Recycling Aluminium Beverage Cans for Renewable Heating: Design and Evaluation of a Double-Pass Beverage Can Solar Air Heater for Greenhouse Applications

This study evaluated the performance of a low-cost, double-pass beverage can solar air heater (BCSAH) constructed from recycled aluminium beverage cans for potential greenhouse heating, supporting United Nations Sustainable Development Goal 7 (Affordable and Clean Energy). The BCSAH was built with plywood, polystyrene insulation, and a plexiglass cover, incorporating 192 recycled 500 ml cans as the absorber plate. Tests were conducted in Pietermaritzburg, South Africa, under winter conditions at three tilt angles (26°, 31°, 36°) based on photovoltaic winter recommended tilt angles. Key parameters measured included outlet temperature, solar irradiance, thermal efficiency, and heat distribution, using 14 K-type thermocouples, a pyranometer, and an anemometer at a constant air mass flow rate of 0.02 kg·s⁻¹. The system achieved significant temperature gains, with second-pass air reaching 128.8°C and maximum outlet temperatures of 94.36 ± 1.35°C. Although tilt angle did not yield statistically significant temperature differences, thermal efficiency increased from 63.36 ± 9.06% for 26° to 67.31 ± 11.78% for 36°. The results highlight the potential of recycled BCSAH to reduce fossil fuel use in greenhouses and other agricultural applications such as soil sterilisation, juice/milk pasteurisation, and pest control. The unit was cost-effective (R 3,470), aligning with circular economy principles and renewable energy goals. Design improvements are suggested, including thinner insulation such as phenolic foam, internal baffles for airflow optimisation, and solar panel integration for off-grid monitoring. Future research should explore multiple units, conduct a broader airflow analysis, and conduct testing across different regions. Integration with heat storage is also recommended.