Smallholder farmers in Ethiopia face significant postharvest losses, particularly with perishable products like onions. Solar dryers offer a promising solution, though their adoption is still early. This research designs, manufactures, and evaluates a box-type direct solar dryer for onions (Allium cepa L.) in the Geray Irrigation Area, Amhara National Region State, Ethiopia. Drying performance was evaluated numerically and experimentally, comparing a solar dryer with passive convection and a solar collector to an open-sun dryer. The box-type solar dryer showed 20% efficiency and a mass flow rate of 0.0074 kg/hr, compared to the open-sun dryer's 16.4% efficiency. The solar dryer reduced onion moisture content from 87% to 7.5% in 77 hours, with a drying rate of 0.0162 kg/hr, drying 21% faster than the open-sun dryer’s rate of 0.0124 kg/hr. The solar dryer maintained uniform temperature distribution, with the drying chamber 3 to 5 °C warmer than the ambient temperature, transferring an average of 7265J of heat energy. This makes direct solar dryers an eco-friendly and cost-effective technology for reducing postharvest losses. Drying data were fitted to seven mathematical models to validate and optimize efficiency, with the Page model being the most suitable. Model efficacy was confirmed by comparing R², chi-square (χ²), and RMSE values between observed and predicted moisture ratios, validating the Page model's accuracy in describing onion drying behaviour. Utilizing locally available materials renders this dryer economically feasible for rural communities.Generally, the box-type direct solar dryer offers a practical and efficient means of onion preservation, fostering sustainability. Keywords: box type solar dryer, onion, drying rate, moisture, mathematical model