Instructables

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....

Qcks2 years ago
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 Qcks1 year ago
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.
smokeypwns1 year ago
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
y not? that zoundz cool
bashers1 year ago
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?
wirkkalaj2 years ago
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.
Jezza Bear7 years ago
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
carbon (author)  Jezza Bear7 years ago
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.
Kiteman carbon7 years ago
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...
lemonie Kiteman7 years ago
Would a lighthouse-clearance lens be any good? I only ask (out of curiosity) because of the size of the things.
Kiteman lemonie7 years ago
You have a light-house lens??? How big is it? You must be able to melt metal with one of those!
lemonie Kiteman7 years ago
No, but since I occasionally see big lenses like this I'm curious to know whether there would be any value in buying one.
Kiteman lemonie7 years ago
Certainly an awful lot of play value...
carbon (author)  Kiteman7 years ago
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. ; )
carbon (author)  Kiteman7 years ago
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?
carbon (author)  Kiteman7 years ago
Smooth like not rough, or smooth like one continuous curve?
I saw a 4ft x 4ft one online for $20, which is cheap :-)
carbon (author)  zachninme7 years ago
4 by 4 ft. what, exactly?
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
Kiteman carbon7 years ago
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.
jtobako Kiteman7 years ago
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).
carbon (author)  jtobako7 years ago
Like this?
carbon (author)  Kiteman7 years ago
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. : )
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
Kiteman7 years ago
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.
lemonie7 years ago
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
Kiteman lemonie7 years ago
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.
carbon (author)  lemonie7 years ago
I've never seen them that cheap! I was saving to buy one for my Dad, so thanks for the link. : )
lemonie carbon7 years ago
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)
carbon (author)  lemonie7 years ago
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.
westfw7 years ago
20x36 inch fresnel Lens. at Electronics Goldmine, for about $40.
water expands when it turns to ice.
carbon (author)  dogsrcool2me7 years ago
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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