Study of solid particle materials as high temperature Thermal Energy Storage and Heat Transfer Fluid for Concentrating Solar Power

Abstract

Renewable energies have a major role in today’s energy systems development, energy security and climate change fight. Thermal Concentrating Solar Power (CSP) has the potential to get up to 11.3% of world’s electricity production with the adequate support. This type of renewable energy has proved to be price competitive and to have the advantage of integrating Thermal Energy Storage (TES). This adds the generation flexibility that other renewable energies, like wind or photovoltaics, does not have integrated. In order to continue developing this technology, solid particle CSP has been proposed. This design uses granular solid materials as Heat Transfer Fluid (HTF) and TES material in solar towers in order to be able to achieve higher operation temperatures, than current commercial CSP. Higher temperature means more efficiency in heat-to-electricity conversion, due to the use of better power generation cycles. The main objective of this thesis is to enhance relevance and provide theoretical and experimental background for solid particles to be used as TES material and HTF for CSP tower power plants, from the materials perspective, by using existent or new methodologies. During this dissertation, current scientific output and relevance were studied in two separate contributions, one for CSP and the other for TES, both by using bibliometric methods. For the CSP study, additional analyses were carried out according to the harvesting technologies (parabolic trough, solar tower, Stirling dish and linear Fresnel). For the TES study, the additional analyses were performed according to the different ways to store thermal energy (sensible, latent and thermochemical). For both analyses, most productive countries, regions, authors, journals and research communities were identified. Moreover, funding impact and cooperation between countries and authors were analyzed. For developing these bibliometric analyses, a specific methodology was implemented following Bibliometrics principles. For these purposes, two existing software programs were used for a part of the analysis, while for performing the rest of the analysis a special software was developed ad-hoc for this study. For providing background, two state-of-the-art analyses were performed in order to get current development status of solid particle CSP. The first one was oriented to the plant design itself. Several solar receivers were analyzed, as well as TES, Heat Exchanger (HEX) and conveyance systems. During the second state-of-the-art, a material driven study was carried out in order to understand the behavior expected by the particle media and to identify some of the materials proposed by the most relevant researchers in this field. Next step of this dissertation was focused on establishing the design criteria for solid particle CSP technology, from the materials science perspective. This was achieved by finding the most relevant objectives that a power plant of this kind must comply, as well as the influence of the particle media properties and parameters. Last part of this dissertation is related with two studies regarding the durability of some of the most promising solid particle materials from high temperature exposure effect perspective. The first study was focused on analyzing the effect of long term high temperature (900 °C) in the optical, mechanical, thermal and chemical properties and parameters of the solid particle material. The second study was focused in the effect of long term thermal cycling, in which is considered that the materials should resist several thousand charge-discharge cycles remaining with acceptable operational conditions. For achieving an accelerated thermal cycling test with realistic thermal conditions, a novel device was developed to perform the thousands of thermal cycles required. Electronic, software and hardware design was developed and implemented. Current device has performed more than 20 thousand cycles for different kind of materials, analyzing the same properties and parameters as the first study.

Para continuar desarrollando la energía solar de concentración (CSP), se ha propuesto el uso de sólidos particulados. En este nuevo tipo de planta CSP de torre, se utilizan materiales sólidos granulados como Fluido de Transferencia de Calor (HTF) y material para el almacenamiento de energía térmica (TES). El objetivo principal de esta tesis es establecer la relevancia y proporcionar antecedentes, tanto teóricos como experimentales, sobre el uso de sólidos particulados para esta nueva tecnología. Durante este trabajo, la producción científica actual y la relevancia científica fueron estudiados mediante dos estudios bibliométricos, una para CSP y otra para TES. Para ambos análisis, se identificaron los países, regiones, autores, revistas, comunidades de investigación más productivos, el impacto del financiamiento y la cooperación entre países y autores. Para este fin, se utilizaron tres programas informáticos, de los cuales uno tuvo que se desarrollado a la medida. Se realizaron dos análisis del estado del arte para obtener el estado actual de desarrollo de las plantas CSP con uso de sólidos particulados. En el primero, se analizaron varios receptores solares, así como sistemas TES, intercambiadores de calor (HEX) y sistemas de transporte del material granulado. En el segundo, se llevó a cabo un estudio basado en los sólidos particulados, comprendiendo el comportamiento de estos materiales, así como recopilar los materiales potenciales. Se establecieron los criterios de diseño desde la perspectiva de los materiales, logrando encontrar los objetivos relevantes, y la influencia de las propiedades y parámetros de estos materiales. Se realizaron dos estudios sobre la durabilidad en cuanto a la exposición a altas temperaturas. El primero, se centró en analizar el efecto de la temperatura a largo plazo y su efecto en las propiedades ópticas, mecánicas, térmicas y químicas. El segundo, se centró en el efecto de los miles de ciclos térmicos esperados. Se desarrolló un nuevo dispositivo capaz de realizar los ciclos térmicos requeridos en las condiciones requeridas. Se desarrolló e implementó el diseño electrónico, de software y de hardware. Se caracterizaron las mismas propiedades analizadas en el primer estudio.