In the 21th century, renewable energy has to play very important role in socio-economic and industrial development. This paper evaluates the exergy- energy analysis, which is based on the second law of thermodynamics. The triangular solar heater is developed to determine the heat transfer rate, thermal efficiency, exergy efficiency and Bejan number. In addition, we have examined the effects of entropy generation with respect to solar radiation and ambient temperature of air. Absorber plates coated with graphene and copper oxide nano-particles by the different percentages (0.1%, 0.2%, 0.3% & 0.4%) doped into black paint which increases the absorption of heat. The Reynolds number (4500 ≤ 𝑅􀯘 ≤ 22700) varies for the fixed selective coating on absorber plate and mass flow rate. The experimental observations were performed for constant mass flow rate of air ranging from 0.0035kg/s to 0.018 kg/s. The experimental result gives the average thermal efficiency enhancement of 3.58% for 0.3% graphene/CuO-black paint. Entropy generation is more for 0.1% and minimum for 0.3% graphene/CuO-black paint coating. The entropy generation analysis concludes that the entropy generation increases with increasing the mass flow rate. Exergy efficiency enhancement can be found 0.169%for 0.3% with respect to 0.1% graphene/CuO-black paint.