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Simple Home Solar Roaster
brodystylez
This is my contribution to the roasting game. I designed it myself in the months after I graduated college. It took me quite a while to get right, but I am finally roasting decent coffee using only the sunshine. It definitely has its limitations, but I think it might be of interest to some, and can be replicated for the cost of a new purpose built roaster. The most expensive part is definitely the lens. I haven't worked out a solar cooling unit yet though. Check it out.

Here is a picture of the lens.

i1023.photobucket.com/albums/af353/bengblac/009-1.jpg

Here is the spindle that is placed in the light's path.

i1023.photobucket.com/albums/af353/bengblac/009.jpg

This what it looks like in action.

i1023.photobucket.com/albums/af353/bengblac/010.jpg

And the finished product. This batch definitely wasn't a Spanish roast, which is not to say it can't be done, but my dad won't stand for the dark stuff.

i1023.photobucket.com/albums/af353/bengblac/006.jpg

Hope you like it!
dBndbit
Great project! Care to share any details on roast times, temps or numbers on the Fresnel lens? Did you consider any reflectors?

Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
Koffee Kosmo
Now that's something different
Quote from dBandit

Quote

Care to share any details on roast times, temps or numbers on the Fresnel lens? Did you consider any reflectors?


I will add another question
What is the maximum capacity of this device

KK
I home roast and I like it. Designer of the KKTO
Roaster Build information
https://forum.hom...ad_id=1142

https://docs.goog...lide=id.i0
Blog - http://koffeekosm...gspot.com/

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
brodystylez
Sure. The lens itself is supposed to put out the equivalent of 2kw of heat, but I don't have any real way to test it. The surface temperature of the beam when it is at the optimal distance is around 1000 degrees F, but if one plays with the distance the same amount of energy is imparted over a greater surface area. I have only produced a few batches so far, but the quickest I brought 8 oz to second crack was around 20 minutes, but things can get a little hectic so I haven't spent much time quantifying data just yet. As far as capacity, I feel like it could do 1.5lbs at a time, but I assume the time it would take to roast the extra amount would offset any benefit of stuffing it with more coffee. Something like a Qin=Qout equation. I tried some reflectors when I was experimenting with other container methods (I found them to be very difficult), before I settled on this one, but I am totally broke and this is gets the job done for now. The lens is 54' across and I got it on ebay for $90 with shipped, and I can also use it with a siphon coffee maker, but is more for novelty than function. The weather pattern here is pretty consistent this time of year, and I just bought 50 lbs of green coffee, so hopefully I can hook up my data-logger tomorrow and break out the stop watch. Thanks for your interest!
seedlings
o_O

^AWESOME!^

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
John Despres
Very COOL!

John
Respect the bean.
John Despres
Fresh Roast 8, Gene Cafe, JYTT 1k, Quest M3, Mazzer Mini, Technivorm, various size presses and many more brewers.
Clifford
Awesome +1
May the Force be with your cup
brodystylez
Thanks for the positive feedback, guys. I did a roast this morning just to gather additional data. I did the standard a 10oz batch in 24 minutes, but I think that could be improved, I just need to put my thinking cap on. This is how it turned out.
i1023.photobucket.com/albums/af353/bengblac/005-1.jpg
It is a bit harder to do than my heatgun setup, because the darker the beans get the more light they absorb, so the first part is a lot slower because the beans don't absorb light, but as they darken they absorb heat much more quickly. I will be vary pleased when I find a way to hook up my thermocouple and see this occurring graphically. Thanks again for your encouragement.
Koffee Kosmo
Just an observation
It could also be that you don't have actual stirring & churning of the beans
I assume they slide around the glass without mixing

KK
I home roast and I like it. Designer of the KKTO
Roaster Build information
https://forum.hom...ad_id=1142

https://docs.goog...lide=id.i0
Blog - http://koffeekosm...gspot.com/

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
brodystylez

Quote

Koffee Kosmo wrote:
Just an observation
It could also be that you don't have actual stirring & churning of the beans
I assume they slide around the glass without mixing

KK


This problem occurred to a greater degree when I attempted to roast popcorn, but the coffee seems to be circulating very well at low rpms. I have considered adding additional agitators, but have yet due to NCRI (non-coffee related issues).
I recall reading somewhere that in drum roasters most of the heat is transferred from bean to bean, rather than from the heat source into all the beans. Can any experts confirm this? There are certainly some improvements that can be made; any professional input helps. I feel like if I had a way to insert my thermocouple into the spindle I could base my results on empirical evidence, rather than my poorly educated assumptions (I am an ag economist, not an engineer). But I am hesitant to go back to the drawing board until I find a job, which doesn't look like it is going to happen anytime soon. At any rate, thanks for the help and stay caffeinated!
Koffee Kosmo
Yes your information is correct that heat transfers from bean to bean
However
All commercial drum roasters have stirring vanes
If the beans are not stirred and agitated they are not roasting the are cooking (or just browning)

KK
Edited by Koffee Kosmo on 07/24/2009 7:48 AM
I home roast and I like it. Designer of the KKTO
Roaster Build information
https://forum.hom...ad_id=1142

https://docs.goog...lide=id.i0
Blog - http://koffeekosm...gspot.com/

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
seedlings
Try these:

Make a template of the glass curve and trace it to inexpensive aluminum flashing. Add an inch or so of thickness, plus an inch to each end. Bend over the extra inch at each end to use as tabs to rivet. Add 3 or 4 of these.

Also, you might make a reflector curve opposite the sun, to catch more light and/or prevent heat loss.

CHAD
seedlings attached the following image:
13vanereflector.jpg

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
peterz
Nice idea, and I am glad to see someone got it working! :):)
You can find similar lenses at yard sales and in thrift stores here in Lake Havasu City, Arizona. We have lots of sun here too ;)

I got one for a dollar, but it came with a junk projection TV.
So I had to take it apart and get rid of everything but the front (fresnel lense) screen. It is sandwiched between two nice layers of plexiglass :)
YMMV

The second one I had to pay three dollars for at a thrift store. I guess because someone had already removed it from a junk projection TV.

You should know that I used one in Oatman, AZ to win their annual Fourth of July, Fry an Egg on the Sidewalk contest one year.
They come in all different sizes.
Maybe there are some electronic junk stores in your area, or you could try the thrift stores. What I have learned is that the thrift store tries out their donations, and if they work, they just go into the dumpster. So you may want to have them keep an eye out for you.

Maybe put an ad on Craig's list or in the local ad mag or newspaper and you may get one for just hauling it away,,, and then taking it apart.
Good luck,

Peter Z
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