Energy analysis of drying basil (Ocimum basilicum) leaves in an active greenhouse solar dryer

The need for better utilization of solar greenhouses during summer in the hot climate conditions of Mexico led to the development of the concept of active greenhouse solar dryers. The objective of this research was energy analysis of an active greenhouse solar dryer for basil leaves drying. The effect of variable solar irradiation on drying was accounted for by monitoring instantaneous effective diffusivity. Our experiments showed that the effective diffusivity of basil leaves increased with solar irradiation 100 times from 0.08 × 10⁻¹⁰ m²/s in the morning to 8.11 × 10⁻¹⁰ m²/s at the solar noon. The air temperature in the solar dryer was ranging from 42 to 48°C at the solar noon with solar irradiance of 806 W/m². The energy required for moisture evaporation of basil leaves depended on the air temperature, reaching 337.6 kJ/mol just before solar noon. The amount of energy available in the solar dryer at noon was 124.14 MJ, much exceeding the energy required for basil leaves drying (16.94 MJ). The results of our study showed the feasibility of basil solar drying. The predictive model of basil drying in an active greenhouse solar dryer was developed. Practical Applications: The feasibility of adaptation of an active greenhouse solar dryer to variable solar irradiance to ensure energy-saving drying is a contribution in the field DSG's. For this purpose, we propose to evaluate the energy transferred to the solar greenhouse, the instantaneous effective diffusivity of basil leaves accounting for air thermophysical properties Cp(T_a,x), k(T_a,x), as well as material thermophysical [Cp(T_i,x), k(T_i,x)] and mass transport properties Deff, (t) as time-dependent values. These, leads to monitoring the drying process under uncertain weather conditions, which allows to minimize risks of product quality loss and introduce advanced energy-saving control of active greenhouse dryers. Furthermore, the greenhouse driers can be uses as a cheap technology, with low energetic cost.