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Reduced optical transmittance of encapsulants resulting from ultraviolet (UV) degradation has frequently been identified as a cause of decreased PV module performance through the life of service in the field. The present module safety and qualification standards, however, apply short UV doses only capable of examining design robustness or “infant mortality” failures. Essential information that might be used to screen encapsulation through product lifetime remains unknown. For example, the relative efficacy of xenon-arc and UVA-340 fluorescent sources or the typical range of activation energy for degradation is not quantified. We have conducted an interlaboratory experiment to provide the understanding that will be used towards developing a climate- and configuration-specific (UV) weathering test. Five representative, known formulations of EVA were studied in addition to one TPU material. Replicate laminated silica/polymer/silica specimens are being examined at 14 institutions using a variety of indoor chambers (including Xenon, UVA-340, and metal-halide light sources) or field aging. The solar-weighted transmittance, yellowness index, and the UV cut-off wavelength, determined from the measured hemispherical transmittance, are examined to provide understanding and guidance for the UV light source (lamp type) and temperature used in accelerated UV aging tests.

Practical multi receiver ultra high (1000+ Suns) concentration photovoltaic (UHCPV) systems experience large radiation, thermal and electrical loads in addition to large power density transients under routine operation. This report is a summary of the issues involved in determining the practical limits to concentration. How high is too high? Explorations into UHCPV have both theoretical and experimental aspects. Understanding the theoretical device physics and circuit limitations is often essential to determining which experiments to do and in interpreting results. On the experimental side the work can be divided into two fields depending on the type of light source. The first is artificial or simulated sources and the second is working in the field with direct solar irradiation. Both fields have advantages and disadvantages. Direct solar radiation was selected for the current experiments due to the low cost and ability to produce ultra high concentrations (4000+) over relatively large areas (25+ mm2). Several experimental examples from these direct solar measurements shed light on some of the basic theories of how concentrated light affects the performance of multi junction photovoltaic cells. Out of these examples and theoretical foundations we conclude that for practical devices the first order constraint to optimum efficiency at ultra high concentrations is the series resistance. We also present a simple model based on published data and our results that can be used to predict the total system series resistance needed to optimize a system for a particular concentration.

Practical concentrator photovoltaic systems operating at high solar concentration levels up to 2000 suns experience large thermal and electrical loads in addition to large power density transients under routine operation. These systems require efficient cooling systems to manage the associated incident power densities up to 200 W/cm2. Photovoltaic cells and thermal interface materials experience considerable stress under these load conditions. Reliability data is sparse for operation above 500 suns. We present high power test results for a commercial triple junction cell cooled through a high performance metal thermal interface using active liquid cooling methods for power densities up to 200 W/cm2.