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Milian Y.E.,University of Antofagasta | Gutierrez A.,University of Antofagasta | Grageda M.,University of Antofagasta | Grageda M.,Solar Energy Research Center Chile | And 2 more authors.
Renewable and Sustainable Energy Reviews | Year: 2017

Phase change materials (PCM) are characterized for storing a large amount of thermal energy while changing from one phase to another (generally solid-liquid states) at a specific temperature and presenting a high specific heat of phase change process. PCMs can be classified as organic, inorganic and eutectic. Such materials present some limitations, including subcooling, phase segregation, flammability, low thermal conductivity and thermal instability, among others. In order to overcome these problems, encapsulation of PCMs is being successfully developed, providing decreased subcooling, large heat transfer area, and controlling the volume change of the storage materials when the phase transition occurs. A considerable amount of studies has been published in the field of encapsulation methods for organic PCMs. Nevertheless, the information available on inorganic PCMs is scattered. Furthermore, the influence of the encapsulation techniques on thermophysical properties of PCMs is not reported in these reviews most of the time. Hence, the aim of this review is to summarize the encapsulation and characterization techniques for inorganic PCMs and to provide the analysis about the influence of synthesis parameters on thermophysical properties of encapsulated PCMs. Two principal types of encapsulated inorganic PCMs were found: core-shell PCMs (core-shell EPCMs) and shape stabilized PCMs (SS-PCMs). Classification of encapsulation methods of core-shell EPCMs and SS-PCMs are reported in this work. Among all the microencapsulation methods, inverse Pickering emulsion, electroplating, solvent evaporation–precipitation method and mechanical packaging are the most common methods described in the literature for the production of core-shell EPCM. On the other hand, for SS-PCMs, mainly sol-gel process, infiltration and impregnation encapsulation methods were found. Scientific works report a reduction in the heat of phase change for core-shell EPCMs. This is mostly because of the low content of salt in the final material. Moreover, an improvement of thermal conductivity was procured for SS-PCMs. Finally, PCM percentage, particle size, stirring rate, type of crosslinking agent and solvent properties were established as principal factors influencing the final properties of the encapsulated materials. For the best of our knowledge, this is the first profound review of encapsulation techniques for inorganic PCM. © 2017 Elsevier Ltd


Fernandez A.G.,Complutense University of Madrid | Fernandez A.G.,University of Antofagasta | Fernandez A.G.,Solar Energy Research Center Chile | Galleguillos H.,Solar Energy Research Center Chile | Perez F.J.,Complutense University of Madrid
Oxidation of Metals | Year: 2014

The enhancements in the storage systems developed by thermo solar centrals have provided to renewable energy a considerable increase in efficiency. This improvement also fosters the design of innovative storage fluids with lower melting point and thermal stability as new molten salts mixtures. In this research, the corrosive effects of a molten nitrate mixture composed by Ca(NO3)2–NaNO3–KNO3–LiNO3 were assessed at 390 °C on a carbon steel (A516) and on low-Cr alloy steels (T11 and T22). The corrosion rates were determined by gravimetric tests, measuring the weight gain during 2,000 h, identifying the corrosion products via scanning electron microscopy and X-ray diffraction. Study of T22 steel revealed a better behavior under corrosive environment, identifying the formation of MgCr2O4 protective spinels mainly. Fe2O3 and Fe3O4 were the others important products found on the tests performed at 390 °C, being observed also the formation of some stable compounds with the impurities of the salt, as carbonates and sulphates. © 2014, Springer Science+Business Media New York.


Fernandez A.G.,Complutense University of Madrid | Fernandez A.G.,Solar Energy Research Center Chile | Fernandez A.G.,University of Antofagasta | Ushak S.,University of Antofagasta | And 4 more authors.
Solar Energy Materials and Solar Cells | Year: 2015

Enhancements to energy storage systems developed for solar thermoelectric technologies can yield considerable increases in efficiency for this type of renewable energy. Important improvements include the design of innovative storage fluids, such as molten salts possessing low melting points and high thermal stabilities.


Fernandez A.G.,Complutense University of Madrid | Fernandez A.G.,University of Antofagasta | Fernandez A.G.,Solar Energy Research Center Chile | Cortes M.,University of Antofagasta | And 4 more authors.
Renewable Energy | Year: 2015

The enhancements in the storage systems developed by solar thermal power plants have provided to renewable energy a considerable increase in efficiency. Thermal Energy Storage (TES) using HITEC mixture could be used as Heat Transfer Fluid (HTF) in concentrated solar linear technology.In this research, the corrosive effects of HITEC mixture composed by 40wt% NaNO2+7wt%NaNO3+53wt%KNO3 were assessed at 390°C on a carbon steel (A516) and on low-Cr alloy steels (T11 and T22). The corrosion rates were determined by gravimetric tests, measuring the weight gain during 2000h, identifying the corrosion products via scanning electron microscopy and X-ray diffraction. T22 steel shows a corrosion layer of 6.05microns, with a protective layer formed in the inner zone to the material, identified through DRX as the K2CrO4 protective spinel.Fe2O3 and MgO were the others important products found on the tests performed at 390°C, being observed also the formation of some stable compounds with the impurities of the salt, as carbonates.The use of the HITEC mixture in solar technology would provide a less aggressive behaviour for materials in contact with it, providing an increase in operational life cycles in current solar technology. © 2015 Elsevier Ltd.


Fernandez A.G.,Complutense University of Madrid | Fernandez A.G.,University of Antofagasta | Fernandez A.G.,Solar Energy Research Center Chile | Galleguillos H.,Solar Energy Research Center Chile | Perez F.J.,Complutense University of Madrid
Solar Energy | Year: 2014

Chile's Atacama Desert is one of the world's premier locations for the study and application of solar power. The typical impurities present in Chilean nitrates are Mg, SO4 - and Cl-, among others. Developing a heat treatment to eliminate impurities and optimise the quality of the salts from the solar flats of the Atacama Desert is one of the most important goals of the inorganic chemistry industry in northern Chile.In this study, a full characterisation of the binary solar salt 60% NaNO3+40% KNO3 was performed by studying the influence of the most important impurities on the thermal processes and corrosiveness at the storage temperatures of the most important solar thermal plants.Moisture is another parameter that is important for this technology. The corrosion test results improve after heat treatment.The corrosion characteristics were determined using gravimetric tests, measuring the weight gain of three alloy steels with low Cr contents at 390. °C over 2000. h and identifying the corrosion products using scanning electron microscopy (SEM) and X-ray diffraction (XRD).Fe2O3 and Fe3O4 were the most important corrosion products. Additionally, some stable compounds were formed from the impurities in the salt, such as magnesium ferrite (MgFe2O4). © 2014 Elsevier Ltd.


Fernandez A.G.,Complutense University of Madrid | Fernandez A.G.,Solar Energy Research Center Chile | Ushak S.,University of Antofagasta | Ushak S.,Solar Energy Research Center Chile | And 3 more authors.
Applied Energy | Year: 2014

In this study, the effect of the addition of LiNO3 and/or Ca(NO3)2 to the solar salt NaNO3/KNO3, which is used as a storage material in CSP plants, on the physicochemical properties thereof was studied. Thermal analyses were performed by differential scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC) and thermogravimetric analysis (TGA), obtaining the phase transitions, melting points, heat capacities and thermal stability of the materials studied. In addition, viscosity measurements were carried out at different temperatures close to the melting point of the salt mixtures to determine their flowability.The study of these low-melting-point mixtures was executed through the synergistic effect exerted by a 30% LiNO3+60% KNO3+10% Ca(NO3)2 mixture, and it was observed that the addition of LiNO3 increases the thermal stability of the tested salts, whereas the addition of Ca(NO3)2 reduces the melting points and improves the economic cost of these mixturesThese mixtures were designed such that the melting point of the molten nitrates would be reduced, allowing for the mixtures' direct use as storage materials in parabolic-trough solar power plants, therefore replacing the synthetic oil currently used as a heat transfer fluid (HTF) and heat exchanger oil. The use of these mixtures is intended to reduce the economic costs and improve the thermal storage of current solar technology. © 2014 Elsevier Ltd.


Parrado C.,University of Antofagasta | Girard A.,Adolfo Ibáñez University | Simon F.,University of Granada | Fuentealba E.,University of Antofagasta | Fuentealba E.,Solar Energy Research Center Chile
Energy | Year: 2016

This study calculates the LCOE (Levelized Cost of Energy) on the PSDA (Atacama Solar Platform) for a solar-solar energy mix with the objective of evaluate new options for continuous energy delivery. LCOE was calculated for three 50 MW (megawatt) power plants: A PV (photovoltaic), a CSP (concentrated solar power) plant with 15 h TES (thermal energy storage) and a hybrid PV-CSP plant constituted with 20 MWp of PV and 30 MW of CSP with 15 h TES. Calculations present two scenario projections (Blue Map and Roadmap) until 2050 for each type of plant. Due to the huge solar resource available in northern Chile, the PV-CSP hybrid plant results to be a feasible option for electricity generation, as well as being effectively able to meet electricity demand profile of the mining industry present in the area. This type of energy could mitigate long-term energy costs for the heavy mining activity, as well as the country CO2 emissions. Findings point out that PV-CSP plants are a feasible option able to contribute to the continuous delivery of sustainable electricity in northern Chile. Moreover, this option can also contribute towards electricity price stabilization, thus benefiting the mining industry, as well as reducing Chile's carbon footprint. © 2015 Elsevier Ltd.


Cabeza L.F.,University of Lleida | Gutierrez A.,University of Antofagasta | Barreneche C.,University of Lleida | Barreneche C.,University of Barcelona | And 7 more authors.
Renewable and Sustainable Energy Reviews | Year: 2015

Lithium, mainly used in electrical energy storage, has also been studied in thermal energy storage. It is recognized as a "critical material" and is produced from minerals and from brines. Chile is one of the biggest producers, here from brine and with lower costs than in other countries. With sensible heat storage, in solar power plants lithium is seen as a way to improve the properties of molten salts used today. The low melting point in these ternary salts with lithium, represent a considerable reduction in the maintenance and operational costs associated with current solar technology, demonstrating that the fluids showed, are potential candidates for thermal energy storage (TES) in concentrated solar plants (CSP) plants. Many materials have been studied and proposed to be used as phase change materials (PCM). Between the multiple materials studied to be used in PCM, lithium materials and mixtures are listed as potential PCM for building applications and for high temperature applications. In thermochemical energy storage, lithium compounds have been used mainly in chemical heat pumps, following their use in absorption cooling. © 2014 Elsevier Ltd. All rights reserved.


Ushak S.,University of Antofagasta | Ushak S.,Solar Energy Research Center Chile | Gutierrez A.,University of Antofagasta | Galleguillos H.,University of Antofagasta | And 6 more authors.
Solar Energy Materials and Solar Cells | Year: 2015

Physical characterization and thermal properties of bischofite, a by-product from the non-metallic industry, were determined and compared with those to MgCl2·6H2O with the idea of using it as phase change material in thermal energy storage applications. The melting point and heat of fusion were measured in the temperature range from 30 °C to 150 °C, where Tfus and ΔHfus were 100 °C and 115 kJ/kg for bischofite, and 114.5 °C and 135 kJ/kg for MgCl2·6H2O. The solid heat capacity was determined from 25 °C to 60 °C, being 2.1 kJ/(kg K) at 60 °C for both samples. The measurements of the liquid heat capacity of bischofite were done from 115 °C to 125 °C and the Cp showed linear increase from 1.71 kJ/(kg K) to 3.01 kJ/(kg K). The thermal stability test (30 heating/cooling cycles) of bischofite and MgCl2·6H2O shows subcooling of about 37 K and 29 K, respectively. The solid and liquid densities were determined using the pycnometrically method; for bischofite, ρsolid decrease from 1686 (at 30 °C) to 1513 kg/m3 (at 50 °C) and ρliq was 1481 kg/m3 (at 115 °C). Based on the thermophysical properties evaluated, the energy storage density was evaluated for both materials, being 170 J/cm3 for bischofite and 192 J/cm3 for MgCl2·6H2O. This study established that bishofite is a promissory PCM with similar thermophysical characteristics to magnesium chloride hydrate, but with a lower cost. Nevertheless, further work is needed to overcome the two main problems found, subcooling and segregation of the material. © 2014 Elsevier B.V.


Parrado C.,University of Antofagasta | Marzo A.,University of Antofagasta | Marzo A.,Solar Energy Research Center Chile | Fuentealba E.,University of Antofagasta | And 3 more authors.
Renewable and Sustainable Energy Reviews | Year: 2016

The solar conditions in northern Chile, in particular the Atacama Desert, which presents an annual global radiation value of 2500 kW h/m2 and an index of direct normal irradiance (DNI) of 3500 kW h/m2, are among the best worldwide for capturing and storing solar energy. These features are of major importance when considering the saline deposits that are concentrated in this area. There are several factors that make CSP technology an ideal resource for a successful development in northern Chile, highlighting the excellent solar resource and their combination with storage could supply energy to mining industry, which requires energy 24 h per day. The focus of this paper is to develop an economic analysis for computing a projection of LCOE between 2014 and 2050 from a 50 MW CSP plant with five different composition of salts for it TES. Two different scenarios are considered for this study: IEA BLUE Map Scenario and Roadmap Scenario. Additionally, a comparison between the LCOE in the north of Chile and the most influential countries in solar energy (Spain and USA) is made. The research basis lay on contribution of recent Chilean plans together with international researches in order to support the great potential of the implementation of CSP plant in the north of Chile. The results show that new proposed molten salts reduce considerably the storage cost. Thus, it can contribute to a promising future of the growth of CSP in the Plataforma Solar del Desierto de Atacama (PSDA) at north of Chile. © 2015 Elsevier Ltd. All rights reserved.

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