Solyndra emerges from stealth
mode
with cylindrical approach to CIGS thin-film photovoltaics
2009/04/06
Until the end of 2008 Solnydra had been one of the stealthiest
thin-film photovoltaics operators, its glistening, prominently
logoed headquarters building reminding tech-savvy commuters plowing
up and down the I-880 corridor near Fremont, CA, of how little
they knew about the company. But Solyndra has finally let the
sunshine in and come out of the closet - even if it hasn't quite
changed some of its stealthy ways. After a well-planned media
and analyst rollout, the public knows that for this copper-indium-gallium-(di)selenide
(CIGS) thin-film PV manufacturer, the world - or at least its
solar-module form factor - is not flat. As the "solar energy
system of the month" solarserver.com in cooperation with
PV tech.org presents Solnydra' tubular PV module and its Fremont
production site. This feature by Tom Cheyney (Senior Contributing
Editor – USA; Photovoltaics International) is an abridged/edited
version of a three-part blog series on Solyndra originally published
in "Photovoltaics International" (2nd issue 2008.)
View below a PV System
by Solyndra. Source: Solyndra Inc.
Like many TFPV purveyors, Solyndra loves glass
as a substrate, but the company's meter-long CIGS-coated cylindrical
modules look like a fluorescent light-bulb tube, not just another
rectangular slab of the smooth stuff.
Tubular PV for the commercial rooftop market
During a recent visit to Solyndra (see Figure 2), Chris Gronet
and Kelly Truman, the company's CEO and VP of Marketing/Sales/Business
Development, told me about Solyndra’s technology and
manufacturing and its plans for targeting the commercial rooftop
sector. Gronet says the market potential adds up to 30 billion
square feet in the U.S. alone, translating into potential electricity
capacity of 150GW and a PV market of around $650 billion. With
more than a billion square feet of CoolRoof and other reflective
roofing material being put down every year in the U.S., the
opportunity to turn rooftop space into revenue-generating PV
exists today.
Figure 2. Solyndra’s
Fremont, CA, headquarters sits alongside the I-880 freeway. Figure
3. Solyndra’s cylindrical PV modules include 150 CIGS cells
and a proprietary glass-to-metal endcap seal. Courtesy: Solyndra
Inc.
Gronet showed me one of the tubular
modules, the critical element that has captured the attention
of venture capitalists and private equity investors who've sunk
about $600 million so far into Solyndra (see Figure 3). The glass
cylinder is black, about an inch or so in circumference and is
actually a tube within a tube. One can see that the inner CIGS
portion of the monolithically integrated device has a series
of swirling helical scribe lines, differentiating the 150 cells
within. Between the inner and outer glass cylinders, a common
industrial liquid described by the exec as an "optical coupling
agent" fills the cavity and actually creates a modest concentrator
effect--about 1.5x--when struck by sunlight.
There are no moving parts, as the sunlight automatically refracts
through the outer tube to the inner substrate where the absorber
layers do their thing. The endcaps are the only mechanical part,
which are hermetically sealed using a proprietary glass-to-metal
process (with no elastomers involved) that is then helium-leak-tested,
according to the Chief Executive.
Tubular PV to harvested sunlight from almost every direction
Being tubular has its advantages when it comes to PV, says
Gronet. Photons are not only collected directly from all angles,
a kind of "self-tracking" mechanism, but diffused
light is also harvested from almost every direction, and the
sun's rays that don't get absorbed by the PV cylinder at first
are captured when they reflect off the white membrane underneath
(see Figure 3). The circular design also provides convective
cooling advantages and the tubes don't get as dirty on the
roof as conventional flat-plate units.
Figure 4. The tubular design of Solyndra’s modules
optimizes the collection of direct, diffuse, and reflected sunlight.
When pressed about the thicknesses of the various film layers, Gronet
claimed Solyndra "has the thinnest layers of anyone out there...the
absorber layer is about a factor of two thinner" than competing
technologies. Since the CIGS stack is generally in the 1.0 to 2.5 micron
range, and you can't go too much thinner than a micron, it's likely Solyndra
is achieving something slightly submicron with its co-evaporation process.
By using less of the active materials, the company reduces its deposition
process times and thus might boost throughputs and bring down overall
manufacturing costs.
As for conversion efficiencies, the CEO cites figures in the "12-14%
range" for the inner cell. But he wouldn't discuss the module- or
panel-level numbers, saying that "we don't measure efficiency at
the module level" because of the widely varying "rooftop efficiencies" caused
by different temperature, wind and sun conditions. He also stressed the
company's focus on the system as a whole, not the components therein.
Differentiating nomenclature for "module" and "panel"
While much of the solar industry uses "module" and "panel" interchangeably,
Solyndra has instituted its own differentiating nomenclature. Forty of
the tubes or "modules" are mounted in what Solyndra calls its "panel," a
1.8 meter long by 1.08 meter wide, relatively simple non-penetrating
framework that sits flat about a foot off the roof. The whole unit
weighs about 32kg (70lbs).
Traditionally, the total expense of installed PV comes about half from
the price of the manufactured panel and half from the cost of installation.
While Gronet would not disclose Solyndra's current or projected cost
per manufactured watt for its modules and panels, he did tout the
system's simple design, ease of installation and superior electricity
output
per rooftop (see Figure 4).
He says that customers have validated that the Solyndra racks can
be installed in one-third the time of a normal flat plate PV system,
at
about half the cost. The panels seem easy to carry and the proprietary
mount hardware can be bolted down with simple hand or power tools.
It doesn't take much time to place the panels, plug in the DC connectors
and set up the ground strap. To connect one panel to another, a
clip does the trick.
Tubular fields: Solyndra panels to cover large
roofs. Source: Solyndra Inc.
Each non-penetrating system is self-ballasted. The mounting design follows
the contours of the average not-so-flat flat roof, Truman told me, and
allows the panels to sit over most low-lying obstructions. A team of
five workers can install about 40KW of Solyndra panels in a day, according
to Gronet, and the system is as easy to take apart as it is to put together,
offering mobility and flexibility for those who might want to move the
PV to another location or do some work on the roof itself.
A highly automated manufacturing facility
When you enter Solyndra's Fab 1, you notice a few things right off the
bat. It's a biggish facility, but not mega-scale, with about 180,000
square feet of factory floor and related manufacturing space. Floor space
is at a premium, with little room left for more tools. The conditions
are tidy, but not ultraclean, nowhere near the stringent contamination
control specs of a semiconductor or a hard-disk-drive fab.
The fab is highly automated with robots and conveyor
systems of various sizes and shapes--from AGVs scurrying past on the
floor to large, strong-armed palletizing robots, their limbs moving around
with that mindless yet almost anthropomorphic precision of the industrial
robot class (see Figure 5). Scores of 25-high stacks of tube-module trays,
each holding 48 CIGS PV cylinders, are grouped on the floor in various
spots.
Picture source: Solyndra Inc.
The company took the keys to the Fremont facility in
February 2007, and after some construction and equipment installation
had its first PV tube modules coming off the line by late summer of that
year, according to Truman. Over the next year, the team focused on improving
tube performance and enhancing yields.
Gronet told me that the first volume shipments of Solyndra's panels
began in July 2008 and that more than 10 beta sites are running in the
U.S. and
Europe to validate the system’s performance.
The company puts a nameplate capacity of 110MW on what it calls its "front-end" fab.
It has borrowed this terminology from the chipmaking realm to differentiate
its core CIGS tube production from the "back-end" processing
down the road in Milpitas, where an outer tube sheaths the inner one, the
unit’s endcaps are plugged in and sealed, the optical coupling liquid
is injected between the inner and outer tubes and the finished cylinder
modules are inserted in the panel arrays, 40 at a time.
Because Solyndra's front-end fab building once housed a succession
of HDD fabs, it was not purpose built for the company's process. The
floor plan
isn't bad, especially with the level of automation helping out, but the
flow is less than optimal. Truman told me that in the second factory,
they "will
do the layout optimally for the logistics."
He leads me around to the large, multi-dunk-tank cleaning equipment
where the incoming soda-lime glass tubes are cleaned and prepared for
process.
Truman pointed out that there's quite a bit of worldwide capacity with
this kind of glass since the medtech/pharma crowd has been switching
over to plastic for their test tubes and vials. “We actually have
a segment of the glass industry where there's an excess of supply," he
related.
The robots transport the tubes to the molybdenum deposition
tool, where, like with CIGS done on flat glass or flexible foil, the
metallic back contacts are put down on the glass substrates. The individually
RFIDed tubes are rotated, with careful attention to film uniformity.
The Solyndra fab boasts a proprietary manufacturing control system with
an arsenal of sensors, creating a closed-loop metrology system reminiscent
of a flat-panel display or chipmaking plant.
Picture source: Solyndra
Inc.
"We have alot of custom metrology in these things," Truman
explained. "At every step of the way every tube is tested, whether
it's in deposition or scribing for the monolithic integration. Even during
our monolithic integration steps, there are metrology devices on the
head of the scribing machines measuring a variety of properties as we
go along.
Every tube is tracked through the automation system and through every
aspect of the deposition--each tube has its own identifier."
After the moly layers are deposited and a quick patterning-step is
completed, the PV cylinders are robotically transported to the most important
equipment
set on the floor--the CIGS absorber tool. Solyndra designed and built
(with the help of subcontractors) the 45MW system, which boasts an
impressive footprint, stretching about 100 feet. The company uses the
co-evaporation
approach to lay down its copper, indium, gallium and (di)selenide because,
as Gronet reminded me, the highest conversion efficiencies for CIGS
have been achieved using that type of deposition.
Once the CIGS film stack has been put down, the tubes move to the junction
partner/buffer layer tool. The company uses a proprietary wet solution
process here, in which the tubes are spray-coated with nanometer-scale
layers of cadmium sulfide (although there's apparently work going on
to make the buffer cadmium-free). Finally, the transparent conductive
oxide
(TCO) topcoat, reportedly an optimized i-ZnO/Al:ZnO cocktail, is sputtered
on.
Then the tubes are moved to Solyndra’s proprietary laser-scribing
tools for the monolithic integration process. Truman told me that the scribes,
done six tubes at a time, are mostly helical, with "one linear scribe
done at the very end to define each cell." He showed me how the
individual cells, rather than being cylindrical per se, are slightly
curved in a croissant-like
shape.
Before the cylinders are sent down to the back-end facility for packaging
and paneling, each one is tested for its performance, electrical output
and the like on a tool familiar to any PV manufacturer--the solar simulator
and its pulsing bright lights.
Impressive debut, but questions remain
Solyndra’s launch story may be impressive, but there remain several
areas of concern in need of clarification so that the company’s
prospects for success can be more comprehensively evaluated.
Aside from the difficulties facing any manufacturer seeking capital
during the emerging global recession, Solyndra could be more open about
the
actual retail or wholesale price tags of the panels and systems. There's
been ample lip service paid to the company's ability to drive toward
a variety of definitions of unsubsidized grid parity, but without those
dollar figures, we have to take their word for it.
They also aren’t ready to talk about their current cost-per-watt
manufacturing metric, let alone the roadmap to getting to that buck-a-watt
sweetspot and beyond. They may have a fully automated, highly controlled,
even high yielding factory and a proprietary process that uses less absorber
materials than other CIGS schemes, but what was on the fab floor did
not strike me as a disruptively inexpensive approach. Three out of the
four main process steps use vacuum deposition, the other (for the junction
partner/buffer layer) employs a wet-spray technique--none of which screams "low-cost
manufacturing solution."
The claimed 12-14% conversion efficiencies for Solyndra's
tube modules are certainly competitive with other CIGS, CdTe and amorphous-silicon
TFPV players and even match up well with the low end of the crystalline
silicon module spectrum.
Picture: Solyndra Inc
But what's lacking is a third-party, NREL or NREL-like
evaluation of the cylinders' efficiencies, let alone any efficiency numbers
for the panels or reporting on the tightness of their product’s
overall efficiency distribution curve.
Of course, the actual geographics and climatic placement of the PV
systems have a big impact on their ultimate efficiencies and at the end
of the
day, it's about the electricity produced by the panels, not just how
well they convert those photons to electrons. But there's a bit of gamesmanship
in Solyndra's refusal to play by the established rules of stated conversion
efficiencies.
The ingenious glass-to-metal sealed end-cap on each tube seems to be
an elegant, robust approach to keeping CIGS-killing moisture out. But
can
the hermetically sealed caps survive the necessary 20 to 25 years and
demonstrate the level of reliability needed to compete with silicon
and other thin-film
PV? The Solyndra systems have all been run through their testing paces
and they apparently passed with flying colors. But testing's one thing,
actual field life is another.
Then there's the question of scalability. The initial 40MW line in
Fab 1 is running close to capacity, I'm told. The second line--the
to-be-standard
70MW--is still a work in progress, with a limited amount of product
coming off of it and heading for the back-end facility. Some tools
remain in
what Truman called "various stages of startup." The plan
is to build out capacity in the second fab (and future ones) in increments
of 70MW,
cookie cutter-style.
Before building out the new factory, the Solyndra crew has to crank
up the initial 70MW line in a timely, high-yielding manner. Some
CIGS aficionados
question the ultimate ability of a co-evaporation-style process
like that in use at the Fremont fab to scale economically to high volume.
At the
end of the day, nameplate is not the same as run rate. PV factories
of many flavors are notorious for their low capacity utilization
numbers, and CIGS companies still have yet to prove their high-volume,
100MW-plus
production mettle.
Large amounts of Solyndra panels were ordered
by German PV integrators. Source: Solyndra Inc
Despite these questions, with $1.2 billion
in orders already booked, the likes of customers Phoenix Solar, Solar
Power Inc. and GeckoLogic must obviously believe in the company and its
product. Solyndra must now demonstrate a First Solar-like focus on executing
the remaining ramp of its first fab and then building, equipping, and
scaling its planned six-line, 420MW factory up in order to take its place
in the photovoltaic pantheon.
Addendum: Solyndra offered $535 million loan guarantee by the U.S.
Department of Energy
Solyndra on March 20th, 2009 announced that it is the first solar energy
company to receive an offer for a loan guarantee by the U.S. Department
of Energy (DoE) under Title XVII of the Energy Policy Act of 2005.
Solyndra, manufacturer of innovative cylindrical photovoltaic (PV)
systems, reports that it will use the proceeds of a 535 million US-dollar
loan from the Treasury's Federal Financing Bank to expand its solar
panel manufacturing capacity in California. According to the press
release, the guaranteed loan is expected to provide debt financing
for approximately 73 percent of the project costs, allowing Solyndra
to initiate construction of its second solar panel production facility
in California. On completion, the new facility, dubbed "Fab 2," is
expected to have a manufacturing capacity of 500 megawatts (MW) per
year.
Author: Tom Cheyney, Senior-Editor Photovoltaics International,
USA. Translation: Johannes Baral and Rolf Hug.
