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

• Effectiveness of geothermal/solar drying system for onion in cloudy and rainy weather is studied. • Energy, exergy and environmental analysis of the drying system have been determined. • Solar fraction and geothermal fraction have been verified. • Average payback period of the system was found to be 0.74 years. • Low total color change of dried onion was observed. 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 geo-exchange heat exchanger (GHE) with inlet temperature of 80 °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 °C, respectively. Drying process took 28 consecutive hours. Average diffusivity was found to be 2.81 × 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 CO 2 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.