PV: RE: pvusers V1 #365

[Robert Warren <robertwarren@mail.com>]

pvusers           Tuesday, January 18 2000        
Volume 01 : Number 365



Messages in this digest:
Re: PV: embodied energy in PV modules

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Date: Mon, 17 Jan 2000 22:50:50 -0700
From: Marc & Marcy <marc@aculink.net>
Subject: Re: PV: embodied energy in PV modules

ForestHaven wrote:
>
> Hello,
>
> We are currently having a discussion on another
list about whether or
> not a PV module uses more energy in its
manufacture than it produces in
> the course of its useful life.  Does anyone have
the answer to this?
>Subject: Re: PV: embodied energy in PV modules

Hello, Marc & Marcie,
This subject keeps coming up. Sometimes I think
that the last couple generations have had so many
disappointments in having our beliefs shattered,
from believing in Santa Claus, on down.  People
start to think, "Whatever we do, it is a losing
battle, entropy wins, goodbye Planet Earth."
But no, PV panels really do make a net gain in
energy, and it doesn't take all that long to
recoup the energy expended. It does, however,
depending, not as you might think-- on how you
measure the total inputs--but rather, on which
solar cell technology we are discussing.
We recently had an interesting discussion of this
a couple months ago at a BP Solar sponsored
conference in New Orleans about 3 months ago, and
we had a lot of people from various aspects of the
industry, including Richard Perez of Home Power
magazine, David Katz of Alternative Energy, Dr.
Jean Posbic, Sr. Technical Director for BP Solar,
Gerry Braun, Thin Films Dept., BP Solar, and about
40 or 50 of the who's who in the industry.
OK, enough credentials. Taking worst case
scenario, old method of making silicon ingots from
scratch, in an electric induction furnace,
starting from raw silica sand to liquefy, purify,
cast, and then cool the ingots gradually, slicing
them with a diamond saw (all of which is how
Siemens still makes their cells), it takes maybe 6
years at the most to re-coup the kilowatt hours
that went into production. Remember, the
production process itself is done on a mass scale,
so the costs are spread out by thousands of
kilowatts of PV panels made every year. The PV
manufacturers themselves are always trying to save
steps, save money, and above all, save
electricity. There are a lot of factories out
there whose years production is somewhere on the
order of a couple of megawatts per year.
Next, it is no longer necessary to start from raw
silica oxide sand. A PV cell only requires 1 part
per million purity. Computer chips have to be 1
part per billion impurities. There is now so much
computer chip scrap silicon on the market, that it
has become a major source for PV production.
There are a lot of new technologies which have
brought the energy cost of making PV modules down
to about 3 years.  Some of these include the
extruded ribbon technology, which has many
variations. The most efficient of this particular
method is the production line of ASE, Americas, in
Billerica, MA. They extrude six ribbons in one
continuos six-sided hollow tube. There is no
waste, as they cut the tubes first into 3-inch
high six-sided rings (for lack of a better term),
with a laser. Then they cut the edges of these so
that they end up with six - 3"square thin cells,
with no waste. It is all computer controlled and
robotized.
The thin film people have really got it down, now,
too. Then there are the people like Amonix, who
use only a tiny piece of silicon chip, the size of
your little fingernail, and they make it precisely
like a computer chip, with pins integral to the
back of the chip. Think of what a Pentium chip
looks like, only about 1/4 the size. Then, they
put a huge Fresnel lens on the front and a heat
sink on the back and focus 300+ suns on that
little chip. You don't hear about this technology,
as it isn't available for the home market: it is
only reserved for huge arrays, as they use a
sophisticated tracker with high precision
accuracy. They are not to be confused with Midway
Labs out of Chicago, who are now out of business.
Amonix has put up some 3 and 5-megawatt power
stations, feeding the grid.
Finally, a physicist down in Brazil did and
interesting calculation a couple of years ago,
which was reported in Renewable Energy magazine,
which is a European journal. He compared the
energy it takes to derive, refine, and produce
power from something like 5 grams of plutonium to
the energy produced by 5 grams of silicon, using
the same criteria, and figuring in all the aspects
of manufacture, ganging cells into modules, etc.
He came up with a figure, if I remember correctly,
of around 7 years for the silicon, and something
like 120 years for the plutonium. However, the
waste disposal of the plutonium was not even
entered into the equation, as it wouldn't have
been fair to the silicon, as silicone isn't
poisonous!
-- Robert Warren




A while back this thread was on about energy
useage in
construction of cells. At the risk of being off
topic I
found this claim at:

http://www.cellulose.org/builder.htm that

"mineral fiber production actually requires 59%
more energy
then cellulose production,"

and thought it may be of interest. My apologies if
this is
too far off topic.

Marc S. Nameth
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