Solar Glass Recycler (aka Fresnel Lens Glass Melter - FLeGM)

Sorry I'm just getting caught up on this.  Can I join the team?

If I'm understanding correctly, the device is being readjusted 6 times and it's at the point where the solar death ray has passed over the bed of broken glass.  So we're kind of baking the glass in passes that take many minutes to transpire.

I think an experiment (as suggested by our mad scientist Josiah) to reorient the lens quite frequently to keep it shining on the same bit of glass would be very helpful.  Perhaps for an hour with reorientations every 5 minutes.  Then the variable of heating and cooling as the solar blast travels across the furnace is eliminated.  From that point you could play with focal length or glass lid removal or wind blocking and get quicker answers.

IE, from 9-10am you get a baseline of how well the glass melts when under the beam full time.  Then 10-11 is a different focal length, 11-12 is with the glass lid off, 1-2 is with a wind blocker, 2-3 is something else.  

I'm good at coming up with crazy ideas so here are some:

You're sending radiant energy at a clear material.  Is there a way to darken the glass so it absorbs more of the energy?

Could something dark be put under the glass that would help heat it?

Could two lenses be built into a version to double the power?

Would it be worth trying some crushed brown or green glass to see if that melts easier?

What if the glass was held in a steel or cast iron pan?  Would the iron melt or hold heat for the glass to melt in?

To further Mike Jay’s comments, and as a fwiw-
I emailed a friend who does glass blowing and fires pottery and teaches that sort of stuff (and also lives off grid and knows a bit about solar) and sent the link for this project. Here’s the response-
“While this is interesting and noble, glass does not behave in ways that make this specific design possible. Yes, a fresnel will create sufficient heat to melt glass, but no, it’s not a practical setup. And the farther from solstice, the less practical it becomes. Firebricks insulate and trap heat, but do not store heat well. This needs thermal mass, like a big slab of stone or cast iron, to both store and stabilize heat, which is needed to melt more than a tiny bit at a time, as well as anneal, which would be part of the ultimate success. Then, a couple more fresnel lenses to heat the mass. Then a tracking device since the sun moves a degree every few minutes. Given all that, while research and new ideas are always valuable in ways we anticipate as well as ways we never expect, ultimately the best ‘permie philosophy’ glass melter would likely be an RMH designed for that purpose. Wood is also solar power. Sometimes the straight path IS the simplest and best.”

So, figured I’d share that, from someone who knows way more about the properties of glass than I do!

Thanks for all the productive responses Y’all!

Test rodeo of FLGM 0.2
I’m going to attempt to try a number of things today as per Mike’s suggestion (welcome to the team!)

The first three tests today starting at 10 am

3. Clear glass on firebrick with 5 minute sun tracking and lid
4. Clear glass on firebrick with 5 minute sun tracking and no lid
5. Clear glass on steel plate on firebrick with 5 minute sun tracking and lid

I found a large sheet of stainless steel in the shop and decided to build a reflector like solar ovens have to concentrate additional sunlight towards the Fresnel lens. However, because of the light was coming at a slightly different angle, it does not appear to join the focal area but instead follows its own path creating a secondary focal point. Also due to the steep angle that it takes to the sun, it is adding an extremely small amount of light to the furnace.

Test 3 of FLGM 0.2

Method:
Clear glass on firebrick with reorientation every 5 minutes.
Focal area of approximately 1 inch across
Start at 10:55 am
End at 11:55 am

Results:
Firebrick read 760 degrees F at the end of the test.
There was significant fusing on the base of the glass mound where it contacted the firebrick

I was wondering if a reflection would work but suspected it would do what you found.  Now for a silly question:  

If you set the fresnel lens 5 degrees away from perpendicular to the sun, what happens to the light?  Does it still focus it to a spot or does it make a band or something else?

Mike - The answer is "it depends" but up to a certain angle it will simply be an ellipse. A circle is just a special case of an ellipse and results from the focal axis being a perfect 90 degrees from the plane of the surface you're focusing on.

Here is a video showing the results of test 3

Test 4

Method:
Clear glass on firebrick with reorientation every 5 minutes
The glass lid is removed creating open air between the lens and the focal point.
Focal area approximately 1 inch across.
Start at 12:20 pm
End at 1:20 pm

Results:
Firebrick read 970 degrees F at the end of the test.
A majority of the crushed glass melted completely and formed a single 1 x 1.5 inch pool.

Test 5

Method:
Clear glass on steel plate on firebrick.
Reorientation every 5 minutes.
Focal point approximately 1 inch across.
No glass lid.
Start at 1:30 pm
End at 2:30 pm

Results
The steel read 880 degrees F at the end of the test
Hardly any fusing occurred

Test 6

Clouds disrupted testing after only 15 minutes of direct sunlight, but the amount of melting that ocurred in that 15 minutes is very promising.

Method:
Brown glass on firebrick.
Reorient every 5 minutes.
Focal area approximately 1 inch across.
Glass lid in place.
Start at 2:50
End at 3:05

Results:
Firebrick read 680 degrees F after 15 minutes of direct sun.
A large proportion of the crushed glass fused together after only 15 minutes.

here is a comparison of the three medallions created today. These are each a single piece of fused glass. From left to right–tests 3, 4, and 6.

Great job Josiah!  So it sounds like the big block of black steel didn't help at all.  But the one hour tests seem to be kicking out faster results and more data.  Yay!

I may have missed it but did you do a test comparing the lid on vs off?  If not, I'd suggest doing that comparison so you can do further tests with the best conditions.

Is there a thin piece of something black that the glass could be sitting on?  That hunk of steel may be too big and be absorbing and storing a lot of the energy.  Maybe a dark piece of sheet metal or soot blackened tinfoil?

The brown glass is very interesting.  So it seems like if there is something to stop the radiation from traveling through the glass and just bouncing around, it helps.  IE dark pigment in the glass.  

Keep at it, I can't wait to see what tomorrow brings

Phil Stevens wrote:Mike - The answer is "it depends" but up to a certain angle it will simply be an ellipse. A circle is just a special case of an ellipse and results from the focal axis being a perfect 90 degrees from the plane of the surface you're focusing on.

Thanks Phil!  I'm thinking ahead to a smelter with two or four fresnel lenses to power it.  I was wondering if two could be angled so they point the light at the same place.  I assumed not and still suspect it wouldn't work.  So to get more lenses we'd need to do something with mirrors or prisms to get the beams to converge.

If the glass lid off works better then perhaps having a reflective lid that can slide in to cover the chamber for the anneal phase might be considered.  It would reflect the IR from the hot glass back down to it to help slow the cooling while helping to stop convective loss.  

When I started typing this I was thinking this would be up where the glass lid is, but thinking about it while typing this it occurs to me that having it come in from the side just above the hot glass would be best as slowing the cooling.  It also could be easily used with or without the lid.  Would probably just want to keep the shutter plane well outside the focal point of the Fresnel.  

I love all the updates Josiah...thank you!  

Goals for today are to determine the influence of sun angle (optimum time of day), the influence of the glass lid, and see if I can make a uniform brown glass tile 2 inches across.

Test 7

Repeat of test 4, only it’s being run at the same time of day as test 3. This will help clarify the effect of proximity to solar noon and glass lid IR filtering.

Method:
Clear glass on firebrick with reorientation every 5 minutes
The glass lid is removed creating open air between the lens and the focal point.
Focal area approximately 1 inch across.
Start 10:58
End at 11:58

Results:
Temperature at the end of the test was 1020 degrees F.
A majority of the glass fused and a small amount in the center completely melted.

Discussion:
This test proves to me that the glass lid significantly decreases solar gain. To some degree there is less melting than there was in test 4, this indicates that the 12 o’clock hour has higher solar gain than the 11 o’clock hour. It seems as though the 2 hours prior to solar noon have the most melty melty.

Test 8

Brown Glass on firebrick with reorientation every 5 minutes.
No lid between lens and focal point.
Focal area approximately 2 inches across.
Start at 12:15 pm
End at 2:30 pm

Results:
By 12:35 a significant amount of glass has melted
At 12:50 the glass read 1200 degrees F.
At 1:15 all the crushed glass within the focal area has melted.
At 1:30 I began to allow the focal area to move slightly off target to attempt to make the pool larger.
At 2:30 the glass read 970 degrees F. Remove lens and allow the glass to cool slowly in the furnace.

Unfortunately the 2.5 inch square “tile” fractured upon cooling. This is probably the result of allowing the focal area to move around a bit towards the end as the small medallions are very durable.

Today was my final day of testing for the foreseeable future as I’m leaving the Lab. However, Paul convinced me to come back for the September PEP event. Hope to see y’all there!

Here are some concluding thoughts as reference for the next time this project gets picked up.

1. It appears that having a surface that absorbs the solar energy is key. The difference between the clear and brown glass is significant. An intermediary heat absorbing material could potentially be used if a suitable substance is discovered to make it out of.

2. The two hours prior to solar noon seem the best for melty melty

3. The glass lid filters out some of the IR

4. Brushing ceramic fiberboard dust onto the firebrick under the glass works pretty well to prevent sticking.

There have been many good suggestions on this thread and I’m looking forward to the design for prototype 0.3!!

Here are more photos:

Great work Josiah!  Nice summary and helpful hints for the next time.  Have fun on your journeys in the meantime