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"Designer" for solar reflectors - Page 2

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Posted by Robert Scott on November 19, 2009, 10:40 pm

That's right.  Another way to see this is to think of the situation in reverse.
Suppose the collector was the source of the radiation and the whole sky was the
target.  Where in the sky would the radiation from the collector go?  By
symmetry, if most of the radiation from the sun that hit the reflector went to
the collector, then most of the radiation from the collector that hit the
reflector would have to point right back to the sun.  In the case of a pure
parabola, this is exactly what happens.  But of course it can't happen with a
moving sun.  So if you are sitting at the collector and looking at the
reflectors, they could not all look sun-bright.

Robert Scott
Ypsilanti, Michigan

Posted by brian white on November 20, 2009, 12:07 am
I am a little disapointed that people have refused to look into it.
Decision made, game over!
And I am also dissapointed that people did not bother to go to the
bottom and check the link.
There are cusp reflectors that can take nearly 180 degrees of light and
get it to hit the target.  (The target has to be a pipe in line with the
cusp).   There are also winston w troughs that have large acceptance
All I am trying to do is revolve shapes like that into "dishes" or
"flowers" that work.  You are not going to revolve in a circle (like
every parabolic dish in the world because we know a circular revolving
will not work.
  The objections would be correct if the cooking vessel or target is a
point.  Nowhere in the real world is the target a point.
It has area, it has volume. and this means we have leeway up and down
and left and right.  Also note that I am not doing the same thing as Gross.
  I am lining up the long axis of the "dish" or "flower" with the path
of the sun. That is crucial.  There might be one flower or 2, I am
pretty sure there will not be more.
Robert Scott wrote:

Posted by Morris Dovey on November 20, 2009, 1:10 am
 brian white wrote:

Eh? What were your expectations - that people would immediately inundate
you with 3-D renderings (or actual photographs) of the compound
reflectors they've built since reading your post?

That's not much of a rational basis for your snap judgement.

Ok. I watched the youtube video and didn't find anything that I can use
in the context of the work I'm doing. Having reached that conclusion, I
didn't, in fact, choose to see more of the same. We have disappointment
in common, but for differing causes.

Sure. Now please show me one that costs less other methods and that will
give me an adequate supply of air heated to 1000F for 6 hours/day.

Agreed - the target in my application is a full inch wide.

You might have that leeway - but I do not. I'm working with a 1"
diameter tubular target and any "leeway" results in lost energy.

And so (why not)? Is there a cost tradeoff? A performance tradeoff? Is
there a point of diminishing returns such that two petals are good and a
third is wasted?

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by brian white on November 20, 2009, 3:18 am
Best of luck with your projects.
If this does not apply to yours, that is fine.
You did not comment in the first round of comments
  so I have no problem.
And I see now that a lot of people confused me with the video makers.
I took issue with much of the video too.
The important part for me was "The video shows something resembling an
old Victrola audio horn that focuses varying light angles to a focal
point, some with multiple bounces.
-- Clarence A Dold - Hidden Valley Lake, CA, USA "
I am designing a simple way to make these flowers or horns.
I just hope it is useful to somebody.
Ok, for the rest of you, it is NOT my video.
  I only linked to the video so that people could get the idea that
dishes and troughs are not the ONLY option. People do not hear me
because I am nobody. Gross is the opposite and people listen.
His 6 flower thing probably cost about $0,000 to design.  A 2 flower
thing designed with my method might cost less than $0 to design.
  The  trumpet flower thing with 6 horns was what I was trying to show
people.  (I think it is very overbuilt, by the way)

I knew most people would not be interested. (My post  is solar cooking
related and very few here are interested in solar cooking).

  Currently parabolic solar cookers are been paid for by carbon offsets
and given away in villages in India. People even get paid to use them.
But there are problems because they have to be adjusted a lot and people
complain about getting flashed by the light in the eyes.
I was just hoping that 1 or 2 people might take a look, and try out the
designer to see what they came up with.
(I did not expect replies for a few days).
A 2 trumpet flower system with a 2 hour acceptance angle would need
adjustment only at the start of the cooking period  and there would be
minimal flash risk.
Gross used different parameters than I use for the trumpet flowers.
Designs  made with the set up that I show must be alligned with the path
of the sun so most likely 2 trumpet flowers would be the outcome.

Morris Dovey wrote:

Posted by Morris Dovey on November 20, 2009, 5:14 am
 brian white wrote:

Thanks. I like what you're doing - but felt that your expectations of
response were a bit much.

Good. My personal focus is fairly narrow - and I didn't feel that I
really had anything worthwhile to contribute. I read, I looked, and I
kept my mouth shut, which is how I try to conceal my ignorance and/or
lack of inspiration. (The vastness of my ignorance amazes even me. :) )

I read it a little differently. I think it was Gross who was being
faulted for claiming that a (mathematically) interesting project is more
significant than it really is as a practical solution to a real problem.

Yeah. That multiple-bounce part might an efficiency killer. Maintaining
the optical precision of a surface that complex - and providing
adequate reflectivity might present serious production cost problems;
and that will (I think) keep it out of reach for the people who most
need solar technology. :(

I kinda liked the independently-controlled petal concept (but not the
control system). Gross talked up what could be done with tiny motors and
micro-controllers - but I wonder how that system might behave in
breezy/gusty conditions, and how a user in (for example) Rwanda might go
about diagnosing and repairing a problem with their collector/generator

You might be surprised - but being interested doesn't necessarily mean
being involved. People here are working on all kinds of different
projects - but we all learn from one another. It's entirely possible
that you may arrive at some insight from which we all benefit.

I think what you're working on could be important to a great many more
than read this newsgroup - but that's really unknown until you produce
some improved result (true for all of us, not just for you).

At least one person took a look and rough-drafted a program to create
and model a reflector (that may or may not end up looking like what
you've done). The math involved is mostly trig and, as Gross pointed
out, computers can do a lot of number crunching once there's software to
crunch /with/. I have enough on my plate to be able to guarantee that
it'll take me a _lot_ longer than a few days to know if I'm even on a
right track.

FWIW, I make a point of _not_ registering at sites that require me to
remember yet another user ID and password. Which means that I was
looking at your work through a figurative peephole - which (for me) made
understanding as difficult as it could be made. I don't blame this on
you, but it's something you might take into consideration.

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

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