Concentration of solar energy.

Discussion in 'Science and Nature' started by Blunted123, May 5, 2011.

1. Just a few questions to those who are very learned on the subject of heat/light, or any energy in general, as I'm sure you'll be able to answer this fairly well.

Let's try to keep this hypothectical to avoid details which hinder our ability to reach a conclusion. I would like to learn the application rather than ponder the details.

Say I have 2 magnifying glasses of average quality from a craft store, approx. 4" in diameter, each with a focal point of ~.2" and a focal length of 3.5". While concentrating the Sun's rays and heating a piece of iron, I reach a temperature of, let's say 500 degrees fahrenheit, or 260 celcius. (Keep in mind, the numbers are hypothetical.) Now, if I were to focus each (2) magnifying glass at the same point, would the temp. reached at the focal point be twice that of 1 glass? I.e., in this situation, would focusing both points at the same point give me an operating temperature of 990-1000 fahrenheit? Aside from radiation, and clouds blocking the sun and what not.

2. #2
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It would probably be close to double yes. although it'd be on the bottom side of it because one would provide not quite as much energy as the other.

although I will say I don't think the temp would increase very much. Your adding more energy but it's only a small amount so the second would get you a little closer to what the theoretical max of the first lens would be. of course it also depends on how well focused the light is.

3. Well, technically if I had one parallel with the sun, it would reach it's max temp., with the other as a supplementation, correct? I guess my question is how much of a supplementation will it be, when it's light loss is at a minimum?

Anyone know an easy way to reach 2500 fahrenheit using lenses+solar?

4. parallel doesn't really matter because you can refract the light to a non-parallel angle. It wouldn't reach it's max because of the air and it's humidity (among other factor's, like air pollution). Also remember your not actually converting all of the sunlight into energy, only the visible light portion so your not really getting all the power from the sun that is possible.

Why do you want to use lens? It'd be easier to use a concave mirror. And why are you trying to get to 2500F? It's a whole lot easier to just make a furnace to get to that temp than to focus sunlight. Nevermind there's not much need for that high temp unless your going to be welding or forging metals (in which case it's easier to use a furnace or an actual welder).

5. I'm actually majoring in optical engineering and sciences, so I think I might be a bit of help to your question.

First off, heat is a BAD thing. This will effect the density of states in the semiconductor, and essentially will go against getting the energy that is wanted [heat makes the semi-conductor(solar panel) less efficient].

Mirrors, like the post above me said, are ideal. They're going to be the future of solar due to being so cheap and essentially perform the exact same tasks as lens would do for this type of application (focusing light).

This is the principle of superposition, in which you can simply add one thing to another (in this case, adding the heat that would be produced by two lenses focusing at the same spot). This would have to be linear for your idea to work, which I'm almost 100% positive wouldn't happen. I'm only saying this due to the magnitude of heat you're talking about. If you were simply talking a few degrees, it might work.

6. #6
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I realize I can't reach an optimal temperature, but that's not what I'm asking. As I said, I'm not trying to hammer out details, I'm trying to sharpen a concept. My reasons are aside from the point, and not relavant to the conversation. And there are many more uses for high temps in a small area, use your imagination. Please refer to ther OP for my plea on ranting posts that don't quite hit the nail on the head. Aside from that, thank you for the reference to a parabolic mirror. This would hinder it's transportability due to the size of mirror+mount needed, as opposed to set of lenses+mount, or a Fresnal lens+mount. If magnifed point of light at a mirror on the ground, can I deflect the rays to a wall while still maintaining it's energy? I.e., making a magnifying glass-laser?

Anyway, I'll ask again, with not much room for detail. If I aim 2 magnifying glasses at the same point, will I reach roughly twice the temp. as using 1?

Hello Moose,
Interesting major, I find it quite headache, working with light. Kudos to you for your comprehension of the field. Anywho....
This is a solar application completely void of a solar panel, and heat is exactly my goal.

Also,
Have you heard of the solar panels that employ a plane of Fresnal lenses with a secondary optical...something?

7. Hello Moose,
Interesting major, I find it quite headache, working with light. Kudos to you for your comprehension of the field. Anywho....
This is a solar application completely void of a solar panel, and heat is exactly my goal.

Also,
Have you heard of the solar panels that employ a plane of Fresnal lenses with a secondary optical...something?

8. Yea, not sure why I brought solar panels into this haha.

But I'm actually not sure how much spherical or parabolic mirrors are, but this would probably be what you're looking for. Magnifying glasses would take quite a bit more work to match a nice curved mirror. The magnifying glasses of course can work, just might need a lot more of them and would have to keep them aligned, which I'm sure would be a pain if you had too many (sun always moving, assuming the sun is your source).

I keep re-typing my paragraph on your heat question, so I'm just going to say what you're doing seems like it'll be relatively close to what you want. There are non-linear effects that will take place, but I'm not sure how that would be weighted in.

And yes, I do know what a Fresnel lens is and does, but am not sure how they use them for solar panels as I only used them in lens design :/.

9. That's why I was hoping for a large, single piece of glass. Possibly opting for the PCV Fresnel lens.

And about the mirror. If I magnified a point on the glass, would it heat the glass, or simply deflect the light and create a laser?

10. That Fresnel lens would be fine, but again, I have no real knowledge on the costs of these materials.

Also, are you trying to amplify the light by using the mirror? If so, focusing the mirror on the lens would only create losses. If you were thinking of concentrating the light to make the smallest point possible, well then you've entered the realm of lens design

Lasing is an entirely different process, but you're correct about about the reflection.
The lens does reflect some light (possibly invest in some anti-reflection coating for extreme efficiency, as it won't reflect much with incident light hitting the lens parallel, like you described before).

It depends what light is going through your lens. Visible light will transmit and not heat the lens, while other lights (infrared, microwaves) will have absorb and not transmit, therefore heating the lens.

11. #11
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Remind me to rep you in a few hours. I can right now, but this is very nearly the exact answers I've been searching for all morning.

But, no, I was simply trying to create a focal point of 1 or several magnifying glasses/Fresnel lenses/parbolic mirrors in some combination, to create an efficient heating devices reaching ~2,500 fahrenheit, but probably no higher than 3,000.

Again, remind me to rep you, even though I only have 22 points.

12. Haha I'm just here to take a break from studying and talk about optics, glad I could help!

13. wow ok, well next time I know just to not answer in the thread at all. good luck in whatever your trying to do.

p.s. try reading my very first post again.

14. Lmao. You re-read it. You said, "yea, probably close to double but not quite." Then the next section says, "but actually I don't think it will be adding much energy and even if it does it's only closer to the max of the first."

I mean, you nearly contradicted yourself in the very next section, which led me to believe that I should search for an answer from someone who is sure of themselves, not someone who probably is right.

It's not like I didn't appreciate your input, and I obviously read the post as I replied to it the first time. Sorry for over-looking your insight, Thunder.