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Could I build a giant magnifying glass? (And maybe incorporate it into a steam engine?)

Optics are fun, and so following that logic, scaled up optics should be even more fun. And so this leads us to: How do I build a giant magnifying glass?
The sun has a lot of power, and I want to harness that energy, and try out a few things, including the interesting prospect of using it to power a steam engine. (Heat up something, run water over it, and run the steam through a turbine).
Several methods have come to mind, including: acrylic, freezing some water in specially-shaped bowls, and sandwiching water (which has a slightly higher refractive index than ice) between two parabolic pieces of plastic. I'm personally concentrating on the last one, as it would be more permanent than the ice.
Just thought this up: freezing a lens, and then coating it with something immediately so that it will stay once it melts. What do we have that is clear, dries quickly, and readily available?

Does anybody else have experience with this?

UPDATE: Some relevant links...
An ideal result.
Parabolic mirrors are another possibility, but I'm still more interested in a lens.
Where a lot of this sprang from.
Indices of refraction. Is it Indices or Indexes?
Hmmm....

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Qcks says: Feb 22, 2012. 11:16 AM
I have a question:

Are we trying to make a magnifying glass or are we trying to turn water into steam using solar energy?

IF we're making giant magnifying glasses, you can probably disregard 90% of what I'm about to say.

If you want to turn water into steam, parabolic mirrors coupled with black/dark absorption mediums would work better then magnifying glasses.

Here's why:

A magnifying glass, due to the smooth curve, captures a bunch of light, which gets refocused into a concentrated point.
The concentrated point can be used to heat things up and burn stuff, but any light that gets reflected is wasted.

If you place a black pipe filled with water above a concave mirror, you still have a bunch of light focused on a point, but the light gets 2 chances to heat up the water and thus heat up the pipe.
Further, you could combine this with a convex glass lens on top of the pipe that's ontop of the concave mirror, bringing in more light, and generally increasing the intensity of the heat generated.
abrown75 in reply to QcksMay 31, 2012. 9:07 PM
That does sound viable and is an extension on a similar idea I posted here:
http://keihatsu.blogspot.com/2009/07/perpetual-energy-machine-effectively.html

My question is that while it does absorb more energy from the sun, I am wondering if it is really more efficient to extract useful work that way or through powering steam engines. I don't know the answer to that. Simply making a distinction between the two. Just because it's harnessing more energy from the sun, doesn't necessarily mean it is more efficient in providing useful work. An engineering question I guess.

What I would like to see is an investment website where a few like-minded individuals could get together and build such a thing.
smokeypwns says: May 22, 2012. 5:15 AM
what it sounds like you need is a big fresnel lens which you can get from one of those old projection TVs they will harness enough sun to melt a penny
♥VaMpIrE☻ says: May 15, 2012. 8:07 AM
y not? that zoundz cool
bashers says: May 8, 2012. 7:50 AM
I am developing a large lens to power a turbine.. it can be done.. i hope to join up with turbine manufacture to assist in development as i beleive solar power can be used in this way..how far have you got?
wirkkalaj says: Feb 22, 2012. 9:47 AM
Hey Carbon. I've been tossing a similar idea around in my head for years. I think you should test the idea out on a small scale first. Large magnifying glasses are hard to come by without a lot of money. I'm hoping to finish a small scale prototype this weekend. I'm using a 6 inch magnifying glass to heat the water in an enclosed system (kind of like a pressure cooker) to steam, and using that steam to push a turbine in hopes of generating any amount of electricity. If the concept works, I'll want to make some alterations and then a larger scale model. In the future I'm hoping the system can be made to work perpetually. I'm thinking that after the steam pushes the turbine, the steam would then enter into some sort of condenser to be turned back into water where it would be heated again to start the process all over again. I'm just glad somebody else out there is thinking of things like this. I figure it can work If I can get the water hot enough. I've built successful solar ovens, but this will be a first.
3
Jezza Bear says: Mar 15, 2007. 4:16 PM
I know it is not a lens but my site has this (it was an old Instructable here before I deleted it)Solar Kettle.

I have burnt my fingers with this!

I think I have seen articles on Ice lenses, not very good I am afraid , very difficult to get the curve
2
carbon (author) in reply to Jezza BearMar 15, 2007. 4:21 PM
Is it really that hard to get the right curve? I see it as just a matter of getting the right bowl-shaped thingy to put the water in.
3
Jezza Bear in reply to carbonMar 16, 2007. 3:08 PM
Hey Carbon

I knew I had seen this....this is a web site of a really cool (pardon the pun) television programme we have in the UK

Rough Science

They seem to have done t using a balloon. I remember the programme when it was on air and they were not to impressed by it, but worth the experiment anyway..enjoy
164
Kiteman in reply to carbonMar 15, 2007. 4:56 PM
It has to be a smooth curve.

I'd be more inclined to try fresnel lenses. You can buy quite large examples, but I have a couple (just over a foot across) that came off old OHPs since my school went digital. I'm just waiting for a lighter, sunny evening to try and set fire to something...
49
lemonie in reply to KitemanApr 1, 2007. 3:54 PM
Would a lighthouse-clearance lens be any good? I only ask (out of curiosity) because of the size of the things.
164
Kiteman in reply to lemonieApr 2, 2007. 4:10 AM
You have a light-house lens??? How big is it? You must be able to melt metal with one of those!
49
lemonie in reply to KitemanApr 2, 2007. 2:03 PM
No, but since I occasionally see big lenses like this I'm curious to know whether there would be any value in buying one.
164
Kiteman in reply to lemonieApr 2, 2007. 4:06 PM
Certainly an awful lot of play value...
2
carbon (author) in reply to KitemanApr 1, 2007. 2:25 PM
I found a 1.5 ft. by 1.5 ft. Fresnel lens at a podunk hardware store. (From what I understand, it gets mounted in the rear window so truckers can see where they're backing up). It's a flexible sheet of plastic, by the way. I stashed it behind a shelf so I can come back later and buy it. ; )
2
carbon (author) in reply to KitemanApr 1, 2007. 2:20 PM
In an overhead, is the lens solid or just a flexible sheet? Do the lenses you have focus light down to any sort of a point? Or do they have a pretty broad focus point?
2
jtobako in reply to KitemanMar 15, 2007. 6:47 PM
i saw someone's setup made from a projection tv, something like 4' (1.2 m?) across. they were having fun melting low temp metals (copper coated zinc pennies in seconds).
2
carbon (author) in reply to jtobakoMar 15, 2007. 10:03 PM
Like this?
2
carbon (author) in reply to KitemanMar 15, 2007. 5:03 PM
Hehe, I'm actually finagling my way in next to the IT guys at my school, as they are systematically phasing out the over-head's... I'm also trying to get salvage rights / first dibs, on a planetarium projector that is being replaced by a digital one. : )
2
carbon (author) in reply to KitemanMar 15, 2007. 4:59 PM
Smooth like not rough, or smooth like one continuous curve?
164
Kiteman in reply to carbonMar 16, 2007. 11:40 AM
Smooth like one continuous parabolic curve. Maybe stretch an elastic membrane over a circular frame and pour in water - the weight of the water will (maybe) stretch the membrane into the right curve - then freeze the whole thing. Use boiled water to cut down the cloudiness caused by air coming out of solution as it cools.
6
zachninme in reply to carbonMar 15, 2007. 6:34 PM
I saw a 4ft x 4ft one online for $20, which is cheap :-)
2
carbon (author) in reply to zachninmeMar 15, 2007. 10:04 PM
4 by 4 ft. what, exactly?
6
zachninme in reply to carbonMar 16, 2007. 2:18 PM
Wow, sorry, I think this got tagged onto the wrong comment :P Frensnel lens, that is. WestFW's link is probably the best, I think it was a "blowout" sale I saw mine at :P
164
Kiteman says: Mar 16, 2007. 11:50 AM
If you're using solar, why not use it to drive a stirling engine instead?

http://pesn.com/2005/08/11/9600147_Edison_Stirling_largest_solar/

And I'm sure gyroscope.com does one, but their site is down at the moment. Do a google image search for solar stirling parabolic to see what I mean.
49
lemonie says: Mar 15, 2007. 5:00 PM
I agree with JB you're best with a parabolic mirror. And old satellite dish might be an easy starting point?
You should easily power one of these(?):
http://www.mamodonline.co.uk/index.php?crn=238
164
Kiteman in reply to lemonieMar 16, 2007. 11:42 AM
My Science Clubbers once wrapped an old dish in foil and used it to melt chocolate. They documented it and won an award for their investigative skills.
2
carbon (author) in reply to lemonieMar 15, 2007. 5:06 PM
I've never seen them that cheap! I was saving to buy one for my Dad, so thanks for the link. : )
49
lemonie in reply to carbonMar 15, 2007. 5:31 PM
Those are more advanced than the basic model I have (in bits, with worn parts...). Do you live in the UK?
Perhaps your dad might like something from here:
http://www.gyroscope.com/
(It wasn't loading for me tonight, but I'm sure it's the correct site)
2
carbon (author) in reply to lemonieMar 15, 2007. 10:09 PM
Yeah, you seem to be right about the page being down. Anyway, I live in the States. The thing was that my dad had a steam engine when he was a kid, but he left it behind when they moved, so I'd like to get some good son points and buy him one.
29
westfw says: Mar 16, 2007. 3:05 AM
20x36 inch fresnel Lens. at Electronics Goldmine, for about $40.
2
dogsrcool2me says: Mar 15, 2007. 8:01 PM
water expands when it turns to ice.
2
carbon (author) in reply to dogsrcool2meMar 15, 2007. 10:05 PM
True, and I have anticipated this. It would be a simple matter of drilling a hole and squirting in some water, I would imagine.
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