Optical and Thermal Performances of Black Nickel and Black chrome Selective Coating based Solar Thermal Collectors
Authors: Bhim P. Kafle, Nayan Acharya, Sunil Lohani, Manoj Bista, Ritesh Dev
Abstract— Flat plate solar water heating system (SWHS) with black paint based solar absorber layer is one of the widely used solar thermal technologies in Nepal and other south Asian regions to meet the thermal energy needs. Although, easier to fabricate and robust than the vacuum tube collectors, due to higher thermal emissivity, poor stability against intense solar radiation and environment of black paint absorber, SWHS’s practical application has been decreasing gradually. To address these issues, in the present contribution, we have produced black nickel and black chrome selective coating based solar thermal collectors (STCs) deposited on Cu and Al substrates and studied their optical and thermal performances in Nepalese climatic conditions. The optical properties of STCs, prepared by electro-deposition, were studied by measuring optical reflectance using spectrometric reflectometer from 0.2µm – 1.1µm and IR spectroscopy from 1.1 µm to 4.5 µm. The STCs were optimized by varying deposition time and electric current during electro-deposition process. Both types of coating yielded absorption above 95% in the visible and NIR regions, black chrome being slightly more superior with 98 % absorption than that of black nickel. In case of black nickel coating, deposition time 3 min. – 9 min. and current density in the range of 2 – 6 mA yielded optimal absorption and emission properties. However, in case of black chrome coating, for achieving good quality coating we had to apply almost 300 – 500 times higher electric current density than that of values applied to prepare black nickel STCs of same size. Photo-thermal response of the STCs were extracted from the measured reflectance curves and also from measured surface temperature of the STCs. While the black chrome samples are still under investigation, our preliminary results of black nickel STCs deposited within the above controlling parameters yielded temperature as high as 85 ˚C. From these observations, considering the high cost of chromium coating and its toxicity, it may be inferred that black nickel coating may be the appropriate solution for improving the quality of FP-SWHS.
Keywords— Selective coating, Black nickel, Black chrome, solar thermal collector, solar water heating system
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Published In: International Conference on Role of Energy for Sustainable Social Development in ‘New Normal’ Era (RESSD-2020)
Date of Conference: 28th-29th December 2020
Conference Location: Kathmandu, Nepal
Publisher: IEEE Power and Energy Society Nepal Chapter
Cite the paper as:
B. P. Kafle, N. Acharya, S. Lohani, M. Bista, R. Dev, “Optical and Thermal Performances of Black Nickel and Black chrome Selective Coating based Solar Thermal Collectors”, International Conference on Role of Energy for Sustainable Social Development in ‘New Normal’ Era, 28th-29th December 2020, Kathmandu, Nepal