Commercial acceptance and the economics of solar power generation using direct steam technology in parabolic troughs require the design and development of efficient, cost effective high temperature latent heat thermal energy storage systems (HTLHTES). Here, the heat transfer enhancement in the HTLHTES by using aluminium foils is presented. The phase change material (PCM) is initially liquid, and fills the space around the tube, foil and shell, while the heat transfer fluid (water) flows inside the tube. Transient two dimensional heat conduction problems are solved using the Fluent 6.2 software when heat is extracted from the PCM during the discharging process, yielding the phase interface position, temperature distribution, liquid fraction and surface heat flux as functions of time and the time of complete discharge. Parametric studies are conducted to assess how the performance of the storage is affected by the geometry, thermal and boundary conditions, which leads to correlations for the time of complete discharge. The computation results show that adding aluminium foils is an efficient way to enhance the heat transfer in the HTLHTES, and with the help of the correlations presented, the performance and optimum design of the HTLHTES can be investigated under different conditions. (C) 2007 Elsevier Ltd. All rights reserved.