Enhancement of absorptance of absorber surfaces of a flat plate solar collector using black coating with graphene

The effect of graphene-based selective coating on the absorber plate of a flat plate solar collector (FPSC) is investigated experimentally. The absorber plate is a mild steel substrate with a mixed coating of graphene and black paint. Three samples are prepared, the different ratios of black paint to graphene being 1:1, 1:2, and 1:3. The average absorptivity of the graphene and black paint coated samples are determined to be about 0.87 and 0.82, respectively. The absorptance capacity of the collector plate surface for shortwave solar radiation is found to increase by about 6.1% due to graphene presence. Real-time experiments are conducted to determine the thermal efficiency of the FPSC using air as the heat transfer fluid. The absorber surface with 1:3 ratio of black paint and graphene coating is observed to have an average thermal efficiency of 36.65% for the airflow rate of 0.2 kg/h, which is about 6.25% more than that of the standard black paint coating because of higher thermal conductivity of graphene particles. The provision of a serpentine path in the absorber plate is useful in eliminating additional absorber tubes or fins.