Energy and enviro-economic (3E) assessment of greenhouse solar dryer (GHSD) for drying and quality evaluation of medicinal Ocimum sanctum leaves: A sustainable path for preservation

This article presents an experimental analysis of greenhouse solar dryer (GHSD) under natural and forced convection for shelf storage of Tulsi (Ocimum sanctum) leaves, and the obtained results are compared with conventional open sun drying and shade drying to determine the optimal drying method. The GHSD, being capable of raising the interior temperature 15-25 degrees C higher than the ambient temperature, took only 2.5 and 2.0 h for drying of 100 gm Tulsi under natural and forced convection mode compared to 5.0 and 7.0 h in open sun and shade drying, respectively. The peak drying rate under natural and forced convection GHSD drying was 0.57 and 0.70 gm of water per gram of dry solid, while dryer efficiencies were estimated as 14% and 16%, respectively. The findings revealed a reduction in drying time by 50% and 60% compared to open sun drying, and by 64% and 71% compared to shade drying under natural and forced convection, respectively. The calculated energy payback time (EPBT) was 0.78 years with earned carbon credit of US$ 60.22 for 10 years of intended life span while the economic payback period was 1.3 years associated with potential saving of Rs 1,11,916. In quality evaluation, total phenolic and flavonoid content (73.39 mg GAE/g and 5.09 mg QE/g) along with antioxidant potential (IC50 value: 55.09 mu g/mL) have been recorded higher for the leaves dried in GHSD compared to open sun drying. The findings established a sustainable, eco-friendly and economical path for the blooming herbal medicine industry.