2022 | Instituto IMDEA Energía

Category: 2022

2022, Artículos Científicos

Soiling effect in solar energy conversion systems: A review

Soiling effect in solar energy conversion systems: A review, R. Conceição, J. González-Aguilar, A. A. Merrouni, M. Romero, Renewable and Sustainable Energy Reviews, 162, art. no. 112434, 2022, Online version, https://doi.org/10.1016/j.rser.2022.112434

Abstract

This review provides a comprehensive, detailed description and contextualization of soiling research evolution in the solar energy field throughout time. The analysis consists of past soiling research, including important notes on notable works and main researches. The current state of the art is presented, followed by an extended literature survey covering from 1942 to 2019, facilitating the finding of primordial research concerning each of the available technologies, and enriching knowledge regarding the existing extensive research database. Moreover, soiling analysis and comments are made for several specific topics, such as cleaning techniques and environmental effects on soiling deposition. Finally, future prospects and research directions on the soiling effect are given.

2022, Artículos Científicos

Optical and thermal integration analysis of supercritical CO2 Brayton cycles with a particle-based solar thermal plant based on annual performance

Optical and thermal integration analysis of supercritical CO2 Brayton cycles with a particle-based solar thermal plant based on annual performance, R. Chen, M. Romero, J. González-Aguilar, F. Rovense, Z. Rao, S. Liao, Renewable Energy, 189, 164-179, 2022, Online version, https://doi.org/10.1016/j.renene.2022.02.059

Abstract

Central receiver concentrating solar power (CSP) plants based on particles as heat transfer fluid in solar circuits and supercritical CO₂ (S–CO₂) Brayton cycles can fulfil the requirements for next generation CSP to improve solar-to-electric efficiency and reduce energy storage costs. However, effective incorporation of these two concepts requires an in-depth understanding of their characteristics and an appropriate approach to match them. This paper addresses the importance of the design features and annualized performances of the optical subsystem (heliostat-receiver) and the thermal-to-electricity subsystem (solar receiver-energy storage-power block) on the global optimization of any integrated CSP plant. The analysis lies in a complete model of a particle-based CSP plant, which includes detailed modeling for the solar field, a cavity solar receiver with an up bubbling fluidized bed (UBFB) tubular panel, particles storage tanks and a recompression S–CO₂ Brayton cycle. The design incident irradiance on the receiver aperture (IR) and the particles temperature at the receiver outlet (T_p) are identified as key parameters determining the solar-to-electric integration procedure and affecting the overall plant design and annual performance. Regarding subsystems located upstream and downstream of the receiver, the effects of heliostat and power block characteristics on the optimal IR and T_p are also evaluated, represented by the heliostat beam quality and main compressor inlet temperature. Results show that IR around 1,200–1,500 W/m² provides the maximum system design efficiency and annual efficiency. Improvements on heliostat beam quality and power block efficiency help to increase the optimal IR and overall system efficiency. In the optimal range of IR, increasing T_p leads to higher system design efficiency, but lower system annual efficiency and annual electricity output. The optimal combination of IR and T_p contributes to a minimum heliostat design area, representing the integration trade-off between the system optical and thermal characteristics.

2022, Artículos Científicos

Designing a flat beam-down linear Fresnel reflector

Designing a flat beam-down linear Fresnel reflector, S. Taramona, P. Á. González-Gómez, J. V. Briongos, J. Gómez-Hernández, Renewable Energy, 187, 484-499, 2022, Online version, https://doi.org/10.1016/j.renene.2022.01.104

Abstract

A linear beam-down solar field consists of two reflections that concentrate the solar irradiation on heavy materials located on the ground. Several rows of linear Fresnel reflectors, which have the same width, aim the solar irradiation to a secondary mirror with a hyperbolic shape that redirects the solar concentration towards the ground receiver. This paper overcomes the main limitation of the previously proposed hyperbolic secondary reflector. A new secondary reflector composed by several fixed flat mirrors located at the same height is proposed. A model to calculate the optimal layout of this novel solar field, as well as the efficiency and concentration, is developed and validated against a Monte-Carlo Ray-Tracing software, obtaining relative errors lower than 15%. Two new dimensionless parameters are proposed to facilitate the design of the flat beam-down linear Fresnel reflector. The concentration, optical efficiency and receiver width can be easily obtained, without performing any simulation, as a function of the dimensionless parameters. This novel solar field can achieve concentration ratios of up to 31 and optical efficiencies of up to 60%, obtaining similar concentrations with better optical efficiency than a field using a hyperbolic reflector.

2022, Artículos Científicos

Evaluating the Corrosion Resistance of Inconel 625 Coatings, Processed by Compact Plasma Spray, for Applications in Concentrating Solar Power Plants

Evaluating the Corrosion Resistance of Inconel 625 Coatings, Processed by Compact Plasma Spray, for Applications in Concentrating Solar Power Plants, F. Rubino, D. Merino, C. Munez, P. Poza, Key Engineering Materials, 926, 1736-1745, 2022, Online version, https://doi.org/10.4028/p-d3uuc2

Abstract

Thermal energy storage (TES) systems have paramount importance in the design of Concentrating Solar Power (CSP) plants. TES systems allow storing the energy collected from solar radiation as heat energy in a thermal fluid and, in that way, extending the energy duration period of the plant and making the produced electricity dispatchable, depending on the actual demand and not only on the availability of the sun. The thermal fluids, synthetic oils, or molten salts, usually operate at temperatures from 500°C up to 800°C. The harsh operative conditions bring out issues related to the compatibility with the construction materials of CSP components, i.e., carbon and stainless steel. Coating of low-alloy structural steel with high-resistant materials has been addressed as a promising solution for mitigating the corrosion in TES system components. Compact plasma spray process was used to deposit Inconel 625 alloy onto T22 carbon steel coupons. Nitrate salts mixture, 60%NaNO₃-40KNO₃, commonly employed in CSP systems as operative and thermal storage fluid was used as corrosion medium. The tests were conducted by immersing coated and uncoated samples in molten salts at 500°C for 1, 3 7, and 14 days to assess the corrosion behavior of the In625 coatings. After 24 hours of exposition to molten nitrate salts, the T22 surface showed a pronounced oxidized layer having a thickness of approximately 20 µm. This layer is mainly composed of oxygen, iron, and chromium, which are the main constituents of carbon steel, with a few traces of sodium and potassium derived from the reaction of salts with the steel. Inconel 625, on the other hand, showed the formation of very thin scales of corrosion products localized only on the surface of the sample. Longer exposition is expected to produce a more pronounced degradation of uncoated steel, but barely affect the Inconel 625 coating.

2022, Artículos Científicos

Alternative low-power plasma-sprayed inconel 625 coatings for thermal solar receivers: Effects of high temperature exposure on adhesion and solar absorptivity

Alternative low-power plasma-sprayed inconel 625 coatings for thermal solar receivers: Effects of high temperature exposure on adhesion and solar absorptivity, D. Merino-Millan, C. J. Múnez, M. Á. Garrido-Maneiro, P. Poza, Solar Energy Materials and Solar Cells, 245, 111839, 2022, Online version, https://doi.org/10.1016/j.solmat.2022.111839

Abstract

Over recent years, renewable energy technologies have focused on increasing performance and efficiency, and on the reduction of maintenance costs. In this work, thermal-sprayed Inconel 625 coatings have been studied as an alternative for concentrated solar power plants receivers. A low-power compact plasma spray system was used to deposit coatings onto two substrates: grade 22 ferritic steel and AISI 316 L austenitic steel. This system may be used for in-situ maintenance or repair purposes. The coatings were heat-treated at two temperatures: 520 °C and 800 °C, at different exposure times. The aim of this work was to evaluate the effect of this treatment on the adherence and solar absorptivity of the Inconel 625 coatings. The results showed that, at higher temperatures and longer exposure times, better adherence and absorptivity are achieved. Adherence values above 60 MPa were obtained due to diffusion in the coating-substrate interface. Additionally, absorptivity values above 93% were measured due to oxide formation on the coating surface during heat treatment. Furthermore, the highest temperature of the oxidized treatment reported the highest values of absorptivity. These results show that the developed Inconel 625 coatings could be considered as a possible alternative to improve the performance of concentrated solar power plants.

2022, Artículos Científicos

An optimisation method for the cold-spray process: On the nozzle geometry

An optimisation method for the cold-spray process: On the nozzle geometry, L. Alonso, M. A. Garrido, P. Poza, Materials & Design, 214, 110387, 2022, Online version, https://doi.org/10.1016/j.matdes.2022.110387

Abstract

Currently, the cold-spray process, or simply cold spray, is an extensively used technique in coating applications. The low temperature of the deposition process is the distinctive feature that makes it suitable for many additive manufacturing activities such as repair and restoration of damaged components. The reliability of the coatings is strongly dependent on the velocity of the powder during its impact on the target surface. Spraying conditions such as the pressure and temperature of the carrier gas and the geometry of the nozzle control the acceleration of the powder particles. Consequently, there is an increasing interest in the optimisation of nozzle geometry so as to maximise the acceleration of the particles through the nozzle path that they follow. In contrast with various extant approaches to achieve this aim (finite element modelling, experimental approach, and analytical methods), an alternative model based on the one-dimensional isentropic theory that accounts for the dynamics of the dilute two-phase flow was developed in this study. First, an analysis of the common hypotheses used to obtain the equation of motion of the particle was carried out. Subsequently, with the new insights revealed from the previous analysis, a new theoretical model for the optimisation of the divergent part of the nozzle was performed considering a geometric angle restriction. This model is based on the numerical integration of the equation of motion of the particle, ensuring the maximisation of the particle drag force by means of the Lagrange multiplier method. Once the analytical model is formulated, a set of curves describing the optimal geometric parameters for different conditions is obtained. Moreover, some optimal geometries are presented demonstrating the low influence of the angle restriction. Additionally, the inversely proportional relationship between stagnation pressure and temperature is revealed.

2022, Artículos Científicos

Development of stable porous silica-coated Ca(OH)2/γ-Al2O3 pellets for dehydration/hydration cycles with application in thermochemical heat storage

Development of stable porous silica-coated Ca(OH)₂/γ-Al₂O3 pellets for dehydration/hydration cycles with application in thermochemical heat storage, L. Briones, C. M. Valverde-Pizarro, I. Barras-García, C. Tajuelo, E. S. Sanz-Pérez, R. Sanz, J.M. Escola, J. González-Aguilar, M. Romero, Journal of Energy Storage, 51, 104548, 2022, Online version, https://doi.org/10.1016/j.est.2022.104548

Abstract

Thermochemical heat storage based on the CaO + H₂O ↔ Ca(OH)₂ system is extremely promising in CSP plants that can reach medium to high temperatures, such as those equipped with tower and heliostats. However, the attrition of pure CaO pellets is a major drawback that hampers an actual commercial development. This work proposes the dip-coating of mixed Ca(OH)₂/γ-Al₂O₃ spherical and cylindrical pellets with dense silica and Al-MCM-41 (mesoporous silica) gels. The original hardness of pure Ca(OH)₂ pellets (<2 N) can be increased up to 31 N using 40 wt% alumina as binder and applying a silica coating. Both gels formed a hard calcium silicate layer upon calcination that helped keeping the structural integrity of the samples after dehydration/hydration cycles. The samples were tested in 10 consecutive cycles at dehydration and hydration temperatures of 600 °C and 250–425 °C, respectively. Cylindrical pieces displayed higher hardness values and hydration yields compared to the spherical counterparts. Interestingly, porous silica-coated cylindrical pellets achieved a remarkable hydration yield of 85% and presented a hardness value of 8 N after cycling. This was due to its porous nature and the composition of the coating, formed by thin sheets and small grains, which allowed preserving the outer porous structure of the pellet.

2022, Artículos Científicos

Air solid packed-beds for high temperature thermal storage: practical recommendations for predicting their thermal behaviour

Air solid packed-beds for high temperature thermal storage: practical recommendations for predicting their thermal behaviour, E. Alonso, E. Rojas, Applied Thermal Engineering, 202, 117835, 2022, Online version, https://doi.org/10.1016/j.applthermaleng.2021.117835

Abstract

An advantageous solution for thermal energy storage is an air solid packed bed that consists in a tank filled with a solid material through which an air stream passes transferring heat to the filler in charge and collecting it in discharge. Effective tools to predict the thermal behaviour are required to optimize efforts towards the technology consolidation. To contribute to it, an experimental and numerical study on an air solid packed bed is presented here including some novel assumptions. The model is based on two energy balances applied to the solid and air phase separately. It also accounts for the thermal capacity of the tank walls by means of a correction of the solid density. The effective conductivity of the solid was evaluated through two components: one for the conduction through the solid and another for the radiative heat transfer. The last one gains relevance as the system average temperature rises, although it can be neglected below 500 °C. Convective heat transfer coefficient was introduced according to published correlations that were adequate for the operation conditions. The model was validated with experimental results from an own facility. The most critical parameter in the system behaviour is the thermal capacity of the filler. This fact points out the need of an accurate measurement of the specific heat. Finally, the possibility of simulating this kind of systems assuming an effective medium and solving an only heat balance was proposed if the convective heat transfer coefficient between solid and air is above a limit established in 100 W/m²K. These conclusions serve as reference to optimize efforts in predicting the thermal behaviour of air solid packed beds systems.

2022, Artículos Científicos

Hydrogen production by thermochemical water splitting with La0.8Al0.2MeO3-δ (Me= Fe, Co, Ni and Cu) perovskites prepared under controlled pH

Hydrogen production by thermochemical water splitting with La0.8Al0.2MeO3-δ (Me= Fe, Co, Ni and Cu) perovskites prepared under controlled pH, A. Pérez, M. Orfila, M. Linares, R. Sanz, J. Marugán, R. Molina, J. A. Botas, Catalysis Today, 390, 22-33, 2022, Online version, https://doi.org/10.1016/j.cattod.2021.12.014

Abstract

Aluminum based perovskites, La0.8Al0.2MeO3-δ (Me = Co, Ni, Fe, Cu), were synthesized following the Pechini method at different pHs and evaluated for hydrogen production by water splitting in a two-step thermochemical cycle. The pH of the synthesis medium showed a critical influence in the redox properties of the aluminum-based perovskites during the thermochemical cycle. Both the thermal reduction and the hydrolysis step produce irreversible changes in the crystalline structure of La0.8Al0.2MeO3-δ perovskites prepared at acid pH, avoiding the cyclability of the material and a stable production of hydrogen during consecutive cycles. However, these changes are not observed when the perovskites were synthesized at basic pH and operated at isothermal conditions at 800 ºC. In this case, the materials keep the crystalline structure leading to stable hydrogen production during consecutive cycles. Among all the studied materials, the nickel-based La0.8Al0.2NiO3-δ perovskites exhibited the best hydrogen productivity per cycle, 4.4 cm3 STP /gmaterial·cycle (Standard Temperature and Pressure conditions), which is a remarkable result considering that the thermochemical water splitting is conducted under isothermal conditions at just 800 ºC. Moreover, this result is accompanied with a good performance of the perovskite in terms of solar to fuel efficiency (being 0.46 the ratio between the potential energy recovery from the produced hydrogen and the solar heat required for its production), comparable or even higher than values reported in the literature for other metal oxides. These results confirm the La0.8Al0.2NiO3-δ perovskite as an auspicious material for a full-scale H2 production from water splitting by solar-driven thermochemical cycles at low temperatures.

2022, Eventos: Jornadas, foros, ferias

Jornada «Generación de calor solar para procesos industriales»

Resumen

El Pacto Verde Europeo establece el objetivo de alcanzar la neutralidad climática en 2050. Para ello, la Unión Europea se ha propuesto que al menos el 40% de la energía proceda de fuentes renovables de aquí a 2030, de conformidad con el Plan del Objetivo Climático. El pasado 18 de mayo, la Comisión Europea hizo pública la estrategia europea en energía solar. Se trata de una ambiciosa iniciativa dirigida a disminuir nuestra dependencia en combustibles fósiles en todos los sectores económicos, desde el sector residencial hasta los procesos industriales. La energía solar térmica adquiere un interés renovado en la industria, donde el calor supone el 70% de la demanda industrial. Más allá de las limitaciones de tipo administrativo y financiero, la industria encara nuevas oportunidades que requieren tecnologías más eficientes, que hagan uso de menos recursos (espacio, materiales, agua…), con mayor circularidad en el uso de materias primas y más sostenible en su ciclo de vida (incluyendo su fabricación). También surgen nuevas oportunidades en el uso de tecnologías solares térmicas, como por ejemplo en la hibridación con electricidad solar y con bombas de calor y en la producción de calor e hidrógeno renovable, ambos dirigidas a su uso en procesos industriales. En esta jornada, se debatirá sobre el apoyo de la I+D para responder a este reto y reúnen a varios ponentes que trabajan en este ámbito tanto desde el punto de vista empresarial, como de centros de investigación. La sesión proporcionará un panorama sobre la I+D asociada al calor solar en procesos industriales y finalizará con una mesa redonda abierta a la participación de los asistentes.

Ponentes

Sandra Cubero, SolarConcentra, ProtermoSolar

José Ignacio Ajona, SEENSO Renoval y ASIT

José González, IMDEA Energía e ISES

Antonio Rovira, UNED, ASTEP

Marcelino Sánchez, CENER y EERA

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Soiling effect in solar energy conversion systems: A review

Abstract

Optical and thermal integration analysis of supercritical CO2 Brayton cycles with a particle-based solar thermal plant based on annual performance

Abstract

Designing a flat beam-down linear Fresnel reflector

Abstract

Evaluating the Corrosion Resistance of Inconel 625 Coatings, Processed by Compact Plasma Spray, for Applications in Concentrating Solar Power Plants

Abstract

Alternative low-power plasma-sprayed inconel 625 coatings for thermal solar receivers: Effects of high temperature exposure on adhesion and solar absorptivity

Abstract

An optimisation method for the cold-spray process: On the nozzle geometry

Abstract

Development of stable porous silica-coated Ca(OH)2/γ-Al2O3 pellets for dehydration/hydration cycles with application in thermochemical heat storage

Abstract

Air solid packed-beds for high temperature thermal storage: practical recommendations for predicting their thermal behaviour

Abstract

Hydrogen production by thermochemical water splitting with La0.8Al0.2MeO3-δ (Me= Fe, Co, Ni and Cu) perovskites prepared under controlled pH

Abstract

Jornada «Generación de calor solar para procesos industriales»

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