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'[TECH] Printed solar panels'
William \Chops\ Westfield
On Jul 15, 2008, at 6:55 AM, Jinx wrote:
> One other big improvement is that the film is omni-directionally
> receptive and doesn't need to track the sun.
Claims like this set off alarms in my head. Regular solar cells, and
certainly thermal collectors of the "black pipe" variety aren't
particularly "directional", are they? And they still benefit from
This set off alarms for me, too. The reason why it helps to track the
sun is not because of any directionality of the panel. It is because
you want to maximize the amount of watts per square meter which the
panel receives. The closer you can make the line of sight to the sun
match up with the vector perpendicular to the solar panel surface, the
more light you receive. Think about it from the sun's perspective:
when the panel is way off, the sun would only "see" a thin line, but
when the panel is broadside to the sun, the panel appears as big as it
On Tue, Jul 15, 2008 at 5:02 PM, William Chops Westfield <mac.com> wrote: westfw
|Whilst it does sound 'dodgy' I'm not so sure, here is a link from
yesterdays BBC webpage using a solar film:
and I recall the CSIRO tried unsuccessfully to get funds to further
research into a flexible and new way of depositing solar cells onto
:: This set off alarms for me, too. The reason why it helps to track
:: sun is not because of any directionality of the panel. It is
:: you want to maximize the amount of watts per square meter which the
:: panel receives. The closer you can make the line of sight to the
:: match up with the vector perpendicular to the solar panel surface,
:: more light you receive. Think about it from the sun's perspective:
:: when the panel is way off, the sun would only "see" a thin line,
:: when the panel is broadside to the sun, the panel appears as big
:: as it
:: can get.
cdb, btech-online.co.uk on 16/07/2008 colin
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Maybe if you used glass with a treated surface in a half-cylinder
shape that directed the solar energy to edge-mounted solar cells, you
would get decent efficiency without having to move anything.
If the material is cheap enough then it would probably be cheaper and
more reliable to just cover the total area available for your solar farm
rather than trying to put in a bunch of steerable panels.
that makes it "omnidirectional" I spose.
William Chops Westfield wrote:
William \Chops\ Westfield
On Jul 15, 2008, at 6:22 PM, Cedric Chang wrote:
> Maybe if you used glass with a treated surface in a half-cylinder
> shape that directed the solar energy to edge-mounted solar cells, you
> would get decent efficiency without having to move anything.
You probably get "decent efficiency" with a flat panel pointing
straight up. But that's not the same as "maximum efficiency."
Perhaps the real trick is to get ENOUGH output (efficiency be
damned), in a "small enough" area, at low enough cost, rather than
maximal efficiency. I think you could prove that a flat plate has
the best efficiency of any non-tracking shape?
The purpose of tracking is to maximize the output, not per land area,
which is relatively cheap, but for solar cell area. They actually waste
quite a lot of the total incoming energy.
Take for example a system that can track the sun until it's 30 degrees
above the horizon before elements start to overshadow each other. To do
that the elements will have to be spaced in a way that when the sun
crosses the meridian half of the incoming light will fall straight to the
ground (by simple geometry).
If your cells are insensitive enough to the light direction, and cheap
enough to be used in such a way, laying them flat will be the most
efficient configuration, as it captures all of the incoming light.
But this is a big if, of course :-)
On Tue, Jul 15, 2008 at 07:04:33PM -0700, William Chops Westfield wrote:
A claim was made these new cheap cells don't need to be aimed.
Well, the point it they are really cheap (much, much cheaper) than standard
Thus, the claim could probably be worded (but not as nicely for the makers
of the new cells):
"Our cells are so cheap that it is cheaper to double (triple, N x) their
area) than to build them into some sort of aimable array."
It probably costs much more to build the structures/controls for aiming than
to just plaster the entire surface with the new cells and then take the Sun
at whatever angle its at.
Perhaps the best arrangement would be a fixed orientation chosen to maximize
the integral of the luminous flux per unit area over a year. This would be
slanted relative to the ground, so you'd end up with a series of panels
spaced apart as necessary to avoid one shadowing the next at any point in
the year. The slanted panels would probably be a lot easier to keep clean
than panels parallel to the ground.
-- Bob Ammerman
|Fixed arrangement that maximizes the total yearly output of the system
is also what I came up with trying to think how such technology might be
The reason why such hypothetical systems bare little resemblance to
current solar power plants, however, is that photo-Voltaic cells, in any
configuration, still have a very poor efficiency relative to other
When optimized over the cost of materials, installation and operation,
cheap, easy to produce, photo-Voltaic arrays seem indeed to be a great
solution, but such optimization fails to take into account one other
resource solar power plants consume in gluttonous amounts - land.
Taking the average solar energy flux to be of the order of 100W per m^2,
a 1GW power station will need 10km^2 if it is 100% efficient. The value
of such vast areas is such that in most places it is the limiting
factor. The technology used to build the field can afford itself to be
quite expensive and cumbersome to install, if it can offset this cost
even by a small advantage in conversion efficiency.
I guess that is the reason why places where large deserts can be found,
like south western USA and Australia, are the main investors in
researching and developing large scale photo-Voltaic installations,
while the fields being built in places like southern Spain all use aimed
parabolic mirrors and steam turbines. It's not just that turbines are an
old and proven technology, it's also that it doesn't seem likely that
their conversion efficiency will face serious competition any time soon.
On Wed, Jul 16, 2008 at 06:35:09AM -0400, Bob Ammerman wrote:
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