Brij M. Arora

Visual Degradation in Field-Aged Crystalline Silicon PV Modules in India and Correlation With Electrical Degradation

This paper presents the analysis of visual degradation data collected during an All-India Survey of Photovoltaic Module Degradation conducted in 2013, in which 57 crystalline silicon modules were inspected in the five different climatic zones of India. Analysis of the data indicates that the highest percentage of modules suffered discoloration in the Hot and Dry climatic zone, with the Hot and Humid zone coming in second in the list. A higher percentage of modules have suffered corrosion in the Hot and Humid zone, as compared with other zones. The modules installed in the Cold climate suffered the least degradation. Both discoloration and corrosion have been seen in modules across all age groups, even in some of the modules installed less than five years ago. On the other hand, delamination and backsheet degradation have been seen only in modules more than a decade old. The visual degradation data have been correlated with the electrical performance data and reaffirm the direct relation between encapsulant discoloration and reduction in short-circuit current and output power, as well as that of series resistance with metal corrosion.

Performance degradation in field-aged crystalline silicon PV modules in different indian climatic conditions

A survey of field-aged crystalline silicon modules in various climatic conditions in India was carried out, focusing on modules, which show visible signs of degradation. Analysis of the survey data indicates that the power degradation rate is highest in the Hot & Dry climatic zone, followed by the Hot & Humid zone, while it is least in the Cold zone. The degradation in power output of crystalline silicon modules is primarily due to reduction in the short-circuit current, followed by decrease in fill factor while the decrease in open-circuit voltage is very small. Analysis of the survey data also indicates that degradation rate of multi-crystalline silicon is slightly higher than that of mono crystalline silicon.

Linking performance of PV systems in India with socio-economic aspects of installation

A survey of PV modules in the field for more than 5 years in India has been conducted The analysis revealed that module degradation rates are linked with the social and behavioral issues of the end users. The appropriateness in system installation, maintenance and hence the degradation depends on the type of ownership of the system, the financial model for the installation and the end purpose. We found that whenever there are cash flows associated with the installations in terms of savings or income generation, the maintenance activities are properly done, irrespective of the type of ownership of the system. Community owned PV installations were found to be better installed and maintained than individual systems because of the presence of institutionalized mechanisms for operation and maintenance.

All India Survey of Photovoltaic Module Degradation 2014: Survey methodology and statistics

This paper presents an overview of the 2nd All India Survey of Photovoltaic Module Degradation, conducted in the months of September to December 2014. A total of 1080 modules belonging to different photovoltaic technologies were inspected from 45 different sites which are spread across the 5 different climatic zones of India. This is the first survey in India in which electroluminescence, illuminated and dark I-V measurements, insulation resistance and various other tests were carried out on PV modules installed in the field. The goal of the survey is to determine the degradation in the field-aged PV modules and find correlations between visual, electrical and physical degradation of the PV modules. The purpose of this paper is to present an overview of the survey methodology and statistics to the PV community.

Measurement of temperature coefficient of photovoltaic modules in field and comparison with laboratory measurements

The performance of photovoltaic modules depends on temperature and irradiance. It is necessary to translate the measured I-V characteristics to standard test condition for assessing degradation, and such translations require temperature coefficients for voltage and current. Prediction of the annual energy yield also requires knowledge of the temperature coefficients. IEC 60891 provides a standard procedure for measurement of temperature coefficients and this methodology has been utilized to obtain the temperature coefficients of modules of different PV technologies, both in laboratory and in the field. Comparison of the values obtained in the field with those of the laboratory show good conformance. Also the variation of the temperature coefficients with change in irradiance has been investigated.

Correlation of electrical and visual degradation seen in field survey in India

This paper presents an analysis of the electrical and visual degradation data gathered in the 2nd All India Survey of Photovoltaic Module Reliability, conducted in 2014, in which a total of 1148 modules were inspected in different climatic zones of India. The modules in the Hot Climates are seen to degrade faster than modules in the Non-Hot climates. Fill Factor (FF) reduction has been found to be the main cause for power reduction in young modules (less than 5 years old), while for old modules (more than 5 years), Isc reduction is the main culprit. Visual degradation in the modules has been quantified and correlated with the degradation in various electrical parameters. The degradation in Isc correlates with the discoloration and delamination of the encapsulant and the degradation in the FF correlates well with the extent of the corrosion in the metallization.

“Teach a 1000 Teachers”: A methodology for the rapid ramp-up of photovoltaics manpower required for India's national solar mission

Indias Jawaharlal Nehru National Solar Mission (JNNSM) envisages that 100,000 trained personnel will be needed by the solar industry in India. To achieve this, a rapid ramp-up methodology is required to first create trained teachers of solar energy courses. We have used a novel method to run a 2-week course on “Solar Photovoltaics: Fundamentals, Technology and Applications”. Over 1200 teachers from 370 colleges and institutions across India attended the program at 35 “remote centers”. This paper describes this effort which simultaneously trained a large number of teachers, and generated palpable excitement for solar PV among educators.

Imaging of carrier lifetime variation during c-Si solar cell fabrication

The present work investigates the variation of minority carrier lifetime of silicon wafers after each processing step during the fabrication of silicon solar cells. Contactless photoconductance technique provides quantitative measure of the average lifetime. The spatial variation in the minority carrier lifetime is obtained by photoluminescence imaging. By combining these two techniques, we obtain the following significant results: i) edge isolation process degrades the lifetime near the wafer boundaries, ii) removal of phosphosilicate glass after POCl3 diffusion degrades lifetime in the central region of the wafer, iii) high temperature processing steps e.g. emitter diffusion and contact firing result in improving / recovering the lifetime.

Synthesis of oriented and passivated polycrystalline silicon films on glass by hot wire chemical vapor deposition

We report synthesis of highly (220) oriented and passivated polycrystalline silicon films on glass by using Hot Wire Chemical Vapor Deposition (HWCVD) without using any buffer. Oriented growth is initiated by deposition at 400°C using dilute mixture of Silane(SiH₄) and Hydrogen(H₂), a condition which favours growth of (220) oriented nuclei. After that most of the growth is done at 600-700°C using less dilute SiH₄ + H₂. Films are passivated by in-situ soak in atomic hydrogen between 400-300°C. At 300 K, films have dark conductivity about 10^-6 (Ω-cm)^-1. Illumination with a white light LED of flux about 1 sun increases the conductivity to 1-2x 10^-5 (Ω-cm)^-1. In addition photoluminescence emission is observed both at 18 K and at 300 K. These features suggest films are well passivated.

Structural characterization of oriented crystalline silicon film grown on SiO 2 , Sapphire, TiO 2 and Nickel Substrate by Hot Wire Chemical Vapour Deposition

We have investigated the possibility of growing oriented crystalline silicon films, 2 to 3 micron thick, from silane-hydrogen mixture, by hot wire chemical vapour deposition (HWCVD). Several substrates i) amorphous SiO2, ii) oriented TiO2 layer on glass, iii) textured nickel-5% tungsten metal strip, and iv) crystalline sapphire have been used in this work. The growth is performed in two stages; a) nucleation step using dilute mixture SiH4:H2 in the ratio 1:20 at 400°C, followed by b) thickening step at 540°C, in which SiH4:H2 ratio is gradually enhanced to 8:20. The nucleation step promotes directional growth and leads to (220) oriented thick layers. Several characterization techniques, scanning electron microscopy (SEM), x-ray diffraction (XRD) have been used for structural investigations such as preferred crystal orientation, grain size, grain shape and surface topography.