Thermal energy storage evaluation in direct steam generation solar plants

Existing commercial parabolic trough power plants use thermal oil as a heat transfer fluid, with working temperatures in the region of 400 degrees C. In order to achieve more efficient generating systems, a second generation of parabolic troughs that operate at temperatures higher than 400 degrees C is being developed. One possibility Abengoa Solar is assessing is the use of direct steam generation (DSG) inside parabolic troughs in order to achieve higher temperatures; in a first stage heating up to 450 degrees C and in a second stage heating up to 550 degrees C. For the future market potential of parabolic trough power plants with DSG, it is beneficial to integrate thermal energy storage (TES) systems. Different TES options based on the most known technologies, steam accumulators, molten salts (MS), and phase change materials (PCM), are presented and compared in this paper. This comparison shows as main conclusion of the study that a combined system based on PCM-MS has a clear advantage in the ratio with 6 or more equivalent hours of storage, while with lower than 6 h, steam accumulators are considered the best option.