Solar Coffee Roaster

The Solar Coffee Roaster has been designed by Craig Bergland living in northern Nevada, USA. He has considerable experience reusing and adapting existing materials to fashion various solar cooking devices. Here, he has incorporated an evacuated tube with a trough style reflector with a parabolic profile to become an effective way to roast coffee beans. His intent is to pass along useful ideas for others to replicate. Below is the designer's description on making your own coffee roaster. 
All photos credited to Craig Bergland
===Forming the reflector trough with the parabolic profile===
It’s not that hard to build a parabolic trough, lots of people make them, but this project is kind of cool because it uses existing materials that ‘fit’ together well. The base is a common plastic or metal milk crate, the reflector is an old 18 x 24” campaign sign (or new sheet of coroplast), and the collector is a $15 evacuated solar tube which are still available online. Plus a bit of mylar and an old plastic bottle, a few zinc clad nails and some good old duct tape. Use the guide shown below from Direct Use of the Sun’s Energy, by Farrington Daniels to mark out the parabolic shape.
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SCR 2, 3-24-23.jpg|Laying out the parabolic shape per Farrington Daniels 
SCR 3, 3-24-23.png|Positioning the tube in the sidewall
SCR 5, 3-24-23.png|Cutting the reflector back to bend
SCR 4, 3-24-23.png|Forming the curve
SCR 6, 3-24-23.png|Cover the reflector with Mylar
5 sheets of coroplast campaign signs will make 3 troughs, or 1 and 2/3 will make a single. Since the coro is 18” wide, and the inside length of your milk crate is likely 18 also, it may not hurt to trim about 1/8 inch off of the coroplast side for a better fit. Otherwise it may be a bit snug.
In order to get the reflector panel to bend easily, the back side should be cut halfway through every inch or so. I use a rounded edge pocket knife and slide it along the square chamber. A sharp edge is liable to dig in and cut through both sides which is what we do not want. Or you could carefully use a single edge razor blade but that takes quite a bit of time and a lot of work. The more cuts you make the rounder it will get, but we really do not need high precision for this.
One end of the trough is cut out to fit in the top of an old plastic juice container. This allows for protection of the fragile pointy end, and allows for easy turning of the tube when roasting to distribute the beans to keep from burning. The other end is drilled to fit the tube in snugly, which keeps it from accidentally falling out.
I used 1 and 1/2 inches as the focal point and it seems to work fine.
===Using the evacuated tube===
The optional end cap is cut from an old beer can, and this allows for containing more heat in the tube for higher temperatures as well as a thermometer. This cap is removed after the beans start smoking to help modulate the temperature. This thing will easily reach 450F, and i have measured over 500. Note that you can distinctly hear the different stages of the beans ‘cracking’.
The two ends of the trough are firmly secured to the reflector by pushing a few thin nails through the coroplast as shown, then covered with a bit of duct tape.
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SCR 7, 3-24-23.png|The tube meets the sidewall
SCR 8, 3-24-23.png|Parts to fit on the tube
===Adapting the milk crate base===
The interesting thing about this assembly is how well it all fits into the milk crate. The crate can also be weighted with a couple of bricks, or bungee cords used to help keep it stable, but really not needed so far. These things are wings which will tend to fly about your yard if not put into a milk crate or secured somehow. The trough actually helps protect the tube. Milk crate is ideal, and can be tilted to adjust to sun height, and the pointy end side is easily lifted to empty the tube and to refill it.
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SCR 10, 3-24-23.png|Reflector and tube resting in the milk crate
SCR 11, 3-24-23.png|Open end of tube at other end 
SCR 9 3-24-23.png|The Solar Coffee Roaster
===Using the roaster===
A nail or two can be added as to show when the roaster is positioned correctly to the sun, letting you know when it is out if focus. The roaster should be able to roast 8oz of beans in an hour. However, further tests will probably show that it will do a larger amount of beans in considerably less time. Still waiting for a good sunny day. Guessing half an hour in a preheated tube…?
Interestingly, if the mouth end of the tube is lower than the pointy end, when the tube is rotated by hand, the darker beans tend to gravitate to the opening and fall out leaving the lesser roasted ones behind. This is probably because the bean I suspect. So far, the few roasts i’ve done have come out remarkably well, and am looking forward to more if the weather ever permits. One adaptation would be to add an automatic rotating motor to this, but that’s not something i can do right now. 
===Tips===
When not in use, or raining, the unit can be placed upside-down, to keep it from the elements, tho’ it is basically water resistant. This unit can roast coffee, soybeans, cacao, grains, possibly malt sprouted barley for beer, and will boil 20 oz of water in under an hour when placed vertically. It also makes a handy reflector for starting your seedlings with a strip of LED lights fastened on. Etc.
Total cost under $20.
With a collecting window of 18x16 inches, or 288 inches square, this in theory can generate 166watts of heat energy. Assuming 1HP of heat per square yard. Similar to a crock pot.
If you build one please let me know how it goes, and you are certainly encouraged to share this post if you found it interesting.
-Thank you
==External links==
*https://www.secretsolarinstitute.com
==See also==
*Craig Bergland
==Contact==
Category:Solar cooker designs
Category:Solar cooker plans
Category:Solar trough cooker designs
Category:Solar trough cooker plans
Category:USA