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DOE OSTI2022

Uncertainty Quantification of Bifacial Performance Modeling: Preprint

Analysis on uncertainty in the annual energy of PV systems that can be attributed to parameters of particular importance to bifacial PV modules is presented. Monte Carlo simulations are used to evaluate the effect of uncertain module bifaciality factors, module transmission fractions, albedo values, and ground clearance. The analyses cover a wide spectrum of potential PV array archetypes through variation of installation parameters. The results of the Monte Carlo analysis reveal that the uncertainty is largely dependent on albedo uncertainty, but more simulations are needed to identify trends across system archetypes. The simulations are aimed at attributing an annual energy uncertainty factor for bifacial considerations that can be applied in post-processing of project probability of exceedance analysis.

energy modeling↗

DOE OSTI2021

Spread Spectrum Time Domain Reflectometry (SSTDR) Digital Twin Simulation of Photovoltaic Systems for Fault Detection and Location

Utilizing spread spectrum time domain reflectometry (SSTDR) to detect, locate, and characterize faults in photovoltaic (PV) systems is examined in this paper. We present a method to obtain the model parameters that are needed to produce digital twin SSTDR responses for PV systems. The digital twin SSTDR responses could be used to predict faults within the PV systems. Here, the model parameters are the reflection and transmission coefficients at each impedance discontinuity in the PV system along with the propagation coefficients across each PV cable segment. We obtain model parameter by applying inverse modeling techniques to experimental SSTDR data associated with PV systems. Our model parameters can be used in any digital twin simulation method for modeling reflectometry in frequency-dependent and complex loads. For validation, we used the model parameters in a graph network simulation engine and adapted it to be used for SSTDR digital twin simulations in PV systems. We produced simulations for 0 to 10 PV modules connected in series. We also simulated SSTDR responses for open circuit disconnections in a PV setup containing 10 PV modules in series. Results show that all but one simulated disconnect locations match experimental disconnection locations of the same setup with an error of less than 5%.

14 SOLAR ENERGY↗

DOE OSTI2022

Uncertainty Quantification of Bifacial Performance Modeling

energy modeling↗

DOE OSTI2021

Impact of illumination and encapsulant resistivity on polarization-type potential-induced degradation on n-PERT cells

Power loss caused by polarization-type potential-induced degradation (PID-p) in a variety of high-performance photovoltaic cell types has been observed to be recoverable via subsequent illumination and in some cases preventable via simultaneous illumination. In this report, we describe the results of a study in which the front faces of n-PERT cells encapsulated in polymers with a broad range of electrical resistivity were exposed to varying and controlled irradiance during PID testing. For a low resistivity ethylene-vinyl acetate copolymer encapsulant, no reduction in the rate or extent of power loss was observed for irradiance as high as 1,000 W/m 2 , whereas for high and intermediate resistivity polyolefin encapsulants, 100 and 300 W/m 2 , respectively, prevented power loss. We introduce a simple model based on charge accumulation that facilitates interpretation of these results whereby degradation via charge accumulation under voltage stress and recovery due to light exposure are opposing and interdependent phenomena that describe the susceptibility of a module to power loss.

14 SOLAR ENERGY↗

DOE OSTI2023

Life cycle cost assessment of material recovery from perovskite solar cells

Perovskite photovoltaic (PV) cells have created a significant interest over the last few years due to their low-cost and high-power conversion efficiencies. While perovskite PVs are still under development, we analyze cost of alternative sustainable end-of-life management for perovskite PV cells; this allows to reuse economically valuable materials and prevent environmental contamination. Here, we studied the life cycle cost assessment of recovering metals such as lead, aluminum, gold, nickel, and silver and other valuable materials such as glass from waste perovskite PVs. We also developed a recycling scheme to optimize the material recovery and determine the economically feasible ways to separate the cells layer-by-layer. Further, we assessed the cost and the net cost of the perovskite PV recycling processes. We found that the most feasible recycling technique’ cost is $\$$10.70 and its net cost is $\$$– 2.95 per 1 m 2 module. These values could be further improved by optimizing and reusing chemicals involved in process. These results indicate that the cost of perovskite PV recycling is economically feasible and there is potentional to gain benefit from sustainable end-of-life management of perovskite PVs.

14 SOLAR ENERGY↗

DOE OSTI2022

Nondestructive Evaluation (NDE) of Cable Anomalies using Frequency Domain Reflectometry (FDR) and Spread Spectrum Time Domain Reflectometry (SSTDR)

This report presents a comparative assessment of the performance of frequency domain reflectometry (FDR) and spread spectrum time domain reflectometry (SSTDR) in detecting a wide range of electrical cable anomalies. All tests and results reported herein were performed at the PNNL Accelerated and Real-Time Environmental Nodal Assessment (ARENA) cable and motor test bed. The primary objective of this work was to evaluate the effectiveness of SSTDR, a fledgling cable monitoring technique that shows promise for application in online monitoring of energized cable systems, against FDR, an offline technique widely employed in the nuclear power plant (NPP) industry. FDR tests are becoming more widely used in nuclear power plant cable aging management and test programs – particularly for low voltage cables. FDR capabilities for these kinds of tests have been reported by PNNL and others. The FDR test is performed on de-energized cables by connecting the FDR instrument to two of the cable conductors, or one conductor and the shield. A broad band low voltage (< 5 V) chirp is introduced in the cable, and any reflected response is captured in the frequency domain. The captured reflection is then processed by performing an inverse Fourier transform to a time domain response which can then be converted to a distance response based on the cable velocity of propagation (VoP). SSTDR measurements are functionally similar to FDR measurements in that a broad-band voltage signal composed of a square or sine wave modulated pseudo-random sequence of chips (< 5 volts), is injected onto one of the cable conductors. The injected signal will experience partial energy reflection and transmission at each impedance discontinuity along the transmission line. Any reflected response is detected by computing a cross-correlation between the reflected signals and a delayed copy of the incident SSTDR signal. the time delay for the reflected signal to experience the best matched correlation with the incident signal, indicates the travel time for the signal to reach a change in impedance. By knowing this time delay and velocity of propagation (VoP) of the signal, one can compute the physical distance. A big advantage that SSTDR measurements have over other methods is the ability to be connected to energized or live wires (currently up to 1kV) thereby enabling online monitoring of cables. SSTDR has been used successfully in several applications, e.g., aircraft, rail, and photovoltaic systems. In this work FDR and SSTDR cable assessment techniques were used to characterize a variety of cable anomalies and faults including: (1) Presence or absence of a motor; (2) Ground faults and short circuit faults; (3) Moist environments and water ingress faults; (4) Accelerated thermal aging. Both shielded and non-shielded cables were evaluated in this report. Offline measurements were made using FDR and online measurements were made by SSTDR for a range of test scenarios. Based on the results across all cable anomalies evaluated in this study, FDR displayed high sensitivity towards cable condition assessment, while SSTDR showed promise for future application in monitoring NPP cable systems. However, further developments are suggested to improve the resolution and sensitivity of SSTDR towards faults and anomalies in low voltage cables.rt presents a comparative

42 ENGINEERING↗

DOE OSTI2021

Perovskite Photovoltaic Devices with Carbon-Based Electrodes Withstanding Reverse-Bias Voltages up to –9 V and Surpassing IEC 61215:2016 International Standard

One of the key challenges of perovskite photovoltaics (PV) is the long-term stability. Although efforts are made to improve the lifetime of perovskite PV devices, their degradation under reverse-bias conditions is barely addressed. Herein, perovskite solar cells with carbon-based electrodes are presented which demonstrate superior resilience against reverse-bias-induced degradation. Although their breakdown voltage is identified to be at approximately -3.6 V, cells do not degrade until the applied reverse-bias exceeds -9 V. Two main degradation mechanisms are identified: 1) iodine loss due to hole tunneling into perovskite, which takes place even at low reverse-bias but decomposes the perovskite only after long time durations; and 2) rapid heating at large reverse-bias leading to formation of PbI2, which starts at shunts and then follows the path of the least resistance for the cell current, which is primarily influenced by the electrode sheet resistances. Finally, perovskite solar modules with carbon-based electrodes are demonstrated, which are subjected to a "hotspot" test described in the IEC 61215:2016 international standard at an accredited module testing laboratory. Passing this accelerated test for the first time confirms the superior stability of perovskite PV devices with carbon-based electrodes and highlights their large industrialization potential.

14 SOLAR ENERGY↗

DOE OSTI2020

bifiPV2020 Bifacial Workshop: A Technology Overview

The virtual bifiPV Workshop was held in July 2020 to provide the solar industry with a forum for sharing and discussing research into bifacial photovoltaic (PV) technology. This report outlines major insights from the workshop to give the reader an overview of the latest developments in bifacial PV technology worldwide, from the lab to the field. Citations are drawn from this workshop unless otherwise noted, with all proceedings available online at bifipvworkshop. com. Presentations for the bifiPV2020 Workshop focused on the following areas: bifacial power plant modeling and simulation, albedo improvements, the development of encapsulants, the durability and reliability of current bifacial technologies, performance comparisons between glass-glass and glass-transparent backsheet configurations, the future of passivated emitter and rear contact (PERC) solar cells, and the growing adoption of n-type solar cells. With 650 GW total PV installed worldwide and 1 TW to come very soon, PERC is now the standard PV cell type produced en masse. However, it is already reaching 23% efficiency, the upper limit for this type of technology. PV modules breaking the 0.5-kW barrier are starting to appear, and the costs of standard PERC technology are already below 0.2 USD/Wp. In 2019, five GW of bifacial PV were installed worldwide. In 2020, the majority of bifacial installations are expected to be located in the United States, China, and Middle East and North Africa (MENA) states. N-type bifacial technologies are becoming increasingly viable and have huge potential to dominate the market in the coming years. With bifacial technology mounted on horizontal single-axis trackers (HSAT), bids below 10 USD/MWh will soon be observed in the MENA region, and later in Chile and the United States. Factory audits and reliability testing can reduce field failures by helping buyers to select producers that follow rigorous quality assurance and quality control processes.

14 SOLAR ENERGY↗

DOE OSTI2024

Contactless Production Testing of Silicon Solar Cells

Critical cost reductions in silicon solar cells are made by minimizing silver usage in their metal contacts. The reason why is both clear and unavoidable—silver is not only expensive, but also a potential limiting resource for scale-up (the PV industry alone used 10.3 % of the global silver supply in 2020 [1]). The result is solar cells with vanishing electrical contact area that are extremely difficult to test prior to module manufacture, when they must be sorted for quality to maximize power output and reliability of the subsequent modules. This project developed a new measurement instrument that enables the transition to solar cells with very low silver content, including cell designs with both minimal busbars and no busbars at all to electrically contact. The resulting instrument at project completion demonstrated the ability to sort cells with comparable—or better—results than existing technology. Compared to existing cell-test instruments, the new tool has minimal contacting requirements, which lowers the maintenance costs and use of consumable parts. We demonstrated innovative, yet pragmatic, solutions for reporting a comprehensive set of measurement results useful for both cell sorting (going forward in the line for module manufacture) and process control (looking backward in the line to identify cell manufacturing issues from wafer to cell-test). In addition to the traditional current-voltage characterization at cell test—short circuit current, open-circuit voltage, power, efficiency and fill factor—the new tool maintains all the advanced parameter characterization of our existing product line such as a substrate doping measurement, carrier recombination (lifetime) analysis, and surface recombination analysis.

14 SOLAR ENERGY↗

NASA NTRS1983

High-temperature optically activated GaAs power switching for aircraft digital electronic control

Gallium arsenide high-temperature devices were fabricated and assembled into an optically activated pulse-width-modulated power control for a torque motor typical of the kinds used in jet engine actuators. A bipolar heterojunction phototransistor with gallium aluminum arsenide emitter/window, a gallium arsenide junction field-effect power transistor and a gallium arsenide transient protection diode were designed and fabricated. A high-temperature fiber optic/phototransistor coupling scheme was implemented. The devices assembled into the demonstrator were successfully tested at 250 C, proving the feasibility of actuator-located switching of control power using optical signals transmitted by fibers. Assessments of the efficiency and technical merits were made for extension of this high-temperature technology to local conversion of optical power to electrical power and its control at levels useful for driving actuators. Optical power sources included in the comparisons were an infrared light-emitting diode, an injection laser diode, tungsten-halogen lamps and arc lamps. Optical-to-electrical power conversion was limited to photovoltaics located at the actuator. Impedance matching of the photovoltaic array to the load was considered over the full temperature range, -55 C to 260 C. Loss of photovoltaic efficiency at higher temperatures was taken into account. Serious losses in efficiency are: (1) in the optical source and the cooling which they may require in the assumed 125 C ambient, (2) in the decreased conversion efficiency of the gallium arsenide photovoltaic at 260 C, and (3) in impedance matching. Practical systems require improvements in these areas.

Berak, J. M.↗

DOE OSTI2022

Nanometer-Scale Measurement of Grid Finger Electrical Conduction Pathways to Detect Series Resistance Degradation of Utility-Scale Silicon Solar Cells

Here, we report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility-scale photovoltaic power plant by imaging the local resistance at the Ag/Si interface of the c-Si front metallization. Scanning spreading resistance microscopy imaging with nanometer (nm) scale spatial resolution revealed that the number of point or small-area electrical contacts decreased substantially in a degraded cell compared to an unaffected cell, demonstrating the root cause of Rs degradation. The decrease in electrical contacts is likely caused by a structural change - the Ag particles in contact with the Si cell (or via a nm-thickness tunneling glass layer) aggregate into bulk Ag, and a highly resistive glass frit forms a belt shape at the Ag/Si interface. This resistive belt, with a thickness of ~1 um, blocks the current conduction from the cell emitter to the Ag grid. Our microscopy results help to unravel unambiguously the degradation mechanism and demonstrate an example of the multiscale characterization approach for understanding degradation in field-weathered PV module.

14 SOLAR ENERGY↗

NASA NTRSDate not supplied

Analysis of Glint During the Artemis I Mission

Glint occurs when light reflects off a specular (mirror-like) surface. In the context of spacecraft, glinted light can land in places that may cause unintended negative effects. During the Artemis I mission in November and December of 2022, the Orion vehicle was configured intentionally to cause glint to occur to study its effect on the Orion electrical power system (EPS). With the vehicle in a nose-to-sun attitude, light was reflected off the crew module’s reflective skin and onto forward-pointed solar array wings (SAWs), producing more current than would result from direct solar flux alone. Along with this flight test, glint was unexpectedly observed several other times during the mission, primarily due to light reflecting from one SAW to another. The planned glint events helped to anchor the models previously used to study this phenomenon and to understand what parameters have the most significant impact on glinted current generation. With refined models, the SAW-to-SAW glint occurrences were studied with the goal of characterizing its potential impact on vehicle operation.

Photovoltaic↗

NASA NTRS1993

Study of the Staebler-Wronski degradation effect in a-Si:H based p-i-n solar cell

Conversion of solar energy into electricity using environmentally safe and clean photovoltaic methods to supplement the ever increasing energy needs has been a cherished goal of many scientists and engineers around the world. Photovoltaic solar cells on the other hand, have been the power source for satellites ever since their introduction in the early sixties. For widespread terrestrial applications, however, the cost of photovoltaic systems must be reduced considerably. Much progress has been made in the recent past towards developing economically viable terrestrial systems, and the future looks highly promising. Thin film solar cells offer cost reductions mainly from their low processing cost, low material cost, and choice of low cost substrates. These are also very attractive for space applications because of their high power densities (power produced per kilogram of solar cell pay load) and high radiation resistance. Amorphous silicon based solar cells are amongst the top candidates for economically viable terrestrial and space based power generation. Despite very low federal funding during the eighties, amorphous silicon solar cell efficiencies have continually been improved - from a low 3 percent to over 13 percent now. Further improvements have been made by the use of multi-junction tandem solar cells. Efficiencies close to 15 percent have been achieved in several labs. In order to be competitive with fossil fuel generated electricity, it is believed that module efficiency of 15 percent or cell efficiency of 20 percent is required. Thus, further improvements in cell performance is imperative. One major problem that was discovered almost 15 years ago in amorphous silicon devices is the well known Staebler-Wronski Effect. Efficiency of amorphous silicon solar cells was found to degrade upon exposure to sunlight. Until now their is no consensus among the scientists on the mechanism for this degradation. Efficiency may degrade anywhere from 10 percent to almost 50 percent within the first few months of operation. In order to improve solar cell efficiencies, it is clear that the cause or causes of such degradation must be found and the processing conditions altered to minimize the loss in efficiency. This project was initiated in 1987 to investigate a possible link between metallic impurities, in particular, Ag, and this degradation. Such a link was established by one of the NASA scientists for the light induced degradation of n+/p crystalline silicon solar cells.

Naseem, H. A.↗

DOE OSTI2025

High-Intensity UV Exposure for the Rapid Screening of Silicon Photovoltaic Architectures

Advanced Si photovoltaic architectures incorporate different materials and processing pathways that influence degradation modes. Ultraviolet-induced degradation (UVID) is an understudied degradation mode for advanced cell architectures and is of increasing concern to industry due to growing adoption of UV-transparent encapsulation and bifacial technologies. In order to adopt new and evolving technologies confidently, novel component materials and processing techniques must be evaluated and designed for long-term stability, in addition to the conventional design focus on efficiency. In this work, a study protocol framework is presented for the rapid screening of unencapsulated devices against UVID. Unencapsulated passivated emitter rear contact (PERC) and tunnel oxide passivated contact (TOPCon) devices were aged under different UV irradiance intensities and measured via conventional nondestructive electrical characterization methods to assess performance degradation. Based on the results, protocol efficacy and recommendations for further study are discussed. As a result, this work is part of a broader effort to develop rapid screening processes that cut across architectures and exposure conditions to aid module manufacturers in vetting new materials choices for long-term stability.

Accelerated exposure↗

DOE OSTI2025

On-demand formation of Lewis bases for efficient and stable perovskite solar cells

In the fabrication of FAPbI 3 -based perovskite solar cells, Lewis bases play a crucial role in facilitating the formation of the desired photovoltaic α-phase. However, an inherent contradiction exists in their role: they must strongly bind to stabilize the intermediate δ-phase, yet weakly bind for rapid removal to enable phase transition and grain growth. To resolve this conflict, we introduced an on-demand Lewis base molecule formation strategy. This approach utilized Lewis-acid-containing organic salts as synthesis additives, which deprotonated to generate Lewis bases precisely when needed and could be reprotonated back to salts for rapid removal once their role is fulfilled. This method promoted the optimal crystallization of α-phase FAPbI 3 perovskite films, ensuring the uniform vertical distribution of A-site cations, larger grain sizes and fewer voids at buried interfaces. Perovskite solar cells incorporating semicarbazide hydrochloride achieved an efficiency of 26.1%, with a National Renewable Energy Laboratory-certified quasi-steady-state efficiency of 25.33%. These cells retained 96% of their initial efficiency after 1,000 h of operation at 85 °C under maximum power point tracking. Additionally, mini-modules with an aperture area of 11.52 cm 2 reached an efficiency of 21.47%. This strategy is broadly applicable to all Lewis-acid-containing organic salts with low acid dissociation constants and offers a universal approach to enhance the performance of perovskite solar cells and modules.

14 SOLAR ENERGY↗

NASA NTRS1991

The status of lightweight photovoltaic space array technology based on amorphous silicon solar cells

Ultralight, flexible photovoltaic (PV) array of amorphous silicon (a-Si) was identified as a potential low cost power source for small satellites. A survey was conducted of the status of the a-Si PV array technology with respect to present and future performance, availability, cost, and risks. For existing, experimental array blankets made of commercial cell material, utilizing metal foil substrates, the Beginning of Life (BOL) performance at Air Mass Zero (AM0) and 35 C includes total power up to 200 W, power per area of 64 W/sq m and power per weight of 258 W/kg. Doubling of power per weight occurs when polyimide substrates are used. Estimated End of Life (EOL) power output after 10 years in a nominal low earth orbit would be 80 pct. of BOL, the degradation being due to largely light induced effects (-10 to -15 pct.) and in part (-5 pct.) to space radiation. Predictions for the year 1995 for flexible PV arrays, made on the basis of published results for rigid a-Si modules, indicate EOL power output per area and per weight of 105 W/sq m and 400 W/kg, respectively, while predictions for the late 1990s based on existing U.S. national PV program goals indicate EOL values of 157 W/sq m and 600 W/kg. Cost estimates by vendors for 200 W ultralight arrays in volume of over 1000 units range from $100/watt to $125/watt. Identified risks include the lack of flexible, space compatible encapsulant, the lack of space qualification effort, recent partial or full acquisitions of US manufacturers of a-Si cells by foreign firms, and the absence of a national commitment for a long range development program toward developing of this important power source for space.

Hanak, Joseph J.↗

NASA NTRS1996

Mir Cooperative Solar Array Project Accelerated Life Thermal Cycling Test

The Mir Cooperative Solar Array (MCSA) project was a joint U.S./Russian effort to build a photovoltaic (PV) solar array and deliver it to the Russian space station Mir. The MCSA will be used to increase the electrical power on Mir and provide PV array performance data in support of Phase 1 of the International Space Station. The MCSA was brought to Mir by space shuttle Atlantis in November 1995. This report describes an accelerated thermal life cycle test which was performed on two samples of the MCSA. In eight months time, two MCSA solar array 'mini' panel test articles were simultaneously put through 24,000 thermal cycles. There was no significant degradation in the structural integrity of the test articles and no electrical degradation, not including one cell damaged early and removed from consideration. The nature of the performance degradation caused by this one cell is briefly discussed. As a result of this test, changes were made to improve some aspects of the solar cell coupon-to-support frame interface on the flight unit. It was concluded from the results that the integration of the U.S. solar cell modules with the Russian support structure would be able to withstand at least 24,000 thermal cycles (4 years on-orbit). This was considered a successful development test.

Hoffman, David J.↗

DOE OSTI2021

Updates to the Instant Online PV LCOE Calculator Tool

Levelized cost of energy (LCOE) is an important metric for techno-economic analysis of PV modules, systems, and performance. An NREL team within DuraMAT has developed a simplified PV-specific LCOE calculator as an alternative to the NREL System Advisor Model (SAM) for applications that do not have the degree of detail required by SAM. This webinar will review recent data and new features that have been added to the simplified calculator this year, including breakeven buttons, commercial system options, and inverter loading ratios. It will also review the structure of the source code on GitHub, how to edit a local version of the calculator, and walk through some example use cases for the calculator.

calculator↗