Hybrid Al2O3-MWCNT nano-coatings for advanced solar thermal systems: enhancing energy conversion and sustainability

• Hybrid Al 2 O 3 /MWCNT coating boosts ETC thermal efficiency to 82.7%. • Achieved 93.6 °C fluid temperature and 623.1 W heat absorption in ETCs. • Enhanced heat transfer coefficient of 561.9 W/m 2 K with 2 mm coating. • Exergy efficiency improved to 20.7%, ensuring better energy utilization. • Annual CO 2 reduction cost of $64.71 with 548.1 kWh energy output. Evacuated tube collectors (ETCs) are advanced solar thermal systems designed to capture and retain solar energy for heating, offering reliable performance even in low-temperature environments. This study is motivated to improve the thermal performance and efficiency of evacuated tube solar collectors by developing a durable, high-absorptivity coating. Conventional coatings often suffer from heat loss and limited energy conversion. By introducing a hybrid Al 2 O 3 –MWCNT nano-enhanced coating, this study aims to enhance solar absorption, thermal conductivity, and overall energy utilization, contributing to more efficient and sustainable solar energy systems. The hybrid nano-enhanced coatings were applied using the spray pyrolysis technique at 300 °C, with two thickness variations: 1 mm and 2 mm. The results reveal that the 2 mm hybrid Al 2 O 3 /MWCNT coating significantly enhances ETC performance. The maximum fluid temperature reached 93.6 °C, with a heat absorption of 623.1 W. The heat transfer coefficient improved to 561.9 W/m 2 K, achieving a thermal efficiency of 82.7 %. Exergy efficiency increased to 20.7 %, indicating better energy utilization. The enviro-economic analysis demonstrated an energy output of 548.1 kWh, CO 2 savings of 5.12 kWh/$, and an annual CO 2 reduction cost of $64.71. These findings highlight the potential of hybrid nano-coatings in optimizing solar thermal systems for sustainable energy solutions.