IEEE Photovoltaic Specialists Conference
The 43rd IEEE Photovoltaic Specialists Conference ran from June 05 to 10 in Portland, Oregan. PV veteran, and founder and chief market research analyst, SPV Market Research, Paula Mints reported her impressions and takeaways from the event for pv magazine.
Day two: Rooftop PV fire safety
As residential rooftop PV has increased in the US fire safety has become increasingly important. At the IEEE a Wednesday morning Plenary included a paper on Fire Safety – from the fire fighter’s perspective. PV professionals sometimes forget to consider how the solar industry and its technologies can be and often are misunderstood, and that the industry has many stakeholders all of which have interests and concerns that solar industry professionals need to address. Once a homeowner buys or leases a solar system and it is installed on their roof they become part of the solar industry and their concerns and needs become the industry’s concerns and needs.
And … When a firefighter climbs a roof to put out a fire and save property and potentially lives their safety concerns are the solar industry’s safety concerns.
The rate of PV caused fires is actually and thankfully low, at least in Europe. A study from Europe found that of 1.3-million PV rooftop installations there were only 400 fires and only 180 of the 400 were caused by the PV system. Nonetheless, the PV industry needs to address the concerns of the people, firefighters, who are the front lines.
The concern for firefighters is the potential of shock from a PV system and though the potential can not be 100 % eliminated, it can be mitigated by rapid shutdown protocols (NEC Article 690.12).
The top two firefighter concerns are the inability to eliminate shock hazards and the inability to verify de-energization.
Module level data control such as offered with DC optimizes and micro inverters offer potential, but these technologies are new and there is not enough data.
Rapid shutdown capability reduces the risk to firefighters of accidental shock and this, along with education and training, is crucial to the continued rollout of DG commercial and residential solar.
During a morning thin film session Solar Frontier (CIS) offered a bit of detail on the company as well as a celebration of its 22.3% efficiency champion cell. Research into PV technology began in 1970. In 1993 the company focused on CIS. In 2006 the commercial arm of the company was established as Showa Shell Solar. In 2007 Showa Shell entered commercial production. By 2015 the renamed Solar Frontier had shipped a cumulative 3-GWp into the global market for solar modules.
In the same session, First Solar, CdTe, discussed its 22.1% champion cell result. In 2013 the company announced a >900 mV 19% champion cell result. In December 2015, it reached 22.1% with an >900 mV cell. First Solar also discussed challenges, for example doping.
Day one: Delamination
The IEEE PVSC started off bright and early on June 7 with an update about CPV, a solar technology that gets very little press currently, with the speaker noting that CAPEX is lower for CPV and to make climate change goals a huge investment is needed. Comment: Returning to a theme from June 6, ongoing research is the only way to ensure progress. Unfortunately, it is a tough and uphill fight for the CPV industry as flat plate crystalline continues with conversion efficiency increases and energy production increases with one axis tracking.
John Wohlgemuth, NREL, offered observations on different types of delamination. Problems with module quality fall roughly into this order: Discoloration/browning, delamination, corrosion, glass breakage, Jbox, cell breakage, cracked back sheet, hot spots, soiling, Mismatch and LID. As delamination is currently number two on the poor quality hit parade, it deserves some discussion. One problem is that modules that pass IEC 61215 and therefore should not be vulnerable are susceptible to delamination in the field.
There are different types of delamination:
Encapsulant/Glass: Typically found with a non-EVA encapsulant that is no longer sold and that never stuck well to glass. EVA has a very high adhesion strength to glass. This type of delamination typically effects the same type of older modules with the same type of non-EVA encapsulant.
Encapsulant/Cell: Seen between the EVA and the cell surface and selectively around the interconnect ribbons and grid lines.
Back sheet: Blisters indicate an aluminum vapor barrier layer. This is a safety issue, not a performance is sure. Multi-layer back sheets tend to fall apart.
Snail Trails: Delamination where the snail trails are typically caused by using EVA with no UV protection.
The challenge is to develop accelerated stress tests to demonstrate delamination and identify fabrication processes or material selections that make a module susceptible even though it passes IEC 61215 and before it becomes a problem in the field.
Dr. Antiye Bayman, MiaSole, offered an update on the company’s CIGS technology. The company recently announced a champion cell – NOT PRODUCTION – result of 22.3% conversion efficiency. MiaSole began commercial production in 2009 and has shipped a cumulative 80-MWp into the market.
Dr. Bayman noted that MiaSole is a cell and equipment provider. Though the company still manufactures rigid modules on glass substrates its primary focus is flexible modules.
MiaSole introduced its first flexible product in 2013. It produces a narrow single string product and a wider three string product. Dr. Bayman pointed out that the original vision for MiaSole was to produce a flexible product.
An afternoon session on PV system safety brought forth commonly known but nonetheless reminders about arcing. Arcing signals in the field are significantly influenced by fault locator and PV generator configuration and impedances. Current test methods for arc fault detectors are not able to reproduce these characteristics appropriately.
A paper on module level power electronics noted MLPE advantages of safety, that module failures resulted in less energy loss and that there were higher energy yields from systems. Disadvantages included poorer performance in extreme environments and requests from customers for longer warranties consistent with module warranties. As a caveat, MLPE technologies have only been in the field for ~10 years. Current failures for these devices have been manufacturing failures and the mean time between failure (MTBF) assessment is currently primarily theoretical.
IEEE Photovoltaic Specialists Conference
The 42nd IEEE Photovoltaic Specialists Conference ran from June 14 to 19 in New Orleans. PV veteran, and founder and chief market research analyst, SPV Market Research, Paula Mints reported her impressions and takeaways from the event for pv magazine.
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.