Giant Fresnel Lens Deathray: An Experiment in Optics

Step 12: Conclusion

Conclusion

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Clearly, a giant Fresnel lens with an area of ~1.2m² is a powerful asset. Assuming the maximum available solar energy hitting the ground is around 1000W/m², this lens could theoretically concentrate 1200W of power into a square centimeter. Of course, at this latitude and time of year, around half of the maximum sunlight is available so this would make an excellent summer project. But even during winter, the fact that I could easily melt solid copper and make a nickel red hot is pretty damn cool.

Additional Information

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There are a good number of websites about the joys of giant Fresnels, namely:

• "Now We're Cooking with Light"
• "Random Destructive Acts via Focused Solar Radiation"
• "How to Melt a Penny"
• Howstuffworks Article
• Wikipedia Article

Other uses

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Perhaps the most valuable thing you can get out of this instructable is the source for these giant lenses. There are loads of of them heading for landfills, or recycling, or god knows what else, so reclaim these things and put them to use!

Note: You may think, as I did, "Gee, I bet I could make a super efficient solar panel with one of these". But according to this discussion board that isn't a very good idea, and could ruin your expensive solar panel. You could certainly power a small heat engine like this stirling engine though, by trapping all the light in a black container thermally connected to the boiler. A company working on this technology, but using reflectors instead of lenses, is Stirling Energy Systems.

Thanks to everyone for your comments and suggestions.
Special thanks to foobaz utne for solving my problem with the Fresnel lens focusing properly.

I hope you enjoyed this project, and I will either update this if I further develop it, or post other solar-related projects in the future.

Comments

[FirstSpear]

OK, the big electricity companies will poo poo it, but I'm thinking that this could be a cheap approach to desalination by condensation. The steam could simultaneously be used to supply the water vapour, and also spin a generator to pump cold sea water through the condenser in one swell foop. Stopping at night is irrelevant as the output is storeable.

Love this site, and its participants.

[Deadalus]

Were you ever able to work out the problem with the secondary lens ?  It ,may be that some form of lasing element would work.  The guts of small laser pointers which are almost free may be worth trying.

[mgalyean]

Trying to be nice here, but what part of physics and engineering are you actually basing this comment upon?

[Infinite_minus_zero]

This would be awesome with bugs crawling everywhere.
KILL IT WITH FIRE!

[spamattakky]

Did you see the article where the Israelites concentrated the beam into a glass fiber optic cable and was able to use in in surgery?

http://www.newscientist.com/article/dn4009-optic-fibre-delivers-solar-surgery.html
http://www.newscientist.com/articleimages/dn4009/0-optic-fibre-delivers-solar-surgery.html

[Unit042]

I once read a book about many different science projects, including one just like this instructible: using a fresnel lens to melt a penny, but I figured the lens would be too expensive to acquire. Now that I know where to look, I will be melting metal, experimenting with thermal collection experiments etc. in no time! Thank you for putting up the rear-projection TV tip! :)

[John S]

It may not work on a solar panel but it it should enhance the efficiency of the passive solar heater I have been thinking of building to help heat my house. By building a metal frame with soda pop cans stacked inside and a clear front and mounting a lens like this in front of the glass front I should multiply the amount of heat collected from the air flowing past the stack of solar heated aluminum cans. I just realized it would only be in focus a small part of the day since the solar heater box will be mounted on the south wall of my house. Still it shouldn't hurt anything. I might have to make the back of the box out of heaver metal.

[Helioskannon]

Be careful with that, Aluminum melts at 1200 F... (Copper at 2000, and it _destroyed_ the penny) It could well work if it's not in perfect focus, just be careful and don't burn a hole in your house. Though, a well designed solar furnace to melt metal would be awesome. If I can find one of those lenses anywhere, I'll see what I can do, and if it works, post an instructable.

[Silence]

Thats some intense heat.
You could purpose that heat for electricity in 1 of 2 ways.
Stirling engine, Steam turbine !!

[Shiftlock]

Both of these ideas have been done. There's a Youtube user called GREENPOWERSCIENCE that has posted videos of these in action. He plays with all kinds of solar. In his most recent video, he cuts a beer bottle in half by lightly scoring it, then using a small parabolic mirror to stress the glass. It's neat.

[badideasrus]

i found a source of the lenses. craigslist. search for rear projection tvs. most are free for the haulin, and over 55 inches. start the burnin!

[BtheBike]

Yes . I got 2 from curbside garbage also. Right now with black friday ,these things are all over the place like old CRT's . Maybe there should be a mandate to collect these lenses for 'green' industrial use ,or ship to 3rd world countries for use.

I wonder if the lens from old seeing glasses could also be used for the focal lens in a pinch .

[badideasrus]

that was a similar idea that i had. use fresnel lens to heat metal ffor forging and smelting. no need for coal or wood. just stick the metal bar under the light for a few seconds and then continue forging. i've heard of parabolic mirrors being turned out of alluminum (lathed.) why? it would be simpler to just take molten metal and pour it on on a spinnin disk. the liquid metal would take a parabolic shape, and you would not need an insanely large lathe to make it. i'm seeing 12 foot mirrors made with an old car motor.

[qualia]

please elaborate on your pouring molten metal on a spinning disc idea, whichever way i picture this, i always end up with molten metal being thrown out from the edges of your parabolic shape towards faces, via inertia and gravity.

[badideasrus]

the disk would have to have edges.... like a pie pan shape. my comment does sound kind of silly, doesnt it?

[qualia]

lol its algoods, it just sounded like an alarming methodology, with the oversimplification on a site full of people ready to follow instructions down to the letter. and yeah i think they are used in certain telescopes or something, mercury mirrors, i think that when you're getting close to 12 feet its trickier to control the depth of the curve precisely via the speed of rotation because of all the stuff to do with the fluid dynamics and inertia and friction and suchlike. would be fully awesome to use a fluid mirror to reflect energy to heat a boiler that powers a steam turbine that drives a generator that charges a battery which drives the motor for the mirror as well as a surplus charge.

[badideasrus]

..... if only that was possible. ... also, for all you 'down to the letter' people, please look at my user name. my ideas usually are dangerous even with COMPLETE instructions.

[qualia]

well i must admit, the fun is usually directly proportional to the danger.

[jerbear1978]

So, if I read through your instructable correctly, I read that you never got your smaller lense to work correctly? Could this be fixed by re aligning your lense holding structure?

[badideasrus]

ANGST! i reply to myself about a problem with my reply, and it moves my seco;nd reply to the top! i'm havin a bad day.

[badideasrus]

dang it. i put a space between the topic of lenses and the topic of mirrors and instructibles goes and deletes it. how do i maintain clarity here? >(

[Leejin]

Hell, use it to coil water then use the steam to turn a turbine on your home. If 4 square feet of the suns power can do this... then why the heck has no one applied this to creating energy on a massive scale. I've heard of the mirrors heating up that huuuge column and boiling water, but this seems like an IMENSE form of energy. Ugh, the gubmn't annoys me.

[michael_p_fogarty]

LOL if it aint fossil fuel then they dont get rich (Down with all earth killing capitalists). look up sterling hot air and sterling steem engines just emagin what you could do adding a fresnel lens to those woot woot.

[DrSimons]

Well yeah...I've done some research into what people are already doing with this. 1 design doesn't use water, it just uses an air-based Sterling engine, which is heated by mirrors. Parabolic mirrors are infinitely more logical than fresnel lenses, because they're easier to make and can be much bigger, and won't fade in the sun.

In Spain (and other places now, I imagine) there is a 20MW solar power concentrator. Unfortunately I think there is a theoretical maximum temperature you can reach solely by concentrating sunlight (which I believe is the surface temp. of the sun) but you can still get an insane amount of power. The best thing is all our power plants are already based on heating water in some way or another, so the turbine/generator part has already been perfected through a century of engineering.

I have absolutely no clue why people aren't covering the entire surface of Arizona, New Mexico, Nevada, etc with mirrors.

[nutsandbolts_64]

For one thing it's the cost. The second is they can't find a way around the most obvious problem: The sun goes up, and it goes down. And I guess I consider myself lucky being in the equator:D

[DrSimons]

Well compared to PV cells, mirrors are pretty dang cheap....for solar thermal, they don't need to be very fancy. Also, tracking the sun is extremely easy because with parabolic troughs, you only need to move them in one dimension. The movement of an entire field of collectors could be managed by a $10 circuit board. However, it's probably sill cheaper to burn coal, and cost is the only thing that anyone seems to care about...

[perfectfire]

So you don't even have to adjust for the time of the year (regarding the tracking in one dimension)?

[nutsandbolts_64]

 Well, looks like I stand corrected at the "cost" part, but they do have to do something about loosing sunlight when they needed it most. Yes, I have heard of using liquid salt to keep the water boiling through the night, but there should be a more commercially viable solution. Never mind car batteries for large scale power production that's for sure. 

[Leejin]

boil water * not coil water...

Haha

[michael_p_fogarty]

Boil in copper coils woot woot free power and distled water!!!!!!

[thedubman]

Would a less powerfull beam (out of focus, larger focal point of light area) give same amount or more power, relative to area of solar panel exposed to light. (ie a v small solar panel, with death ray frensal machine Vs standard size solar panel in normal sunlight = same power?) Ive allways wonderd that.

[sujitksharma]

A very well illustrated Instructable. Good work!