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

I finished sealing up the furnace this morning and gave it a nice fluffy jacket of Dura Blanket ceramic fiber insulation. Wear a particulate mask whenever working with this stuff!

Test 1 of Fresnel Lens Glass Melter (FLGM) 0.02

The goal of this test is to attempt melting crushed glass using a concentrated beam of sunlight inside of the new insulated furnace.

The focal area in this test is slightly diffused to approximately 2 inches across.

The technique involves reorienting FLGM to the suns movement when the focal area passes off of the crushed glass. So the process will involve the focal area making multiple slow passes over the crushed glass as the day wears on.

I’ll be giving live updates during the test!!!

The progress looks great!  How does the back pane affect the focused light?

Activate welding goggle vision!

I reoriented after taking the picture at 12:10

Kyle,

It doesn’t seem to effect it much. When I was putting the lens on there was a moment that the focal area hit the dura board in the upper right corner and there was instant scorching! You can see it in the welding vision pics.

However, the glass lid is starting to get quite hot. I’m super curious if it will crack.

There is a slight reflected focal point that wasn’t there without the glass lid. I’ll be keeping an eye on Fresnel lens temperature

Isn't having sheet glass at the highest point, which is likely the hottest part (unless I miss my guess) after the focal point itself, a design flaw? I mean, to my way of thinking, it makes sense that the solar furnace would be horizontally-oriented, with a mirror, or a few mirrors, redirecting the sunlight before it hits the fresnel lens panel. This would ensure that the heat rising from the focal point isn't rising to gather up against the sheet glass.

I would honestly be surprised if that sheet glass stood up for very long before starting to slump.

I really love the project, and the idea behind it, but there is a reason glass furnaces are so large and heavily-built. I hope you get enough data in this trial to justify further experimentation, as a solar-powered glass recycler could greatly impact the economics of glass recycling and glassblowing, at least in areas with enough year-round sun powerful enough to power such an enterprise.

I mean, think of it. All you'd need is a desert and a fraction of the number of mirrors in those solar-thermal array plants, one with a rail spur, or on an active rail line, or with a direct rail link to sea freight. Conceivably, a fossil fuel-free glass recycling industry could be developed. The economics of the industry would be identical to that of the glass recycling industry as it stands now, save that no money would be spent on energy to power the process; the only energy not being provided directly by the sun could be provided photovoltaically, powering sun tracking systems and conveyor belts.

-CK

Looking at that desert / 3d printer one I wonder if you could get a robot to build glass bricks, they could be filled with sand like https://www.brikawood-ecologie.fr/concept-en/ to create a desert city from sand and sunshine

End test at 3:30pm

Results:

Over the 4 hours that the test ran, FLGM was reoriented towards the sun 6 times.

Highest recorded air temperature inside the furnace was 147 degrees F

At the end of the test the firebrick was 394 degrees F

There was no slumping or cracking in the lid

A majority of the crushed glass did not fuse. Small amounts of crushed glass on the top fringe did melt and fuse.

Discussion:

The area of glass that did melt was exposed to a slightly tighter and hotter focal point due to the angle of the sunlight to the firebrick.

The quality of the melted glass is different than what I have seen from past trials, it is very clear and some of the glass dust melted into a very thin sheet. I suspect this is due to higher firebrick temperature reducing the overall fluctuation that the glass experiences.

Tomorrow I will repeat the test but try raising the lens a small amount to allow a slightly hotter focal area.

Josiah, I wonder if there's any chance that the glass plate might be acting as a partial filter for the wavelengths that the broken glass absorbs.  I know you want to hold the hot air in, though at 147F it seems that the air might not be contributing a lot, but as a diagnostic check you might also consider rerunning the set up you used today with the top glass sheet off.  Then you'd find out if the glass below gets hotter and melts more just due to the lack of the coverglass.  If that ends up being true we can consider a few alternative materials to replace it that are transparent at these wavelengths.  I've got several ideas running through my head right now.  First thing to check....make sure that glass isn't low-E coated.  You don't want it to reflect away all the near IR...that's half the solar flux you're trying to focus.

Looking forward to more!!!

Josiah special ordered the glass to make sure it didn't have any coatings, nor anything filter-ish in the glass.  

First and foremost, I hope that’s a #12 lens if you are looking directly at the sun!
Second, I’m very puzzled that over 4 hours the highest internal air temp was not even 150 degrees... something is amiss. And of course, needing to have 1800 to melt bottles, the focal point is doing it’s job (barely?) but definitely need better heat retention. Seems like tracking is a key element. Keep plugging, this is interesting!

Greg,

This is the most out of focus that I have ever set the lens to and was unexpectedly surprised that any melty melty occurred. I’m curious about materials that might filter different wavelengths than the glass absorbs for a window, that sounds like a very smart optimization.

Julie,

Don’t worry, I had my eyes closed
The sun is directly transferring heat to the glass via radiation, so getting the air temperature up is not necessary for success here. I agree that we need slightly more heat retention. If we could hold the fire brick at 500 degrees F-ish then whatever melted would be able to anneal. I’m excited to see what happens tomorrow. While I’ve had a design in my head for simple automated tracking from pretty early on, I’m not yet convinced its necessary.

paul wheaton wrote:Josiah special ordered the glass to make sure it didn't have any coatings, nor anything filter-ish in the glass.  

Perfect!  Wasn't sure if it was salvaged from a window or not.  You guys are good.

The very best glass for this purpose will still filter about 30% of the light.  But without the glass, the slightest breeze will cool the hot point.

And to riff on the citrus-outdoors-in-Montana theme, if the design were perfected to the point that you could have a solar glass recycler that worked into late fall and in early spring, as long as there was light, that would definitely be proof-of-concept.

It's no volcano, but it would be a hell of a lot hotter than the hollowed-out mountain variety. And talk about a sun trap.

I don't want to be discouraging, but I wish you guys had a gimbal-mount for what you've already built, and maybe one of those electronic sun trackers. There's so much potential in this concept, but I think, especially if it is to work on days other than the summer solstice in Montana, that anything that will heat up to the temperatures you'll want even to fuse crushed glass into tile will need more solar input.

That simple solar tracker you mentioned could easily be used on anywhere up to a half-dozen mirrors, all directing sunlight towards the fresnel lens, which wouldn't need to move with a properly calibrated array of mirrors. The focal point would be on the glass the whole time. You'd probably be able to do better than fuse glass at that point.

I love it. I want to see it writ large. Glass fresnel lenses for each mirror, a large fresnel lens as solar collector immediately before the solar furnace, and a new use for part of the north face of a slope. Float-glass tile production, perhaps even float-glass window and greenhouse glazings, all from recycled glass, consuming no more fossil energy than what it takes to gather it and bring it to the solar furnace.

Oh, and of course, an auxilliary shop, where more fresnel lenses and mirrors are made, from recycled glass, so that the clean recycling of glass, and tinkering with solar thermal applications, can be decentralised, to use less of that energy to gather materials. That seems very permaculturally-aligned to me. Plus, clean industry for intrepid and industrious permaculturalists to generate the capital to do other permacultural things.

GO WHEATON LABS! GO JOSIAH GO!

-CK

This morning I installed longer mounting bolts for the lens to allow more focal area adjustment. It’s one of the instances where everything happens to work out because you can probably find what you need in Paul’s shop

Test 2 of FLGM 0.2

The goal of this test is to attempt to melt glass. The only difference from the first test will be a slightly more focused beam of light. I will set the focal area to be approximately 1.25-1.5 inches across. I’m using the same crushed glass from the first test.

Unfortunately the test was disrupted by cloud cover starting at 1:30 p.m. making the results inconclusive.

However, There was a slightly more fusing and melting compared to the first trial.

When the clouds first rolled in, I opened up the furnace and the firebrick read 580 degrees F.

Later in the day there was a sun break and I turned the preverbial dial to 11. The 1/4 circle of glass melted within a minute.

On one hand I feel compelled to repeat the test and hope for clear skies tomorrow. On the other hand, it appears that although there would have likely been significantly more fusing with clear skies, it still would not have been enough fusing.

We have options here.

I think the next test involves reorienting FLGM more frequently to try and have the focal area confined to a smaller amount of crushed glass.

I would also like to run Greg’s test with and without the glass lid to get idea about how much IR it is filtering out.

Anyone else have ideas for tests I can run on 0.2 before we start getting into modifications and design for 0.3?

I think a test would be to do it without the glass and lots of air under the lense.   If that doesn't work, it might be good to come up with something to block breezes better.