Re: [Vo]:Dual-Use solar panels?

[Stephen A. Lawrence]

Jones Beene wrote:
--- R C Macaulay wrote:

Question? How do you reconcile the heat trapped in
the parabolic collector with the thin film materials
mechanical properties that portend fast degradation
due to heat?

OK - I didn't make it clear that as envisioned, the
photovoltaic surface is not placed around the
collector tube. Instead, this film replaces the
mirrors.

Since the mirrored reflective surfaces would not be
enclosed, heat build-up would not be the problem to
overcome, and would actually be less than in the
normal usage of these cells. 

As Michel pointed-out - the problem with this concept
would be: can you efficiently reflect only the
photonic energy (mostly IR) which you are NOT going to
use in the cells? 

I think that you could reflect most of it, based on
the analogy below, but that critical point is far from
proved.

As envisioned, the solar cells would replace what was
formerly mirrors. Imagine the trough shown here:

http://www.rise.org.au/info/Tech/hightemp/image003.jpg

... except that the reflective surface, not the
collector tube (which is unchanged), is covered with
the flexible printed solar cells, *except* that the
protective coating on the surface of these
photovoltaic cells is designed somewhat like a two-way
mirror. 

So why not just use an interference filter?  By multicoating a clear 
substrate and carefully choosing the thicknesses and refractive indices 
of the coatings you can selectively reflect certain frequencies.  This 
is very mature technology.  Old fashioned color enlargers typically used 
filters which worked this way.  Those fancy gold film ribbons which you 
can get at any party supply store use the same trick.

I'm not sure how easily this would let you reflect IR while passing 
visible light, tho, but I dare say some google searching on interference 
filers would turn up a fair chunk of info in it.

I don't see the need for either nano particles here, nor for any kind of 
weird flourescence (which is a way of transforming frequencies you don't 
want into frequencies you do want, rather than a way of *sorting* the 
frequencies, which is what you really want to be doing here).



IOW the coating allows that (mostly) the spectra of
solar photons which can be collected by the "ink"
which is used pass through, but the rest of the
photons are reflected, which is mostly the infrared
spectrum... and "mostly" is the operative word here. 

I could cloud the issue by throwing-in "nano" i.e. the
possibility of adding a nano particle to the coating
(which is usually a thin Teflon film) and suggest that
the nano-particles would do this efficiently, but I do
not know that such a particle of the correct
specifications actually exists now (to be honest). 

I am *hoping* that (and this idea is really dependent
on the possibility) a photo-luminescent nanoparticle
like titania or zirconia, when added to the teflon
coating, would not only reflect longer frequencies to
the heat pipe collector (for raising steam) but also
would "semi-cohere" the most active solar wavelengths
and slightly improve the efficiency of the direct
conversion. That is part and parcel of Dicke
"superradiance" and it has actually been demonstrated
to some extent, so it is not all "pie-in-the-sky" so
to speak.

If you can imagine a tall glass office building, which
uses the highly tinted glass, the glass may look to be
shiny black from a distance, but yet it is highly
reflective.

By analogy (revers analogy), only the photons which
pass through the solar film would be collected for
direct conversion and the others are reflected to the
tubular collector which heats up a molten salt, which
is then piped over to a steam plant. 

This is of course a very 'green' idea (in more ways
than one), and ultimately it depends on the economics
of trying to hybridize two dissimilar methods and at
the same time to apply superradiance techniques to
solar radiation.

Jones