A family of composite sorbents was prepared by impregnating silica gel in the solution of the hygroscopic salt CaCl(2) for solar heat storage. The characteristics of water adsorbed on the composite sorbents prepared under different impregnating conditions were measured by a micromeritics gas adsorption analyzer, a Calvet-type microcalorimeter and an open-type gravimetric method. From the results of these dynamic sorption measurements, the effects of impregnating variables on the characteristics of water adsorbed on the composite sorbents were evaluated. The composite sorbents prepared under different impregnating conditions were also tested on an open-type sorption storage system. The composite sorbent prepared by impregnating in the CaCl(2) solution of 30% showed a high and stable storage capacity of 1020 J g(-1) at the charging temperature of about 90 degrees C. This study demonstrates a great potential in controlling the sorption characteristics as well as the storage properties of the composite sorbents by optimizing the impregnating variables to meet the specific demands of solar heat storage. (c) 2006 Elsevier Ltd. All rights reserved.