For parabolic trough power plants using synthetic oil as the heat transfer medium, the application of solid media sensible heat storage is an attractive option regarding investment and maintenance costs. In the project WESPE that is described in this paper, solid media sensible heat storage materials have been researched. Two storage systems with a storage capacity of about 350 kW h each and maximum temperatures of 390 degrees C have been developed. The test storage units of WESPE are erected at the Plataforma Solar de Almeria in Spain. The thermal energy is provided by a parabolic trough loop with a maximum thermal power of 480 kW. The first tests were performed at storage temperatures up to 325 degrees C by March of 2004; testing will be continued during 2004 to achieve the nominal operation conditions of 390 degrees C and to gain experience for long term behaviour. These storage systems are composed of modules with two different storage materials to identify the characteristics of these materials. A tubular heat exchanger is integrated into the storage material. This heat exchanger demands a significant share of the investment costs. The selection of geometry parameters like tube diameter and number of tubes therefore play an important role in the optimisation. The design of the WESPE test module is based on results provided by a numerical tool for simulation of the transient performance of storage systems. (c) 2006 Elsevier Ltd. All rights reserved.