Multilayer solar selective coatings for high temperature solar applications: from concept to design

Increasing the share of renewables in the energy mix has a key function for the security of energy supply and the reduction of greenhouse gas emissions from fossil fuels. The purpose of this thesis is to develop new solar selective coating (SSC) designs for high temperature applications in order to improve the performance of concentration solar power (CSP) plants. The main part of this thesis has been carried out in the company Abengoa, which is a world leader in the development of CSP plants, but also with the collaboration of other well-recognized academic organizations (Instituto de Ciencia de Materiales de Sevilla-CSIC, Center Tecnologic Manresa and the Helmholtz-Zentrum Dresden - Rossendorf) and the SME Metal Estalki. The improvement in efficiencies in solar thermal energy plants partially means the increase in the receivers’ temperature, reaching up to an average maximum temperature of 650ºC for superheated steam and molten salts receivers. There are several R&D approaches to substitute commercial absorber paints due to the degradation problems they show at high temperatures when exposed at air. The different routes include the development of new solar selective coatings fabricated using physical vapour deposition techniques. In this thesis, two potential candidates as solar selective coatings were selected: i) carbon–transition metal carbides nanocomposites (a-C:MeC) and ii) aluminium titanium oxynitride (AlTi(OxN1-x)) based coatings. The methodology followed in this thesis contains aspects of very high novelty including optical simulation, coating deposition using cathodic vacuum arc (CVA) and advanced characterization. The computer program CODE was used to simulate the reflectance spectra of different complete coating. Simulated reflectance spectra were compared with the measured reflectance of the deposited films to verify the agreement between simulations and experimental results. The simulations allowed predicting the optical properties of solar selective coatings with different thicknesses and with different materials avoiding a try and error approach. Special attention was paid to the simulation of optical constants. The knowledge of the coating microstructure revealed critical for a proper design of solar selective coatings. In this thesis, valuable insight into the most accurate way of simulating nanocomposite materials and oxynitrides is given. Several optical models were evaluated and their appropriateness described in detail. Different SSC stacks were deposited with pulsed filtered cathodic vacuum arc (PFCVA) and non-filtered CVA setup comparing different materials, compositions and thicknesses for each one of the layer that conforms the coating. After the deposition of single layers and complete SSC, the stacks were characterized employing a wide range of techniques. The optical properties were characterized by UV-Vis-NIR and FT-IR spectrophotometers; the elementary compositions were determined by Rutherford Backscattering Spectroscopy (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection (ERD) ion beam techniques; the crystal structure was studied with X-ray diffraction and Raman spectrometry was used to determine the chemical bonding of the carbon atoms; and finally, SEM and HR-TEM were employed to determine the morphology of the deposited thin films. The unique cluster tool (sited at HZDR) allowed the in-situ characterization of the films performance at high temperature. This novel technique provided a detailed study of the diffusion processes occurring at extreme temperatures in solar selective coatings of interest and the identification of their failure mechanism. The simulations, depositions and characterizations performed for the two selected candidate materials for SSC are thoroughly described in the following chapters. The introductory chapter 1 starts with a brief description of the advantages of thin films and coatings versus their bulk counterparts, followed by a summary of physical vapour deposition (PVD) techniques and the main growing mechanisms of thin films. The fundamental principles of the interaction of light with materials are also introduced, in order to get a better understanding of the thin film optical properties. The chapter ends with a summary of the current state of the art of SSC and the mechanisms employed to maximize the absorption of sunlight and to minimize the losses by thermal radiation. The methodology followed in this thesis for a complete design of solar selective coatings is fully explained in chapter 2. The design process starts with the selection of the material that composes each layer in the multilayer stack. Then, the different deposition systems employed are described followed by the complete characterization performed on the deposited thin films. Finally, the thermal treatment tests included in this work to analyse the durability in air at high temperatures and to predict their service lifetime are explained. Chapter 3 introduces the properties of transition-metal carbides and carbon as the individual components of the nanocomposite (a-C:MeC). Nanocomposite thin films consisting of interstitial metal carbide embedded in an amorphous carbon matrix exhibit a unique combination of properties which makes them very attractive candidates as absorber layer of SSC for thermo-solar applications. In a first step, optical simulation based on literature optical constants was employed for optimizing SSC. After this initial simulations, the selected a-C:MeC candidates were deposited and characterized. Following a thorough analysis of their composition and microstructure, the simulations were feedback with experimental data. The simulated complete coating based on these measured properties provided excellent selective optical selective properties (α>96% and ε600ºC<14%). A complete solar selective coating was deposited and analysed and afterwards a heating test was performed to study the stability of the coating at high temperature. Aluminium titanium oxynitrides were selected as candidate materials for SSC on basis of the state of the art described in the introduction of chapter 4. In this chapter, initial thermal treatment tests were performed to validate the stability of single oxynitride layers in air, showing no degradation at temperatures above 600ºC. A set of individual AlTi(OxN1-x) layers deposited by CVA were analysed in terms of composition, morphology and optical properties. A thoroughly study of the microstructure of the films, as a function of the oxygen content, was found to be key for a comprehensive analysis of the optical properties. A complete multilayer SSC was designed and deposited with optical simulations based on measured optical constants of each of the individual layers. Excellent agreement was found between simulated and experimental reflectance spectra. A solar selective coating with a simulated absorptance of 94,7% and an emittance of 5,6% is designed. To conclude, the thermal stability in air of the complete SSC was analysed by asymmetric and cyclic heating tests. Remarkable stability at temperatures as high as 650ºC after 750 hours of annealing was found for solar selective coatings based on oxynitrides. Chapter 5 described a novel technology for the in-situ characterization of coatings at high temperatures. This characterization is performed at the two materials candidates. In particular, an accurate knowledge of the variation of the dielectric function of thin films with the temperature and its relation to compositional and microstructural changes could help to prevent failures. The methodology employed combines a sequence of analytical techniques. An a-C:TiC thin film was studied first following the described methodology. Then, AlTi(OxN1-x) thin films with different oxygen concentration were investigated in order to understand the influence of the oxygen to nitrogen ratio on the optical properties and their failure mechanisms at high temperatures. No significant changes in optical properties and composition were found when heating oxynitride films in vacuum atmosphere at temperature above 800ºC, showing excellent high temperature stability. It is worth noting than a worldwide record of in-situ RBS measurement at 840ºC was performed in the framework of this thesis. The main conclusions of the thesis are discussed in chapter 6, including a comparative review of the different materials employed for SSC, along with the strengths and weaknesses observed for each one.Aumentar la cuota de energías renovables en el mix energético es fundamental para asegurar el abastecimiento de energía y disminuir las emisiones de gases de efecto invernadero asociadas al uso de combustibles fósiles. El objetivo de la presente tesis es desarrollar nuevos recubrimientos solares selectivos (SSC por sus siglas en inglés), estables a alta temperatura, que supongan una mejora en el rendimiento de las plantas de energía solar de concentración (CSP). La mayor parte del trabajo descrito en esta tesis se ha llevado a cabo en la compañía Abengoa, que es líder internacional en el desarrollo de plantas CSP. Sin embargo, ha sido fundamental la colaboración con centros de investigación como son el instituto de Ciencia de los Materiales de Sevilla, el Centro Tecnológico Manresa, el centro Helmholtz Zentrum Dresden-Rossendorf, y la compañía Metal Estalki. El incremento de la eficiencia de las plantas CSP pasa en parte por conseguir un aumento de la temperatura de trabajo del receptor, llegando a una temperatura media máxima de 650ºC en el caso de receptores de vapor sobrecalentado y de sales fundidas. Desde un punto de vista de investigación y desarrollo de materiales ha habido diferentes intentos de sustituir las pinturas comerciales usadas actualmente en los receptores pero que presentan degradación en aire a altas temperaturas. De especial interés es el desarrollo de SSC fabricados usando técnicas de deposición al vacío realizado por diversos grupos en el mundo en los últimos años. En esta tesis, se han seleccionado dos tipos de materiales para formar recubrimientos SSC: i) nanocompuestos de carbono y carburos de metales de transición (a-C:MeC); y ii) oxinitruros de aluminio-titanio. La metodología que se ha seguido en este trabajo contiene aspectos novedosos en materia de simulación, deposición por arco catódico (CVA) y caracterización avanzada de recubrimientos selectivos. Para simular la reflectancia de los distintos recubrimientos se ha utilizado el programa de simulación óptica CODE. La validez de los resultados de simulación se ha confirmado mediante la comparación de los espectros de reflectancia simulados con los medidos experimentalmente. La simulación permite predecir el comportamiento óptico de los recubrimientos en función de parámetros tales como el material del que están formados o el grosor de sus distintas capas. Durante este trabajo se ha prestado especial atención a la simulación de las constantes ópticas de los materiales. Se ha demostrado también, que el conocimiento de la microestructura del material es en muchas ocasiones fundamental para el diseño de recubrimientos solares selectivos. La idoneidad de varios modelos ópticos se ha evaluado y descrito en detalle, y como consecuencia, esta tesis supone una valiosa aportación al correcto modelado de las propiedades ópticas de materiales nanocompuestos y oxinitruros. Utilizando como técnicas de deposición el arco catódico pulsado y filtrado (PFCVA), y el arco catódico no filtrado (CVA), se han depositado numerosos capas finas individuales, y también recubrimientos solares selectivos completos. Sus propiedades se han caracterizado de una manera exhaustiva utilizando un gran número de técnicas de análisis. Las propiedades ópticas de las películas se han caracterizado usando espectrofotómetros UV-Vis-NIR y FT-IR. La composición elemental se obtuvo mediante las siguientes técnicas de análisis de iones: espectrometría retrodispersión de Rutherford (RBS), análisis de reacción nuclear (NRA) y detección del retroceso elástico (ERD). La estructura cristalina se analizó por difracción de rayos X, y la espectroscopía Raman se usó para determinar el enlace químico en los átomos de carbono presentes en los nanocompuestos. La morfología y la microestructura se estudiaron mediante SEM y HR-TEM. Mediante el sistema de cluster tool situado en el centro HZDR, fue posible llevar a cabo una caracterización in-situ del comportamiento de los recubrimientos a alta temperatura. Este sistema supone una técnica novedosa para estudiar los procesos de difusión que tienen lugar a alta temperatura en los recubrimientos solares selectivos, permitiendo identificar sus mecanismos de fallo. En los distintos capítulos que conforman la presente tesis se describen en detalle las simulaciones, las deposiciones y la caracterización llevada a cabo en los dos tipos de materiales seleccionados como candidatos para recubrimientos solares selectivos. El capítulo 1, que sirve de introducción, comienza con una breve descripción de las ventajas de las películas finas respecto a los materiales en volumen, seguida de un resumen de algunas técnicas de deposición física al vacío (PVD) y los principales mecanismos de crecimiento de las películas finas. Con el objeto de conocer mejorar los principios que determinan las propiedades ópticas de estos recubrimientos, se incluyen en esta introducción algunos aspectos fundamentales de la interacción de la luz con los materiales. El capítulo termina con una revisión del estado del arte en SSC, incluyendo los distintos mecanismos que han sido empleados para intentar maximizar la absorptancia y disminuir la emitancia de este tipo de recubrimiento. En el capítulo 2 se describe en detalle la metodología seguida en la presente tesis para el diseño de un recubrimiento solar selectivo completo. El proceso comienza con la elección de los materiales que van a formar las distintas capas del recubrimiento, seguido de la descripción de los distintos equipos que se van a utilizar para su fabricación. Finalmente, las técnicas de caracterización empleadas así como los procedimientos para testar la durabilidad de los recubrimientos son descritos. El capítulo 3 comienza con una descripción de los materiales que forman los nanocompuestos a-C:MeC: el carbono y los carburos de metales de transición. Como se describe en detalle en este capítulo, los nanocompuestos formados por carburos de metales de transición embebidos en una matriz de carbono amorfo presentan una combinación única de propiedades que los hace ser candidatos muy prometedores para formar la capa absorbedora de un SSC para aplicaciones termosolares. En un primer momento se llevaron a cabo simulaciones ópticas basadas en constantes ópticas obtenidas de la literatura para optimizar el comportamiento de los SSC. Estas simulaciones sirvieron para hacer una primera selección de materiales nanocompuestos que fueron posteriormente depositados y caracterizados. Después de un completo análisis de su microestructura y composición, las simulaciones se retroalimentaron con los datos experimentales obtenidos. Estas simulaciones dieron lugar al diseño de un recubrimiento basado en nanocompuestos de carbono con excelentes propiedades ópticas (α>96% and ε600ºC<14%). Finalmente se fabricó un recubrimiento completo y se sometió a un tratamiento térmico a alta temperatura. La elección de los oxinitruros de aluminio titanio como candidatos para fabricar recubrimientos solares selectivos está ampliamente justificada en el estado del arte recogido en el capítulo 4. El estudio de estos recubrimientos comienza con una prueba de estabilidad inicial que muestra que son estables en aire por 2 horas a temperaturas por encima de 600ºC. Capas individuales de AlTi(OxN1-x) depositadas por CVA se analizaron en términos de composición, morfología y propiedades ópticas. Como se verá en este capítulo, un estudio exhaustivo de la microestructura de las películas ha resultado ser crítico para el análisis de las contantes ópticas de estos materiales. En base a simulaciones que emplean constantes ópticas medidas experimentalmente en capas individuales, se han diseñado y depositado recubrimientos SSC completos, encontrándose una excelente concordancia entre la reflectancia simulada y la medida experimentalmente. Se ha diseñado un recubrimientos solar selectivo basado en oxinitruros de aluminio titanio con una absorbancia simulada del 94,7 % y una emitancia del 5,6%. Finalmente, los recubrimientos depositados se sometieron a distintos tratamientos térmicos, presentando una excelente estabilidad tras un tratamiento térmico con una duración de 750ºC y una temperatura de testado de 650ºC. El capítulo 5 describe una novedosa metodología para caracterizar in-situ recubrimientos a alta temperatura. Esta caracterización se lleva a cabo en los dos materiales candidatos descritos en los capítulos anteriores. El objetivo de esta caracterización es conocer cómo las constantes ópticas varían con la temperatura y cómo este cambio se relaciona con variaciones de la microestructura para así prevenir posibles mecanismos de fallo. La metodología empleada comprende una serie de técnicas de análisis que se aplican sobre las muestras de manera secuencial. Primero se ha analizado un nancompuesto de a-C:TiC siguiendo la metodología descrita en este capítulo. Tras este análisis, películas de AlTi(OxN1-x) con distintos contenidos de oxígeno se han caracterizado para ver cómo la composición influye en los mecanismos de fallo a alta temperatura. Los recubrimientos de oxinitruros presentaron una excelente estabilidad en vacío a temperaturas por encima de los 800ºC. También es importante resaltar que en esta tesis se describe el récord mundial de medida de RBS in-situ a alta temperatura (840ºC). Las principales conclusiones se resumen en el capítulo 6, que incluye una comparativa de los distintos materiales empleados, así como las ventajas e inconvenientes detectados en el uso de cada uno de ellos como SSC

On the effect of thin film growth mechanisms on the specular reflectance of aluminum thin films deposited via filtered cathodic vacuum arc

The optimisation of the specular reflectance of solar collectors is a key parameter to increase the global yield of concentrated solar power (CSP) plants. In this work, the influence of filtered cathodic vacuum arc deposition parameters, particularly working pressure and deposition time, on the specular and diffuse reflectance of aluminium thin films, was studied. Changes in specular reflectance, measured by ultraviolet–visible and near-infrared spectroscopy (UV-vis-NIR) spectro photometry, were directly correlated with thin film elemental concentration depth profiles, obtained by Rutherford backscattering spectrometry (RBS), and surface and cross-sectional morphologies as measured by scanning electron microscopy (SEM) and profilometry. Finally, atomic force microscopy (AFM) provided information on the roughness and growth mechanism of the films. The two contributions to the total reflectance of the films, namely diffuse and specular reflectance, were found to be deeply influenced by deposition conditions. It was proven that working pressure and deposition time directly determine the predominant factor. Specular reflectance varied from 12 to 99.8% of the total reflectance for films grown at the same working pressure of 0.1 Pa and with different deposition times. This transformation could not be attributed to an oxidation of the films as stated by RBS, but was correlated with a progressive modification of the roughness, surface, and bulk morphology of the samples over the deposition time. Hence, the evolution in the final optical properties of the films is driven by different growth mechanisms and the resulting microstructures. In addition to the originally addressed CSP applications the potential of the developed aluminium films for other application rather than CSP, such as, for example, reference material for spectroscopic diffuse reflectance measurements, is also discussed

Multiscale thermo-mechanical analysis of multi-layered coatings in solar thermal applications

Solar selective coatings can be multi-layered materials that optimize the solar absorption while reducing thermal radiation losses, granting the material long-term stability. These layers are deposited on structural materials (e.g., stainless steel, Inconel) in order to enhance the optical and thermal properties of the heat transfer system. However, interesting questions regarding their mechanical stability arise when operating at high temperatures. In this work, a full thermo-mechanical multiscale methodology is presented, covering the nano-, micro-, and macroscopic scales. In such methodology, fundamental material properties are determined by means of molecular dynamics simulations that are consequently implemented at the microstructural level by means of finite element analyses. On the other hand, the macroscale problem is solved while taking into account the effect of the microstructure via thermo-mechanical homogenization on a representative volume element (RVE). The methodology presented herein has been successfully implemented in a reference problem in concentrating solar power plants, namely the characterization of a carbon-based nanocomposite and the obtained results are in agreement with the expected theoretical values, demonstrating that it is now possible to apply successfully the concepts behind Integrated Computational Materials Engineering to design new coatings for complex realistic thermo-mechanical applications.Peer ReviewedPostprint (author's final draft

On-design and off-design thermodynamic analysis of a hybrid multi-stage solar thermal tower power plant

[ENConcentrated solar power (CSP) is one challenging renewable technology for the future production of electricity. Within this concept central receiver solar plants combined with gas turbines are being investigated because of their promising efficiencies and reduced water consumption. Hybrid plants incorporate a combustion chamber in such a way that in periods of low solar irradiance power output can be kept approximately constant and so, electricity production is predictable. An integrated, non-complex solar thermodynamic model of a hybrid multi-stage gas turbine solar plant is developed employing a reduced number of parameters with a clear physical meaning. The solar subsystem is modelled in detail, taking into account the main heliostats field losses factors as cosine effect, blocking, or attenuation. The model is implemented in our own software, developed in Mathematica® language, considering as reference Gemasolar solar field (Seville, Spain). First, an on-design analysis is performed for four different working fluids (dry air, nitrogen, carbon dioxide, and helium), for different number of expansion and compression stages, and for recuperative and non-recuperative modes. Moreover, heliostats field configuration is determined for the design point and its associated efficiency is computed. A pre-optimization process is carried out regarding the pressure ratio of the gas turbine for different configurations. Some significant efficiency and power rises can be obtained when pressure ratio is adapted for each specific configuration and working fluid. Three particular plant configurations are chosen for the off-design analysis due to their interesting behaviours. For these configurations, a dynamic study is performed for four representative of each season. Then, efficiencies and solar share are plotted against time. In addition, fuel consumption and greenhouse emissions are computed for all seasons. Heliostats efficiency varying with the season and the solar time is also forecasted. Keywords: Dynamic analysis, On-design pre-optimization, Multi-stage gasJunta de Castilla y León of Spain (project SA017P17

Thermo-economic study of hybrid parabolic dish solar power plants in different regions of Spain

[EN]Small-scale hybrid parabolic dish Concentrated Solar Power (CSP) systems coupled to a micro-gas turbine are a promising option to obtain electrical energy in a distributed manner. During the day, solar energy is used to produce electricity and the absence of sunlight can be overcome with the combustion of a fossil or renewable fuel. This study presents the technical feasibility and thermo-economic model of a hybridized power plant in different regions of Spain, considering the local climatic conditions. The implemented model aims to provide a realistic view of the behaviour of the system, using a reduced number of selected parameters with a clear physical meaning. The irreversibilities taking place in all subsystems (solar part, combustion chamber, micro-gas turbine, and the corresponding heat exchangers) have been considered in the model, developed in Mathematica® language. The model considers the instant solar irradiance and ambient temperature dynamically, providing an estimation of the power output, the associated fuel consumption, and the most relevant pollutant emissions (CO2, CH4 and NO2) linked to combustion, for hybrid and combustion only operating modes at selected geographical locations in Spain. The considered power output ranges between 7 to 30 kWe which is achieved by varying the design specifications. The levelized cost of electricity (LCoE) indicator is estimated as a function of investment, interest rate, maintenance and fuel consumption actual costs in Spain. The electricity costs from hybrid parabolic dish are between 22% and 27% lower compared to pure combustion power plant, while specific fuel consumption and therefore CO2 emissions can be reduced up to 33%. This model shows the potential of hybrid solar dishes to become cost-competitive against non-renewable ones from the point of view of electricity costs and significant reduction in gas emission levels in regions with high solar radiation and low water resources.Junta de Castilla y Leó

On-design pre-optimization and off-design analysis of hybrid Brayton thermosolar tower power plants for different fluids and plant configurations

[EN]A working fluid performs a Brayton cycle that is fed by a heat input from a solar power tower and from a combustion chamber, which burns natural gas. This hybrid system is described by a complete model that includes all the main losses and irreversibility sources (optical and thermodynamic). Numerical implementation and validation is performed based on a Spanish commercial plant. On-design computations are carried out varying the pressure ratio for four working fluids (dry air, nitrogen, carbon dioxide, and helium), for different number of stages and for recuperative and non-recuperative configurations. When adjusting the pressure ratio, an improvement of about 7% in overall thermal efficiency is predicted for a dry air single-stage recuperative configuration with respect to a standard commercial gas turbine. A study about the main energy losses in each plant subsystem for some particular plant layouts is accomplished. A two-compression and expansion stages recuperative Brayton cycle working with air is expected to give overall thermal efficiencies about 0.29 at design conditions, which is about a 47% increase with respect to the simplest single-stage configuration. It is stressing that fuel consumption from the reheaters maybe higher than that of the main combustion chamber for multi-stage layouts. Off-design hourly curves of output records for the four seasons throughout a day are analyzed. Greenhouse emissions are also analyzed. Specific carbon dioxide emissions are smaller for helium than for dry air, when they both work in a single-stage non-recuperative configurationJunta de Castilla y León SA017P1

Thermodynamic and Cost Analysis of a Solar Dish Power Plant in Spain Hybridized with a Micro-Gas Turbine

[EN]Small-scale hybrid parabolic dish concentrated solar power systems are a promising option to obtain distributed electricity. During the day, solar energy is used to produce electricity, and the absence of sunlight can be overwhelmed with fuel combustion. This study presents a thermo-economic survey for a hybridized power plant in different regions of Spain, considering the local climatic conditions. The developed model considers the instant solar irradiance and ambient temperature dynamically, providing an estimation of the power output, the associated fuel consumption, and the most relevant pollutant emissions linked to combustion. Hybrid and combustion-only operating modes at selected geographical locations in Spain (with different latitudes, mean solar irradiances, and meteorological conditions) are analyzed. The levelized cost of electricity indicator is estimated as a function of investment, interest rate, maintenance, and fuel consumption actual costs in Spain. Values of about 124 e/MWhe are feasible. Fuel consumption and emissions in hybrid operation can be reduced above 30% with respect to those of the same turbine working in a pure combustion mode. This model shows the potential of hybrid solar dishes to become cost-competitive against non-renewable technologies from the point of view of costs and reduction in gas emission levels in regions with high solar radiation and low water resources.University of Salamanca Grant Number PC-TCUE18-20-002, Junta de Castilla y León of Spain Grant Number SA017P17

Heliostats field for a hybrid Brayton concentrated solar power plant

[EN]Concentrated solar power plants, a renewable energy technology, constitute one of the best ways of producing dispatchable and clean energy. In central receiver plants, a heliostats field concentrates the Sun energy into a receiver located in the top of a central tower. This receiver transfers the solar heat to a power cycle. The present work is focused on modeling the heliostat field of the power plant. For that, some geometric and size parameters of the receiver, the tower and the heliostats are taken into account. In the solar energy transfer process, there exist several losses factors as the solar radiation blocking between heliostats or the solar radiation attenuation due to the atmospheric particles. The heliostats field model has been implemented in Mathematica®, creating our own software. For the model validation process, Campo Code software (a standard well-accepted package) [1] has been employed. Results from our model have been compared to the ones of Campo Code getting similar values. Optical efficiency has been evaluated at the design point (see Fig. 1) and at dynamic conditions through different seasons and along a day. For the design point (21st June 2013 at 12h), this efficiency gets values around 0.674. Heliostats field efficiency maps for the different simulations show that the highest efficiency is always related to the heliostats opposite the Sun, which agrees with the results obtained by W. Stine and M. Geyer [2]

Hybrid parabolic-type thermosolar gas-turbine power plants: working fluid analysis

[EN]This work provides an integrated design of a small-scale hybrid solar power plant aimed at distributed generation of electrical energy. This technology may be especially interesting for remote areas with no access to electricity and advantageous solar conditions. The inherent limitations of a solar-only power plant (seasonal and meteorological sun fluctuations, nights) may be overcome with a hybrid operation mode. These systems can work uninterruptedly with an approximately constant power output, since the pressurized air of the cycle is heated from the concentrated solar irradiance and, when necessary, from the combustion of a fossil fuel. Then, the transformation of thermal energy to mechanical one is carried out by means of a Brayton thermodynamic cycle and a system of alternators