I want to model rays of light bouncing off a parabolic dish with technical drawing, How do I do it?

Basically I want to model the sunlight as it bounces from both a parabolic and a compound parabolic dish. I want just to use technical drawing. It is no problem to model if the dish is pointed straight at the sun but I want to model the rays if the dish is NOT pointed at the sun.
On a curve, I will gestimate a tangent to an arc and light bouncing off goes off it at the same angle as it hits it.
NO problem it the light arrives parallel to the plane of the dish but most of it will not arrive like this.
How do I do it? Just with elevation plan and sideviews and sections through the dish.
Thanks Brian It is in relation to

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NachoMahma8 years ago
. Your "tangent method" should work with any angle of incidence. Whether or not the light source is "on axis" shouldn't matter. . Not 100% sure, but no one else has answered. What happened to make you think it won't work?
gaiatechnician (author)  NachoMahma8 years ago
Anyway, I finally did it with art of illusion software and I did it for parabolic dish, compound parabolic dish, hemisphere and winston w dish. (All different dish curves). None of the dishes are great!
I believe that if people put in a bit of effort, we can design a dish with a 2 3 4 or 5 hour acceptance angle for solar cooking or solar electricity generation.
That provides better concentration for a known time. I think that video shows the way forward. It will be shaped like 2 leaves joined at the back of the focus, The basic dish curve would be compound parabolic or winston w but there will be a little extra up curve close to the edges of the leaves. The leaves up curve will increase near to the cooking pot and may even form a tube close to it.
I think it will be really wort it to desigh this new dish shape.
I have done a combined trough alternative to it in the following video
why make a dish with a 2-5 hour acceptance angle? If you use a regular parabolic dish you can heat salt (which is very cheap) to store that energy. And molten salt as you may or may not know, will slowly dissipate the stored heat for hours. I believe the salt needs to be heated to 1000F to get to this molten stage. No problem with my dish..ive melted copper(1984.32F) 
gaiatechnician (author)  jlp.media7 years ago
Your dish is a precision instrument that requires constant tracking.  I agree it is an option. But it is  pretty high tech.  If you design a dish with a 2 hour acceptance angle, that can be good enough for a meal or to solar pasturized a large batch of water, that is a much more financially viable option. Carbon offsets are being used in India to provide parabolic solar cookers now. People are even paid to use them!
But users are complaining about having to constantly readjust them. And  every time you readjust, you risk flash injury to your eyes.
Providing a dish and pot with a 2 or 3 hour acceptance angle would be so much more practical, if your object is to reach as many people as possible.
you're absolutely right. And I am currently working on a program that will find the optimum shaped dish for the longest acceptance angle. But the problem with the acceptance angle dishes is that the solar energy gets dispersed more over a bigger focal point. which is why you can do nothing more than boil water. and thats great for people who cant get/have that luxury. But over here in the states, especially during this economic slump, 100s of thousands of people wont have heat this winter.
From all the research that I've done I can get a single axis tracker for $35 add that to the cost of supplies for my dish/heater that I got at Home depot. you're looking at maybe $80 + a window fan. I'll tell you something, I'd much rather pay $80, than the thousands I typically would spend for heating oil.
i dont mean to sound cocky when I say this, but I believe I can make a solar tracker for even cheaper than the $35 listed. Thats my next project after I finish that compound parabolic dish calculator/program.
Practical, you say? call me selfish, but i can already boil water. I guess its all a matter of perspective. I must say, i AM glad that there are people like you who are willing to help people outside the US.
gaiatechnician (author)  jlp.media7 years ago
I think your heating a material hot will also be useful for room heating.  You can have your Parabolic dish heating up the insulated salt or iron block all day, then at the end, wheel in the block, take off the insulation, cook your meal on the hot top, and then just let the heat radiate to keep the room warm. 
I made my "compound parabolic" dishes but later testing showed that they did not quite achieve what I wanted. 
The Winston w dish did best in my crude software simulations. (And since then, another guy has confirmed this with other software) but nobody has tested the winston w dish for real as far as I know!
If smarter people than me work on it a little, I think a 2 or 3 hour dish with good concentration can be achieved pretty quickly.
I found a great website just now that has a list of concentrators
and whats better is it has the potential output linked to each one.
When you design your winston dish it makes sense to me at least, to have it at one end, an extreme parabola ((2x^2) and then have it gradiate to a less extreme sloped parabola(.5x^2) on the opposite side. It may look a bit silly and you may or may not have to shift the focal line on one side but its my only logic on achieving a much higher acceptance angle time.

Theres only a couple ways to get a longer acceptance angle.... have more mirrors or a shape like the aforementioned one. with your application it  doesnt seem Ideal (for lack of a better word) to have more mirrors. and if you have that odd shaped one you can at least absorb the sunlight for longer at the expense of losing a bit of heat. I dont know...let me know what you think.

maybe this idea seems a bit out of the box, but i was playing around with 'snap switches' on my last solar oven. and what happens is when the heater gets to a certain temperature the switch (comprised of the same metal coil found in old thermostats) "snap" as to complete or disconnect the electronic circuit.
well if you take the same concept but apply it to a parabolic lens....you have x-shaped mirror and when the switch activates the x-shaped mirror snaps open to a newly shaped mirror to get those extra 2 hours or so of sunlight in. granted you will have to manuanlly close the dish in the PM so come morning time....
and honestly...having to adjust a mirror, who's stupid enough to stand between the mirror and the sun.... theres always a critic. :)
gaiatechnician (author)  NachoMahma8 years ago
It is hard to actually measure the angle of incidence on a drawing except at the edges and then only if the light is going parallel with the paper. And I have to draw a tangent with the same problem too! I have decided to make a small model from cob with mylar stuck to it. Then I can shine the laser level down on it to simulate the sun. I can put the model on various angled mounts to simulate the sun moving across the sky and I can also mount it to simulate it being pointed not correctly. A bit of a pain though! Brian
The sun's arc across the sky stays in a single plane (that plane moves over the course of the year, but just pick a day :-). You should model that plane. If you're using a parabolic dish (circular), then it doesn't matter how the plane is oriented -- the dish is symmetric. You just need to specify in your drawing what orientation you've assumed.
gaiatechnician (author)  kelseymh8 years ago
My problem is that I want to model it as the sun is moving across the sky and the dish is not pointed exactly at the sun. Therefore the rays will not be striking the dish symetrically. The dish might be pointed up to 30 degrees off target (off the plane). That would be the very maximum and not something I want to do, but useful as an example. Brian
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