IEEE Photovoltaic Specialists Conference

The 42nd IEEE Photovoltaic Specialists Conference is currently underway in New Orleans. PV veteran, and founder and chief market research analyst, SPV Market Research, Paula Mints will be reporting her impressions and takeaways from the event, which runs from June 14 to 19, for pv magazine.

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Day four: Perovskite

Perovskite Solar Cells are popular of late with many assuming the technology represents a new and disruptive direction.  Dr. Henry Snaith, University of Oxford, offered a perspective on perovskite solar cell technology in his Thursday, June 18 Plenary at the IEEE PVSC in hot, humid New Orleans.

Serving to illustrate the long time line required for researching advanced technologies, research into Perovskite technology is not new.  In 1892 a paper on halide perovskites was published. In 1978 a paper on hybrid Pb and Sn halide perovskites was published. From 1978 to 2009 not much appears to have been done in terms of exploring the technologies semiconductor properties though the luminescent properties of perovskites were explored.  Between 2009 and 2012 there was only one paper published on the semiconductor properties of the technology.

Suddenly, however, much like the lonely teenager at a high school dance, there has been an acceleration and the subject of perovskite solar cells has been quite popular at conferences and in scientific journals. 

The material has an extremely varying dielectric nature and the research is still in an early state with concerns about structural stability, thermal stability and moisture sensitivity yet to be solved.

An interesting route pursed by Dr. Snaith and others is the use of perovskites and Si in a tandem architecture similar to the concept of Panasonic’s HIT cell.  Dr. Snaith noted that potentially, this direction could lead to >30% modules using Si and Perovskite material with 17% conversion efficiency. 

Current lab results from Dr. Snaith include a 0.7 cm2 area, 1.8 volt, .74 fill factor tandem perovskite cell with 21.3% conversion efficiency.

Dr. Sarah Kurtz, NREL, presented a plenary paper on quantifying reliability.  Dr. Kurtz posed the rhetorical questions: Why is reliability important now? Is reliability a feature that commands a premium? And What reliabilities need to be quantified?  
Dr. Kurtz noted that there are failures in the field due to poor quality control and postulated that quality testing cannot be generic as modules are installed in different environments.  Points to be considered are the environment in which the module will be installed, the bill of materials used, and the process window.

Dr. Kurtz made the point that where the module is installed counts in terms of understanding the warranty that is, a module that lasts 25 years in Munich may last two years in Arizona. 

Day 3: O&M and failures in focus

Wednesday’s coverage from the IEEE PVSC will focus on a single session.  Papers included in this session cover the important topics of soiling and module failures in the field.  These two topics often come in second to presentations and announcement of market size.  With gigawatt levels of PV already deployed and more coming on line monthly, O&M will become more important while module failure could prove a disaster quietly awaiting many a developer.  Concerning O&M, as it is often undervalued and the specifics glossed over, many an LCOE model should be rethought in terms of regional requirements.

Dr. Larry Kazmerski, formerly of NREL, is currently conducting research on the adhesion of dust to PV module surfaces.  Dr. Kazmerski discussed preliminary results for this ongoing work.  The physical and chemical nature of dust, that is, the make up of dust, differs by region. For example, in Saudi Arabia 80% to 90% of dust is made up of quartz, while in Latin America silicates make up 80% of the dust in many countries.  As there are regional differences in the chemistry and morphology by region this must be considered on a case-by-case basis when assessing O&M requirements as soiling can significantly affect the performance of modules.  Even within countries the environment in which the PV system is installed must be considered. For example, a system installed in an urban environment will encounter different dust and soiling than a system installed in an industrial or rural environment. 

Another presentation on the topic of soiling focused in part on the manual labor and water requirements for cleaning modules.  High-pressure water jets are the most common practice for mitigation of soiling losses and as water becomes more scarce and in regions where water is already scarce, this is a significant problem. 

A presentation from TUV Rheinland reiterated that soiling is site specific and that it can lead to significant energy yield losses.  As for PPA installations yield is money, this should be of significant concern.  The speaker noted that rainfall, though effective, is not to be relied on. 

John Wohlgemuth, PhD, NREL, presented an evaluation of module failures in the field. The system installation timeline was 1994 through current and covered crystalline and thin film technologies.  Failures types across all technologies included broken glass (mounting and maintenance errors and other problems), discoloration, hot spots and delamination. 

Specific to crystalline, discoloration with lower Isc, burns, broken cells and delamination with lower fill factor as well as evidence of heat around the bus bars with complete loss of voltage from the string diode on.  

Specific to thin films visible power degradation due to corrosion and delamination however, causes of power degradation are not always apparent. 

John also noted that the trend to glass/glass modules is not a solution to everything.  

Day 2: Optimistic outlook

Beginning on a cautionary note, Senior NREL analyst, Dr. Robert Margolis, who focused on the U.S. market, said solar’s contribution to global electricity production is still quite small, but that solar’s share of new generating capacity is accelerating and, at least currently, outpacing conventional energy. He added the potential policy impact of the expiration of the Federal 30% ITC in 2017 could be severe, but there could be mitigating factors. "Specifics about the mitigating factors would have been welcome," he said, adding, "Let’s hope that negative mitigating factors do not come along to mitigate the positive factors."

Dr. Margolis went on to discuss a sample of solar value chain gross margins, indicating that there appears to be a degree of recovery. He followed by analyzing a sample of operating margins, which seemed to mitigate the recovery indicated by the gross margin sample, and not in a good way. 

Following the financial overview, Dr. Margolis turned his attention to the SunShot goals, which aim to achieve prices of US$1.00/Wp for utility-scale solar installations, and $1.50/Wp for residential systems. He noted that more cost reductions are needed to reach this goal. "Constant downward price pressure seems unavoidable in an industry where margin constraint has become highly visible," he added. CSP must also become competitive. "Forecasts with timelines past ten years are highly unreliable and likely to be primarily based on the hopes of the forecaster. Concerning CSP, recent disquieting news about poor performance from CSP installations in Spain and the U.S. could prove a depressing mitigating factor for the technology sector," continued Dr. Margolis.

Overall, the analyst painted a positive picture for the U.S. market going forward. He offered up an extremely optimistic forecast for solar deployment stretched out to 2015 of 632 GWp for PV and 83 GWp for CSP. He further projected curtailment at 1.8% of annual demand in 2050, and 5.3% of annual solar and wind generation.

Thin film optimism

In a morning plenary, meanwhile, HyET Solar CTO, Dr. Edward Hamers, tried to insert a degree of optimism into his presentation about the current status and future of thin film (TF) solar. He noted that abundant materials are available for TF development, that shadowing of part of a module does not dramatically affect performance and that TF silicon displays good diffuse light performance. In light of this, Hamers went on companies that have failed in the sector, including United Solar and XSunlight, and Hanergy, which recently canceled its plans to build a 900-MWp manufacturing facility

Posing the rhetorical question, how important is efficiency, Dr. Hamers stated that conversion efficiency is a key driver. The best tandem junction cell on textured glass has an efficiency of 10.9%, stable at 10%. Noting that flexible form factors offer the highest potential of success, he noted the following advantages: durable and moisture resistant transparent conductive oxide (TCO) films, continuous roll-to-roll manufacturing, lightweight, thin and ultra-weight modules, and excellent lifetime stability. TF silicon, according to the speaker, offers advantages for BIPV deployment, though he noted that BIPV remains a small fraction of demand for PV products. 

Finally, Dr. Andres Cuevas, professor and researcher at the Australian National University, presented some intriguing champion cell results on research that creatively borrows from organic PV development. He offered, as an example, a 2015 result (D.Zielke et al.) for a organic-Si heterojunction lab cell with a 20.6% conversion efficiency and Voc = 657 mV. "The result is interesting, creative and should not be mistaken for being reflective of commercial capability," he said.

Day 1: No major breakthroughs

The 42nd IEEE PVSC in hot, steamy New Orleans got off to a positive start, with attendees crowding the opening plenaries and keynote speeches; and the promise of beignets and coffee at the break.

Dr. Pierre Verlinden, chief scientist and vice-chair of the State Key Laboratory of PV Science and Technology at Trina Solar offered a perspective on his expectations for breakthroughs in PV technology. There are no major breakthroughs, he believes, simply thousands of innovations. Dr. Verlinden noted that rolling out new products from lab scale to market takes between 20 to 25 years. "The long time line from lab to commercial production is, unfortunately, often ignored by those assuming that they have found a method of circumventing the realities of physics," he drily commented. Trina’s PERC technology is now appearing on the market and should have a conversion efficiency of 19% in around four years.

Referring to learning curve cost improvements, Dr. Verlinden used a model to estimate learning rates from price data by assuming a gross margin of 20% and holding it steady across a number of years. "Many a manufacturer would be thrilled to hold a modest 20% gross margin steady," he continued. Under this view, crystalline silicon (c-Si) technologies enjoy learning rates of 22.8%, cadmium telluride (CdTe) 16.3%, and Copper indium gallium (di)selenide CIGS 8.1%. 

Offering up some snippets of company news, Dr. Verlinden said Trina had achieved a 21.4% champion efficiency with its p-type PERC cell, and a 20.7% efficiency with a 60-cell multi crystalline 324-watt champion module. "A champion cell or module is years away from commercial production," he said, adding, "In the world of PV manufacturing, it is repeatability that counts."

Efficiency for Trina’s IBC module in pilot production is 22.5% at 320-watts; its HJ+ IBC 24.0% at 345-watts (25.5% in the lab); and 27% for its tandem junction c-Si cell. Dr. Verlinden stressed that these are not commercial efficiencies. “Many doomed expectations have been spawned from the misunderstanding of the difference between commercial and champion products,” he said.

First Solar’s CTO, Dr. Raffi Garabedian went on to present his company’s champion efficiency results: 18.6%, 0.70 m2 aperture area efficiency (full area 18.2%, 0.72 m2); and 19.14%, 1.515 m2 aperture area device records.

Meanwhile, Dr. Andreas Bett of the Fraunhofer Institute for Solar Energy Systems ISE, offered a perspective of the current state of concentrated photovoltaics (CPV), which has suffered setbacks in recent years against a highly competitive pricing backdrop. 

Progress continues, he said, despite consolidation in the sector, including SunCore’s recent acquisition of ConcenSolar, formerly Soitec, and dominating the space with 680-MWp of manufacturing capacity: SunCore has 300 MWp of capacity in China, while ConcenSolar has 380 MWp in San Diego, California. The largest CPV installation to date is SunCore’s 140 MWp installation in Golmud, China.

Dr. Bett pointed out that CPV cell technology has a faster track to commercialization than flat plate PV, noting that CPV moves from record efficiency to commercial production is around two years. 

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