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AbstractBy means of large mirrors, CSP (Concentrated Solar Power) technologies concentrate the solar energy on an absorber where it is collected as thermal energy. The decrease of the kWh cost and the insurance of a 25 years lifetime minimum are the key points to make these technologies cost competitive and ensure their large deployment. The solar field is the first expense item (20 to 30% of the investment) and is composed by the reflectors which concentrate the solar flux on the absorber. The durability of the mirrors is therefore of principal interest and has to be studied since the conception of the power plant. Actually, the majority of this technology uses glass mirrors made with silver and copper layers for a high reflectance. The protection of the silver layer from oxidation is ensured both by the copper layer and backside paint. In service conditions, the mirrors are submitted to arid climate where temperature, humidity and solar irradiation are extreme. Accelerated climatic tests in controlled environment are used to create the same degradations than the ones happening on site. Specular reflectance being the primary function of the mirrors, this is the parameter usually characterized to evaluate the aging of a mirror. Depending on the aging test and specifically for outdoor exposure, it might take a long time before a loss of reflectance occurs. We present here a new methodology based on the monitoring of the protective back layer degradation that can be used to anticipate the reflectance loss. Based on the activated energy calculated via an Arrhenius law, the lifetime prediction in normal condition can be established.

AbstractThe durability of solar mirrors is a critical factor for the deployment of concentrating solar power plants. Accelerated aging test models currently applied in the polymer, electronic, and photovoltaic fields have recently been reviewed, and the issues of their application to solar mirrors have been discussed. This article first reports the results of temperature, humidity, and light irradiance accelerated aging tests performed to assess the dependent parameters of selected models from the literature. These parameters include the apparent activation energy for the Arrhenius temperature law, the Peck and Eyring coefficients for humidity models and the Schwarzschild coefficient for the irradiance law. The experimental values were then assessed for specular reflectance loss of solar mirrors. Finally, using these parameters, acceleration factors were calculated for solar mirrors. An effective temperature considering the Arrhenius degradation law was used rather than the commonly used mean temperature. This question is also addressed for light irradiance by using the dose instead of the mean value.

The Concentrated Solar Thermal Energy (STE) system requires components with a lifetime of more than 25 years to be profitable. Optical materials performances, such as mirrors and absorber coatings, are essential to the efficiency of the system. Any degradation of their optical properties leads to a reduced efficiency. In the frame of STAGE-STE project we are studying the durability of solar absorber coatings on metallic substrate for non-vacuum applications (in air). The definition of the test conditions was based on a critical review of the stress factors affecting the material such as temperature, humidity and saline atmosphere. The optical performances were measured over time for each sample to follow the variation of solar absorbance and emittance. For each test, a comparison of the performance criterion (PC=Δα-0.5e < 0.05) variation gives a relative resistance of each absorber to the corresponding stress factor. In this paper we will present the results of the accelerated tests campaign on the three solar absorbers samples. Materials characterization was used to analyse the degradation process occurring on each sample. A lifetime prediction based on the calculation of the activation energy has been presented for the thermal test. Finally, the relevance of each test has been discussed.

Abstract Solar mirrors for concentrated solar power (CSP) plants are expected to last at least 30 years. As this delay is far too long to obtain useful information regarding in-service degradation, accelerated approaches to weathering testing are performed by manufacturers and research laboratories in order to quickly assess the lifetime of commercial or new technologies. However, most published studies that have been performed in the CSP field are based on phenomenological approaches. The characterization of the degradation, which mostly considers reflectance loss, has rarely been linked to physical or chemical processes that are responsible for the degradation of properties. Furthermore, the general laws that can be established from these data to establish material behaviour are empirical. Ageing tests have been used for many years in other fields, particularly in the domain of polymeric materials. The impacts on the material properties of stress factors such as temperature, irradiation and humidity have been extensively studied, and models have been proposed for different kinds of materials, even though most are based on empirical observations. One of the goals of this article is to determine how these models could be applied to the weathering of solar mirrors, and as such, the goal of this paper is to provide a critical review of the various models that are most used and accepted by the scientific community. All of these models include material-dependent parameters, and the values that have been determined in these studies are reported here to list their order of magnitude.

AbstractCSP technology has a huge potential. However, all the components used in the energy generation process are not yet optimized. Reflectors are one of the most important devices to improve, asthe efficiencyof the power plant is directly linked to their high performance. Because reflectors are costly and cannot be changed frequently, their reflectivity should be maintained as long as possible.For this reason it is important to study their durability under real operation weather conditions.Natural ageing allows the determination of real lifetime mirrors characteristics and better understanding of their degradation mechanisms. For this investigation, polymeric and glass mirrors were exposed in two Moroccan sites with characteristic weather conditions, one close to the ocean and one in the desert, for more than one year of natural ageing. Different characterization techniques such as optical microscopy and UV-Visible-NIR spectophotometry were used to detect and analyze degradation mechanisms. The obtained results are shown in this paper and acomparison of mirrors behavior is proposed depending on the outdoor exposure sites. It can benoted that the desertic conditions are less aggressive than coastal conditions regarding tophysico-chemical degradation of both investigated mirror materials.

CSP power plants are largely planned in Morocco. However, their components are subject of weather ageing at different areas in the country and thermal storage has a very important impact on power plants operation. For this reason MAScIR foundation and CEA-LITEN collaborate on two studies concerning mirrors ageing under Moroccan weather and an improvement of thermal storage on natural rocks. In this paper, description of the methodology is done and some results are given.

Driven by the rise of the electric automotive industry, the Li-ion battery market is in strong expansion. This technology does not only fulfill the requirements of electric mobility, but is also found in most portable electric devices. Even though Li-ion batteries are known for their numerous advantages, they undergo serious performance degradation during their aging, and more particularly when used in specific conditions such as at low temperature or high charging current rates. Depending on the operational conditions, different aging mechanisms are favored and can induce physical and chemical modifications of the internal components, leading to performance decay. In this article, the identification of the degradation mechanisms was carried out thanks to an in-depth ante- and post mortem study on three high power and high energy commercial 18,650 cells. Li-ion cells were aged using a battery electric vehicle (BEV) aging profile at −20 °C, 0 °C, 25 °C, and 45 °C in accordance with the international standard IEC 62-660, and in calendar aging mode at 45 °C and SOC 100%. Internal components recovered from fresh and aged cells were investigated through different electrochemical (half-coin cell), chemical (EDX, GD-OES, NMR), and topological (SEM) characterization techniques. The influence of power and energy cells’ internal design and Si content in the negative electrode on cell aging has been highlighted vis-à-vis the capacity and power fade.