Guidelines Accelerated Aging Testing of Aluminum Reflectors for Concentrated Solar Power

This testing guideline specifies the recommended accelerated aging conditions to reproduce realistic degradation mechanisms on aluminum reflectors, which have been observed during a 3 year outdoor exposure testing campaign at 9 exposure sites with 9 different aluminum reflector types (7 of them protected with a SiO2 based sol-gel coating, 2 of them protected by a polymeric coating). Accelerated aging parameters have been derived to simulate the exposure after 3 and 10 years at three reference outdoor scenarios: “extreme desert”, “desert” and “coastal”. The parameters have been achieved by averaging the 9 tested material types. However, if the material to be tested deviates significantly in its chemical composition, it is likely that other degradation mechanisms will be accelerated and the correlation to the outdoor reference scenarios will not apply. Fig. 1 shows the materials to be tested under the scope of this guideline. In any case, the indicated correlation to the outdoor reference scenarios can only be considered as an estimate. For some of the 9 tested materials the correlation applied better than for others. The expected uncertainty is 4.4 % (pp) specular reflectance, ρ, at a wavelength, λ, of 660 nm, an incidence angle, θi, of 15° and an acceptance angle, φ, of 12.5 mrad to simulate 3 years of exposure on the desert and coastal sites. For the “extreme desert” site the expected uncertainty is considerably higher because of the strong dependence on specific abrasion effects on site. The simulation of 10 years of exposure is based on extrapolation of the available outdoor data after 3 years

Evaluation of anti-soiling coatings for CSP reflectors under realistic outdoor onditions

Soiling of solar reflectors affects their reflectance and has a direct impact on the power output of concentrated solar power (CSP) plants. One way to minimize the efficiency losses is the implementation of anti-soiling coatings on the reflector surfaces. This method is being studied for the past decade, but has not been successfully commercialized yet. The purpose of the coatings is to reduce soiling and improve the washability of the reflectors. In this work results are presented from an extensive outdoor campaign of two potential anti-soiling coatings under realistic conditions at a representative CSP site in southern Spain. Nearly six years of outdoor data are available, which makes this campaign the longest published on this type of coatings. Regular cleaning and reflectance measurements were performed during the exposure and conclusions about the performance and durability of the coatings are drawn. It is shown that in the initial state the coatings show an advantageous behavior, resulting in higher reflectance during outdoor exposure due to less soiling and better cleaning of the reflectors. The second main finding is that durability is an important issue for the implemented coatings, as their properties degrade over time resulting in lower reflectance values after several years of exposure compared to conventional glass reflectors

Deckungsbeiträge

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Advanced cyclic accelerated aging testing of solar reflector materials

ABSTRACT: Lifetime prediction methods for the components of concentrated solar power (CSP) plants have been in the focus of interest of manufacturers and plant developers for the past years. Recently, an accelerated aging standard for solar mirrors was published by the Spanish AENOR committee [1]. This standard allows performing comparative testing but it is not suited to derive meaningful life-time estimations. Firstly, the testing defined in the standard is not aggressive enough to produce significant degradation on most of the materials and secondly, it has been shown that the passing of these tests does not guarantee a high durability during outdoor exposure [2]. These findings have proven the need for the investigation of more realistic procedures. To provoke the mechanisms that are detected during outdoor exposure, a more realistic application of environmental stresses is being investigated. In this work a series of tests is conducted in which several weathering stresses are combined and applied in a cyclic manner. Some of these cycles have shown to correlate better with real outdoor behavior.N/

MVA-based H5N1 vaccine affords cross-clade protection in mice against influenza A/H5N1 viruses at low doses and after single immunization.

Human infections with highly pathogenic avian influenza viruses of the H5N1 subtype, frequently reported since 2003, result in high morbidity and mortality. It is feared that these viruses become pandemic, therefore the development of safe and effective vaccines is desirable. MVA-based H5N1 vaccines already proved to be effective when two immunizations with high doses were used. Dose-sparing strategies would increase the number of people that can be vaccinated when the amount of vaccine preparations that can be produced is limited. Furthermore, protective immunity is induced ideally after a single immunization. Therefore the minimal requirements for induction of protective immunity with a MVA-based H5N1 vaccine were assessed in mice. To this end, mice were vaccinated once or twice with descending doses of a recombinant MVA expressing the HA gene of influenza virus A/Vietnam/1194/04. The protective efficacy was determined after challenge infection with the homologous clade 1 virus and a heterologous virus derived from clade 2.1, A/Indonesia/5/05 by assessing weight loss, virus replication and histopathological changes. It was concluded that MVA-based vaccines allowed significant dose-sparing and afford cross-clade protection, also after a single immunization, which are favorable properties for an H5N1 vaccine candidate

Effect of long term outdoor exposure on antisoiling coatings for solar reflectors

Results of the outdoor exposure campaign of two newly developed anti-soiling coatings for CSP mirrors are presented in this paper. Samples of coated mirrors were exposed for two years under realistic outdoor conditions and the application of two different cleaning techniques was investigated. Mirror samples were analyzed during exposure and their reflectance and cleanliness were measured. The performance of the anti-soiling coated mirror samples was compared to conventional uncoated mirrors. Depending on the selected combination of coating and cleaning technique, an advantage or disadvantage was observed over the exposure duration. One coating presented an overall cleanliness gain of 0.008 with pressurized water cleaning, due to its superior anti-soiling behavior, while presenting a negative gain of -0.009 with contact cleaning, due to its poor durability. The other coating showed a worse anti-soiling behavior, with a negative gain of -0.005 for pressurized water cleaning, due to its poor washability, and a positive gain of 0.005 with contact cleaning

Standardizing Accelerated Aging Testing Conditions for Silvered-Glass Reflectors

To assure the quality of accelerated aging tests for solar concentrators, their standardization is crucial. It guarantees the employment of adequate testing, measurement and characterization procedures and the comparability between results. A committee of the Spanish AENOR standardization agency is working on the draft “Reflector Panels for Concentrating Solar Technologies”. This work focuses on the evaluation of the procedures defined in this standard. The reflector material from the Japanese company Nishio Glass Mirror Co., which showed severe degradation after 7 years of outdoor exposure in Abu Dhabi, is tested according to the AENOR standard to check if its poor outdoor performance could have been predicted by accelerated aging testing. However, after completion of the accelerated tests, in some cases even for considerably longer test durations than the minimum required by AENOR, no considerable degradation was detected. The results suggest that the proposed testing program by AENOR is not aggressive enough to identify material failure. Ways to improve the current standard are proposed through development of more realistic tests

Oldest Ice in Antarctica – the 3d continental ice sheet modelling perspective.

The ongoing quest to find the oldest continuous ice core in Antarctica draws on the expertise of multiple disciplines. Here we present our efforts to inform on the location of potential future drilling sites by 3d continental ice sheet modelling. We present the results of an ensemble of ice sheet model simulations spanning the last 2 million years utilizing a variety of different model setups and boundary conditions including new radar derived bedrock elevation. In our analysis we focus on the physical properties and ice dynamics around the major drill sites such as Dome Fuji and Dome C and discuss the effects of the ice sheets history on the present day flow regime. By using a continental setup and applying a transient forcing created from paleo climate modelling studies and ice core data we are able to take a holistic view of Antarctic Ice Sheet dynamics and its impact on the vertical stratigraphy around the East Antarctic ice domes

UV degradation of primary mirrors in outdoor exposure and accelerated aging

The objective of this work is to quantify de degradation originated by UV radiation and temperature in silvered-glass reflectors exposed in three locations with high solar irradiance and to replicate the degradation mechanisms observed in outdoors through accelerated aging tests