Never mind “you know who”: CIGS thin film survivors Nanosolar, Stion keep going about their business

Oct. 6, 2011 - Tom Cheyney - pv-tech.org

Despite the muddy swirl of controversy surrounding that certain “you know who” CIGS company, many of the “survivors” in the most up-and-coming sector of the thin-film PV community just keep going about their business, driving up efficiencies, pushing down costs, closing deals, ramping production, and shipping products. Two Silicon Valley-based outfits, Nanosolar and Stion, have recently announced National Renewable Energy Lab-certified record conversion efficiencies and are both actively ramping production to feed their pipeline of orders.

Nanosolar, which has been somewhat quiet of late, has started to rev up its PR engine. The company, known for its unique roll-to-roll print/nanoink-based, nonvacuum deposition copper-indium-gallium-(di)selenide cell production process, announced that NREL measured aperture efficiencies of 17.1% for its flexible foil cells.

John Rayfield, VP of worldwide marketing, told me via email that in the case of the test cells evaluated at the national lab, "the aperture efficiency is the same as total area efficiency." The tests were conducted Sept 1 under standard test conditions of one sun or 1000W/m2 at 25°C.

When asked how these impressive cell numbers translate at the module level, he cautiously replied that “At this point, we are not prepared to comment with specifics, but of course it continues to push our panel roadmap forward.”

Although the cells measured were not taken from Nanosolar’s production line, he said “The best indicator of our production line is panel efficiency. Currently, we are producing 10%-efficient panels and our released roadmap is to be at 13% efficiencies by late next year.”

Brian Stone told me at Intersolar North America in July that many pieces of production gear were coming into the company’s San Jose cellmaking fab at that point, and that it was on track to reach 100MW cell capacity in 2012. He also said there would be some new multimegawatt projects to talk about later in the year; apparently, one of those projects will be announced in the next few weeks.

I had a lengthier phone conversation with Stion’s head honcho, Chet Farris, a week or so after his company officially opened its new production facility in Hattiesburg, MS, last month and touted fresh 14.1% NREL-confirmed module efficiencies.

Unlike Nanosolar’s test cells, the CIGSSe firm’s efficiencies were derived on modules pulled from its 10MW pilot production line in San Jose, which now mirrors, at a smaller scale, the capability and toolset of its new Mississippi facility.

Like Nanosolar’s results, the numbers reflect aperture-area efficiencies, but in the case of Stion’s monolithically integrated panels, the total-area numbers equate to about 12.7%, give or take a few tenths of a percent depending on whether it’s a framed or frameless module, according to the president/CEO.

Farris mentioned optimization efforts were under way to squeeze out a few more tenths of module efficiency and increase the active area ratio via a mechanical design rule change associated with how the company does the feedthrough to the junction box from the circuit.

Another efficiency improvement knob to turn relates to the interconnects, which he admitted had "fairly broad" design rules on the first certified modules. By improving the process and tightening up the interconnects, he expects that somewhere between 0.3% and 0.5% absolute module performance improvement can be obtained.

For what he called the Gen 1.5 product, process engineering efforts to replace or eliminate the cadmium-sulfide buffer/emitter process have narrowed down the options to three, two wet and one dry, all of which are in the reliability stage.

Although the proprietary use of the TCO to get rid of the buffer step altogether has its benefits, it may not be the easiest or the most economical, Farris explained. The ultimate winner will be chosen because it offers the most cost-effective solution.

Whichever approach is selected, it will lead to a change in the device structure and require a subsequent recertification of the modules. The target is to have the new process integrated into the production line by Q1 2012.

On the R&D front, he said that work on Stion’s next-generation tandem-junction modules is going well. Efficiencies on 20 X 20cm test panels are “north of 16% and on target to reach 18% by Q4 2011 or Q1 2012,” with the same results expected on full-scale demo modules a little while after that. A new, differently configured and more user-friendly reactive deposition tool will soon be added to the tandem development line, which will allow for the production of full-scale modules.

Down in Hattiesburg, Farris said the factory ramp remains on schedule, with the first panels due to come off the line by late September. The major process equipment — including new prequalified Von Ardenne precursor deposition and back-contact deposition tools — are in place on the initial 100MW nominal capacity line, although the automated glass-handling systems were a little delayed coming from Japan. Eyelit’s manufacturing execution system software is also being implemented at the facility.

He expects the run rate to incrementally reach 80MW by June 2012, and to be close to full capacity shortly after that. The resulting production will be "absorbed by the pipeline, and although we expect price pressure, we have adequate backlog to offtake all of Hattiesburg’s output." The headcount at the plant is around 100, with that number set to climb to double by late 2012.

Farris estimated the capital expenditure per watt at about 85 cents for the nameplate 100MW line, but noted that the initial capacity buildout included significant structural modifications, property improvements, and the like that boosted that figure. As a result, the capex/watt should drop to the mid-to-high 60 cents range on the second line, which will benefit from the facility enhancements done when Stion first took over the site.

He said the building will accommodate up to 600MW of CIGSSe panel-making production capacity without further expansion, representing five 120MW lines benefiting from improved efficiencies and productivity metrics. Actually, the structure could physically hold six lines, theoretically boosting the site’s capacity another 120MW or so, but he stressed that such capability has not been promised.

Farris remains optimistic of Stion’s chances, wryly noting one advantage he thinks his company’s panels have over the competition.

“We are on plan with what we had originally planned to do. We’re happy with the technical results so far, and the product has been well-received. It’s still the prettiest product in the industry in my opinion, kinda sexy to the extent that solar can be.”