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Multi-function solar panels

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Posted by Morris Dovey on January 14, 2007, 3:12 pm
 
[ posting from news:alt.solar.thermal ]

The discussion of panels producing both hot air and hot water started
an interesting (to me) chain of thought...

I already use a slat-type absorber in my panels; and I've built one
air/water heating panel that worked passably well at delivering the
incident energy in whatever mix of warmed air/water was called for.

This morning I was speculating on how convenient it would be if the
slats produced electricity in addition to hot air and hot water - and
how if that could be done at reasonable cost, an all-in-one solution
might be possible. Pure blue-sky stuff - but then a couple of
previously unconnected ideas came together: What if my extruded
aluminum slats could be replaced with extruded silicon slats?

I wasn't particularly troubled that silicon isn't a good candidate for
extrusion processes - but then I thought about how the cylinders (from
which solar cell wafers are cut) are produced; and reasoned that
shapes other than round can be produced by interposing a die at the
top of the molten silicon - and that, depending on the "extruded"
shape, might accelerate the process, eliminate the wafer sawing, and
still provide all of the characteristics required for solar cells.

I've put up a web page at the link below with drawings to illustrate
the mechanism and the process. For simplicity sake, the drawing shows
a flat ribbon; but, in fact, the ribbon could take on any "extrudable"
cross section.

More interesting to me is the fact that if incorporated into my
current air-heating panel design (Thank you, Iain!), the photovoltaics
could produce electricity at both faces!

Just thought I'd share...

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/Ribbon.html



Posted by SJC on January 14, 2007, 6:51 pm
 


  These guys used PVT panels (PV and thermal) They are silicon solar
cells thermally bonded to a plate that has water tubes running behind.
You could create a PVT air panel the same way.

http://www.beaufortcourt.com/rec/sustainable_strategies.htm


Posted by Morris Dovey on January 15, 2007, 12:17 pm
 SJC wrote:

|   These guys used PVT panels (PV and thermal) They are silicon solar
| cells thermally bonded to a plate that has water tubes running
| behind.
| You could create a PVT air panel the same way.

Not bad - but more expensive to produce than using full-width
ribbon-type solar cells and exposing _both_ sides of the cell/absorber
to the solar energy stream (which is what I've been doing with my
aluminum slat design).

Yes, I could do it the same old way - but it's really difficult to
implement significant improvements by copying what's already being
done. <g>

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto



Posted by SJC on January 16, 2007, 4:19 pm
 

  I just wanted to reference what exists and is known to work.
  If some variation could produce a proven benefit, then it would be worth it.
  I am not sure what you mean by:

  "..full-width ribbon-type solar cells and exposing _both_ sides of the
cell/absorber"

  I am familiar with a lot of PV technology, even bifacial cells, but I have not
heard of these.



Posted by Morris Dovey on January 16, 2007, 5:58 pm
 SJC wrote:
|| SJC wrote:
||
|||   These guys used PVT panels (PV and thermal) They are silicon
||| solar cells thermally bonded to a plate that has water tubes
||| running behind.
||| You could create a PVT air panel the same way.
||
|| Not bad - but more expensive to produce than using full-width
|| ribbon-type solar cells and exposing _both_ sides of the
|| cell/absorber to the solar energy stream (which is what I've been
|| doing with my aluminum slat design).
||
|| Yes, I could do it the same old way - but it's really difficult to
|| implement significant improvements by copying what's already being
|| done. <g>
||
|   I just wanted to reference what exists and is known to work.
|   If some variation could produce a proven benefit, then it would
|   be worth it. I am not sure what you mean by:
|
|   "..full-width ribbon-type solar cells and exposing _both_ sides
| of the cell/absorber"
|
|   I am familiar with a lot of PV technology, even bifacial cells,
| but I have not heard of these.

Ok. You have now (although still not as an off-the-shelf product). Old
technology lowered a "seed" crystal to be "wetted" at the surface of a
pot of molten Si; and, once wetted, the seed crystal is raised at
carefully controlled speeds to produce a silicon cylinder (the faster
the speed, the smaller the cylinder; and vice versa). The size of the
cylinder is limited by it's ability to cool (freeze) in a controlled
manner and by how much mass can be supported at the seed crystal
attachment point.

The Si cylinders can be turned/ground to remove side irregularities;
and are sawed into round wafers. The wafers can then serve as a
substrate for IC's or << drum roll >> solar cells. This mechanical
process is very much *not* cheap.

I'll mention in passing that solar cells don't _need_ the same surface
that we like for building 3-micron circuit elements. It can be, by
comparison, horribly craggy and rough - IOW, they can (and perhaps
should be) fabricated to a different standard of fineness using very
much less expensive methods.

What I proposed on the web page I pointed to (and repeat below) is a
different method - one which, instead of producing discrete cylinders
to be sliced and diced, produces silicon ribbons in a continuous
process.

I'll over-simplify again by suggesting that a slotted "boat" be
floated on the molten Si; and that a slot-wide seed crystal be wetted
at the miniscus present at the slot. Once wetted, this seed can be
raised to produce a Si "ribbon" for so long as there is molten Si at
the slot - without any other practical limitation. Moreover, because
ribbons of suitable thickness can "freeze" hugely faster than current
cylinders, the ribbons can be "pulled" at comparatively breakneck
speeds.

What I'm suggesting is that solar cell fabrication can be migrated
from a discrete-step type of process to a continuous process with a
substantial reduction in processing and required precision.

Except for the material being pulled instead of pushed, the process
bears a strong resemblance to extrusion; and it appears that it should
be possible to produce "interesting" cross-sections - including at
least a few that might remove the necessity to bond cells to a
supporting structural element. Conceivably, one might extrude a void
suitable for circulating a fluid through a ribbon segment...

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/Ribbon.html



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