Thursday morning’s Plenary Lecture in Area 1 was given by Dr. Emily Warren from NREL who discussed opportunities in hybrid tandem solar cells in the III-V-silicon system describing both 2T and 3T configurations. Dr Warren discussed several questions including how you define a 3T solar cell, how do you measure such a cell, how you make this device, and how can these devices be implemented in practical modules. NREL have developed several tools to address each of these problems and assessed these experimentally. Dr. Warren also discussed mechanical integration to overcome difficulties in growth using a lamination process (transparent conductive adhesive) to bond (Si/III-V) cells demonstrating both GaInP/Si and new generation 3T GaInP/GaAs/Si devices with a PCE of 27.3%. Module fabrication – multiple devices – was also addressed and parallel string configurations that voltage match such systems proposed, with protoypes demonstrated.
The Plenary Lecture in Area 10 was given by Professor Jan Kleissl (UC San Diego) - who presented in place of Professor Dazhi Yang – and discussed solar forecasting and the dependence of atmospheric sciences and the implications for grid integration. Ground assessment of the solar resource (radiometry) was described as well as the use of global satellite driven data that assesses this resource every few hours, in addition to weather modeling. Dr Kleissl discussed how the framework for solar forecasting requires reproductivity and to follow forecast guidelines, should be physics based, and built upon statistics and improved with ensemble modeling quickly to assess materials parameters under operation.
Thursday morning’s Plenary Lecture in Area 5 was given by Professor Mariana Bertoni from Arizona State University who discussed recent work on the emerging role of operando X-Ray imaging and spectroscopy in assessing PV materials and devices. These techniques are nondestructive measurements that scan over large areas, which allows the assessment of fully encapsulated systems and/or thick device architectures. Professor Bertoni presented example data on CdTe solar cells showing signatures of the elemental composition, defects, and doping profiles that can be assessed spatially and at various depths and, which can be studied as a function of temperature and bias. This powerful technique therefore enables assessment of nonidealities under operational conditions.
In Thursday Morning’s Area 3 session on “Concepts for III-V PV in all Environments” John Hart from the Solaero discussed an on-orbit performance comparison of various advanced 3J, 4J, and 5J technologies as a better way to evaluate radiation hardness and space performance, while Don Walker from Aerospace Corporation discussed an open source software and hardware package available for the community for cheap and rapid measurements of solar cell performance on small and large balloons and on CubeSAT’s. Eric Tervo from NREL discussed simulations and experimental data on InAs based TPV cells that showed promising results including low reverse saturation current.
Highlights in Thursday morning’s Area 4 session on “Metallization, Interconnection, Module Integration, Recycling/Sustainability, Novel PV Integrations, and Advanced Light Management” included a presentation from Brett Hallam UNSW who provided a broad overview of the raw materials consumption challenges facing the PV industry on route to 20-50 TW deployment with focus on Si, Cu, Ag, and Al. Sara Almenabawy from the University of Toronto described a comparison of light trapping and current density enhancements in regular inverted pyramid textured, random pyramid textured, and planar ultrathin silicon solar cells. Thierry de Vrijer from Delft University also presented an innovative device that combined a MJSC with an ion exchange membrane to achieve photoelectrical water splitting.
The Area 2 session on “Contacts in Chalcogenides” provided several highlights including a
presentation from Berengere Frouin from Paris-Saclay who presented promising optical simulations to reduce CdTe thickness while preserving Jsc using a grating at the back interface, while Camden Kasik from Colorado State University showed > 18% efficient undoped CdTe solar cell using a passivating TeO2 buffer layer as the back contact.
Thursday morning’s Area 6 session on “Advanced Characterization of Perovskite Solar Cells” included a presentation from Lukas Wagner from Fraunhofer ISE who showed lessons can be learned regarding current extraction and electrical coupling at interfaces - and at surfaces - via bias dependent photoluminescence and current-voltage and time resolved extraction imaging. Urs Aeberhard from Fluxim AG presented comprehensive optoelectronic simulations of all perovskite tandem solar cells that indicated significant gains from photon recycling when trap concentrations are low and the devices are in the radiative limit, but which reduce as defect densities increase.
Highlights in the “System Design, Optimization, and Performance” session in Area 7 included presentations from Kevin Anderson from NREL who discussed that conventional trackers focus upon direct beam irradiance and track the sun through the course of the day but overlook diffuse radiation. Here, a newly developed irradiance optimized tracking algorithm was presented that can improve insolation gain especially in climates with significant atmospheric cover. Christiana Honsberg from Arizona State University presented a potential climate adaptation/engineering protocol that manages the thermal flux and parasitic heat generated from solar cells with the potential to reduce global warming. Leonardo Micheli from the University of Jaen described projected benefits from floating PV including lower land preparation and lease costs, better performance due to the cooling effects of water, and lower installation costs.
Thursday morning also saw a join session between Area(s) 8.6/11.5 on “Module and System Reliability in the Circular Economy.” Mallika Kothari from Michigan State University described a comparison of the carbon footprint of older residential PV systems in California with those of newer systems showing that both types systems are beneficial, but the carbon payback times are shorter for new systems. Heather Mirletz from Colorado School of Mines discussed energy flows for the expected development of PV in the coming decades including analysis of effects to improve energy efficiency such as recycling or reliability of PV modules. Ian Marius Peters from FZ Julich showed that high innovation rates correlate with fast replacement and repowering of PV system leading to an overall increased energy yield and reduced CO2.
On Thursday afternoon, the Area 6 session on “Scale-Up and Scalable Processing of Perovskite Solar Cells,” Julia Huddy from Dartmouth College described work on flexographic printing for very fast (60m/min) printing speeds and performance similar to spin coating for transport layers, and promising initial results on printed perovskite layers. Mathilde Fievez from CEA described machine learning techniques to analyze slot die coated films and optimize their deposition for thickness and pinhole density and therefore current density, while Mirella Al Katrib from the University of Grenoble Alps described the fabrication of various perovskite systems and devices using electrodeposition techniques.
Highlights in Thursday afternoons Area 8 session on “Accelerated Testing” included the description of a new test set-up for the investigation of cell corrosion that delivers reasonable results within hundreds of hours by Andrew Fairbrother from EPFL, which indicated corrosion phenomena comparable with field measurements. Jiqi Liu from Case Western Reserve University presented the performance losses in double glass and glass-backed PV modules on monofacial and bifacial PERC solar cells under accelerated exposures and suggested that in general double glass modules perform better that simple glass backsheet modules. Gbenga Obikoya from the Institute of Energy Conversion presented accelerated testing of ITO coated silicon heterojunction solar cells that suggested solar cells coated on both faces were much more stable than those with simple top coated ITO configurations.
Thursday afternoon also included an Area 7 session on “Strategies for Performance Monitoring and Rating.” Highlights included a presentation from Nicholas Riedel-Lyngskær from the Technical University of Denmark who described measuring irradiance with bifacial reference panels where performance ratios vary by 2-3% depending on the sensor type. Andre Nobre from Cleantech Solar described assessment or strategies and operational challenges in managing large distribution PV assets in SE Asia indicating heavy soiling, shading, and curtailment are significant operational challenges in urban distributed systems in this region.
Thursday afternoon also saw a joint session in Area(s) 5.5/7.6 and 5.7/8.4 discussing “Advanced Characterization and Reliability of PV Modules and Systems.” Julian Weber from Fraunhofer ISA described measurements of magnetic field imaging that complements electroluminescence (EL) in the imaging of defects in shingle solar modules, while Andrew Gabor from BrightSpot Automation described EL analysis of hail damaged solar cells incorporating statistical and machine learning characterization to assess the invisible damage induced via defects in over 4000 solar cells. Rishi Kumar from the University of California San Diego presented an investigation of moisture ingress and its distribution in bifacial silicon solar cells using water reflectometry detection, which enables a non-destructive quantification of water content in these modules.
Thursday afternoon also included a second joint session from Area(s) 9.5/10.3/11.4 to discuss “Towards 100% Renewables.” Session highlights included discussions of how the integration of photovoltaics into the power infrastructure is progressing. Colorado is on schedule in introducing renewables, and new and better tools for planning become available. Greater PV capacities make the need for closed loop recycling more urgent. Pablo Dias from UNSW presented findings on materials demand for future PV module production and how circularity affects those. Module warranties are 30 years, yet many modules in the field don't last as much. These modules should be recycled, and we need much better recycling. Wenbo Wang from NREL presented on methods to model PV hosting capacities at scale. The presented framework is an open-source tool. Ron Sinton from Sinton Instruments gave an update on Colorado's resource plan towards 80% renewables by 2030. EV charging during the day shifts demand from gas to PV. PV installations increase the value of batteries. Not all PV is installed at low cost. Birk Jones from Sandia showed modelling results for increased PV adoption in microgrids. PV can contribute to microgrids, but more is needed for wide-spread installations. Finally, Upama Nakarmi from Clean Power Research presented a method to infer the configuration of a PV installations from net load. This information and then be used to predict production.
