The primary objective of this study is to develop encapsulated phase change materials (EPCMs) capable of storing thermal energy at temperatures above 750 degrees C. EPCM with magnesium chloride as phase change material (PCM) are considered here for application in concentrated solar power (CSP) systems. MgCl2 is an effective storage medium because of its high melting temperature, 714 degrees C, and high latent heat of fusion, 454 kJ/kg. A specialized calorimeter with requisite size and high temperature capability is designed and built to prove the storage capability of MgCl2 EPCM. The calorimeter is also used to determine heat capacities for MgCl2 in both liquid and solid states as well as its latent heat of fusion. Calorimetric tests for the thermal storage capacities of three MgCl2 EPCM samples show excellent agreement with published data. Based on the measured properties, the latent heat of phase change can contribute about 84% of the storage capacity of MgCl2 PCM for a 100 degrees C temperature swing bracketing the salt's melting point. Repeated thermal-cycles show sustained performance of MgCl2 EPCM capsules with no discernible diminishment in storage capacity. (C) 2012 Elsevier Ltd. All rights reserved.