News feature: NREL confirms 41.4%-efficient Solar Junction CPV cell; firm on DOE loan shortlist

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The U.S. Department of Energy’s National Renewable Energy Laboratory has confirmed that CPV cell supplier Solar Junction has achieved conversion efficiencies of 41.4% on a multijunction cell sampled from the company’s demonstration production line. The early-stage firm also revealed it is one of a small group of candidates—and the only CPV cell company—that have been chosen for “post-selection due diligence” to receive a DOE loan guarantee, which would help support expansion plans for a 250MW factory at its base of operations in San Jose.

Jeff Allen, director of business development, revealed additional details about the latest announcements from the recently de-stealthed concentrator cell outfit in an email interview with PV-Tech.

He said that “the latest NREL efficiency tests concluded approximately two weeks ago.” The efficiency distribution of each of the cells tested at the lab “exceeded 41% peak efficiency.”

The company, which one month ago achieved NREL-verified 40.9% efficiencies on its cells, is preparing more devices for further testing at the national lab, he added.

He confirmed that the highest rated cell “was a standard production cell taken from our existing demonstration line,” a cell that featured “an aperture area of 5.5mm × 5.5mm, which is immediately integratable to many of our customers’ modules.” The company can also provide cells in larger and smaller sizes.

The average conversion efficiencies for cells being processed on Solar Junction’s demo line are “solid above 40%,” with “distributions comparable to the competition,” he said.

Allen explained that there remains significant headroom for conversion efficiency improvements with Solar Junction’s adjustable spectrum lattice matched (A-SLAM) technology, which he claimed has “an extendable roadmap exceeding 50% mean efficiency with the decade.”

The company cites three advantages that its cells have over existing and growing number of next-generation MJCs: materials bandgap tunability of 0.8–1.42eV, which optimizes performance and fosters rapid efficiency improvements; lattice-matched device architecture, which ensures reliability to industry standards; and proprietary ultraconcentration tunnel junctions that can push performance to levels over 1300 suns and eliminate possible damage caused by localized concentration variations.

Solar Junction’s production scheme involves no custom equipment, he noted, relying on “standard manufacturing used for multijunction solar cells or LEDs” and using similar process improvement and yield enhancement “knobs” as other CPV cell makers. 

The Federal loan guarantee process is in the midst of “ongoing negotiations,” so Allen would not disclose any details of the amount, possible timing of award of the loan, or timeline for the proposed production ramp if and when the company makes it through due diligence and receives the loan.

Solar Junction is also “looking at various forms of financing,” to provide additional funding and as its Plan B should the loan guarantee fail to materialize, including the pursuit of a Series D round to help fund the production ramp, according to Allen.

He said that the company has had “extensive discussions with all of the relevant [tool and materials] suppliers,” with equipment to be ordered “once the loan guarantee is approved.”

The proposed 250MW manufacturing hub would be built in the same location as Solar Junction’s headquarters and demo line in San Jose, a facility the company has leased for the past 2½ years, he explained.

The current line’s capacity is “14MW at 1000 suns concentration,” with the processing runs “shared between production and advanced development to further our efficiency lead,” said Allen. The company plans to ship “multiple megawatts” of commercial CPV cells by the end of the year.

Eight different customers are working to qualify the company’s cells at various levels, with results looking “very favorable compared to current market incumbents.” 

As with other CPV cell manufacturers, Solar Junction’s customers conduct the requisite UL and IEC testing certification efforts for their modules, but the business development director pointed out that his company is “working closely with our customers to ensure certification efforts, as a result of [our] cell adoption, do not impede their progress.”

The company also performs extensive internal environmental testing, including running parts of IEC testing “appropriate to a bare cell or [CPV] receiver assembly.”

“As the debate over PV versus CPV continues, we contend that with double the efficiency of traditional photovoltaics, the CPV sector is entering a high-growth period,” said Solar Junction CEO Jim Weldon in the press release announcing the latest news. “These recent NREL results reflect our continued commitment to efficiency gains and validate the advantages of our A-SLAM technology for the CPV sector.”

Companies involved in the burgeoning CPV/III-V multijunction cell sector include incumbent players (Boeing Spectrolab, Emcore, Azur), newer entrants (JDSU, Microlink Devices, Cyrium, QuantaSol, RFMD, Arima, Sumika, Solarpoint), and more vertically integrated companies (Soitec Concentrix).

The overall CPV market is forecast to grow to low double-digits of installed systems in 2011, but to accelerate significantly in 2012 to triple-digit levels.

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