In an old game of mine, there was a monastry driving on wheels through the dessert. The monks spend there days collecting sunlight, smelting sand into "glasstrees", which would then use daylight to collect water (silica gel), pump it up at night (using optic fibres for transport, salt water for storing heat, glass wool for isolation and distills to re-capture the nightly water vapors).. creating a ecosystem in its shade. Nearly all of it made from glas.
While the premise might be idiotic scifantasy, the idea to terraform in situ with what you got, is quite neat.
Just imagine this driving around on mars, with huge halftransparent balloons over it, which like a parabolic mirror pre-collects the light, printing structures for future ecology with the little light that world offers from the material at hand.
I’m not an expert on this, and I might be missing something because to me this sounds like a spectacularly useful idea.
Compared to something I would have thought of, like the trivial idea of raised solar panels that left enough space below for animals and plants to grow, those glass trees have wide manufacturing tolerances and work independently of each other.
Thinking now about their degradation process, they might produce a blanket of fine glass shards which would make animal life impossible. I wonder whether there would be ways of mitigating that.
There’s another name for Blanket of very fine glass shards, it’s sand.
Which suggests the mitigation process might be to insure degradation doesn’t stop in an unpleasant middle ground. Not that glass trees are a good idea…
I think it's not much of a problem, but even so it can probably be mitigated. There are types of glass (tempered safety glass) which break into tiny little cubes instead of shards.
This wouldn't so much be glass, as sintered sand. Energy spent rendering the sand fully amorphous would be wasted.
There are analogous igneous rocks, they aren't good for knapping into blades, leading me to think that broken glass trees wouldn't be especially dangerous either.
Frits used in chemistry are sintered glass, and they don't break into sharp edges either.
I think you could redesign this to be 100% glass with no optic fibers or silica gel. Heat transport can be accomplished heating the water until it becomes steam and then condensing it again at the bottom. Even if there isn't enough heat to produce steam you can still induce flow by exploiting the fact that hot water rises to the top of colder water. Water collection could be accomplished using a fog fence made from glass.
The solar sintering by Markus Kayser looks neet, but it is not practical in its current shape, it does not produce useful outcome. Too brittle.
The main problem is, the heat from the sun is not cohaerent.
There are fluctations in the sky for example, that will make the heat changes drastically. (there is a paper about this from a professional solar furnace, I need to find again)
Reading tip, "The man who sold the moon", from Cory Doctorow. Which also explores the idea of solar 3D sintering (but ignores the limitations).
So I do strongly believe, the whole concept has big potential, beyond entertaining SciFi - it is just not so easy. I think a way to go, could be to have the base load directly from the sun - and then a laser for the exact heat where it is need.
According to the description under a video showing it in use on a good day it melts aluminium - that means 660°C is achieved.
I wonder how much embedded energy is there in that giant fresnel lens. These things are notoriously expensive.
In any case this is a great example of just how much solar power we're given on a daily basis free of charge. Would be a shame to not tap into at least a small part of it in ways other than via agriculture.
It's squared off, which I suspect might be an optimization for production.
In theory, could you mass produce a fresnel lens like that? Either from glass or plastic. I can imagine that in this case, you can get away with imperfections or suboptimal focusing by just sizing it up a bit to compensate.
edit: just had to google to remind me what a fresnel lens is; it's already cheaper (and flatter) than a conventional lens that would have the same power.
I've got a letter-paper sized fresnel that was like $1 at American Science and Surplus. Making a big glass one might be expensive, but plastic ones (which, admittedly, are going to be a bit bad in terms of oil) shouldn't be that much worse than any other formed plastic sheet.
Now, the glass ones for lighthouses, those are expensive.
That's my problem - the small ones are $5 at most, but you cross a certain radius and bam - $10k.
I wanted to build a "fake sun" in my apartment, but lenses of proper size were either unavailable or had to be custom made, ballooning the price heavily.
Plan B is to use a parabolic dish to collimate the light, but such a setup is pretty awkward.
I think there is. Furthermore, the machining should be very simple, as the triangles can be all the same shape as the focus doesn't need to be so sharp. The lenses can be angled so that they focus the sun in the same spot.
thanks, that's interesting. I'm moving back to Australia next year, might give this a try there (where the sun is a little more reliable than here in Berlin)
All the fresnel lenses i've seen have the focus in the center of the panel, because they only expect you to use one at a time. I would imagine it wouldn't be too hard to make an array of n^2 (9?) fresnel lenses where they each have the appropriate pattern for their position in the array. I think you might be able to get away with three molds for a 9-array (middle, side, corner). The resulting lenses would be much cheaper to manufacture and ship because shipping a stack of 9 6-ft squares is much easier logistically than shipping an 18ft square.
Looking at the video posted elsewhere in the comments, I'd say he made his own lens by buying a large rectangular sheet of acrylic and using a (homemade?) lathe to machine correctly shaped groves on it.
That just looks like a laser furnace with extra steps. A whole lot of extra steps.
I suppose you would get higher efficiency from that than if you replaced the mirrors with solar panels and used that to drive the laser, but you also wouldn't be limited to sunny days since you can also just switch to grid power at any time.
Yeah, that's what I'm saying? You'd lose a lot in conversions with the laser setup, but you'd gain flexibility and the setup would be far more compact.
I don't suppose you guys bothered to read the second line then?
Regardless, I would still argue that setting up some panels and connecting them to a laser is fewer steps than setting up an array of carefully aligned mirrors and constructing a whole other building of mirrors that focus bounces from those into a point.
Typically solar panels are 21% efficient and lasers are 10% efficient, so the panel+laser setup is about 2% efficient. The mirror setup can be 70% efficient, depending mostly on your absorber design.
Building a laser normally also requires carefully aligning mirrors, as well as typically other advanced processes like glassblowing and high-voltage arcs (for low-pressure gas lasers) or glassmaking with high transparency and carefully controlled doping (for solid lasers), and in most cases fairly advanced chemistry. You might be able to make a laser out of fluorescein-doped jello, for example, but where do you get your fluorescein? It doesn't grow on trees.
Of course you can just buy a laser off the shelf, in which case you don't have to mess with any of this, but you can also just buy a big Fresnel lens off the shelf.
People have been polishing metal into mirrors for 6000 years, and as I understand it, the mathematics of parabolic reflectors for burning things was known by Euclid's time, 2300 years ago, which is probably why the English word for the point where the rays meet is "focus", Latin for "fireplace" (though that sense of "focus" may be only 400 years old).
Newton was making fairly decent-shaped parabolic mirrors 354 years ago, and interferometry has been good enough to make parabolic mirrors essentially perfect since about 01851.
The great limitation on these processes was historically the cost of materials: from Mesopotamia to Newton we're talking about various shades of copper or bronze, which are very expensive materials. For optical concentrators you don't need such optical perfection; gold leaf on something like polished stone would probably be cheaper, but in the Victorian age we learned the art of silvering glass with mercury, and in the early 20th century we learned the art of vacuum-silvering with silver, gold, or aluminum.
Ancient Egypt evidently made polished stonework on lathes, but may not have had the mathematical sophistication to make paraboloids of revolution, or to know why they were important. And the compound parabolic concentrators which allow you to not have to track the sun precisely are, I think, from the 20th century.
So, you might say, why didn't we have solar furnaces before the Industrial Revolution? Well, actually, before being murdered by the French Revolution, Lavoisier discovered that diamond was a form of carbon by burning diamonds in a solar furnace, in 01772. The solar furnace was crucial for this experiment not only because it allowed him to reach especially high temperatures but because it didn't introduce carbon dioxide.
Lavoisier's solar furnace used a lens like Seegers's, but enormously heavy and thick. Fresnel wouldn't build his first Fresnel-lens prototype until 01820.
Doesn't read that way. Where your first statement was "That just looks like a laser furnace with extra steps", I'd say what you proposed looks like Odeillo with lot of extra steps. Focusing sunlight with mirrors is strictly simpler.
I think that’s fairly low tech. Something like it could have been built hundreds of years ago (with human operators orienting the 63 heliostats to make them reflect the sun’s light into the parabolic part)
> that giant fresnel lens. These things are notoriously expensive.
Didn't read TFA but the picture looks like he got it free off of Craigslist--many people are unloading projection TVs these days and they use Fresnel lenses. That looks like one of them.
I wish there was a project which with minimal materials would convert sand to solar panels using solar heat energy, but somehow without the metal framework of aluminium needed today.
So , in theory we could have a source of energy with minimal materials, no fossil fuels and something that can be used over many decades.
As I understand making polysilicon today is a very energy intensive process. So is making aluminium but like 75% of the global aluminium resources are recycled
AFAICT, aluminium isn't required, merely cheap and plentiful, but if you had a solar economy you can make it cheaply anyway so it doesn't matter.
PV quality silicon, however, I know nothing significant about.
If I was trying to rebuild from mud and sticks upwards, in the style of the Primitive Technology YouTube channel, I'd probably go for thermoelectric heated first by fire and later by a focusing mirror — bronze (copper and tin) is, after all, a bronze age tech.
Silicon is made by reduction of silicon dioxide with carbon in an arc furnace. One heat that furnace with concentrated light instead, I guess, but it requires very high temperature. There is also a process using aluminum as the reducing agent.
Very pure silicon for PV is produced by converting silicon to SiHCl3 by reaction with HCl, followed by distillation and thermal conversion back to silicon. Recycled silicon could be treated the same way for purification; it's going to be less contaminated than the raw silicon coming from silica reduction.
I think you'd probably go a thin film route to make PV yourself; much less semiconductor would be needed. Maybe copper oxide?
Copper oxide is definitely doable as a science fair project. Though I haven't done it, as I understand it, typical efficiencies are around 1%. That's probably still plenty for electrolytic metal reduction to be easier than small-scale smelting.
You mean merely by melting and recasting scrap metals ? There is no proprietary tech in stirling engines that might really make them long lasting/ highly efficient ?
That's definitely one way to do it, but melting and casting is by no means required. A Stirling engine can be built with existing parts of things, especially if diaphragms are used in place of pistons (since rubber and plastic membrane material is common and easier to construct with). Even better if you can find a super robust rubber like from truck air brake diaphragm rubber, but the possibilities are really endless there.
> There is no proprietary tech in stirling engines that might really make them long lasting/ highly efficient ?
Stirling engines are at least as efficient as solar panels, and probably more so. Their efficiency is often overestimated but by default they're relatively efficient.
The difficulty with Stirling engines that no one talks about though is managing excess heat. They're subject to the same issues as internal combustion engines in that they can't convert all of the heat input into work, hence you have to either control the rate of input or you have to use cooling as a corrective measure to maintain a temperature gradient. Otherwise, the engine will stop working. The advantage to powering a Stirling engine with the sun is that the input should be easy to adjust, whether it be mirrors or a lens that respond to a thermocouple.
There's other ways to improve efficiency, none of which is proprietary. There's a Stirling engine variant developed by NASA that's entirely enclosed and uses helium as a working fluid. It's meant to be efficient and robust because there's no crankshafts or direct linkage between the pistons.
Another way to address robustness is to make a Ringbom style engine (still Stirling cycle) that uses a long tube to make a gas vacuum air piston, thus reducing the mechanism to just one moving part:
The downside to thermoacoustics is that they're inherently loud, unlike engines that use the Stirling cycle, but they are less physically complicated than Stirlings. In the above example, the acoustics aren't actually driving anything, but said technology is capable of working a piston like a Stirling does.
A very niche area of thermoacoustics involves using steam as a working fluid to improve efficiency. Here is a video of a "wet" thermoacoustic engine I made recently. This engine is simply two cans taped together, a ~3 cm layer of rice, a balloon with weight attached, and ~100 mL of water.
But it's not a steam engine! When running it performs entirely enclosed without pressure overload.
Thermoacoustics might be too loud, but overall I think that heat engines are underappreciated as energy transducers. Diaphragms are used frequency in amateur toy heat engines, and actually solve a lot of the robustness issues that come with keeping a piston-based engine running, but research usually goes into pistons. A fleet of Ringbom style low-temperature-difference engines using ...
Do you think it is possible in theory to get heat from PVT panel to run the stirling engine ? Or are the temp differences required too high like you mentioned ?
There's speculation that the Inka used that approach to melt stone for construction, but as far as I know not much evidence. It doesn't seem to have been used anywhere else before the last couple of centuries.
This is interesting, and supports some sci-fi-fantasy I have: I'm convinced that this process could be done in zero-G, and could be a way to start processing raw resources in space.
Anything reflective should work but it has to reflect short wavelength. Anything polymer could have a transparent layer on top which could (partially) filters the UV an other short wavelength and heats up the dish instead.
You can also remove the paint and mirror polish the dish itself but that requires tools and it likely will not stay shiny for long.
But UV is what destroys the polymer if it does not reflect it.
Beside that if something is "glossy" and reflects UV like tinfoil (Al) it will almost certainly reflect most of the visible light waves and part of the IR too and that is what you want.
In contrast anything transparent like a clear coating on a polished dish, is very likely only partially transparent to visible light.
It turns out after some reading that a reflective BO-PET should be reflective enough initially but will yellow and become brittle within fewer than 1000 hours of sun exposure. So as a very short-term use in an emergency if it's what's available to build a solar still, oven, or forge it could do the trick if it's the only thing available. Some metal foil should be far more durable though.
The boPET layer in question is thin enough that it will have to yellow enormously before that becomes a problem. On the other hand, metal foils, other than gold and some of the platinum group, are not that good at resisting chemical weathering in the air, especially when water and sulfur are present. So it wouldn't be surprising if, in the rain, boPET-covered aluminum remained a usable mirror without repolishing for longer than unprotected aluminum. Also, replacing aluminized boPET might be both easier and cheaper than repolishing solid aluminum; the amount of aluminum required per square meter is about two orders of magnitude smaller than with aluminum foil. This holds a fortiori for silver.
To correct an earlier poster, tin is not aluminum. Although tin was responsible for the high reflectivity and corrosion resistance of Newton's mirrors, aluminum is far superior on both counts.
Gold has higher reflectivity than aluminum in the infrared but lower in the blue. Because so much sunlight is NIR and so little is blue, this turns out to be an improvement for preventing things in LEO from heating up, which is why astronaut helmets use gold rather than aluminum or silver. I don't know offhand if the same is true of the solar spectrum at the bottom of Earth's atmosphere.
Tin foil and aluminum foil are two different things, although many North Americans do not know this. Tin foil (once commonplace, now hard to find) is made of tin, while aluminum foil is made out of aluminum, which is a different metal from tin. For many purposes the differences are not very important — both are low-melting-point, white, corrosion-resistant, food-safe metals that can take a high polish — but for solar-collector mirrors the differences in reflectivity and corrosion-resistance matter a lot.
This conversation reminds me of a guy on Reddit who learned that old-timey whitewash was lime, so he tried painting things with lime, but it was gardening lime (calcium carbonate) rather than slaked lime (calcium hydroxide), which is what holds whitewash together. As you can imagine, his "whitewash" worked very poorly.
You are wrong on that. It's the same thing just different places use different words.
Just like "pencil lead" does not refer to lead. It refers to the thing inside a pencil. The composition of that changed over time but the name didn't.
There are plenty other fix terms like "gas" (gasoline) or "tin foil hat" (a hat made out of aluminium foil) which everyone knows what is meant by it despite the word(s) describing something different.
Nowhere in this thread anyone but you was taking about foils made out of tin metal.
This is a cool project but I was hoping to see a solar powered machine that turned ore into metal. That is what a smelter is. This is a solar metal melter or what is generally called a furnace, not a smelter. Too bad.
Might not be much of a production line. Very big, very slow, sensitive to weather conditions. What do you do about all the scattered light? The guy in the picture is wearing goggles, but people in the building who see the crucible (while looking out the window) won't be.
I think it's actually fine. Quick back-of-the-envelope calculation:
- The lens collects about 1 m^2 of sunlight.
- At the focal point, the concentration is way higher than sunlight.
- But when the light is scattered away from the focal point, it's distributed over an area of ~4 pi R^2.
- So from the point of view of a person looking out the window, R^2 would be much greater than 1 m^2, so the crucible would be less bright than the outdoor sun.
- The outdoor sun doesn't blind people unless they look directly at it, and humans are good at avoiding that.
So I think the crucible would appear as an annoying glare that people would instinctively look away from, but it probably wouldn't accidentally blind people.
Solar-powered smelting would be great but this is not it.
This is melting metal, not smelting it, which means reducing non-metallic ores to metal and is the crucial technology that allows people to use metals in the first place (other than copper). See https://en.wikipedia.org/wiki/Smelting:
> Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind.
Likely the most effective way to reduce iron or copper from ore with solar power at a human scale would be electrolytic metal reduction: hydrometallurgy or electrometallurgy rather than pyrometallurgy.
Pyrometallurgical processes at human scale are painfully inefficient; see Christopher Roy's documentary "From iron ore to iron hoe: smelting iron in Africa" or John Plant's more recent experiment "Primitive Technology: Iron knife made from bacteria", both available on YouTube for the time being. These are both charcoal-powered rather than sun-powered, but I think the higher temperatures attainable by solar power will only increase the process's efficiency modestly.
The false claim is original to Jelle Seegers (see https://archive.fo/qk3dZ), not introduced by Kris De Decker, but you can be sure that De Decker will not correct the error. He is consistently enthusiastic about continuing to promulgate his false claims even after they are pointed out.
Not sure if it's a false claim per se, as "smelten" is Dutch (Jelle being Dutch also) for melting. A device that melts things in Dutch would be called a "smelter". Of course, in his description he does use the English word melting correctly, but he also describes what it does correctly, so maybe he's just being artistic about it.
Maybe it's just an error due to a false friend? I didn't know "smelten" in Dutch meant "melting". Etymonline says English actually got the word from Dutch:
> smelt (v.) mid-15c. (implied in smelter), from Dutch or Low German smelten, from Proto-Germanic *smelt- (source also of Old High German smelzan, German schmelzen "to melt"), from PIE *smeld-, variant of PIE root *mel- (1) "soft." Thus the word is related to melt (v.). Related: Smelted; smelting.
As usual, once the word was adopted into English, it started rapidly changing in meaning.
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[ 2.1 ms ] story [ 132 ms ] threadWhile the premise might be idiotic scifantasy, the idea to terraform in situ with what you got, is quite neat.
https://imgur.com/gallery/yPU871e
https://www.youtube.com/watch?v=ptUj8JRAYu8 Solar Sintering by Markus Kayser
Just imagine this driving around on mars, with huge halftransparent balloons over it, which like a parabolic mirror pre-collects the light, printing structures for future ecology with the little light that world offers from the material at hand.
Compared to something I would have thought of, like the trivial idea of raised solar panels that left enough space below for animals and plants to grow, those glass trees have wide manufacturing tolerances and work independently of each other.
Thinking now about their degradation process, they might produce a blanket of fine glass shards which would make animal life impossible. I wonder whether there would be ways of mitigating that.
Which suggests the mitigation process might be to insure degradation doesn’t stop in an unpleasant middle ground. Not that glass trees are a good idea…
There are analogous igneous rocks, they aren't good for knapping into blades, leading me to think that broken glass trees wouldn't be especially dangerous either.
Frits used in chemistry are sintered glass, and they don't break into sharp edges either.
https://en.wikipedia.org/wiki/Fog_collection
The solar sintering by Markus Kayser looks neet, but it is not practical in its current shape, it does not produce useful outcome. Too brittle.
The main problem is, the heat from the sun is not cohaerent.
There are fluctations in the sky for example, that will make the heat changes drastically. (there is a paper about this from a professional solar furnace, I need to find again)
Reading tip, "The man who sold the moon", from Cory Doctorow. Which also explores the idea of solar 3D sintering (but ignores the limitations).
So I do strongly believe, the whole concept has big potential, beyond entertaining SciFi - it is just not so easy. I think a way to go, could be to have the base load directly from the sun - and then a laser for the exact heat where it is need.
I wonder how much embedded energy is there in that giant fresnel lens. These things are notoriously expensive.
In any case this is a great example of just how much solar power we're given on a daily basis free of charge. Would be a shame to not tap into at least a small part of it in ways other than via agriculture.
In theory, could you mass produce a fresnel lens like that? Either from glass or plastic. I can imagine that in this case, you can get away with imperfections or suboptimal focusing by just sizing it up a bit to compensate.
edit: just had to google to remind me what a fresnel lens is; it's already cheaper (and flatter) than a conventional lens that would have the same power.
Now, the glass ones for lighthouses, those are expensive.
I wanted to build a "fake sun" in my apartment, but lenses of proper size were either unavailable or had to be custom made, ballooning the price heavily.
Plan B is to use a parabolic dish to collimate the light, but such a setup is pretty awkward.
Optics is not my thing, but I'm fascinated at the possibility of a solar-powered forge
However it's hardly "low tech" :)
I suppose you would get higher efficiency from that than if you replaced the mirrors with solar panels and used that to drive the laser, but you also wouldn't be limited to sunny days since you can also just switch to grid power at any time.
The direct solar setup has what losses between the collection points and the target?
I suspect conversion to electricity is not more efficient. It does, however, provide the convenience of switching power sources as desired.
> That just looks like a laser furnace with extra steps. A whole lot of extra steps.
... implies more conversion steps for the direct solar set-up, while the opposite is true.
Regardless, I would still argue that setting up some panels and connecting them to a laser is fewer steps than setting up an array of carefully aligned mirrors and constructing a whole other building of mirrors that focus bounces from those into a point.
Building a laser normally also requires carefully aligning mirrors, as well as typically other advanced processes like glassblowing and high-voltage arcs (for low-pressure gas lasers) or glassmaking with high transparency and carefully controlled doping (for solid lasers), and in most cases fairly advanced chemistry. You might be able to make a laser out of fluorescein-doped jello, for example, but where do you get your fluorescein? It doesn't grow on trees.
Of course you can just buy a laser off the shelf, in which case you don't have to mess with any of this, but you can also just buy a big Fresnel lens off the shelf.
People have been polishing metal into mirrors for 6000 years, and as I understand it, the mathematics of parabolic reflectors for burning things was known by Euclid's time, 2300 years ago, which is probably why the English word for the point where the rays meet is "focus", Latin for "fireplace" (though that sense of "focus" may be only 400 years old).
Newton was making fairly decent-shaped parabolic mirrors 354 years ago, and interferometry has been good enough to make parabolic mirrors essentially perfect since about 01851.
The great limitation on these processes was historically the cost of materials: from Mesopotamia to Newton we're talking about various shades of copper or bronze, which are very expensive materials. For optical concentrators you don't need such optical perfection; gold leaf on something like polished stone would probably be cheaper, but in the Victorian age we learned the art of silvering glass with mercury, and in the early 20th century we learned the art of vacuum-silvering with silver, gold, or aluminum.
Ancient Egypt evidently made polished stonework on lathes, but may not have had the mathematical sophistication to make paraboloids of revolution, or to know why they were important. And the compound parabolic concentrators which allow you to not have to track the sun precisely are, I think, from the 20th century.
So, you might say, why didn't we have solar furnaces before the Industrial Revolution? Well, actually, before being murdered by the French Revolution, Lavoisier discovered that diamond was a form of carbon by burning diamonds in a solar furnace, in 01772. The solar furnace was crucial for this experiment not only because it allowed him to reach especially high temperatures but because it didn't introduce carbon dioxide.
Lavoisier's solar furnace used a lens like Seegers's, but enormously heavy and thick. Fresnel wouldn't build his first Fresnel-lens prototype until 01820.
Doesn't read that way. Where your first statement was "That just looks like a laser furnace with extra steps", I'd say what you proposed looks like Odeillo with lot of extra steps. Focusing sunlight with mirrors is strictly simpler.
https://en.wikipedia.org/wiki/Mirror#Middle_Ages_and_Renaiss...: “by the 16th century Venice was a center of mirror production using this technique. These Venetian mirrors were up to 40 inches (100 cm) square.”
And those were mirrors for reflecting images. The mirrors for a device like this need not be as good.
It is basically a transparent sheet of plastic with some of the plastic carved out. So likely not much energy.
They are only expensive to buy in large, because there is not really a market yet, except hobbyists.
Didn't read TFA but the picture looks like he got it free off of Craigslist--many people are unloading projection TVs these days and they use Fresnel lenses. That looks like one of them.
https://www.dezeen.com/2011/06/28/the-solar-sinter-by-markus...
So , in theory we could have a source of energy with minimal materials, no fossil fuels and something that can be used over many decades.
As I understand making polysilicon today is a very energy intensive process. So is making aluminium but like 75% of the global aluminium resources are recycled
PV quality silicon, however, I know nothing significant about.
If I was trying to rebuild from mud and sticks upwards, in the style of the Primitive Technology YouTube channel, I'd probably go for thermoelectric heated first by fire and later by a focusing mirror — bronze (copper and tin) is, after all, a bronze age tech.
https://en.wikipedia.org/wiki/Zone_melting
Very pure silicon for PV is produced by converting silicon to SiHCl3 by reaction with HCl, followed by distillation and thermal conversion back to silicon. Recycled silicon could be treated the same way for purification; it's going to be less contaminated than the raw silicon coming from silica reduction.
I think you'd probably go a thin film route to make PV yourself; much less semiconductor would be needed. Maybe copper oxide?
> There is no proprietary tech in stirling engines that might really make them long lasting/ highly efficient ?
Stirling engines are at least as efficient as solar panels, and probably more so. Their efficiency is often overestimated but by default they're relatively efficient.
The difficulty with Stirling engines that no one talks about though is managing excess heat. They're subject to the same issues as internal combustion engines in that they can't convert all of the heat input into work, hence you have to either control the rate of input or you have to use cooling as a corrective measure to maintain a temperature gradient. Otherwise, the engine will stop working. The advantage to powering a Stirling engine with the sun is that the input should be easy to adjust, whether it be mirrors or a lens that respond to a thermocouple.
There's other ways to improve efficiency, none of which is proprietary. There's a Stirling engine variant developed by NASA that's entirely enclosed and uses helium as a working fluid. It's meant to be efficient and robust because there's no crankshafts or direct linkage between the pistons.
https://www.youtube.com/watch?v=P1FwrDZKfKk
One particularly prolific content creator shows how a NASA Stirling can be built with common materials:
https://www.youtube.com/watch?v=dOSGpzGhrJQ
Another way to address robustness is to make a Ringbom style engine (still Stirling cycle) that uses a long tube to make a gas vacuum air piston, thus reducing the mechanism to just one moving part:
https://www.youtube.com/watch?v=_Fz0jsOlL60
^^ That maker refers to it as a thermoacoustic "metronome", but it's actually a form of Ringbom engine.
Then there's actual thermoacoustics, which is a pretty interesting area of research.
Here's an example of a solar powered thermoacoustic pipe:
https://www.youtube.com/watch?v=fMoRkEffFOQ
The downside to thermoacoustics is that they're inherently loud, unlike engines that use the Stirling cycle, but they are less physically complicated than Stirlings. In the above example, the acoustics aren't actually driving anything, but said technology is capable of working a piston like a Stirling does.
A very niche area of thermoacoustics involves using steam as a working fluid to improve efficiency. Here is a video of a "wet" thermoacoustic engine I made recently. This engine is simply two cans taped together, a ~3 cm layer of rice, a balloon with weight attached, and ~100 mL of water.
https://www.youtube.com/shorts/Rh4m8mrB2t8
But it's not a steam engine! When running it performs entirely enclosed without pressure overload.
Thermoacoustics might be too loud, but overall I think that heat engines are underappreciated as energy transducers. Diaphragms are used frequency in amateur toy heat engines, and actually solve a lot of the robustness issues that come with keeping a piston-based engine running, but research usually goes into pistons. A fleet of Ringbom style low-temperature-difference engines using ...
How else can we expect to build megaships?
You can use an old satellite dish and either very reflective tinfoil or many small pieces from a (broken) mirror.
You can also remove the paint and mirror polish the dish itself but that requires tools and it likely will not stay shiny for long.
Beside that if something is "glossy" and reflects UV like tinfoil (Al) it will almost certainly reflect most of the visible light waves and part of the IR too and that is what you want.
In contrast anything transparent like a clear coating on a polished dish, is very likely only partially transparent to visible light.
To correct an earlier poster, tin is not aluminum. Although tin was responsible for the high reflectivity and corrosion resistance of Newton's mirrors, aluminum is far superior on both counts.
Gold has higher reflectivity than aluminum in the infrared but lower in the blue. Because so much sunlight is NIR and so little is blue, this turns out to be an improvement for preventing things in LEO from heating up, which is why astronaut helmets use gold rather than aluminum or silver. I don't know offhand if the same is true of the solar spectrum at the bottom of Earth's atmosphere.
This conversation reminds me of a guy on Reddit who learned that old-timey whitewash was lime, so he tried painting things with lime, but it was gardening lime (calcium carbonate) rather than slaked lime (calcium hydroxide), which is what holds whitewash together. As you can imagine, his "whitewash" worked very poorly.
Just like "pencil lead" does not refer to lead. It refers to the thing inside a pencil. The composition of that changed over time but the name didn't.
There are plenty other fix terms like "gas" (gasoline) or "tin foil hat" (a hat made out of aluminium foil) which everyone knows what is meant by it despite the word(s) describing something different.
Nowhere in this thread anyone but you was taking about foils made out of tin metal.
I think it's actually fine. Quick back-of-the-envelope calculation:
- The lens collects about 1 m^2 of sunlight.
- At the focal point, the concentration is way higher than sunlight.
- But when the light is scattered away from the focal point, it's distributed over an area of ~4 pi R^2.
- So from the point of view of a person looking out the window, R^2 would be much greater than 1 m^2, so the crucible would be less bright than the outdoor sun.
- The outdoor sun doesn't blind people unless they look directly at it, and humans are good at avoiding that.
So I think the crucible would appear as an annoying glare that people would instinctively look away from, but it probably wouldn't accidentally blind people.
This is melting metal, not smelting it, which means reducing non-metallic ores to metal and is the crucial technology that allows people to use metals in the first place (other than copper). See https://en.wikipedia.org/wiki/Smelting:
> Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind.
Likely the most effective way to reduce iron or copper from ore with solar power at a human scale would be electrolytic metal reduction: hydrometallurgy or electrometallurgy rather than pyrometallurgy.
Pyrometallurgical processes at human scale are painfully inefficient; see Christopher Roy's documentary "From iron ore to iron hoe: smelting iron in Africa" or John Plant's more recent experiment "Primitive Technology: Iron knife made from bacteria", both available on YouTube for the time being. These are both charcoal-powered rather than sun-powered, but I think the higher temperatures attainable by solar power will only increase the process's efficiency modestly.
The false claim is original to Jelle Seegers (see https://archive.fo/qk3dZ), not introduced by Kris De Decker, but you can be sure that De Decker will not correct the error. He is consistently enthusiastic about continuing to promulgate his false claims even after they are pointed out.
> smelt (v.) mid-15c. (implied in smelter), from Dutch or Low German smelten, from Proto-Germanic *smelt- (source also of Old High German smelzan, German schmelzen "to melt"), from PIE *smeld-, variant of PIE root *mel- (1) "soft." Thus the word is related to melt (v.). Related: Smelted; smelting.
As usual, once the word was adopted into English, it started rapidly changing in meaning.
https://youtu.be/qKcVwmkJbQM
https://www.youtube.com/watch?v=Td_c8fIiu4M