Sandia scientist, international researchers, author technical reference reports for photovoltaic community

Sandia National Laboratories researcher Joshua S. Stein recently co-led activities resulting in two new International Energy Agency (IEA) Photovoltaic Power Systems Programme (PVPS) reports focusing on bifacial modules and systems, and the design of new photovoltaic materials. Stein is a member of the IEA PVPS Task 13, which focuses on photovoltaics performance and reliability, and aims to “provide support to market actors working to improve the operation, the reliability, and the  quality  of  PV  components  and systems,” according to IEA.

The reports, which were released earlier this spring, act as technical references on the state of the photovoltaics field and address the issues that are important to industry stakeholders, Stein said.

“The bifacial report is the culmination of several years’ work with an outstanding group of researchers from around the world,” Stein said.

“Bifacial Photovoltaic Modules and Systems: Experience and Results from International Research and Pilot Applications,” examines the growing popularity of bifacial photovoltaic cells, modules, and systems. Within the last couple of years, bifacial PV on single axis trackers has become the solar technology with the lowest levelized cost of energy (LCOE) in most parts of the world.  New  cell  designs  that  have  replaced opaque,  monolithic  back  surface  foil  contacts  with  isolated  contacts,  allow  light  to reach the cell from the rear side, and result in bifacial solar cells with rear side efficiencies from >60% to over 90% of the front side. These cells now come in many varieties (e.g., PERC+, n-PERT, HIT, etc.) and many cell lines have converted to producing bifacial cells.

Newly discovered bifacial-specific degradation issues, such as light and elevated temperature induced degradation (LeTID), and rear side potential  induced degradation (PID), are examined, as well as new optimized bifacial systems and models. For instance, a bifacial PV modelling comparison was organized to evaluate the state of the art of bifacial PV  performance models. Four  hypothetical  system  designs  and two  designs  based  on  field measurements  were  defined  and  the  necessary  input  parameters  and  weather  files  were provided  to volunteers  from  13  different  research  and  commercial  entities,  each  with  their own bifacial PV performance model. These models are described in detail, showing that  the  current  bifacial  models  result  in  a  range  of  results,  with  some models  being  unable  to  simulate  all  of  the  scenarios. The  resulting  predicted  bifacial  gains varied  by  as  much  as  a  factor  of  two, demonstrating the  value  of  defining standard test cases to verify and validate bifacial performance models.

The  last  section  of  this  report  provides  a  summary  of  eleven  bifacial  field  test  sites  around the world, along with examples of field results. Many of these sites include a variety of bifacial test arrays with different orientations, designs, and site conditions.

Christian Reise, of Fraunhofer ISE, Freiburg, Germany, and Stein were the report’s lead co-authors. In total, 49 international scientists contributed to the publication, including Sandia researchers, Cameron Stark and Dan Riley.

“Designing New Materials for Photovoltaics: Opportunities for Lowering Cost and Increasing Performance through Advanced Material Innovations,” examines the rapidly growing photovoltaic market, including the dramatic decrease in module prices.

“There is concern in the PV industry that falling module prices may result in lower quality and reliability issues,” says Stein. “This report helps stakeholders better understand the opportunities for higher performance and lower cost that new materials can offer, and also reviews current efforts to ensure long module lifetimes.”

The report provides a global survey from IEA PVPS member countries of efforts being made to design new materials for photovoltaic cell and module applications, and is organized by module component, including reviews of material innovations being made in: (1) front-sheets, (2) encapsulants, (3) backsheets, (4) cell metallization, and (5) cell interconnects. Section 1 is an introduction; Section 2 presents the state of the art in PV module materials, including the functional requirements of each component and the common materials typically used to meet these requirements; Section 3 discusses the motivations for applying new material solutions to PV modules; and Section 4 presents the global survey of novel material solutions being developed and tested for the next generation of PV modules.

Gernot Oreski, of the Polymer Competence Center Leoben (PCCL), in Austria, led the report, with Stein as second author. A total of 24 researchers and scientists from around the world contributed to the publication.

Contact Joshua S. Stein and/or visit the PV Performance and Modeling Collaborative (PVPMC) to learn more about the IEA Photovoltaic Power Systems Programme’s (IEA PVPS) TASK 13 reports. Read more about the International Energy Agency (IEA) programs.

Be sure to Save the Date for the 15th Photovoltaic Performance Modeling Collaborative Workshop to be held in Salt Lake City, Utah, Oct. 19-20th, 2021. The two-day workshop, which is co-sponsored by Sandia National Laboratories, CFV Labs and GroundWork Renewables, will examine the technical challenges and opportunities related to PV Systems.