NECSO

Nanoscale Enhanced Characterisation of SOlar selective coatings

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 Obiettivo del progetto (Objective)

'Optical coatings are commonly deposited over large areas on different substrates: glass, metals (steel, aluminium...) or polymeric foils (PET...). Production processes involve normally large machinery including many times roll-to-roll processes to deposit multilayers over several square meters of substrates. However, properties of these coatings depend strongly on nanometric properties: composition, crystallography, nanostructure, roughness, homogeneity... Solar selective coatings are considered a special case of optical coatings combining several layers with different properties, mainly: antireflection, solar absorbance and infrared mirror. Nowadays the most demanding solar selective coatings are those used in tubes of high temperature parabolic trough solar collectors. Coatings have to operate in an aggressive environment (temperatures above 400ºC, thermal cycling) during 20-25 years. Besides, further developments require higher temperatures, improved scratch resistance and working under oxidant atmospheres (small quantities of water vapour and oxygen). In order to get significant advances in this field it is essential to have:

1. Nanoscale structure related requirements (nanoroughness, nanohardness, crystallography, composition, vibrational modes) and the correlation with performance requirements: optical and, more important, life expectancy. 2. Standard characterisation and degradation protocols to serve as a powerful tool to coating developers, producers and end users for life prediction and to push the collector parameters (temperatures and environment) to higher efficiency parameters.

The main idea behind this NECSO project is to provide tools to the end users namely solar plants builders, to guarantee that the selective coating will work properly during 20 to 25 years. Novel experimental methods for testing materials under extreme conditions (temperature and radiation) are needed providing a deeper understanding of the interaction of electromagnetic radiation with nanomaterials, as basis for design of new spectrally selective absorber coatings. Nanoscale characterisation (roughness, AFM, nanoindentation, scratch-adhesion, crystallography by FESEM-EBSD, Raman, RX, XPS, etc) will correlate the nanostructure parameters with coating performance. The resulting outcomes are expected to contribute significantly to the infrastructure of the solar energy research, development and industrial activities worldwide. Additionally, the designed testing protocols should help coating developers to compare available layers and newly designed ones, with standard procedures. Finally, testing procedures will also be of utter importance to have a fast quality control on the coatings, typically in 4 meter tubes, over some tens of kilometres in a common cylinder parabolic solar plant.'

Introduzione (Teaser)

Harnessing the Sun's unlimited (for all practical purposes) energy supply is one of the most promising alternatives to combustion of fossil fuels. Improved characterisation of coatings for concentrating solar power (CSP) systems will speed development.