Solar Parabolic Trough Charcoal Oven

[freeztar]

Originally Posted by Turtle

By in series do you mean projecting the focused beam of one through the other?

Actually, I was thinking of focusing the unfocused beam of one into the other. Nonetheless, you may still be correct.

I think that to get 'more power' () from the Fresnels you need either a larger single lens or an array of multiple lenses reflecting their beams off multiple mirrors onto the receiver. Does that ring true?

Those are known ways, correct. I'm experimenting to confirm.

PS paint the back of the oven thermometer black & focus the beam there, rather than on the face perhaps? The one I bought has marks to 500F, but I used it inside the receiver rather than directly in the beam.

The thermometer is black actually (except for the face obviously). Unfortunately, from my tests the day before I was unable to get the needle to move and this caused me to aim my trials today directly at the face. I did not think the pyrex would crack, but I should have considered it given the quick temperature increase I witnessed.

[Nitack]

Update:

So I got the lens. It is a big sucker and I can only imagine what I am going to be able to do with it. Unfortunately the sun was not showing on Sunday and I was not able to test. But I got just about everything I need. Just going to build a frame using aluminum for easy deconstruction and storage. Using a cast iron dutch oven and for my temp tests going to have an oven thermometer inside. If it gets above 600 (hoping it does) I may need something more suited for higher temperatures. I will post pictures as the project starts to develop.

[freeztar]

I've decided to get one of the 48" lenses to try out.
Nitack, have you built your frame yet? If so, how did you do it?

I saw one on youtube that looked pretty nice. It looks like he retrofitted an easel or something so the lens could tilt forwards or backwards. It seems that, ideally, one would want a stand that tilts forward and back and up and down to adjust the focal point.
I'm wondering if it might be possible to use a camera tripod, without it tipping from the weight?

Any other ideas?

[Nitack]

Hey Freeze,

I actually got the majority of my frame built last night. I framed out the outside using 1x2 on ends so that the frame is deep. Lined the bottom edge with 1x1 all the way around to create a lip for the lens to sit on. The lens fit in great. Tonight I attach more 1x1 on the other side with the lens in place to lock it in.

For a stand I am going to build a very simple A-frame. Probably use a couple 2x4 and lay them so they meet at the corners, and attach them using an angle bracket on the inside angle. That way it will give me a nice V on the top. Drop some bolts in center mass on either side of the frame and they can sit in the V made by the 2x4s. The weight is not that much so it should be able to hold easy enough. As long as it is balanced I don't need a locking or tightening mechanism, but I am going to use some fender washers and wing-nuts just for the sake of keeping it in place with out supervision. The design is simple, I might improve upon it later, but for now it will allow me to tilt both forwards and back and keep it at what ever angle I need. It is also relatively portable so I can move it to wherever I am working very easily.

The weather is killing me here though. This whole week is hazy or rainy here. According to the weather man I will not get any charcoal weather till next Monday and I will be working during the peak hours. BLAH!

[Turtle]

Originally Posted by freeztar

I've decided to get one of the 48" lenses to try out.
Nitack, have you built your frame yet? If so, how did you do it?

I saw one on youtube that looked pretty nice. It looks like he retrofitted an easel or something so the lens could tilt forwards or backwards. It seems that, ideally, one would want a stand that tilts forward and back and up and down to adjust the focal point.
I'm wondering if it might be possible to use a camera tripod, without it tipping from the weight?

Any other ideas?

I think a camera tripod might be tippy. If you fasten the feet down it should stay in place and has the advantage of built in movements and locking in position.

My bias to a frame to hold the lens flat is to use wood. The general form of the old school blackboards as drawn below, and then affixed to whatever rotating support you care to make. Camera tripod, rotating spindel on a broad base, rotating disk platform, etcetera. I think if you fix the frame solidly to a base that carries the receiver, and then rotate the whole setup to track? (this smilie needs a pencil behind its ear.)

[Nitack]

rough sketch of what I am doing, although not to scale. when turned completely horizontal the focal point of the lens will be six inches above the ground.

[Turtle]

Originally Posted by Nitack

rough sketch of what I am doing, although not to scale. when turned completely horizontal the focal point of the lens will be six inches above the ground.

Nice! I think your design would be more stable than mine in a wind. Put your setup on a rotating base and you're in business. The 'rotating base' could just be a piece of plywood on the ground, as long as you have a base/connection to all the leg ends.

Do I smell smoke??

[Nitack]

I don't know about more stable, but it is very portable as it is essentially three separate pieces that kind of all lean on eachother... Perhaps I will add some footers to the A-frames to increase stability though... perhaps nail a 1x1 piece of plywood to each foot. I don't want to mount the whole thing to one big piece of plywood on the ground given that the firing spot is the ground and it is just begging the whole rig to go up in flames...

Perhaps I can attach wheels on the bottom of each footer for ease of movement. That is all down the line, for now I still have to produce charcoal.

[freeztar]

Originally Posted by Nitack

For a stand I am going to build a very simple A-frame. Probably use a couple 2x4 and lay them so they meet at the corners, and attach them using an angle bracket on the inside angle. That way it will give me a nice V on the top. Drop some bolts in center mass on either side of the frame and they can sit in the V made by the 2x4s. The weight is not that much so it should be able to hold easy enough. As long as it is balanced I don't need a locking or tightening mechanism, but I am going to use some fender washers and wing-nuts just for the sake of keeping it in place with out supervision. The design is simple, I might improve upon it later, but for now it will allow me to tilt both forwards and back and keep it at what ever angle I need. It is also relatively portable so I can move it to wherever I am working very easily.

I'm having trouble picturing the stand.
An A-frame is just 2 pieces of wood correct? How will it stand up?
Also, how will you be able to tilt the lens?

EDIT: nevermind, missed your pic while typing, makes sense now

[Nitack]

two separate A-Frames, one on each site. The bolts (long bolts) would rest in the "V" the the two board ends make. Like I said, not the most stable, but very portable.