Impact of Cover Material on Greenhouse Solar Dryer Efficiency: A Case Study on Mint Leaves

Solar drying is a sustainable option for preserving horticultural products, but cover material strongly affects thermal behavior and drying efficiency. This work experimentally compares two identical natural-convection parabolic greenhouse solar dryers operated side-by-side in Ghardaïa (Algeria): one covered with polyethylene (PE) and the other with polycarbonate (PC). Drying kinetics were analyzed using Fick’s second law and empirical thin-layer models, effective moisture diffusivity was estimated, and internal temperatures were predicted using machine-learning models (feedforward ANN, NAR, and NARX) driven by ambient inputs. The PC-covered dryer exhibited higher internal air and absorber temperatures (by 15.5 and 18.8%, respectively) and shortened mint drying time by 68% relative to PE. The Midilli–Kucuk model best captured the drying curves, and the NARX architecture yielded the most accurate temperature forecasts (R ≈ 0.9998; MSE < 0.11). Overall, polycarbonate cladding materially enhances thermal retention and drying performance compared with polyethylene, while ANN-based prediction—especially NARX—provides reliable thermal behavior estimates that can support control and optimization of solar dryers in arid climates.