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The WASCOP (Water Saving for Concentrated Solar Power) project is an EU project dedicated to water saving in CSP power plants. Among the different technologies and aspects considered in the project, the concept of cold thermal energy storage (cTES) has been developed. cTES is considered in addition to the cooling system and used when ambient temperature is too high and may lead to turbine efficiency and electricity production reductions. In these conditions, heat from the condenser is partially stored in the cTES and evacuated trough the available cooler when ambient temperature is lower, typically during the night. A prototype of cTES has been built in the CEA site of Cadarache. Experimental results are presented and shows the relevancy of the test loop and of the cTES concept. [ABSTRACT FROM AUTHOR]

A 1000 m3 prototype of cold Thermal Energy Storage cTES is currently under design to be installed on the condenser cooling circuit of La Africana CSP power plant in Spain. This high TRL prototype is a proof-of-concept of the cTES concept at large scale, in real environment and real operations. The design step is almost completed and the engineering step has already begun. Construction is planned to be performed in 2020 and commissioning may start at the end of 2020. In parallel, benefits of the integration of cTES as additional cooling system has been evaluated fir the specific case of La Africana power plant, for both electricity production and water consumption. [ABSTRACT FROM AUTHOR]

SOLWATT project started in May 2018 and involve 9 partners (4 research organizations CEA, CIEMAT, CRANFIELD UNIVERSITY and DLR- and 5 industrial partners TSK, BRIGHTSOURCE, FENIKS, RIOGLASS and TECKNIKER). SOLWATT project is devoted to the reduction of water consumption in CSP power plant. For this purpose, mirror field cleaning, turbine condenser cooling and water recovery are considered. Present paper is devoted more particularly to the cTES industrial prototype (cold thermal energy storage) used to reduce the water consumption related to condenser cooling. The cTES is based on a single-media thermocline storage used to partially or totally store the heat flow from the condenser when ambient temperatures are too high. Storage discharge is performed during the night. A 1000 m3 cTES prototype will be designed and constructed in the 50 MWe La Africana CSP power plant. [ABSTRACT FROM AUTHOR]

The WASCOP (Water Saving for Concentrated Solar Power) project is an EU project dedicated to water saving in CSP power plants. Among the different technologies and aspects considered in the project, the concept of cold thermal energy storage (cTES) has been developed. cTES is considered in addition to the cooling system and used when ambient temperature is too high and may lead to turbine efficiency and electricity production reductions. In these conditions, heat from the condenser is partially stored in the cTES and evacuated trough the available cooler when ambient temperature is lower, typically during the night. A prototype of cTES has been built in the CEA site of Cadarache. Preliminary commissioning has been performed. Final commissioning is expected to be done before Spring 2019 and experimental tests will be made during Summer 2019. [ABSTRACT FROM AUTHOR]

Thermal Energy Storage (TES) systems are central elements of various types of power plants operated using renewable energy sources. Packed bed TES can be considered as a cost–effective solution in concentrated solar power plants (CSP). Such a device is made up of a tank filled with a granular bed through which heat-transfer fluid circulates. However, in such devices, the thermal stresses may accumulate from cycle to another due to differential thermal dilatation between filler and tank walls, leading to plastic deformations in the tank shell and the failure of the tank might happen. This paper aims at studying the evolution of tank wall stresses over thermal cycles, taking into account both thermal and mechanical loads, with a numerical model based on the discrete element method (DEM). A higher thermal expansion coefficient is used for the wall compared to the granular medium, allowing the settlement of particles during the loading phases, then an increase of induced stresses during the unloading phases due to the wall contraction against the settled particles. Simulations were performed to study two different thermal configurations: (i) the tank is heated homogenously along its height or (ii) with a vertical gradient of temperature. Then, the resulting loading stresses applied on the tank are compared as well the response of the tank wall. [ABSTRACT FROM AUTHOR]

Thermocline energy storage is a way to store thermal energy by keeping two distinct zone of temperature in a tank, separated by a thin transition zone. Some applications use a granular porous media, filling the storage tank, through which passes the heat-transfer fluid. Most of scientific papers concerning this kind of technology assume that an ideal distribution of the fluid into the porous media is a homogeneous distribution over the diameter of the tank. On the other side, a recent numerical study concludes that a non-homogeneous distribution leads to better storage performances. Considering theses contradictory statements and the limited number of studies concerning the impact of distribution over thermal storage performances, a numerical simulation model is developed to investigate. This model is validated with data from the experimental device existing in CEA, in cases without distribution issues. Planned modifications of the experimental device for investigation of fluid’s distribution and validation of the model in such cases are presented. [ABSTRACT FROM AUTHOR]

An original modeling approach for packed-bed heat storage systems based on the combination of an intra-particle conduction model and a single-phase model is presented. The intra-particle conduction approach enables to model the solid phase whatever the dimensionless Biot number of the particles of the packed bed. The single-phase model approach is used when a part of the packed bed consists of very small particles like sand. This approach assumes thermal equilibrium between the fluid and the small particles. In addition, an energy equation dedicated to the tank wall enables to model small storage systems in which the influence of the wall is significant. The resulting one-dimensional three phase model has been validated with the liquid/solid and the gas/solid heat storage systems of the French Atomic Energy Commission (CEA). Since the model has been validated on two very different setups with various cyclic operating conditions, it is likely to enable accurate and affordable modeling of a wide range of packed-bed heat storage configurations. [ABSTRACT FROM AUTHOR]

Thermal Energy Storage (TES) systems are central elements of various types of power plants operated using renewable energy sources. Packed bed TES can be considered as a cost-effective solution in concentrated solar power plants (CSP). Such a device is made up of a tank filled with a granular bed through which heat-transfer fluid circulates. However, in such devices, the thermal stresses may accumulate from cycle to another due to differential thermal dilatation between filler and tank walls, leading to plastic deformations in the tank shell and the failure of the tank might happen. This paper aims at studying the evolution of tank wall stresses over granular bed thermal cycles, taking into account both thermal and mechanical loads, with a numerical model based on the discrete element method (DEM). Simulations were performed to study two different thermal configurations: (i) the tank is heated homogenously along its height or (ii) with a vertical gradient of temperature. Then, the resulting loading stresses applied on the tank are compared as well the response of the internal granular material. [ABSTRACT FROM AUTHOR]

Two liquid/solid thermocline heat storage systems are compared. Both setups have similar size and operate with thermal oil as heat transfer fluid but one consists of a packed bed of alumina spheres with a void fraction of 0.485, while the other consists of a packed bed of rock and sand with a void fraction of 0.270. A dimensionless approach based on the thermal front velocity (i.e. the velocity of the thermocline) and the discharge efficiency is used to compare the thermal behavior of the two setups. The comparison shows that the dimensionless behavior of both systems is very similar and seems insensitive to the operating conditions in the range tested (temperature level and fluid flow). This dimensionless approach is therefore promising to analyze and size thermocline heat storage systems. [ABSTRACT FROM AUTHOR]

Thermal Energy Storage (TES) systems are central elements of various types of power plants operated using renewable energy sources. Packed bed TES can be considered as a cost-effective solution in concentrated solar power plants (CSP). Such a device is made up of a tank filled with a granular bed through which heat-transfer fluid circulates. However, in such devices, the tank might be subjected to catastrophic failure induced by a mechanical phenomenon known as thermal ratcheting. Thermal stresses are accumulated during cycles of loading and unloading until the failure happens. This paper aims at studying the evolution of tank wall stresses over granular bed thermal cycles, taking into account both thermal and mechanical loads, with a numerical model based on the discrete element method (DEM). Simulations were performed to study two different thermal configurations: (i) the tank is heated homogenously along its height or (ii) with a vertical gradient of temperature. Then, the resulting loading stresses applied on the tank are compared as well the response of the internal granular material. [ABSTRACT FROM AUTHOR]

This work presents some of the experimental results obtained during a test campaign performed at the STONE facility of CEA-Grenoble in collaboration with CIEMAT-PSA supported by both the SFERA-II and the STAGE-STE project. This installation consists of a thermocline tank with thermal oil and rock/sand filler and the tests aimed to study the development of the temperature profile inside the tank at the beginning of charge/discharge processes. The investigation of how this profile is created and which is its dependence on the experimental parameters is crucial for predicting the behavior of a dual-media thermocline tank. Tests have been performed for dynamic processes from initial states with constant uniform temperature or with a thermal gradient already present due to a partial thermocline zone extraction in the former process. Tests at different fluid velocities and temperatures have been carried out as well, in order to evaluate the influence of operating conditions. When a dynamic process of charge or discharge is started, the development of the thermal front is very sharp and localized at tank top or bottom if initial tank temperature is uniform, whereas it is less pronounced if the test begins from a non-thermally uniform initial state. In terms of operating conditions, it has been observed that the development of the thermocline thermal front is independent not only of the fluid velocity but also of its temperatures, within the working ranges here considered. Due to these experimental results, it will be possible to improve simulation models for thermocline tanks and hence to predict their behavior more accurately, especially when they are implemented in annual simulations of CSP plants. [ABSTRACT FROM AUTHOR]