Interview with Gizem Nogay (CSEM), Antonin Faes (CSEM), and Stefan Wendlandt (PI-Berlin)

In this joint interview we discuss with Gizem Nogay (CSEM) and Antonin Faes (CSEM) who are leading WP6 on outdoor monitoring and with Stefan Wendlandt (responsible for R&D projects at PI Berlin) who is responsible for WP7 on indoor characterization and modelling. We first discuss their respective roles in the HighLite project before talking about important topics such as module quality, what is needed to bring sufficient production capacity in Europe, and the future demand for distributed PV applications.  

Gizem Nogay holds an MSc degree in Physics and PhD degree in Photonics from EPFL in Switzerland. She joined to CSEM in 2018 after finishing her thesis. She is a senior R&D engineer with expertise in the field of mainstream c-Si solar cell technologies including production, characterization, module integration and reliability testing. She is responsible for process development and project execution at international level. In parallel she is also working towards her MBA with the focus on technology and innovation management at EPFL. 

Antonin Faes is Focus Area Manager on Energy Harvesting and responsible of c-Si solar cells metallization and interconnection at CSEM PV-Center. Since 2012, he is leading the development of Meyer Burger’s SmartWire Connection Technology (SWCT®) on CSEM side. He graduated as materials science engineer at EPFL in Switzerland and got his PhD in 2010. He is author and co-author of more than 30 peer reviewed papers, cited globally about 2000 times, few patents and books.  

Stefan Wendlandt received his Bachelor degree 2005 and his Master degree 2008 in Renewable Energy Systems in Berlin, Germany. He joined Helmholtz Zentrum Berlin (HZB), Fraunhofer ISE and the Centre for Renewable Energy Systems Technology at Loughborough University in Great Britain as a research student to work in the field of Photovoltaic. After successful completion of the university, Stefan assumed a research position at the PI Berlin, where he is currently engaged in the analysis of PV-Modules and is responsible for grant funded projects. Within HighLite project he is leading WP7 “Characterization and Modelling” as well as T7.2 “Indoor Characterization and Modelling of Modules” and T7.3 “Reliability Testing”. 

Question 1: Can you briefly explain your role in the H2020 HighLite project?   

Gizem & Antonin (CSEM): In the H2020 Highlite project, CSEM is leading the WP6 that focuses on outdoor performance monitoring of the PV module developed in the scope of the project in comparison with the modules that are currently available in the market. Throughout the years CSEM developed advanced expertise in this field by taking part  in former European project H2020 with ENEL Green Power called Ampere where the comparison between mono-facial and bifacial PV modules was studied in detail (www.ampere-h2020.eu/). The research question we target to answer in  WP6 is: “Knowing the installed power, how much energy can be obtained from the PV system at the end of the year ? “.  In fact, this is a central question that concerns everyone installed PV. Of course, the answer is strongly dependent on the implemented technology and integration approach. In HighLite project, we are investigating three main PV technologies: (i) shingle bifacial silicon heterojunction (SHJ), (ii) low-cost bifacial interdigitated back-contacted (IBC) solar cells and (iii) bifacial n-type cells with tunnel oxide passivated contact (n-TOPCon). We are realizing performance monitoring of these 3 technologies for different applications including building-applied PV (BAPV), building-integrated PV (BIPV) and vehicle-integrated PV (VIPV). The first goal is to pass the extended reliability tests based on bill-of-materials that are tailored for each specific application. The second goal is then to demonstrate PV systems with improved energy yield thanks to low thermal coefficients and high bifaciality values. Additional to these advantages, the use of shingle cell interconnection as well as back-contacted cell design increase the cell packing efficiency in the module, therefore improves the final module efficiency while keeping the aesthetics benefit of the full black module. Another important task that CSEM is contributing in Highlite is developing passivating contacts with improved industrial compatibility to integrate into back-contact solar cell pilot line. Therefore, we can say that CSEM is also actively contributing to the project not only for the development at module level but also at cell level. 

Stefan (PI-Berlin): Within the HighLite project, PI Berlin leads WP7 “Characterization & Modeling”. With our experience in determining the long-term stability and in testing PV modules and their components, we support the partners in module development. In turn, we study the stability of novel module designs (e.g. shingle interconnection, lightweight) designed for different applications (BAPV, BIPV, VIPV). For this, we generate characteristic data for extended reliability tests (e.g. 600 thermal cycles, 3000h damp heat, sequential mechanical tests, Hot Spot Risk, potential induced degradation, etc.). Furthermore, we improve our diagnostics tools (e.g. I-V, spectral response, electroluminence, etc.) to achieve more accurate results and reduce measurement uncertainties. In WP6 we realize a façade-integrated PV system for monitoring novel PV modules and compare them with state-of-the-art modules. 

Question 2: The rate at which new cell and panel technologies are introduced on the market has been accelerating in recent years. Have you identified any changes in the quality of PV modules in the recent years?

Stefan (PI-Berlin): First of all, PV modules became more and more powerful in the recent years while costs have rapidly come down which is remarkable. Also, the quality of the PV modules has changed, mostly in the right direction. This is due on the one hand to the R&D progress on the individual components and on the other hand to the fact that the entire value chain is working on developing better products with more stringent quality checks. The production of a high quality PV modules starts at the fab. In particular, the continuous use of inline process controls and supporting offline inspections is key to improve yield and quality. Furthermore, the IEC 61215 standard for the qualification process and type approval of terrestrial PV modules only covers only minimum testing. That’s why additional testing and certifications from independent organisations such as PI Berlin is key to increase the market acceptance of new cell and panel technologies. 

Gizem & Antonin (CSEM): Indeed, recently big changes are occurring in the global PV market. As at CSEM we mainly focus on n-type solar cell development, we are closely experiencing and observing a particular trend towards high efficiency n-type cell technologies such as silicon heterojunction (SHJ) and TOPCon cells with rear passivating contact. These changes will definitely bring new challenges to tackle as seen with PERC modules and their light-induced degradation (LID) problem for example. Another impressive change was the transition from full cell to half-cell design. In less than 4 years the market share of the half-cell design reached over 80 %.  Thanks to reduced resistive loss and better low light performance, half-cell design is boosting the energy output of the latest PV modules in the market. It is important to note that Highlite is also contributing to this topic by testing different cell cutting techniques to determine the best one. 

Question 3: The demand for solar PV technologies is booming in Europe and Worldwide. What do you think is needed to bring back sufficient production capacity in Europe?   

Gizem & Antonin (CSEM): We believe that PV module production will come back to Europe as the PV modules have intensive transport cost and the freight rate from China to Europe has been multiplied by 8 within the last 1.5 years (link). As a consequence, investments are planned for large PV production facilities in Europe (link). To have a successful PV production in Europe there are some important requirements to fulfil. First, product quality and reliability need to be as high or even better than imported modules. Second, high performance is vital to have an attractive return on investment for the end-users. The third crucial point is the aesthetics of the module. The HighLite project partners, including three EU PV module producers (Voltec Solar, Valoe, and Solitek), are focusing on meeting those three important requirements. Bringing PV production to Europe will also help to significantly decrease the carbon-footprint of PV modules which is quite an important parameter in our fight against the climate change. People in Europe start to be more conscious and sensitive to consume locally to decrease their impact on the nature and contribute to build a more sustainable future which is a great step forward. To give one example, CSEM is supporting the PV cells and modules production in Switzerland and in Europe since more than 12 years by collaborating closely with Meyer Burger who was initially an equipment supplier. In 2020 Meyer Burger announced an important strategic change and decided to become a PV cells and modules manufacturer that will bring back the PV industry to Europe. In May 2021 the official online opening of the company’s solar cell factory in Thalheim and module production facility in Freiberg were realized. Operating at full capacity, the plant is expected to produce up to 200,000 solar cells every day, which is the equivalent of covering 400 soccer fields every year with PV modules (400 MWp). As CSEM we are very happy to get recognition for our contribution to this achievement during the Meyer Burger’s product launch and we will definitely continue to give our full support to Meyer Burger to achieve its target. We strongly believe that there is enough demand for solar PV in Europe and Worldwide for other companies to follow the example set by Meyer Burger.  

Question 4: How do you see residential PV, building-integrated PV (BIPV), and vehicle-integrated PV (VIPV) applications evolving in the coming years? 

Gizem & Antonin (CSEM): At CSEM we have long history in developing integrated PV solution for buildings and for vehicles. For the vehicle integration, we see some interesting change in the automotive business with the massive move to electric vehicles. Few start-ups focus their communication on solar mobility like Sono Motors, LightYear and Aptera. The first one proposes an entry market car with the full body covered with back-contacted solar cells and it is well known by the HighLite consortium as the project partner Valoe has signed in April a large “co-operation agreement related to engineering and concept validation project for utilising solar energy in Sono Motors’ vehicles”. LightYear proposes a luxury car with a full glass PV roof covered of laser cut IBC solar cells. Aptera proposes a three-wheels vehicle with back-contact PV cells covered with a thin front-sheet. Until now for the mass production, the Toyota Prius is having a solar roof in option already from 2012 based on SHJ cells from Panasonic, the Fisker Karma is also having a solar roof with nice screen-printed shapes to hide the squared design of the PV cells, and more recently the Hyundai Sonata is proposing a solution based on PERC half-cut cells with 9 wires as busbars. On the other part, we see tier one suppliers doing R&D to propose PV integrated solution to car manufacturers.  

In terms of building integration, even though BIPV can be seen more mature than VIPV, it is still an emerging market with lots of challenges, especially in terms of social acceptance. However, the PV community is making big efforts to deal with these challenges. Examples include improving the PV module’s aesthetic by introducing different color options, such as the solution from Solaxess (a CSEM start-up), as well as by organizing workshops in order to inform architects and builders about PV integration solutions. Today, highly aesthetic BIPV solution for roofs from companies like 3S Solar Plus, FreeSun, Tesla, etc., are getting more and more attention. Integration of PV into building façades is also very important to flatten the electricity production curve throughout the year to be able to use the power grids more efficiently. That’s why in HighLite project, we are working on both next-generation rooftiles and facade elements for BIPV applications.  

Question 5: What special requirements do BIPV and VIPV modules have to meet regarding long-term stability? 

Stefan (PI Berlin): In general, PV modules have to resist mechanical, thermal, humidity and light (including UV) impacts. The IEC 61215 and IEC 61730 standards covers most of those events with a set of dedicated tests that must be passed for qualification and safety. However, these PV standards describe only a minimum number of test cycles or intervals while outdoor the weather conditions can be overlapping. That’s why depending on the cell technology and module application the module qualification tests have to be extended or performed with harsher conditions. Applications such BIPV and VIPV require to also meet specific requirements. Since a BIPV module can be replacing part of the building envelope (roof, cladding, etc.), it also needs to meet basic requirements for construction works such as mechanical resistance, stability at high temperature, safety in case of fire, etc. Another interesting example is for VIPV where often lightweight approaches are pursued which requires using special materials such as polymer front sheets instead of glass. Those materials are not new in PV but the final products have to be well characterized according to automotive standards, in particular for abrasion/scratch resistance as well as the mechanical properties (impact, vibrations, etc.). Of course, higher operating temperatures combined with UV stress can also lead to stronger degradation of the polymers. That’s why in the HighLite project we are performing advanced testing of lightweight PV modules for BIPV and VIPV applications such as combined UV and damp heat testing, hail impact, shaker tests, etc. In addition, we are also spending significant efforts on improving the shading tolerance of PV modules by optimizing the different PV module designs via experiments and advanced simulations. Altogether, the goal is to develop high-performance PV modules that are tailored for those different applications.