Low-Cost Solar Selective Absorbers by Electrodepositing Technique

Abstract

In recent years interest has increased in the production and characterization of high-thermal-stability selective surfaces that have high solar absorptance (α) and low thermal emittance (ε). Different techniques such as thermal evaporation, spray pyrolysis, chemical techniques, ion-beam sputtering, etc. have been utilized to prepare several coatings of high α and low ε values. Solar energy is inexhaustible source of energy. The power from the sun intercepted by the earth is larger than the present consumption rate on the earth. This makes it one of the most promising of the unconventional energy sources. The objective of this research is to study solar selective coatings used in solar thermal collectors, i.e., black nickel coatings using copper substrates. In this work, we investigated the preparation and characterization of black nickel (BN) coatings used in solar thermal collectors. The overall goal has been to obtain efficient absorbers by using low-cost techniques. Reflectance measurements were used to evaluate both (α) and (ε) of the coatings. The measurements of total or diffuse reflectance of samples were performed with instruments equipped with integrating spheres. Electrodeposited (ED) Ni-black on Cu substrate has a moderate selectivity (α/ε = 2.63, when α = 0.95). The durability tests were carried out in the form of elevated temperature exposure in air (250 °C), temperature cycling (30–100 °C), and humidity tests (up to 90% RH). The coatings have been re-characterized after ageing tests, using spectrophotometry and other techniques, such as X-ray techniques. Durability testing of the ED Ni-black coatings indicates that they are sensitive to humidity testing (HMT), and significant changes in (α) or (ε) also occurred during thermal ageing. ED of BN on Cu substrate showed degradation toward the durability tests. In this research, low-cost solar selective absorbers (ED of BN on Cu) have been obtained. And we tried to get rid of some structures or materials which are harm to the environment, that is, car batteries, by using lead sheets [from recycled car battery] as an anode during ED of BN coating.