Experimental evaluation of fuzzy control solar drying with thermal energy storage system

Drying is a highly energy-demanding operation, traditionally taken up from fossil fuels, with high-operating costs and CO₂ emissions. Solar energy has great potential as an alternative energy source. However, variations in solar radiation require the use of additional energy sources, to keep a continuous drying process. An option is to accumulate solar energy using phase-change materials. In the present work, an advanced multivariable control system using fuzzy logic was implemented and applied to a solar dryer equipped with thermal energy storage system, with a capacity of 25?kg of agro-products. Two control systems were implemented: the first considering the ambient temperature and solar radiation as input variables, where the manipulated variables were the opening level of the solar panel and energy solar accumulator valves. The controlled variable in the second control system was the relative humidity content at the outlet of the drying chamber, and the manipulated variable was the opening of the air recirculation valve. The opening of the valves in both control systems was performed properly with variations of solar radiation, ambient temperature, and air moisture during the dehydration of mushrooms, plumbs, and peaches. Solar drying, together with a proper control system, reached 80% energy savings compared to conventional drying.