans are held in the cake pan by some metal clippies and aluminum screen. You should burn the screen with a propane torch first, to remove any chemicals.
This shows the parabolic dish (bottom), and the roasting assembly (top), and also a shot of the focal point. The focal point is adjusted by mounting the pan on a stick of wood which slides into the end of the dish's tube. It also becomes easily removable to load and unload your beans.
Step 5: How Dark Do You Want Them?
Here's what happens if you slow the motor down too slow.
Step 6: Final Thoughts
Here is a photo of a couple of days ago, just after the longest day of the year. Note how low the angle of the device is, as we are now capturing some of the last rays of the day, and it is pointed hard to the West. On this day I roasted some Robusta beans from Viet Nam, as they are beans I had not tried yet. Ewww, they were horrible, as I am used to Arabica beans. Apparently Robusta is used to blend with other beans...?
I have successfully roasted Nicaraguan, India, Jamacan Blue Mountain counterfeits, Brazil Santos, and probably a couple more. I have waiting to roast some Columbian, Maui Red, Mexican Organic Terruno, and Costa Rican coffees, as well as a bag of green Cacao beans. I have on order some green Ethiopian, Rwandan, Indian, Indonesian, and Kenyan beans, and they should be here in another week. Since I have started roasting, a whole new world of coffee is opening up. I have tasted some bad burned beans, but on the whole the flavor of the beans I roast seems very good. In fact, my brother in-law, 'the Turk' who has told me for years how crappy my coffee is, tasted some fresh Brazilian the other morning, and actually complement me. He said it was good coffee. He said it was really good coffee.
This device does not roast enough to be an economic boost for me, however, when it's a sunny day, I can easily roast a pound of my favorite beans in an afternoon, and share them with my good friends. They sometimes even chip in to help buy new green beans.
Note of caution, you MUST always put a silvered parabolic device FACE DOWN when you are not using it, so that you do not accidentally start your house or something else on fire. If left unattended a parabolic can quickly start a terrivle fire if left next to kindling or other wood or flammables. Please, please use extreme caution with these things.