Prospective short-circuit current

The prospective short-circuit current (PSCC), available fault current, or short-circuit making current is the highest electric current which can exist in a particular electrical system under short-circuit conditions. It is determined by the voltage and impedance of the supply system. It is of the order of a few thousand amperes for a standard domestic mains electrical installation, but may be as low as a few milliamperes in a separated extra-low voltage (SELV) system or as high as hundreds of thousands of amps in large industrial power systems. Protective devices such as circuit breakers and fuses must be selected with an interrupting rating that exceeds the prospective short-circuit current, if they are to safely protect the circuit from a fault. When a large electric current is interrupted an arc forms, and if the breaking capacity of a fuse or circuit breaker is exceeded, it will not extinguish the arc. Current will continue, resulting in damage to equipment, fire, or explosion.

Electrical and Thermal Characterization of Commercial Superconducting YBCO Coated Conductors

Daniele Colangelo, Bertrand Dutoit

This paper reports on experimental and modelling activities aimed to identify E(I,T) characteristics of commercial YBCO High Temperature Superconductor Coated Conductors (HTS-CCs). The aforesaid approach is applied to investigate the HTS-CCs behavior in the different regimes: superconducting state, flux-creep, flux-flow and normal state. In order to thoroughly represent the HTS-CCs behavior, parameterized analytical formulations of E(I,T) characteristics have been assumed and then validated through fitting methodologies. Numerical calculation of the electric field as a function of the temperature and of the current density in the HTS-CC, is fundamental to the development of models suitable to design devices based on HTS-CCs. In fact it allows improving the dedicated-software calculation accuracy. This is particularly important for the simulation of Superconducting Fault Current Limiters (SFCL) behavior against short-circuits and/or overloads events, because during the SFCL limitation the HTS-CCs performance strongly depends on the different above mentioned regimes. As matter of fact, numerical simulations are somewhat simpler for high prospective currents as compared to intermediate conditions as for overload or low short-circuit currents.

Institute of Electrical and Electronics Engineers2013

Corrosion testing of solar cells: Wear-out degradation behavior

Christophe Ballif, Andrew Wayne Fairbrother, Luca Gnocchi, Alessandro Francesco Aldo Virtuani

Corrosion is one of the main end-of-life degradation and failure modes in photovoltaic (PV) modules. However, it is a gradual process and can take many years to become a major risk factor because of the slow accumulation of water and acetic acid (from encapsulant ethylene vinyl acetate (EVA) degradation). In this work, an accelerated aging test for acetic acid corrosion was developed to probe wear-out and end-of-life behavior and facilitate screening of new cell, passivation, metallization, and interconnection technologies. In the tests, the top glass and EVA layers were removed from PV modules to expose the solar cells and interconnects. These "opened" modules were then placed in acid baths under varying conditions, including acid concentration, temperature, and elec-trical bias. Three cell technologies were tested, including Al-back surface field (BSF), passivated emitter and rear contact (PERC), and silicon heterojunction (SHJ). For all conditions, the presence of acid accelerated module power loss compared to control tests with water baths. Increased temperature accelerated the rate of degradation by several times. Application of electrical bias led to an initial drop in short circuit current, but these modules eventually outperformed the non-biased modules. In all tests, lead oxides were the primary degradation products detected, and found to accumulate mostly along the printed metallization, especially in proximity to the busbar. SHJ cells with a silver paste-based interconnection outperformed Al-BSF and PERC cells with a solder-based interconnection. The accelerated corrosion test methods can be optimized to match corrosion behavior observed in field modules with greater precision and shorter times than standard damp heat tests, and is espe-cially useful to assess the long-term durability of the continuously increasing variety of corrosion sensitive PV materials and components.

ELSEVIER2022

Luminescent and electronic properties of perovskite solar cells

Brian Irving Carlsen

Perovskite solar cells show great promise to serve as an alternative for traditional silicon-based solar cells, however several problems present obstacles for their commercialization. Standard perovskite cells contain lead, which is toxic to humans and harmful to the environment. Alternative perovskite compositions offer the opportunity to replace lead with non-toxic metals. Lead can be directly replaced by substituting it for tin. Unfortunately, tin-based perovskite solar cells do not show the same efficiency or stability as their lead-based counterparts. Using numerical modeling, a study of a current optimized, tin-based solar cell was performed to understand its efficiency limitations and where the most gains can be acquired. While the short-circuit current of the device is high, its limiting factors arise from those already known, primarily the alignment of the electron transport layer with the perovskite conduction band.Another option for replacing lead is by using a double perovskite. This class of perovskites replaces lead with two different metals that maintain charge neutrality. While providing more compositional freedom compared to the direct replacement of lead, double perovskites offer their own challenges. To better understand transport phenomenon between the transport layers and the perovskite, an investigation into the temperature dependent photoluminescence of Cs2AgBiBr6 with different hole and electron transport layers was performed. No clear trends appear allowing a comparison of the transport layers, but some speculations are provided to explain the results common amongst all the samples.Lead is not the only roadblock for perovskites though, as they also show instability across multiple domains. Two of the most prominent ways instability shows up are closely linked -- ionic motion and reversible degradation. A continuation of an insightful paper by Domanski \emph{et. al.} was performed to further elucidate the effects of ionic movement on reversible degradation processes. We show that these processes can be controlled by the application of a bias voltage and that the enhancement of these processes by illumination is not significant. We continued the examination of these reversible processes by studying their effects under real world conditions. Several perovskite solar cells were subjected to real world conditions in a controlled environment during which we tracked their performance. By comparing the measured data to those calculated if the cells had remained pristine we are able to quantify and separate the reversible from irreversible processes.Finally, a more fundamental investigation was made into the internal mechanisms of the perovskite cells. A temperature dependent study correlating photoluminescence spectra and current-voltage curves was performed revealing different two regimes operation. The potential mechanisms underlying each regime are explored.