Shirish A. Pethe

Recent advances in electroplating based CIGS solar cell fabrication

Electrodeposition based CIGS technology developed by SoloPower is highly attractive route for preparation of precursor layers due to its low cost, efficient materials utilization and scalability to high-volume manufacturing. Several aqueous electroplating solutions both in acidic and alkaline regimes are formulated and optimized for achieving stable plating solutions for roll-to-roll electrodeposition that give adherent and high quality films with controllable molar compositions. An optimized rapid thermal annealing approach was developed to achieve device-quality CIGS absorber layers. In this paper, we discuss various electrodeposition approaches for CIGS precursor formation and present a summary of the recent results for SoloPowers flexible cells.

Correlation between preparation parameters and properties of molybdenum back contact layer for CIGS thin film solar cell

Molybdenum (Mo) thin film back contact layers for thin film CuIn(1−x)GaxSe2 (CIGS) solar cells were deposited onto soda lime glass substrates using a direct current (DC) planar magnetron sputtering deposition technique. Requirements for the Mo thin film as a back contact layer for CIGS solar cells are various. Sheet resistance, contact resistance to the CIGS absorber, optical reflectance, surface morphology, and adhesion to the glass substrate are the most important properties that the Mo thin film back contact layer must satisfy [1]. Experiments were carried out under various combinations of sputtering power and working gas pressure, for it is well known that mechanical, optical, morphological, and electrical property of a sputter-deposited Mo thin film are dependent on these process parameters [2].

Comparative study of various PV technologies in terms of energy yield and annual degradation

Current accelerated tests of photovoltaic (PV) modules mostly prevent infant mortality but do not fully duplicate changes occurring in the field nor can predict useful lifetime. Therefore, monitoring of field-deployed thin film PV modules was undertaken at FSEC with goals to assess their performance in hot and humid climate under high voltage operation and to correlate the PV performance with the meteorological parameters. This paper presents performance analysis of a-Si:H and CIGS PV modules that were field deployed in the hot and humid climate over a period of approximately 30 months. The modules were connected in series so as to build maximum open circuit voltage of less than ±600 V with respect to ground and maintained at near maximum power point conditions. Statistical data analysis of PV parameters along with meteorological parameters that were continuously monitored is carried out on regular basis with PVUSA type regression analysis. Current-voltage (I–V) characteristic of module arrays that are obtained periodically complement the continuous data monitoring. The annual energy yield was calculated for both the PV technologies based on the data averaged over every fifteen minutes. Moreover, comparison of the two technologies was carried out based on the estimated annual degradation.

Statistical data analysis of thin film photovoltaic modules deployed in hot and humid climate of Florida

Current accelerated tests of photovoltaic (PV) modules mostly prevent infant mortality but cannot duplicate changes occurring in the field nor can predict useful lifetime. Therefore, monitoring of field-deployed PV modules was undertaken at FSEC with goals to assess their performance in hot and humid climate under high voltage operation and to correlate the PV performance with the meteorological parameters. This paper presents performance analysis of U.S. Company manufactured thin film a-Si:H PV modules that are encapsulated using flexible front sheets and framed to be outdoor tested. Statistical data analysis of PV parameters along with meteorological parameters, monitored continuously, is carried out on regular basis with PVUSA type regression analysis. Current-voltage (I-V) characteristic of module arrays that are obtained periodically complement the continuous data monitoring. Moreover, effect of high voltage bias and ambient parameters on leakage current in PV modules on individual modules is studied. Any degradation occurring during initial 18 months could not be assessed due to data acquisition and hurricane problems. No significant degradation was observed in the performance of PV modules during the subsequent 30-months. It is planned to continue this study for a prolonged period so as to serve as basis for their long-term warranties.

Long-term performance analysis of copper indium gallium selenide thin-film photovoltaic modules

Abstract. Current accelerated qualification tests of photovoltaic (PV) modules mostly assist in avoiding premature failures but can neither duplicate changes occurring in the field nor predict useful product lifetime. Therefore, outdoor monitoring of field-deployed thin-film PV modules was undertaken at FSEC with the goal of assessing their performance in hot and humid climate under high system-voltage operation. Significant and comparable degradation rate of −5.13±1.53% and −4.5±1.46% per year was found using PVUSA type regression analysis for the positive and negative strings, respectively of 40W glass-to-glass Cu-In-Ga-Se (CIGS) thin-film PV modules in the hot and humid climate of Florida. Using the current-voltage measurements, it was found that the performance degradation within the PV array was mainly due to a few (8% to 12%) modules that had substantially higher degradation. The remaining modules within the array continued to show reasonable performance (>96% of the rated power after ∼ four years).

Long-term performance study of united solar PV modules in hot and humid climate of Florida

Large scale deployment of PV modules that are reliable with consistent performance will greatly help in their commercialization and in reducing the green house gases that are produced by the emissions from fossil fuels. In this paper, the results obtained during the long-term testing of United Solar triple junction a-Si:H PV modules are presented. During the long term testing the observed performance variation of +1.27% and +0.22% respectively per annum for positive and negative arrays has been determined. Estimated energy yield of 1452 kWhr/kWp/Yr has also been determined. This study indicates that these a-Si:H modules have continued to show good performance without noticeable degradation in the hot and humid climate of Florida.

Methods for high-voltage bias testing of PV modules in hot and humid climate

The accelerated tests currently carried out on PV modules reduce the infant mortality as well as improve the production techniques during the manufacture of PV modules. However, the accelerated tests do not completely duplicate the real world operating conditions of PV modules. Hence it is essential to deploy PV modules in the field for extended periods in order to estimate the degradation, if any, as well as to elucidate the degradation mechanisms. Moreover, PV modules should be tested by specially designed tests in harsh climates. At Florida Solar Energy Center (FSEC) high-voltage bias testing of PV modules was carried out in hot and humid climate with the individual modules biased at +/- 600 V. It was observed that the leakage currents flowing from the PV circuit to the ground is directly proportional to the bias voltage. PV systems with maximum voltage of 1000 V are installed in Europe and elsewhere which means higher leakage currents will be produced in the PV modules. Based on this fact and the earlier observations, high voltage bias testing of c-Si PV modules specially designed for high voltage operation was carried out in hot and humid climate with the individual modules biased at +/-1500 V at FSEC and higher. This paper provides results of high voltage bias testing of PV modules. The results indicate that the test can be considered as reliable metric in determination of the long term performance of PV modules.

Long-term performance analysis of CIGS thin film PV modules

Current accelerated qualification tests of photovoltaic (PV) modules mostly assist in avoiding infant mortality but can neither duplicate changes occurring in the field nor can predict useful lifetime. Therefore, outdoor monitoring of fielddeployed thin-film PV modules was undertaken at FSEC with goals of assessing their performance in hot and humid climate under high system voltage operation and to correlate the PV performance with the meteorological parameters. Significant and comparable degradation rate of -5.13% and -4.5% per year was found by PV USA type regression analysis for the positive and negative strings respectively of 40W glass-to-glass CIGS thin-film PV modules in the hot and humid climate of Florida. With the current-voltage measurements it was found that the performance degradation within the PV array was mainly due to a few (8-12%) modules having a substantially high degradation. The remaining modules within the array continued to show reasonable performance (>96% of the rated power after ~ 4years).

Photovoltaic module reliability studies at the Florida Solar Energy Center

The accelerated tests currently carried out on PV modules reduce the infant mortality as well as improve the production techniques during the manufacture of PV modules. However, they do not completely duplicate the real world operating conditions of PV modules. Hence it is essential to deploy PV modules in the field for extended period of time in order to estimate the degradation, if any, as well as to elucidate the degradation mechanisms. Moreover, PV modules should be tested by specially designed tests in harsh climates. In this paper some of the results obtained on a-Si∶H modules from various US companies is discussed.

Outdoor monitoring and high voltage bias testing of PV modules as necessary test for assuring long term reliability

At present the failure modes and mechanism of PV modules are not well understood. The current accelerated tests cannot duplicate the various field failures. It is very important to continue to carry out accelerated testing of PV modules in order to reduce the infant mortality of new technology PV modules as well as to improve the production techniques of the PV modules. However, the accelerate tests need to be complemented with actual field deployment of PV modules and specifically designed tests in real world conditions or preferably in harsh climates. In this work the inclusion of outdoor monitoring of PV modules and high voltage bias testing of PV modules in real world climatic conditions in the current best practices for PV module reliability testing is being proposed. One of the objectives of this paper is to show the importance of carrying out continuous monitoring of field deployed PV modules as well as high voltage bias testing of PV modules over an extended period of time.