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Physics help (again) please - energy given up at reflection - Page 2

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Posted by Morris Dovey on June 19, 2009, 12:50 pm
Curbie wrote:

You're right, but I have what I need in practical terms from work
already done - I'd just hoped to apply some last minute fine tuning with
a more general simulator than I've already written before a hand-off
next Thursday.

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by Curbie on June 20, 2009, 1:14 am

I've never seen a post from daestrom I knew to be wrong so if his
answers are what you're looking for I'd go with them.

If I remember correctly you're a C guy, if your simulator requires a
routine for incident angle or a number of other solar routines, try:


If you dig trough the functions you'll probably find what you need and
how the parameters that feed them are calculated. Email me if
questions about routines within pvwatts, I can't say I'll know the
answers, but after a couple months of porting and thousands of debug
single steps, I might.


Posted by Morris Dovey on June 20, 2009, 3:22 am
 Curbie wrote:

I don't think he walks on water, but when he speaks I listen carefully. :)

I'm most comfortable with C and APL. C is for /SPEED/ and APL is for Q&D
linear algebra and confounding myself six months later later. :)


I think I have the code here - but I'm too short on hours right now to
dig through it. Later perhaps - there are no words to describe how much
I hate slogging through other peoples' code!

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by daestrom on June 20, 2009, 12:15 am

Don't know the answer to all your questions, but here's a couple.

Energy is lost when light is reflected, but the wavelength/frequency doesn't
shift.  Think of it more as "20 photons of wavelength lambda incident to the
surface but only 18 photons of wavelength lambda reflected".

AFAIK, 'ohmic heating' is the same as resistance heating.  Pass an
electrical current (DC or AC) through a substance of some resistance and
heat is generated in the substance (I^2 * R).

Yes, reflection depends on the angle of incidence (and the polarization of
the light)

( http://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.html
is in my browser's favorites, it's a great site for this sort of thing)

Posted by Morris Dovey on June 20, 2009, 3:01 am
 daestrom wrote:

Ok - this makes sense and works for me. Thanks!

Over the past few years I've been trying to 'game' flat panel loss
mechanisms, primarily reflection and radiation, so as to move them from
the "loss" category to the "gain" category. Since those efforts paid off
so nicely, I couldn't help but try to apply the 'gaming' approach to the
targets of solar concentrators.

The flat panel performance really took off at five to seven reflections;
and I've come up with a relatively simple surface geometry that appears
to guarantee more than a dozen reflections of all light impinging on
concentrator targets while (hopefully) significantly reducing radiation
losses. Absorbing 1/9 of energy at each reflection would be a /very/
Good Thing. I might even be able to skip wearing welding goggles. :)

One of the aspects I haven't had time to explore yet is applicability to
other spectral ranges. There might be some advantages for communications
and some medical technologies.

Hmm. I ran across the label in a couple of articles that used the term
to refer to absorption of incident light energy. I scratched my head a
bit and decided to go with the flow. :)

The first seemed 'sorta' intuitive, but I hadn't even considered

New question: is sunlight [a] strongly polarized, [b] weakly polarized,
or [c] random? (and am I likely to care?)

And is now in mine. I haven't looked through it yet, but the page at the
link looks promising.

Many thanks!

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

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