Short-circuit Current Degradation Research Articles

Analysis of various degradations of five years aged mono c-Si, poly c-Si, and thin-film photovoltaic modules from rooftop solar installations in Dhaka’s tropical wet and dry climate conditions

This study evaluates the degradation of mono, poly, and thin-film silicon solar photovoltaic (PV) modules through visual and electrical measurements in Dhaka’s tropical wet and dry climate conditions. For this, several sites of rooftop solar PV installations in Dhaka, aged at least 5 years, were selected for field investigation. A visible inspection for visual degradation followed by experimental testing on various electrical characteristics of the PV modules installed on the rooftop using a portable Seaward I–V Tracer for measuring the electrical degradation was done. The electrical data were used to evaluate the degradation of short circuit current, open circuit voltage, fill factor, and maximum power in the field as compared to the nameplate values. Experimental results showed the varying types of visual degradation types such as visible cracks, snail trails, moisture intrusion, front glass, and discoloration for the investigated PV modules. The degradation of PV modules in terms of short circuit current was 0.7%/year for 85Wp mono c-Si, 7.6%/year for 150Wp poly c-Si, and 9.7%/year for 105Wp silicon thin-film, respectively. We believe this study would guide the maintenance of the solar PV systems installed on Dhaka city’s rooftop buildings.

Degradation analysis of polycrystalline silicon modules from different manufacturers under the same climatic conditions

Different kinds of photovoltaic modules from various manufacturers have entered the PV market. However, the long-term performance of these modules under outdoor conditions is uncertain. This study evaluated the degradation of polycrystalline silicon modules from 11 different manufacturers installed under the same climatic conditions in Kumasi, Ghana with the aim of predicting the long-term performance of the modules. Specifically, this study sought to: (i) analyse the power degradation rates of the modules and determine the correlation between the degradation and the age of the modules, (ii) determine the correlation between the power degradation and other electrical performance parameters of the modules, (iii) identify the modules with visual defects and compare their degradation rates with the modules without any visual defects, (iv) compare the degradations of PV modules from the same manufacturer installed under the same climatic conditions for the same number of years and (v) assess the installation and maintenance practices that could negatively affect the degradation of the modules. Forty-eight PV modules from 11 different manufacturers were sampled from 12 PV systems installed between 5 and 9 years. The methods used were visual inspection, observation, interviews, and current–voltage (I-V) tracings. The results revealed the mean power degradation rates of the modules between 0.79 and 1.67%/year, contingent on the manufacturer. The power degradation rate had no correlation with the age of the modules but the power degradation of all modules was mainly due to the degradation of short circuit current (Isc) of the modules. Light encapsulant discoloration, dark encapsulant discoloration, minor frames corrosion, and minor metallization discoloration were found on modules from four different manufacturers. However, the degradation of electrical performance parameters could not be solely attributed to these visual defects. Slight variations in degradations were observed for PV modules from the same manufacturer installed under the same climatic conditions for the same number of years. The installation and maintenance practices of the system owners were similar and unlikely to impact differently on the degradation of the modules from different manufacturers.

Effects of He ion and electron beam irradiation on a CdTe solar cell dosimeter in a substrate configuration

In this work, the effects of He ion and electron beam irradiation on substrate-type CdTe solar cells that are suitable for the detection of alpha and beta radiation are investigated. He ion irradiation revealed that the induced current proportionally increased with the increase of He ion current and that it is possible to detect alpha radiation using a substrate-type CdTe solar cell dosimeter. Next, the electron irradiation effects were investigated. The induced current proportional to the electron flux was also observed, and the sensitivity depended on the electron energy. In addition, the degradation of a substrate-type CdTe solar cell dosimeter by electron beam irradiation was investigated. No significant degradation in short-circuit current was observed at the electron irradiation of 3 × 1016 cm−2 at 200 keV and 1 × 1016 cm−2 at 400 keV. This result suggests that the substrate-type CdTe solar cell dosimeter is sufficiently resistant to electron irradiation.

Modeling the Effect of PV Module Orientation on the Encapsulant Browning Degradation Rate in Algeria Region

The encapsulant browning degradation mode of photovoltaic (PV) modules is affected by ultraviolet irradiance, ambient temperature, and humidity of the installation site. In this article, the degradation rate for encapsulant browning, measured by short-circuit current degradation, is estimated for different PV module tilt and orientation angles in the Algiers region, characterized by a temperate climate. The activation energy for encapsulant browning is calculated using the acceleration factor modeling of the field-to-field degradation and physical models, in conjunction with the meteorological data of two locations in Algeria, where the same module type is fielded for 9–10 years. The tradeoff between the PV energy production and the PV module lifetime is carried out for different PV module positioning, assuming that encapsulant browning is the main failure mechanism experienced in the field. The results reveal that the orientation angle affects the PV module lifetime, where orienting the PV module from east to west increases the lifetime up to 30%, and the lifetime energy production up to 6%, due to reduced degradation. It is also presumed that although the Saharan region of Adrar receives more UV light and ambient temperatures throughout the year in Algeria, the PV modules fielded in the Mediterranean region of Algiers suffer higher degradation, which isexplained by the high humidity experienced in Algiers that accelerates the encapsulant browning failure mechanism.

Heat degradation of sputter-deposited Cu(In,Ga)Se2 solar cells and modules: Impact of processing conditions and bias

We report accelerated heat degradation studies on fully encapsulated Cu(In,Ga)Se2 modules as a function of film growth parameters, in particular back contact selenization (preSe), as well as the impact of bias (light/voltage) during heat degradation. We show that pre-Se conditions have a profound effect on the heat stability of the device, whereby reduced preSe, while increasing initial efficiency, results in strong heat degradation, driven by a combination of reduced space-charge region and reduced minority carrier lifetime (as evident from external quantum efficiency measurements) in the light-soaked state and resulting in strong degradation of short-circuit current. This is also accompanied by a stronger increase in the shallow acceptor concentration (as measured by capacitance-voltage profiling) in the degraded state, suggesting that the SeCu divacancy complex (VSe-VCu) is likely responsible. In this case, appearance of a high concentration of deep acceptor states accompanies increased shallow doping upon light-soaking, with the former reducing bulk lifetime and the latter further affecting electron collection due to narrow depletion width. This result suggests that bulk structural properties of the absorber film are strongly impacted by the back contact selenization conditions, making the film more susceptible to heat degradation. In the second part of this paper we show that electrical or light bias during heat exposure reduces degradation, in particular almost fully eliminating the above short-circuit current loss. This is a surprising result as usually the positive effects of bias are attributed to interfacial changes, while our results demonstrate that bulk properties can be improved as well.

Laser induced non-monotonic degradation in short-circuit current of triple-junction solar cells

In order to study the continuous wave (CW) laser radiation effects and mechanism of GaInP/GaAs/Ge triple-junction solar cells (TJSCs), 1-on-1 mode irradiation experiments were carried out. It was found that the post-irradiation short circuit current (ISC) of the TJSCs initially decreased and then increased with increasing of irradiation laser power intensity. To explain this phenomenon, a theoretical model had been established and then verified by post-damage tests and equivalent circuit simulations. Conclusion was drawn that laser induced alterations in the surface reflection and shunt resistance were the main causes for the observed non-monotonic decrease in the ISC of the TJSCs.

Reducing the reflection of nanowhiskers on dielectric composite pyramids

A subwavelength structure was fabricated on a textured dielectric composite by nanolithography and dry etching. The facet of the textured surface was covered with many nanospheres as masks and then engraved into whiskerlike nanostructures. These nanowhiskers can absorb light efficiently, even under large-angle oblique illumination. When the nanowhisker structure was applied to solar cells, it provided 20.81% improvement in short-circuit current compared with a similar subwavelength structure, composed of a single-layer dielectric. At an incidence angle of 80°, the proposed solar cell achieved a 51.1% reduction in short-circuit current degradation.

Photovoltaic Platform for Investigating PV Module Degradation

Photovoltaic research is oriented more and further towards study on PV modules degradation. The objective is to understand the different degradation modes of PV modules and associated factors. This paper presents a platform for measures dedicated to do a study related to degradation of electrical characteristics of the photovoltaic modules. It is installed on the site at University of Dakar in Senegal. This work proposes a method for standardization of the direct measures of the short-circuit current (Isc) and the open-circuit voltage (Voc) of PV modules. The approach used for the assessment of degradation of Isc and Voc involves a comparison between baseline values given by manufacturer and those measured in real operating conditions brought back in the standard test conditions (STC). Findings presented on degradation of Isc and Voc photovoltaic modules cover the first ten months of measurements from Mars to January. Degradation of short-circuit current is about 13% for the three days. The degradation of open-circuit voltage measured during the three days is 8%.

Carrier transport mechanism of GaAs/Ge solar cells under electrons irradiation

In this paper, the basic laws of spectral response, open-circuit voltage and short circuit current of GaAs/Ge solar cells are obtained by ground simulation irradiation test under the different-energy electrons’ irradiations, such as 1, 1.8 and 10 MeV. The carriers’ transport mechanism in cells is analyzed using the PC1 D simulation program. The variations of the majority carriers’ concentration and the minority carriers’ diffusion length with the irradiation particle fluence are obtained in GaAs/Ge solar cells under different-energy electrons’ irradiation. Majority carriers’ removal rate and minority carriers’ diffusion length damage coefficient are calculated under different-energy electron irradiations. The results show that majority carriers’ concentration and minority carriers’ diffusion length decrease with increasing the incident electron fluence. The majority carriers’ removal rate and the damage coefficient of minority carriers’ diffusion length increase with increasing the electrons energy. The majority carriers’ removal effect and the minority carriers’ diffusion length shortened are the main reasons of open-circuit voltage and short circuit current degradation of the solar cells, respectively.

Less Reflective Sub-Wavelength Structure Formed on Textured Surface Using Nanosphere Mask

In this study, a new sub-wavelength structure was made on a textured surface by using nanolithography and reactive ion etching. By oxygen plasma hydrophilization and drop-coating processes, we were able to place nanosphere masks on the facet of the textured surface uniformly and then the textured surface was dry-etched into a nanowhisker structure. These nanowhiskers can absorb incident light efficiently, even if they are illuminated at large incident angles. When this proposed sub-wavelength structure was applied to a solar cell, a high photocurrent can be achieved. The short-circuit current of the solar cell with the proposed structure was improved by 15.32% compared with that of the solar cell with an antireflection layer. Furthermore, short-circuit current degradation due to angular dependence was minimal for the proposed solar cell. At the incident angle of 80°, the proposed solar cell achieved a 68.5% enhancement of the photocurrent relative to that of the solar cell equipped with the conventional sub-wavelength structure.

Thermal endurance study of polymers used in low concentration photovoltaic modules

Thermal endurance studies were performed on the major polymeric components used in a Low concentration photovoltaic (LCPV) module using a thermal gravimetric analysis (TGA) method. Activation energy of the various polymers was obtained, and lifetimes were predicted based on the assumption of 5% weight loss for 30 years. Oven aging was used to verify the TGA thermal endurance prediction. Reasonable agreement between TGA prediction and oven baking results were reached, with the exception of ethylene-vinyl acetate (EVA) encapsulant that demonstrated a second-order reaction inconsistent with TGA assumptions. As a result, a more LCPV-relevant way to characterize the degradation of EVA was developed and demonstrated a linear relationship between PV device short-circuit current degradation and yellowness index. For the purpose of this EVA degradation analysis, a 20% reduction in PV device short circuit current was selected as the failure criteria.

Analysis of Proton Induced Defects in Cu(In,Ga)Se2 Thin-Film Solar Cells

AbstractWe investigated radiation-induced defects in CIGS solar cells with a solar-cell simulator to analyze the spectral response of the irradiated cells. The damage constant of the minority-carrier diffusion length of the cells irradiated with 1 MeV protons was determined to be 3.5 ×10-5. This analysis led to the relation between the defect introduction rate and proton energy, and was obtained using the same method, as was the defect annealing rate. This result agreed well with that estimated from an analysis of changes in short-circuit current degradation.

Space-charge-limited-current diode model for CuxS/CdS solar cells and their degradation

A space-charge-limited-current diode model for CuxS/CdS solar cells accurately models their current-density-versus-voltage (J-V) curves for a 9.2% efficient device and a 4.1% efficient device that degraded to 0.3% efficiency in hot-moist air. For a 1-μm-thick, high-resistance region of Cu compensated CdS at the interface to the CuxS, all the measured fill factors from 0.54 to 0.71 and the open-circuit voltages from 0.41 to 0.52 V are well fit for steady-state conduction electron concentrations between 1.2×109 and 6.9×1010 cm−3 and for electron trap densities between 7×1014 and 5×1018 cm−3 eV−1 at energies of 0.3–0.5 eV below the conduction-band edge of this high-resistance CdS region. The trap changes that occur with short-circuit current degradation increase the fill factor. A CuxS/CdS configuration is proposed to reduce reproducibility problems and to eliminate all the known modes of degradation with the possible exception of photoinduced degradation. Efficiency increases of 10%–11% are projected.