Simplified analysis of solar-weighted specular reflectance for mirrors with high specularity

Fernández-García, Aranzazú; Sutter, Florian; Heimsath, Anna; Montecchi, M.; Sallaberry, Fabienne; Peña-Lapuente, Adrian; Delord, Christine; Martínez-Arcos, Lucía; Reche-Navarro, Tomás Jesús; Schmid, Tobias; Heras, Carlos

doi:10.1063/1.4949216

Cited by 9 publications

(13 citation statements)

References 7 publications

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“…Although this approximation is appropriate for reflectors with high specularity in the whole solar spectrum, new research has demonstrated that for some innovative reflector materials a valid and adequate procedure is still missing. Research work of the last few years regarding the reflectance measurement procedure [13]- [15] and instruments [16]- [18] to assess solar reflector materials has advanced significantly.…”

Section: Introductionmentioning

confidence: 99%

“…It deserves to be mentioned the activities ongoing in several working groups during the last decade to stablish a proper protocol to measure the reflectance of concentrating solar reflector materials. A group of experts in the field of optical characterization of solar reflectors has been working since 2009 as members of the SolarPACES Organization (which belongs to the International Energy Agency, IEA) to create a reflectance measurement guideline [9], [15]. Several versions of the guideline have been already published [10].…”

Section: Introductionmentioning

confidence: 99%

“…It is not advisable to use the specular exclusion port to measure the diffuse reflectance and then calculate the specular reflectance by subtracting the diffuse reflectance from the hemispherical reflectance. The exclusion port is usually too large, thus the corresponding φ obtained (around 116 mrad[15]) is not representative of performance for solar concentrating applications[29]. Also, the incident light is not collimated which makes it difficult to determine φ.…”

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confidence: 99%

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Equipment and methods for measuring reflectance of concentrating solar reflector materials

Fernández-García¹,

Sutter²,

Martínez-Arcos³

et al. 2017

Solar Energy Materials and Solar Cells

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The proper optical characterization of solar reflector materials is a challenging task. Although several commercial instruments exist to measure reflectance, they have been developed for other applications and often do not meet all the specific requirements demanded by the solar thermal industry. In particular, the characterization of solar reflectors involve the complete solar spectral wavelength range, an incidence angle range from near normal to 70°and most importantly a very narrow acceptance angle range from near specular to 20 mrad. The accurate measurement of reflectance as a function of all the previously mentioned parameters has not been commercially implemented. This paper reviews the different alternatives to measure reflector materials, describes reflectance models used to approximate the missing information and presents current research work on prototype reflectometers to fill the gap.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Equipment and methods for measuring reflectance of concentrating solar reflector materials

Fernández-García¹,

Sutter²,

Martínez-Arcos³

et al. 2017

Solar Energy Materials and Solar Cells

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“…Several agreements reached by this group are collected in a document in which current version is titled "Parameters and method to evaluate reflectance properties of reflector materials for concentrating solar power technology" (hereinafter "SolarPACES Reflectance Guideline") [15]. This document has been used as a reference by the CST community for the last years and it has even been mentioned by the first standard published about solar reflectors' durability testing, the UNE 206016:2018 [16], as the measurement method to assess durability experiments.The measurement protocol described in this guideline, in order to measure new and clean solar reflectors, has proven to be very accurate and easy-to-use for any laboratory or company equipped with conventional commercial instruments [17,18]. However, the proposed conventional method used to characterize aged and/or soiled reflector samples is insufficient and inaccurate since only some specific spots of the samples are assessed and it does not take into consideration θ i and ϕ dependence.…”

mentioning

confidence: 99%

“…The measurement protocol described in this guideline, in order to measure new and clean solar reflectors, has proven to be very accurate and easy-to-use for any laboratory or company equipped with conventional commercial instruments [17,18]. However, the proposed conventional method used to characterize aged and/or soiled reflector samples is insufficient and inaccurate since only some specific spots of the samples are assessed and it does not take into consideration θ i and ϕ dependence.…”

mentioning

confidence: 99%

Advanced Analysis of Corroded Solar Reflectors

Buendía-Martínez

Fernández-García

Sutter³

et al. 2019

Coatings

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The corrosion of the reflective layer is one of the main degradation mechanisms of solar reflectors. However, the appropriate assessment of the corroded reflector samples is not accomplished by the current analysis techniques. On the one hand, the reflectance measurement protocol of non-damaged solar reflectors for concentrating solar thermal technologies is widely addressed in the SolarPACES reflectance guideline. However, this methodology is not adequate for reflectors whose surface is partially corroded by many kind of corrosion agents. In this work, a new measurement technique to properly assess corroded samples was developed. To check the usefulness of the method, several damaged samples (subjected to two accelerated aging tests) were evaluated with the conventional technique and with the improved one. The results showed that a significant discrepancy is observed between the two methods for heavily corroded samples, with average reflectance differences of 0.053 ppt. The visualization of the reflector images illustrated that the improved method is more reliable. On the other hand, both the corrosion products formed and the corrosion rates were identified after each corrosive test. The chemical atmosphere significantly affects the products formed, whereas the corrosion rates are influenced by the test conditions and the reflector quality.

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The effect of incidence angle on the reflectance of solar mirrors

Sutter¹,

Montecchi

Dahlen³

et al. 2018

Solar Energy Materials and Solar Cells

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Solar reflectors for Concentrating Solar Technologies require a high reflectance in the terrestrial solar spectrum (280 -4000 nm). Besides the wavelength, the reflectance of solar mirror materials is also dependent on the incidence angle of the incoming sunlight. The commonly used measurement equipment measures the reflectance at fixed near-normal incidence angles, typically between 8° and 15°. In this work, the annual incidence angle frequency distribution has been calculated for a LS3/Eurotrough-type parabolic-trough collector located at different sites, and for the heliostat field of the solar tower system CESA-1 located at the Plataforma Solar de Almería in Tabernas, southern Spain. It was found that the most frequent incidence angles registered in the solar field are quite higher than the ones at which reflectance is measured with state of the art instruments, obtaining mean incidence angles in the range of 28 to 35° depending on the type and location of the solar field. A methodology to predict the off-normal reflectance of silvered-glass mirrors based on near-normal reflectance and transmittance measurements of the uncoated glass is presented. The complex refractive index of 2, 4 and 5mm thick solar glass and the deposited silver was determined and used to model the solar weighted reflectance of silvered-glass mirrors at different incidence angles. The model was compared to experimental measurements. For this purpose, the Spectral Specular Reflectometer (S2R) has been improved and updated with a polarizer crystal to measure reflectance at perpendicular (s-pol) and parallel (p-pol) polarizations up to incidence angles of θ=70°. Eight solar mirror materials (three silvered-glass mirrors of different glass thicknesses, two anti-soiling coated glass mirrors, two enhanced aluminum reflectors and a silvered polymer film) have been measured over a broad range of incidence angles and the results have been weighted with the annual incidence angle frequency distribution. The obtained incidence angle-weighted reflectance is a suited parameter to compare the efficiency of solar mirror materials taking into account their use in a specific collector type and location.

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Simplified analysis of solar-weighted specular reflectance for mirrors with high specularity

Cited by 9 publications

References 7 publications

Equipment and methods for measuring reflectance of concentrating solar reflector materials

Equipment and methods for measuring reflectance of concentrating solar reflector materials

Advanced Analysis of Corroded Solar Reflectors

The effect of incidence angle on the reflectance of solar mirrors

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