5 ms·
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
by Tade0 4y ago
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.
- Cthulhu_ 4y agoIt'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.
- wiredfool 4y agoI'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.
- Tade0 4y agoThat'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.
- dzhiurgis 4y agoI still want to make giant parabolic mirror from mylar space blanket
- marcus_holmes 4y agoIs there any way of building an array of small lenses that can output the same power? Optics is not my thing, but I'm fascinated at the possibility of a solar-powered forge
- Gravityloss 4y agoI 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.
- marcus_holmes 4y agothanks, 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)
- bradyd 4y agoYou should look for old rear projection TVs. The screen in these have a fresnal lens the size of the viewable area.
- cwkoss 4y agoAll 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.
- wazoox 4y agoOdeillo solar furnace can reach 3300°C and melt about any metal. https://en.wikipedia.org/wiki/Odeillo_solar_furnace https://en.wikipedia.org/wiki/Odeillo_solar_furnace However it's hardly "low tech" :)
- moffkalast 4y agoThat 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.
- jagged-chisel 4y agoWhat’s the conversion efficiency of solar panels? What are the losses converting that to run a laser? 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.
- moffkalast 4y agoYeah, 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.
- vanderZwan 4y agoI think the miscommunication stems from the fact that this phrasing: > 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.
- moffkalast 4y agoI 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.
- hutzlibu 4y ago"I wonder how much embedded energy is there in that giant fresnel lens. These things are notoriously expensive." 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.
- tomcam 4y ago> 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.