Energy, environmental, economic, and color analysis of geo-exchange energy assisted-insulated north wall solar dryer for onion slices under relatively cloudy and rainy conditions

Preservation of onion surplus during rainy and cloudy days is a big challenge for farmers in the so-far area in northern Sahara of Algeria. Thus, available renewable energies such as geo-exchange and solar energy could be an effective solution. In the current study, an insulated north wall solar dryer (INWSD) integrated with geoexchange heat exchanger (GHE) with inlet temperature of 80 degrees C was tested for drying onion slices under cloudy and rainy weather. Solar radiation and ambient temperature were in the range of 0-447 W m(-2) and 9.65-26.53 degrees C, respectively. Drying process took 28 consecutive hours. Average diffusivity was found to be 2.81 x 10(-10) m(2) s(-1) by considering the variation of relative humidity and temperature inside the drying chamber. Specific energy consumption varied between 0.66 and 1.75 kWh/kg with an average of 1.71 kWh/kg. Thermal efficiency was in the range of 1.48%-48.90%, with an average value of 9.52%. The low CO2 emissions of 46.69 kg/year and average payback period of 0.74 year were obtained using the INWSD. Dried onion was with low total color change at 3.79 compared to fresh samples. Therefore, INWSD is a promising technique by comprehensively considering the 3E (energy, economic, economic-environmental) and color analysis.