Norut Northern Research Institute Narvik AS

Narvik, Norway

Norut Northern Research Institute Narvik AS

Narvik, Norway
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Chen Z.,Norut Northern Research Institute Narvik AS | Chen Z.,University of Tromsø | Bostrom T.,University of Tromsø
Solar Energy Materials and Solar Cells | Year: 2016

A novel tandem type of spectrally selective solar absorber using a homogeneous multi-walled carbon nanotube (MWCNT) coating as absorbing layer has been fabricated. The MWCNT absorber was prepared by facile and efficient electrophoretic deposition and exhibited good spectral selectivity. To assess the durability of the MWCNT absorber, condensation and thermal stability accelerated ageing tests were performed according to the international standard ISO 22975-3: absorber surface durability. The primary results revealed that the MWCNT absorber had a great thermal stability but was not resistant to condensation since the porous MWCNT coating permits water migration through the pores down to the aluminum substrate which as a result oxidizes, confirmed by the analysis of Energy Dispersive Spectroscopy. Therefore, different types of thin films such as dense silica, silica-titania were deposited on top of MWCNT absorbers as protective layer to prevent the penetration of condensed water. Although all MWCNT absorbers coated with protective layer had little or no gain in spectral selectivity compared to those without protective layer, accelerated ageing tests indicated that the long-term durability was significantly improved. In thermal stability test, all protective layer coated MWCNT absorbers showed similar performance to the uncoated samples and had a negligible or even negative performance criterion (PC) value after 600 h testing. In condensation test, the obtained PC values were 0.002, 0.013 and 0.014 for silica, 70/30 and 50/50 silica-titania film coated MWCNT absorbers respectively. All the PC values were less than 0.015 after 600 h of accelerated ageing tests, which confirmed that the absorbers were qualified according to ISO 22975-3. © 2016 Elsevier B.V.


Chen Z.,Norut Northern Research Institute Narvik AS | Chen Z.,University of Tromsø | Bostrom T.,University of Tromsø
Solar Energy Materials and Solar Cells | Year: 2016

Three types of carbon nanotubes (CNT) have been investigated regarding their suitability as spectrally selective solar thermal absorbers. The CNT coatings were electrophoretically deposited on aluminum substrates using kinetically stable CNT aqueous suspensions, of which two CNT aqueous suspensions (N-CNT and P-CNT suspensions) were prepared as part of this study and the third one (T-CNT suspension) was purchased. The CNT suspension systems are simple and consist of only CNTs, DI water and a cathodic surfactant. Heat treated CNT coatings are visibly uniform. The CNT coating thickness, surface morphology and reflectance of CNT absorbers were characterized by White Light Interferometry, Scanning Electron Microscopy and Spectrophotometry, respectively. T-CNT absorber achieved a solar absorptance α of 0.79 and a thermal emittance ε of 0.14. N- and P-CNT absorbers achieved better spectral selectivity, with α=0.90 and ε=0.14 for N-CNT absorber, α=0.90 and ε=0.13 for P-CNT absorber. The effect of CNT coating thickness, deposition parameters and peak heat treatment temperature on the spectral selectivity were studied. For these CNT suspension systems, the thickness and the heat treatment peak temperature are the key factors to achieving a good spectral selectivity. © 2015 Elsevier B.V. All rights reserved.

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