Improving Cost-Efficiency of an Indirect Solar Dryer in Nepal

Sammanfattning

Agriculture plays a central role in the economy of Nepal, serving as a major source of income and employment for much of the population. This study was conducted as part of the Solar Food: Reducing Post-harvest Losses project, a collaboration between Lund University, Kathmandu University, and The Royal Institute of Bhutan. The project aims to design solar dryers to reduce post-harvest losses in rural Nepal and Bhutan. In this study, two prototypes, the Δ-dryer and the newly developed Γ-dryer, were investigated under outdoor conditions at Kathmandu University. The experiments included full-load drying tests and systematic modifications of components, such as removing the internal fan, heat exchanger, or insulation, adding a heating element, and changing the collector cover from glass to plastic. Drying performance was assessed through drying rate and uniformity, while economic feasibility was evaluated via payback period and sensitivity analysis. To obtain more reliable drying-rate results, a multiple linear regression analysis was conducted to minimize the impact of variable weather conditions on the Δ-dryer experiments. There was a lack of data points to do the same for the Γ-dryer. The results showed that removing insulation in both dryers provided a low-cost option without significantly affecting performance or payback time. Adding a heating element increased capital and running costs but resulted in faster drying rates, more uniform drying, and a shorter payback period. The regression analysis indicated that for the Δ-dryer, polycarbonate glazing could outperform the glass cover, although further studies are needed on sheet thickness and sourcing from cheaper suppliers. The Δ-dryer configurations without the fan and without the heat exchanger exhibited less uniform drying and reduced drying rates, making them economically unfeasible. The Γ-dryer design addresses earlier issues raised by farmers: it is more portable and has higher capacity. Experiments showed that the Γ-dryer achieves faster drying rates than the Δ-dryer. Due to its higher cost, the Γ-dryer is recommended for farmers with larger production volumes who require higher capacity and can make additional investment.