DEFECT IDENTIFICATION AND CORRELATION WITH ELECTRICAL DEGRADATION OF FIELD AGED THIN FILM PHOTOVOLTAIC TECHNOLOGIES IN COMPOSITE CLIMATE Rahul Rawat *1 , S. C. Kaushik 1 , O. S. Sastry 2 , Y. K. Singh 2 , B. Bora 2 and Ramayan Singh 2 1 Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi (India)-110016 2 National Institute of Solar Energy, Ministry of New and Renewable Energy, Gwal Pahari, Gurgaon, Haryana (India)- 122003 * Corresponding Author: Tel: +91-11-26596465; Email: rawatktp@gmail.com ABSTRACT: The thin film photovoltaic (TFPV) technologies are emerging out as an alternative to the established silicon wafer based PV technology due to competitive efficiency, and low energy payback period. However, the performance and degradation study of these technologies are important in order to ensure their stability and reliability in terms of operating lifetime. The current-voltage (I-V) characteristic of PV module are most widely used for assessing the electrical performance and degradation. In this paper, the degradation analysis of I-V characteristic of 40 CdTe and 69 micromorph TFPV modules has been carried out after long term outdoor exposure. The degradation rate of electrical parameters i.e. short circuit current; open circuit voltage; current, voltage and power at maximum power point of individual field aged module has been evaluated with respect to the name plate values. The defects of the modules have been identified using visual inspection and electro-luminescence imaging (EL) which are then correlated with the electrical degradation. The degradation of CdTe and micromorph TFPV technologies are found to be 0.55%year and 6.52% in the first year respectively with respect to the nameplate value. The power output of micromorph modules have degraded by 17% after 1 year of outdoor exposure with respect to the power output of unexposed modules due to light induced degradation. Keywords: CdTe; Micromorph; Thin Film; PV Module; Degradation 1 INTRODUCTION The utilization solar photovoltaic systems is growing rapidly for different power generation application i.e. grid connected, water pumping, lighting and standalone systems due to power shortage, inconsistent oil prices and environmental issues [1]. The conventional wafer based PV technology is well proven and hold major portion of PV market worldwide, however, the researchers are interested in new low cost, stable and reliable PV technologies i.e. thin film photovoltaic technology (TFPV). The TFPV technologies have thin layers of PV materials making p-n junction which are deposited and grown on a substrate in a controlled manner [2]. The TFPV technologies offers more energy yield in hot and composite climates due to low temperature coefficient with low cost as compared to the wafer based technology [3]. However, the reliability of these technologies are not yet proven for 25 years of lifetime. Although, the indoor qualification testing of TFPV modules is being done as per IEC 61646 standard in order to ensure the mechanical, thermal and electrical durability, the regress outdoor performance and degradation of study of these technologies are required in order to identify the defects and degradation rates. In this paper the electrical degradation study and defect identifications of CdTe and micromorph TFPV technologies have been carried out after outdoor exposure of 3 and 1 years respectively in composite climate. The CdTe technology has CdS and CdTe layer in order to make p-n junction while the micromorph technology is multi junction tandem solar cell of micro-crystalline and amorphous silicon layers. Both the technologies are glass to glass in which the PV materials and other layers are sandwiched between the two toughened glasses. Jordan and Kurtz (2013) have reviewed the degradation rates of different PV technologies and found the degradation rate of CdTe modules to be 0.4%/year [4]. The micromorph TFPV technology exhibits light induced degradation during initial months of outdoor exposure and requires about 16 months to stabilize its performance with a degradation of approximately 16.5% in 12 months [5-6]. 2 METHODOLOGY The TFPV modules are installed in different grid connected PV systems at National Institute of Solar Energy, India which is considered to be in composite climate zone. The I-V characteristics of each field aged PV modules has been measured in outdoor conditions using the PVPM 1000C I-V curve tracer of Photovoltaik Engineering GmbH. The outdoor IV characteristics of two different CdTe modules and 3 micromorph modules are shown in figure 1(a&b). The device uses 4-wire cabling for accurate voltage, reference cell for irradiance and Pt100 RTD for module temperature measurement. The measured values and the nameplate values of the TFPV technologies have been translated to the alternate reporting conditions (ARC) which are close to the actual measurement conditions so as to reduce translation errors (Table I). The technical specifications of PV modules (name plate values) at standard test conditions (STC) and ARC has been presented in Table II. Table I. Alternate reporting conditions Parameter Environmental Conditions Technology CdS/CdTe Micromorph Irradiance 900 W/m 2 800 W/m 2 Module Temperature 60 °C 45 °C The measured as well as name plate value of short circuit current (ISC), open circuit voltage (VOC), current (IM) and voltage (VM) at maximum power point have been translated to alternate reporting condition using eq. 1 and eq. 2 [7-9]. 32nd European Photovoltaic Solar Energy Conference and Exhibition 2286