A significant proportion of the global onion harvest is annually lost as a consequence of excessive production and insufficient processing techniques. Concurrently, the practice of drying represents a time-honored method of processing agricultural commodities, which has been historically regarded as a means to extend the shelf life of food products. In this context, the present study employed a photovoltaic-thermal solar dryer for the drying of white onions. In order to optimization of onion specimens, the response surface methodology was employed to analyze the influence of air temperature at three levels (50, 60, and 70 degrees Celsius) alongside the drying air flow rate at three varying levels (0.008, 0.016, and 0.024 kg/s). To achieve this objective, the optimum drying conditions were determined through the identification of the maximum values of the effective moisture diffusion coefficient, drying energy efficiency, specific moisture extraction rate, and vitamin C concentration, alongside the determination of the minimum durations of drying time and alterations in color. Based on the results obtained, the optimal drying conditions for white onion slices were established at an air temperature of 62.35 ˚C and an air flow rate of 0.024 kg/s. Moreover, at the point of optimality with a desirability of 0.59, the resultant values for the response variables, namely the effective moisture diffusion coefficient, drying duration, colorimetric differences, vitamin C content, specific moisture extraction rate, and drying energy efficiency were determined to be , 196.82, 5.20, 797.37, 0.30, and 53.98, respectively.