heat is stored when the material changes phase from solid to a liquid. Thermo-chemical storage is a technique, which involves chemical reactions.Sensible heat storage is the most simple and inexpensive way of energy storage system although there are few advantages of phase change energy storage over sensible heat storage, but the technological and economical aspects make sensible heat storage superior. Packed beds represent the most suitable storage units for air-based solar system. A packed bed storage system consists of loosely packed solid material through which the heat transport fluid is circulated. Heated fluid (usually air) flows from solar collectors into a bed of graded particles from top to bottom in which thermal energy is transferred during the charging phase.Solids have been reported as widely used storage materials on low temperature range. Energy can be stored up to 800 °C in sand, cast iron, steel, aluminium, aluminium oxide, magnesium oxide and granite. Metals have good conductive characteristics and thus require only a small heat transfer area. Sand and rocks on the other hand, need a relatively large heat transfer area. Solar greenhouse driers can be used very effectively for crop drying. Many studies have been conducted by the researchers in different regions of the world with different climatic conditions for the drying of fruits, vegetables, cereals, grains, oil seeds, spices, fish etc. using solar greenhouse dryer. Thermal energy storage either sensible or latent heat are required to improve the utility and performance of the solar greenhouse dryers. Many studies have been conducted by the researchers using various sensible heat storage materials like water tanks, gravel beds, ground, sand, concrete etc. where energy is stored in the form of sensible heat. Hasnain [1] reported that solid materials such as rocks, metals, concrete, sand and brick can be used for low as well as Abstract Experiments were conducted in a natural convection solar greenhouse dryer using different sensible heat storage materials (concrete, sand and rock-bed) in order to study their thermal performance. For both sand and rockbed, 4″ thickness was found to be optimum as it provides better drying environment both during day and night. The dryer reduced the moisture content of coconuts from 52 (w.b.) to 7 % (w.b.) using concrete as heat storage material in 78 h saving 55 % of drying time compared to open sun drying which takes 174 h for reducing the moisture content to the same level. The sand took 66 h saving 62 % of drying time whereas rock-bed took only 53 h thereby saving 69 % of drying time compared to open sun drying. The efficiency of the dryer was found to be 9.5, 11 and 11.65 % using concrete, sand and rock-bed respectively.
