Modification approach of Northern Wall to improve the performance of solar greenhouse dryers: A review

Globally interest is shifting toward green energy due to its environmental appeal.
Therefore, to promote energy and environmental conservation in drying, several solar dryers has been developed which offers limitless, clean, and free energy to dry agricultural product. Among this solar dryers, solar greenhouse dryers offers a very simple low temperature, energy efficient structure capable of drying large beds of crops by harnessing thermal radiation energy from the sun. To improve the thermal performance in the passive mode especially, several modification approaches have been adopted. This article, therefore, reviewed various possible modification methods that have been adopted to improve the thermal performance of the greenhouse with a focus on the modification of the northern wall. The various strategies involved in the modification of the north wall structure include creating an opaque north wall with black painted materials, installing a reflective north wall using a mirror, integrating heat storage materials like pebbles or brick, integrating phase change materials into the
north wall, digging the soil depth to form a north wall and creating a variable southern roof with a modified north wall. Modifying the northern wall showed higher drying chamber temperature compared to completely transparent convectional greenhouse dryers in all the studies. These modifications can increase the temperature of the modified greenhouse by 13.38 to 21.1 % for a natural convection solar greenhouse dryer compared to the conventional type. With this approach, the radiation losses from the northern wall can be minimized and the energy management system of the greenhouse can be optimized for higher performance making it more sustainable and eliminating the use of fossil fuel in agricultural product drying.