Solar Parabolic Trough Charcoal Oven

[freeztar]

I like the "greenhouse" idea. It's like a solar oven. I wonder how hot those can get?

[Nitack]

Originally Posted by freeztar

I like the "greenhouse" idea. It's like a solar oven. I wonder how hot those can get?

I actually thought of a passive design with the same setup. Put your vessel in the center, put angled mirrors on all four sides to redirect light, and a sheet of glass up top to trap heat but let light through.

Interesting thought going back to the parabolic mirror and pipe design...

Why not run the pipe through a cinder block structure like this? One of the main reasons that the pipe did not work was probably it's being exposed to wind, however it was still able to get up over 200 degrees... so why not shield it from the wind?

[MarkB]

Originally Posted by Nitack

I actually thought of a passive design with the same setup. Put your vessel in the center, put angled mirrors on all four sides to redirect light, and a sheet of glass up top to trap heat but let light through.

Interesting thought going back to the parabolic mirror and pipe design...

Why not run the pipe through a cinder block structure like this? One of the main reasons that the pipe did not work was probably it's being exposed to wind, however it was still able to get up over 200 degrees... so why not shield it from the wind?

This seems the right idea to me. The sunlight is providing an energy (heat) input, to get a high temperature you just need to insulate the system well enough that it loses heat slower than it comes in.

I would be trying to design something with roughly 2 boxes, one above the other :
- the bottom one would be enclosed on 3 sides (maybe partly dug into the ground?) with a glass cover on the 4th side. Light would enter through here and roughly focus on a metal receiver which would form a pillar of some kind inside the box.
- the box on top would be your chamber to put stuff in and would sit on top of the heated pillar. This would be heavily insulated on all sides and the top to retain the heat rising from the heating element. You would need a air escape somewhere and I imagine that would be best as some kind of hole/pipe at the bottom of the oven chamber leading down to minimize hot air loss.

The idea is that light doesn't have to be accurately focused on the heating pillar - my understanding is that it doesn't make any difference how tight you focus it, a given size of lens is going to supply the same total energy whether it's going into a half-inch spot or into a 4 inch spot ... the point is that you want to keep that heat in there. So you enclose the heating element behind glass/similar and cover the oven itself up completely. (I'm not good on insulation at these temps, so suggestions gratefully received.)

A question from me - how many hours would this need to be getting the sun? I'm wondering if you could half-dig this into a South or SW facing slope to help with the insulation? I'm thinking maybe a foot wide window, with an 8 inch heating element a couple of inches behind it, would allow a fair range of angles, assuming your lens arrangement could be moved around it ...

MB

[freeztar]

Mark, I would need to see a diagram to fully envision what you are proposing. I think I have the idea, but I'm not quite sure.

Originally Posted by MarkB

A question from me - how many hours would this need to be getting the sun?

It depends on lots of factors such as efficiency of the system, wind, cloudiness, etc.

I'm wondering if you could half-dig this into a South or SW facing slope to help with the insulation? I'm thinking maybe a foot wide window, with an 8 inch heating element a couple of inches behind it, would allow a fair range of angles, assuming your lens arrangement could be moved around it ...

Ah yes, the moving problem...
When I was doing my initial trials, I had to move the stand and or lens every couple of minutes to maintain a strong beam. We've proposed solutions to this earlier in the thread, but all propositions are quite complex/expensive. If you have any ideas on this, I'd sure like to hear them.

Welcome to Hypography btw.

[Turtle]

Originally Posted by freeztar

...Ah yes, the moving problem...
When I was doing my initial trials, I had to move the stand and or lens every couple of minutes to maintain a strong beam. We've proposed solutions to this earlier in the thread, but all propositions are quite complex/expensive. If you have any ideas on this, I'd sure like to hear them.

Welcome to Hypography btw.

I heard this guy on the radio the other night; he is using an array of fresnels on a single mount, and drives it by computer to track the Sun. He said his steam system operates at ~400 lb/in^2, and that he & his crew have custom made a turbine to drive a generator. You might get some ideas here: >> Xenotech Research Forum :: View topic - Solar energy