Performance analysis of cost-effective single-slope solar greenhouse dryer for drying of bay leaf (Laurus nobilis) and neem leaf (Azadirachta indica)

Greenhouse dryer (GHD) offers a promising and sustainable alternative to traditional drying methods for agricultural products. However, achieving true sustainability requires an environmentally and economically feasible drying solution. This study investigates the design, operation, economic advantages, and environmental benefits of drying bay leaves and neem leaves at varying load conditions of 100 g, 200 g, and 300 g inside a single-slope greenhouse dryer operating in natural convection in the climate of Northeast India. Results showed that both the crops dried significantly faster in the GHD (5.5-9.5 h) compared to open sun drying (OSD) (7.5-11 h). The GHD drying efficiency ranged from 15.65 % to 25.75 %. Energy efficiency varied within the GHD itself. The upper portion achieved 43.4 %-92.2 % efficiency, while the lower portion ranged from 25.3 % to 78.01 %. Similarly, the energy utilization ratio varied significantly, from 8 % to 83.8 %. Exergy flow of GHD at inlet varied from 4.5 kJ/kg to 22.9 kJ/kg, at outlet varied from 0.3 kJ/kg to 3.9 kJ/kg, while a maximum of 19.32 kJ/kg exergy losses were observed. Environmental and economic parameters were also evaluated. The total embodied energy of the GHD was calculated to be 215.95 kWh. The payback period was 0.91 years, and the energy payback time was even faster at 0.37 years. Over a 15-year lifespan, the GHD is estimated to mitigate 17.40 tonnes of CO2 emissions, with an initial CO2 emission of 14.36 kg associated with its production. Finally, the quality of the dried bay leaves and neem leaves was also assessed, showing that the leaves inside the GHD were of superior quality than those dried using OSD.