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The dark ink flows up from the adjacent storage cabinet, filling the translucent tubing before it courses through a stainless-steel manifold that dispenses the nanoparticle solution uniformly across the moving web of microthin aluminum foil in the custom-built Nanosolar tool. As the flexible substrate continues its ascent, the stain of still-wet CIGS ink morphs constantly in mesmerizing, smoky patterns, before drying and blending into a uniform, lighter tone when the 750mm-wide foil methodically rolls out of sight into the guts of the gear. Before the web is respooled, removed from the coater, and transported to the next production sequence, a curing process dries the still-damp-to-the-touch solution covering the surface.
“We can go faster; the line speed we’re running right now is fairly slow,” a process engineer told me, snapping me out of my ink-stained trance stare. “This machine has the capability to go five times this speed, so we could go five times the capacity of what we’re running on the other tools.”
“We’re not a fully balanced line yet, as you’d expect, so this tool, if it were running 24 by 7, we’d need a lot more equipment to catch up with it,” piped in Brian Stone, VP of sales and product management.
“We’re in commercial production, and we’re ramping up our volumes and our factories,” added Eugenia Corrales, Nanosolar’s exec VP of ops and engineering. “What you’re going to see is the beginnings of that. You’re not going to see our full-fledged capability--you’re going to see where we are today.”
“Various tools are in various places,” explained Stone. “Some may be running production rolls, others may be running experiments.”
“We share the shop floor with development areas where some of our engineers are doing work,” said Corrales. “The pilot line is also on the floor right now, our waste management is on the floor right now: long-term, it’s going to be outside the building.”
“At some point, it will be more automated in this part of the evolution, but right now we don’t even have all the equipment lined up in a true end-to-end line, because that’s how this evolved.”
Corrales, a new kid on the Nanosolar block (six weeks on the job when I visited in mid-July), has her work cut out for her. But her c.v. suggests she should be up to the task of bringing order to the Nanosolar factory floor, with its mix of R&D/pilot activities as well as front- and back-end CIGS solar-cell production. She brings years of manufacturing, product development, and operations management experience from stints at SolFocus, Cisco Systems, and Hewlett Packard.
I asked her what struck her, both expected and unexpected, about her new employer.
For starters, she told me, “the foil is thinner than I expected it to be.” (The flexible aluminum-alloy substrate, in rolled lengths between one and two kilometers, is 150um thick.)
“There’s a tremendous amount of innovation that goes on in Nanosolar,” she then generalized. “That’s really the history of the company. I expected that to some degree, but there’s just a whole slew of scientists that are very impressive.
“The production, as we discussed, it is where it is in its evolution. I’ve spent most of my career taking things from prototype to high-volume production, and it’s definitely in that window. We need to continue to evolve it, to mature the technology.”
Production is not the only thing in need of evolving at Nanosolar, according to Corrales. “We are evolving the team. We now have a dedicated product design team, which is responsible for the mechanical and materials aspects.
“We’re also creating an electrical characterization team that’s really focused around the production test strategies. When you look at other industries and when you have something in production, there’s a very well-documented test strategy, from development all the way through to the end of life. So we really need to define all those tests and make sure we’re deploying them as we increase production.”
“We’ve added a couple of business processes,” she continued. “One is a central planning function, because we have two factories right now, and we should have more factories, so the whole coordination of who gets what when becomes much more complicated. And a supply chain function [has also been created].”
As we continued our walking tour of the facility, several rolls of partially processed foil were in transit on heavy-duty handcarts. From the coating process, the web material moves to what Stone called “the three sintering or heating tools that are the alternative to vacuum tools that you see in other CIGS processes.”
“The first one is an annealing process, [where the CIGS foil] starts at the beginning and runs through select temperatures to bring together the different elements. The next tool,” which is at least 35 meters long, “is the rapid thermal processor, again a CIGS tool.
“The first couple of heating tools are really about the CIGS and the first part of the p-n junction, while the third heating tool is about the interface layer, the CdS” (cadmium sulfide, also known as the buffer layer), which is a fairly standard horizontal wet-process system.
I asked Stone whether Nanosolar might eventually replace the cadmium-imbued production step with a more benign (and drier) material set and process.
“We’re constantly looking for ways to innovate and reduce costs,” he said, reading from the playbook. “That includes the top electrodes, the interface layers, etc. We have so much innovation throughout our process, just with the coating process, the annealing, the rapid thermal processing, and the metal wrap-through. Other things, like the cad sulfide, the top electrode, we’ll look to innovate but it wasn’t necessary at the beginning.”
“At the highest level, we’re very happy with the processes we have,” explained Corrales. “I don’t see us making a significant change at this point.”
Stone described the TCO or top electrode sputtering system as “one of two vacuum tools on the line,” along with the back-contact/bottom-electrode tool that sputters down the molybdenum at the beginning of the process. He said that Nanosolar uses aluminum zinc-oxide as its TCO material, reiterating that the cocktail “might be something that could possibly change.”
Before we headed to the back end of the production line, I asked my tour guides if any antireflective coatings were being used on the cells or panels.
“We’re continuously evaluating things like AR coatings and alternative finishes on the glass, the different manufacturing processes for that,” explained Corrales. “[But] we don’t have a product today with an AR coating solution.”
At the heart of Nanosolar’s back end is its proprietary metal wrap-through (MWT) process. “We have a number of tools punching holes into the foil, then we’re laminating a second piece of aluminum foil to the first with an adhesive, to create the back contact, and then we’re splicing the cells, testing, sorting, and packing them,” said Stone.
“For this MWT process, we’ve essentially gone through two screen-printing processes, where we’ve screen-printed a metal ink that goes through the vias we’ve created and then we also printed the fingers on top. And those are designed to conduct current out of the solar cell, and also to be as small as possible to maximize sunlight capture.”
“Then we stack these cells a thousand to a carrier, and we run them through the flash tester,” he continued. “This is the first of three places where we can bin the cells. We’re measuring them for voltage and current, so when they get assembled in Germany--and they go through the same tool there to make sure there’s been no change in electrical characteristics-- we want to lay them out in the module to minimize mismatch.
“When the panels are manufactured and assembled, they’re also tested in a flash tester, and they’re binned according to power and current and rated accordingly. They’re also binned based on a set of parameters, including shunt resistance, because we’re looking at things like temperature coefficients, low light performance, etc., because we want to build the mostly highly tuned panel that we can assemble.”
A strong and growing area of concentration at Nanosolar is reliability testing. As Stone explained, there are two places the company performs its tests, along with “outside institutes” such as Fraunhofer. “One is here on the cell level. We take two cells and encapsulate them in two pieces of glass, [creating a minimodule] with edge seal, busbar, and connector.
“We put them into light soaking at accelerated one-sun continuous, run them for 10,000 hours, which we believe simulates 25 years-- the first 1000 hours would be like the first year,” he said. “This is without any recovery period, so it’s a truly accelerated test. We have all the standard chambers for that, and we have the same setup [for full panels] at the Luckenwalde facility.”
Nanosolar, like most other thin-film PV companies, has realized that the new normal must be to run internal tests that go well beyond the specs set in the IEC and UL certification protocols.
“We run everything to failure, so we don’t just stick to the IEC standard,” noted Stone. “IEC is a great starting point, especially for things like infant mortality. So we’ll take temperature cycling to failure; our norms are not 200 cycles, but 500 cycles, we’re not doing 1000 hours of damp heat, but 1250.”
“We’ll test to the standard, retest it, then put it back in test to 50% failure,” added Corrales. “That allows us to really characterize the device. We’ve also done some innovative things at the lab level, which allows us to test cells individually or even individual pixels, and measure things like temperature coefficients and the uniformity of the CIGS layers.”
“In this part of the factory, we do a lot of experimentation, as you might imagine,” rejoined Stone. “We’re working on efficiencies, on performance, on cost reduction. We make minimodules, we take cells that have been run in designs of experiments, and we now have a new director of planning to bring some maturity to what was chaotic, which was when are we running production and when are we running experimentation.”
“The minimodules allow us to really fine-tune our processes,” Corrales. “In a factory like this, in the front end, there are thousands of process parameters. As we continue to go up the learning curve and really fine-tune those [parameters], this is an easy way for us to verify what the outcomes of those experiments are without having to build a full-scale panel.”
Like any self-respecting solar cell or module company, Nanosolar has dozens of its own and competitive panels up on its roof.
“We’ve got a 2KW array being monitored by BEW Engineering for outdoor performance,” said Stone. “We also put up minimodules in different experiments, to get them out into real-world conditions. Do we plan to put modules on our roof to help power our factory? Yes, but it’s just not a primary focus right now.”
There’s that term again, focus, what Stone calls “the operative word” at Nanosolar these days. With the obvious space constraints in the current San Jose facility, part of the focus is on expansion and having a chance to set up a properly balanced, end-to-end CIGS cell-making line.
“There is an adjacent building next door, which is another 100,000 sq ft, and ultimately the goal is to fill up both of these buildings and add a little more flow to the process,” revealed Stone. “At our last board meeting, our directors approved expansion; as new equipment comes in, we’ll have optimizing to do, and then we’ll have some expansion next door.”
Even with the additional production space, the Luckenwalde panel plant would still be able to handle everything the California lines could produce, he said.
“Running the panel factory will be a nice opportunity, but filling that factory up with cells won’t preclude us from building additional panel factories in the future in places like North America and Asia, as demand necessitates.”
There’s no denying the sense of optimism and determination that one feels when talking with the Nanosolar team and walking the production floor. Of course, their reticence to share certain key facts—such as manufacturing costs and cost roadmaps, yields, throughputs, total installed system costs, and the like—make it difficult to properly evaluate the CIGS company’s chances as it makes its midcourse correction in the race.
But that disruptive dream of creating a very-low-cost, high-volume path to solar PV market domination hasn’t died for the true believers like Stone.
“We’re very focused on building a great, high-quality product for hot and sunny locations, because we’re really about enabling grid parity and the levelized cost of energy. That’s why Nanosolar was founded in 2002. That mission hasn’t changed.”
To check out the initial installment of the two-part blog-feature about Nanosolar, click here.
PHOTOS COURTESY OF NANOSOLAR, EXCEPT BOTTOM PHOTO BY TOM CHEYNEY
