Environmental and energetic exergetic sustainability of stevia leaf drying in a PVT indirect solar dryer with variable airflow and tray levels

Abstract

Abstract During the current study, Stevia rebaudiana leaves were dried using a photovoltaic thermal–indirect solar dryer (PVT-ISD), and the influence of tray position inside the drying chamber was assessed using six trays under two airflow rates (0.08 and 0.13 m 3 /s) with a uniform layer thickness of 3 cm. The fastest drying occurred on the lowest tray, closest to the hot air inlet, particularly at the higher airflow rate, achieving a final moisture content of 5.7%. Energy analysis showed that thermal efficiency of the solar collector reached up to 55.7% at the higher airflow. Exergy analysis supported this improvement, with maximum exergy efficiency of the solar collector increasing to 14.68%. Conversely, the drying room performed better at the lower airflow, reaching a maximum exergy efficiency of 37.89%. Sustainability indicators revealed slight improvements in the solar collector but declines in the drying room at higher airflow. Environmental indicators further demonstrated enhanced performance of the solar collector at higher airflow, with maximum reductions observed in the environmental destruction coefficient (19.6%), environmental impact factor (20.6%), and environmental effect factor (20.4%).