Development and performance evaluation of a dual energy source solar dryer for tomatoes

Solar energy is the most promising of the renewable energy sources in view of its apparent limitless potential. A Dual energy Source Solar Dryer was developed under Bauchi weather at latitude 9°14′ N and longitude 12°26′ E using locally available materials and the performance was evaluated. The essence of the dryer was to achieve the effective method of tomato preservation and eliminate the drudgery and product deterioration associated with traditional methods of open sun drying of tomatoes. This is in view of alleviating the weather limitation experienced by farmers in crop drying especially for tomatoes. The solar dryer consists of tray, reflective walls and glass roof, a preheating air absorber plate, inner panels for removal of moisture and chimney through which air stream passes across the dryer. Evaluation of the dryer showed a raised temperature of about 47 ℃ attainable in the drying chamber. The dryer temperature and drying rate was found to be higher than the natural open sun drying method. The dryer was able to reduce moisture content of tomato from initial moisture content of 94% wet basis to 4% in three days with effective drying time of 24 h, efficiency of 64%, air mass flow rate of 0.025 kg s-1 and drying rate of 0.03906 kg h-1. The results showed a considerable advantage of solar dryer over the traditional open sun drying method in terms of drying rate and less risk for spoilage.