Matching accelerated test results to field observations is an important objective in the photovoltaic industry. We continue to develop test methods to strengthen correlations. We have previously reported good correlation of FTIR spectra between accelerated tests and field measurements. The availability of portable FTIR spectrometers has made measurement in the field convenient and reliable. Recently, nano-indentation has shown promise to correlate changes in backsheet mechanical properties. A precisely shaped stylus is pressed into a sample, load vs displacement recorded and mechanical properties of interest calculated in a nondestructive test. This test can be done on full size modules, allowing area variations in mechanical properties to be recorded. Finally, we will discuss optical profilometry. In this technique a white light interferogram of a surface is Fourier transformed to produce a three-dimensional image. Height differences from 1 nm to 5 mm can be detected over an area of a few cm. This technique can be used on minimodules, and is useful to determine crack and defect dimensions. Results will be presented correlating accelerated tests with fielded modules covering spectroscopic, mechanical, and morphological changes.
Polymeric backsheets are an important component affecting the performance and durability of photovoltaic modules. The optical properties of the backsheet should be considered in the design and performance of a photovoltaic module and the stability and durability of optical properties have an impact on power, safety and appearance. Changes in optical properties in fielded modules and accelerated durability testing are compared. IR analysis was conducted on various backsheet materials in accelerated durability testing and compared to outdoor performance to better understand the relevant chemical changes and associated degradation mechanisms. The connection between optical properties and chemical changes is discussed.
Simple and accurate methods are needed to monitor and assess PV systems. It is important to characterize and understand the value of the system with regard to safety and performance (including seasonal and geographical variations) as well as operation and maintenance. This documentation is becoming necessary for the secondary or resale value of PV assets. We report the results from an analysis of a commercial c-Si PV array owned and operated by DuPont. Our technical assessment consists of remote monitoring, field inspection with visual examination and thermal imaging to create a pareto chart of degradation modes, and laboratory analysis. A comparison of remote monitoring and site inspection is presented as well as laboratory analysis (nondestructive and destructive test methods) of modules removed from the service environment. Degradation modes and quality issues became evident as electrical, optical, physical or chemical defects developed with system age. This evaluation provided system data, documented quality issues, and quantified the cost of ownership.
Continuing to better understand the performance of PV systems and changes in performance with the system life is vital to the sustainable growth of solar. A systematic understanding of degradation mechanisms that are induced as a result of variables such as the service environment, installation, module/material design, weather, operation and maintenance, and manufacturing is required for reliable operation throughout a system’s lifetime. We wish to report the results from an analysis of a commercial c-Si PV array owned and operated by DuPont. We assessed the electrical performance of the modules by comparing the original manufacturers’ performance data with the measurements obtained using a solar simulator to determine the degradation rate. This evaluation provides valuable PV system field experience and document key issues regarding safety and performance. A review of the nondestructive and destructive analytical methods and characterization strategies we have found useful for system, module, and subsequent material component evaluations are presented. We provide an overview of our inspection protocol and subsequent control process to mitigate risk. The objective is to explore and develop best practice protocols regarding PV asset optimization and provide a rationale to reduce risk based on the analysis of our own commercial installations.
Polymeric backsheets form the outer protective layer of most crystalline and multi-crystalline silicon cell photovoltaic panels. The mechanical, electrical, optical and chemical properties and durability of these backsheets are critical to the long term reliability, durability and safety of the photovoltaic modules. The stability of these backsheet properties is typically determined based on accelerated testing using individual stresses. However, the impact of multiple stresses applied sequentially or simultaneously can lead to changes in materials properties that are more predictive of performance in the field. An important consideration in the development of accelerated test protocols is the level and duration of the stress, including temperature variation, light intensity and spectral power distribution, humidity, rainfall and powered module current. In this paper, we discuss observations of the aging and degradation of solar panel from the field. Then how these changes correlate to accelerated testing results, and how accelerated tests can be modified to better match observations in the field.
In the last several years, holographic elements have been introduced into a wide array of display applications. Holographic Reflectors are incorporated with liquid crystal displays to shift optimum viewing angle away form specular glare and raise brightness by concentrating light at a convenient viewing angle. Reflectors can be produced in blue, green, gold, red, or white colors. Denso GlassVision projection screens incorporate transmission holograms to efficiently direct projected light to the viewer in a screen that reverts to clear glass When the projection image is turned off. JVC has introduce da large-screen HDTV that uses a holographic color filter to separate blue, green, and red light from the illumination beam, and direct the sorted colors to the appropriate color pixel, raising brightness with a passive component. Most recently, HOE prototypes have been produced to improve the efficiency of portable liquid crystal color display. Front diffuser are affixed to the face of reflective color LCDs and direct output light from the LCD to the viewer at a convenient viewing angle in a concentrated view cone. Reflective Colors Filters are pixelated diffuse reflectors internal to the LCD structure and aligned to the LCD matrix. These reflective filters provide higher brightness, larger color gamut, and better color saturation including a holographic grating are under development to provide wider view angle in direct-view LCDs.
DuPont holographic photopolymers have been used to fabricate high quality holographic optical elements. The wide spectral sensitivity possible in these materials allows imaging near the desired HOE playback conditions. Multicolor imaging with ion and dye lasers using these materials is discussed. Mastering materials and methods are described for reflection and transmission HOE replication. HOE performance is compared to performance predicted by coupled- wave theory and HOE applications using these materials are described.