Solar thermal energy, especially concentrated solar power (CSP), represents an increasingly attractive renewable energy source. However, one of the key factors that determine the development of this technology is the integration of efficient and cost effective thermal energy storage (TES) systems, so as to overcome CSP's intermittent character and to be more economically competitive. This paper presents a review on thermal energy storage systems installed in CSP plants. Various aspects are discussed including the state-of-the-art on CSP plants all over the world and the trend of development, different technologies of TES systems for high temperature applications (200 °C -1000 °C) with a focus on thermochemical heat storage, and storage concepts for their integration in CSP plants.TES systems are necessary options for more than 70% of new CSP plants. Sensible heat storage technology is the most used in CSP plants in operation, for their reliability, low cost, easy to implement and large experimental feedback available. Latent and thermochemical storage technologies have much higher energy density thus may have a bright foreground. New concepts for TES integration are also proposed, especially coupled technology for higher operating temperature and cascade TES of modularized storage units for intelligent temperature control.The key contributions of this review paper consist of a comprehensive survey of CSP plants, their TES systems, the ways to enhance the heat and/or mass transfers and different new concepts for the integration of TES systems.

Abstract:This paper focuses on the characterization and modeling of a solid/gas thermochemical reaction between a porous reactive bed and moist air flowing through it. The aim is the optimization of both energy density and permeability of the reactive bed, in order to realize a high density thermochemical system for seasonal thermal storage for house heating application. Several samples with different implementation parameters (density, binder, diffuser, porous bed texture) have been tested. Promising results have been reached: energy densities about 430-460 kWh.m -3 and specific powers between 1.93 and 2.88 W.kg -1 of salt. A model based on the assumption of a sharp reaction front moving through the bed during the reaction was developed. It has been validated by a comparison with experimental results for several reactive bed samples and operating conditions. Keywords:Thermochemical process, seasonal thermal storage, sharp front model, high-density reactive salt, permeability.

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This paper proposes and investigates novel concepts on the integration of a thermochemical energy storage (TCS) system in a concentrating solar power (CSP) plant. The TCS material used is calcium oxide reacting with water and the power cycle studied is a Rankine cycle driven by CSP.Firstly, three integration concepts on the coupling of the TCS system with the Rankine cycle are proposed, including the thermal integration concept, the mass integration concept and the double turbine concept. Then, an energy analysis is performed to determine and compare the theoretical overall energy efficiency of the proposed concepts. After that, an exergy analysis is also carried out for the selected integration concepts so as to evaluate and compare the overall exergy efficiency of the installation with TCS integration.The results show that the turbine integration concept has the highest overall energy efficiency (0.392), followed by the thermal integration concept (0.358) and the mass integration concept (0.349) under ideal conditions with 11 h of charging and 13 h of discharging. The energy storage density using calcium hydroxide as the storage media is estimated to be about 100 kWhel•t -1 . Exergy analysis results also indicate that the turbine integration concept seems to be the best option under the tested conditions.

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This article presents technical data for concentrated solar power (CSP) plants in operation, under construction and in project all over the world in the form of tables. These tables provide information about plants (e.g., name of the CSP plant, country of construction, owner of the plant, aim of the plant) and their technical characteristics (e.g., CSP technology, solar power, area of the plant, presence and type of hybridization system, electricity cost, presence and type of TES, power cycle fluid, heat transfer fluid, operating temperature, operating pressure, type of turbine, type and duration of storage, etc.). Further interpretation of the data and discussions on the current state-of-the-art and future trends of CSP can be found in the associated research article (Pelay et al., 2017) [1].