Smelting Solar Style

If you attended the 2022 Supercon, you might have heard the story about the SMD soldering challenge table nearly catching on fire. A magnifying lamp caught the sun just right and burned a neat trench into another lamp’s plastic base. While disaster was averted, [Jelle Seegers] does this on purpose using a huge 5-meter lens to smelt metal.

The Design Academy Eindhoven student is participating in Dutch Design Week and built the machine which is able to manually track the sun to maximize the amount of solar energy applied to the metal.

According to [Seegers], the smelter is more sustainable and uses less energy than the normal procedure which he worked with during an internship.

The lens was also made manually by cutting into a sheet of polycarbonate with a custom-made machine. The operator has to turn the hand crank every 5 or 10 minutes to track the moving sun. The machine can heat to about 800 to 1,000C with an estimated 4 kilowatts of energy. It can melt 20 kg of zinc or 5 kg of aluminum.

This is probably more efficient than using a microwave. You can do a lot with direct solar energy instead of a laser.

32 thoughts on “Smelting Solar Style

    1. I was visiting Shanghai a few years ago and saw the very thing in the flesh (I believe it was the same one, unless somebody replicated it) at a science and technology museum. I was super excited.

  1. When talking efficiency its helpful to have an idea what you wish to compare it to, and what actually matters to your goals…

    As building this rather simple machine has an upfront cost that is probably barely any more than the tank of propane you might use otherwise and that runs out… Not like the electric ones don’t cost money to keep running either, so fiscally its probably a winner, ecologically its probably as close to impossible to beat as makes no odds (at least with current techs).

    But on the other hand time efficiency and man hours required to actually use it likely are pretty terrible in comparison, and if you wish to compare it to something solar PV duty cycle really comes into – strap a PV cell to the wall and tie to the grid or a big battery and get the energy back in that ‘short’ intense burst one those rare occasions you actually need to melt metal could be the winner by a mile…

    Do think this is a great idea myself, though entirely impractical for many as its just soo large and needs storing careful of the lens when not in use if you can make use of it in your space why not! Cheap plentiful metal melting that with the size of that lens is probably only a little weather dependent (as in any day its not so nasty you wouldn’t want to be out there it probably works just fine).

    1. I picked one up for little at a hamfest and looked at the seller straight so he knew I was picking up a loaded weapon and was about to test it. The ground began to smoke. Yellowjackets beware! I have wanted to set it up in some kind of mount.
      Sadly many of these big box TV’s seem to have gone to dual Fresnel optics, one is circular like normal but the other side is a lens cut to spread the light horizontally across the living room as these TV’s got brighter than the first gen ones. Look closely and you can see 2 sets of grooves instead of one and the pattern of interference. Spread spot instead of spot of highest intensity, good for a cooker though.

  2. I had something similar ( but smaller scale ) in our yard in the late 60s when Edmund Scientific sold big Fresnel lenses. I still look for big screen projection TVs when I’m at the dump.

    1. This .. if I see a projection tv at the curb, it’s pretty much getting strapped in to my half-open trunk.

      Most of the older tvs are empty space inside, and the cabinetry is mostly wood and particle board .. so once you salvage the optics and speakers, they are pretty easy to dispose of. Much easier, in fact, than a mid-sized crt.

      1. Looking at it, it is the compound slide off a lathe so he has angular and depth control. This is then mounted on a rod with a sucker (or other clamping method) and bearing in the centre to guide it. Then just a case of setting the tool right for the ring and spinning it around.

        Yep more info on that please.

        1. Absolutely. I would be especially interested in the setting of the cutting angle for each ring. Is it possible to gear it so that it cuts as an unbroken spiral out from the center? Do such Fresnel lenses exist that are spirals instead of concentric?

          1. @TG you could make a rotary, scaling pantograph with a z-depth adjustment, and follow a standard convex lens, since the angles of the fresnel are the same as a standard lens, only more compact in the Z axis (parallel to the light rays).

          2. First of all, thanks a lot for your interest in my project. I have to say that i did not consider the posibility of cutting an unbroken spiral from the center. It would be amazing, but you could unfortunately not cut the entire lense in one motion as every 5 to 10 facets you need to chance the router bit. The facet in the middle has an angle of just 0,1 degrees. The angle of the outer facet is 39,7 degrees. if you dont switch (or grind differently) router bits, you would cut away a lot of material next to the facet, losing valuable usable surface. I sent some extra pictures to the owner/moderator of this website, i hope he adds them so you can have some more insight. At the moment i’m working on an improved method for making more precise and even way bigger lenses (this time 5 meters in diameter instead of 5 sqm ;) as i now found out people are interested in this, I will document this better and share.
            Have a good day, Jelle Seegers

  3. if this works in Holland, from what I know of the comparison to where I call “here” (Western Australia) I’d guess some parts of the year we’d be able to, I don’t know…. double or more the mass of metal this would handle, or make it significantly smaller.
    In summer it can FEEL like putting some low melt point metal out on the road just in the sun, non magnified, will get it close to melting!

  4. I’d love to know how feasible it is to use this type of solar to heat/boil water for heating purposes on a small scale. I have seen the giant mirror boilers that produce electricity, but a more automated sun tracking system and a small loop for the water would be interesting to see.

  5. Jelle said : ” but you could unfortunately not cut the entire lense in one motion as every 5 to 10 facets you need to chance the router bit”.
    Could you not gradually tilt the router from near-vertical at the center to the 40 degrees at the periphery? When I first read the article I had a vision of rotating plastic sheet with a relatively stationary router.

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