In order to investigate the effect of system and operating parameters on heat transfer and pressure drop characteristics of packed bed solar energy storage system with large sized elements of storage material, an extensive experimental study has been conducted and reported in the present paper. Five different shapes of elements of storage material have been investigated. Correlations have been developed for Nusselt number and friction factor as function of Reynolds number, sphericity and void fraction. The present correlations can be used to predict the performance of the actual packed bed solar energy storage system having packing material elements of different shapes and bed porosities within the range of parameters investigated. (c) 2005 Elsevier Ltd. All rights reserved.