Optical, structural and thermal performances of black nickel selective coatings for solar thermal collectors

In the present study, the possibility of devising efficient and durable black nickel selective coating based solar thermal collectors (STCs) at ambient temperature was explored. For this, NASA electrochemical bath initially formulated by Peterson and Lin [Final Report: NASA-CR-149928, 1976] was employed. Quality of the STCs were optimized by evaluating pH, temperature, electric current density (I-d) and deposition time (T-d) dependence of optical, structural and thermal performance of the black nickel coating on the copper sheets and tubes. The optical measurements in the UV-Vis-NIR and NIR-MIR ranges inferred us that at pH approximate to 5.8, temperature in the range 20-25 degrees C, 2 mA/cm(2) <= I-d <= 4 mA/cm(2) and 5 min. <= T-d <= 7 min. result in reasonably good black nickel coatings with optimal selectivity factor. Moreover, from the analysis of XRD spectra, for the first time we observed the significantly larger crystallites size of coatings on Cu sheets than that of the coating on tubes. Observed thermal performances (evaluated by measuring the collector efficiencies) indicate that the electro-deposited black nickel-based STCs were superior by more than 20% over black paint based STCs.

Automated summary

This study explored the possibility of developing efficient and durable black nickel selective coating solar thermal collectors at ambient temperature. The quality of the collectors was optimized by evaluating the effects of pH, temperature, electric current density, and deposition time on the optical, structural, and thermal performance of the black nickel coating. The results showed that the electro-deposited black nickel-based collectors had superior thermal performance compared to black paint-based collectors.