Advances in the design of solar concentrators for thermal applications

This thesis presents advances in the design of solar concentrators. Based on the study of the Compact Linear Fresnel Re ector Concentrator "Etendue-Matched" (CLFREM), this thesis developed optical solutions based on the Simultaneous Multiple Surface method (SMS) and new approaches of analysis of the characterizing parameters of a solar concentrator. This thesis is organized into ve sections. In the rst section (Chapters 1 and 2) an introduction to the topics addressed in this work is presented together with a revision of the underlying basic optics. In the second section (Chapters 3, 4, and 5) a study of the concentrator CLFR-EM is presented. In the third section (Chapters 6 and 7) a XX SMS concentrator for continuum primaries is developed and presented. In the fourth section (Chapter 8) the application of the concept XX SMS for Fresnel primaries is explained and shown. Finally, in the fth section (Chapters 9 and 10) prospects for future developments and conclusions concerning this work are presented; Avan cos no desenho de concentradores solares para aplicações termicas Resumo: Esta tese apresenta desenvolvimentos na an álise de concentradores solares térmicos. Partindo do estudo realizado sobre o concentrador Compact Linear Fresnel Re ector "Etendue-Matched" (CLFR-EM), esta tese propoem solucoes opticas baseadas no método de Simultaneous Multiple Surface (SMS) e novas abordagens a análise dos parâmetros caracterizadores de um concentrador solar. A tese está organizada em cinco secções. Na primeira secção (Cap itulos 1 e 2) e realizada uma introdução aos temas abordados neste trabalho e uma revisão dos conceitos básicos de optica. Na segunda sec ção (Capitulos 3, 4 e 5) e apresentado um estudo do concentrador CLFREM. Na terceira secção(Capitulos 6 e 7) e apresentado um concentrador XX SMS para primários continuos para concentração máxima e receptores xos. Na quarta secção(Capitulo 8) mostra-se a aplicação do conceito XX SMS a prim arios Fresnel. Por ultimo, na quinta secção(Capitulos 9 e 10) são apresentadas perspectivas para desenvolvimentos futuros e realizadas conclusões sobre este trabalho

Évora Molten Salt Platform (EMSP) – Current Status and Perspectives

The construction of a molten salt test facility in Évora ( is converging to the finalization of its erection and commissioning phase It aims at the development of applied research in molten salt driven CSP, SHIP and thermal energy storage components, systems and technologies The EMSP is jointly managed and operated by the Renewable Energies Chair of the University of Évora and the DLR Institute of Solar Research Here, we present the projects which are currently set up at the EMS

New Optical Designs for Large Parabolic Troughs

The potential for cost reduction in parabolic troughs (PT) large collector fields is real and will be achieved in a variety of different ways. One problem certainly contributing to the costs of Solar Thermal Electricity (STE) PT fields is certainly the fact that large fields have a significant quantity of receiver lines and pipes bringing the heat transfer fluid to and off from them. The very large pipe length in large collector fields (for instance the 50MW fields in Spain) is a source of heat losses and parasitic losses due to significant pumping power, but also a source of other costs related to the number of pumps, to the amount of (costly) circulating fluid etc. In any given large field, receiver length and pipe length are determined by the aperture size of the PTs and one way to reduce these impacts on cost would be to increase aperture size. This has been the idea behind developments like the Ultimate Trough. In this paper new optical solutions are presented to obtain much larger troughs, using the same “standard” evacuated 70 mm inner radius tube, which in fact amounts to a substantial increase of concentration, but without sacrificing the acceptance angle of the optic. The Simultaneous Multiple Surface (SMS) method is used and practical solutions are obtained for apertures nearly close to twice the present standard of ≈ 6m width. The case of troughs for fixed receiver tubes is also discussed in this context. The solutions developed minimize transmission losses due to the glass cover and in that sense are an improvement on previous work. They also achieve a higher optical performance than other second stage solutions, because they are designed to eliminate optical losses through large gaps, something that is associated with the fact that the outer glass envelope has a much larger diameter than the inner receiver tube. The paper presents new examples of larger troughs with second stage concentrators, characterizing and comparing them with a “conventional” PT. The comparison is done for optical properties and for the energy collected on a sunny location (Faro, Portugal). The paper ends with a similar exercise done for fixed receiver troughs, an exercise that also leads to larger troughs (since it is done for the same 70 mm inner (evacuated) receiver tube) and concentration is increased. Again optical properties and energy performance are presented and compared with the conventional PT. The new solutions represent a potential reduction in field costs or even in O&M, as suggested, and this exercise will enable manufacturers the pondering of the manufacture of larger troughs (perhaps cheaper on a sqm basis) but with the extra cost of a secondary concentrator, knowing how much energy to expect from the adoption of solutions that benefit non-imaging optics design methods

Efficiency Improvement and Potential LCOE Reduction with an LFR-XX SMS Plant with Storage

Several forms of renewable energy have in the last decade achieved a remarkable technological improvement and cost effectiveness, including Solar Energy. Photovoltaic systems (PV) are reaching grid parity in the sunniest regions of Europe. Apart from PV, a promising technology is Concentrated Solar Power (CSP) with thermal storage, because it enables higher power plant availability throughout the year as well as dispatchability, a highly important and valuable feature for a power plant. However significant cost reductions are still to be achieved, for CSP to be competitive with conventional electricity production and with PV. In this paper a few technological improvements are described and a proposal is made to combine them in a system that is more efficient and has, simultaneously, the potential of being cheaper. The goal is to show the potential for advanced LFR concepts in combination with high temperature molten salt mixtures and energy storage as being also important contenders to the objective of bringing STE- Solar Thermal Electricity to the market in a competitive way. The concept presented and developed includes a higher ΔT of the heat transfer fluid (HTF), a particular storage strategy and a new optical concept based on a new Linear Fresnel Concentrator (LFR XX SMS-Simultaneous Multiple Surface, Fig.1,2, [1] enabling an important increase in the overall yearly solar to electricity conversion efficiency and generating an important potential for electricity cost reduction. It is shown that values approaching 10eurocents/kWh, for a 50MW plant with 7 hours storage capacity are possible in Southern Europe

Increasing the Cost Effectiveness of CSP Technologies Through the Development of a New CLFR “Etendue Matched” Collector

A new CLFR “Etendue Matched” is a promising CSP technology to achieve a better cost effectiveness with a lower levelized cost per m2 . This new technology can significantly reduce shading and blocking existing in a conventional LFR (Chaves, 2009; Chaves, 2010), while at the same time optimizing primary and secondary concentration to the limits allowed by first principles in optics. A preliminary evaluation of the optical and thermal performance has been performed (Canavarro, 2010, Horta 2011), and a configuration for a full scale CSP power plant proposed, with two secondary receivers (Fig.1), i.e a multiple receiver solution

Etendue-Matched Solar Tower Beam-Down System for High-Temperature Industrial Processes

The standard Concentrating Solar Thermal (CST) mono-tower technology, which uses one receiver placed on top of a tower to which all heliostats in the heliostat field aim to, is regarded as one of the best and most promising technologies for various CST-driven applications, namely CST power plants, solar metallurgical processes, thermochemical production of solar fuels and waste materials recycling. However, the technology has some technical challenges concerning optical performance/tolerances, system dimensions, operation and maintenance issues, etc. An alternative to this standard CST mono-tower technology is the so-called beam-down technology, where a special mirror is placed on the top of the tower, instead of a receiver, to redirect the incident radiation from the heliostat field onto a receiver/reactor placed closer to the ground and potentially delivering higher concentrations at the receiver than the standard CST mono-tower technology. This paper presents a new approach to improve the optics of beam-down systems, applies it to the optical design of a specific system, and shows the optical behavior of this design at two locations: Évora (Portugal) and Hurghada (Egypt). The approach uses etendue-matching between all the optical stages to minimize the optical losses between them. To analyze the optical behavior of the system designed, as an example, using the etendue-matching approach, raytracing simulations were carried out and are presented also in the paper.Projecto H2020 INSHIP - Grant No. 731287

INIESC : infraestrutura nacional de investigação em energia solar de concentração

A INIESC, Infraestrutura Nacional de Investigação em Energia Solar de Concentração, parte integrante do Roteiro Nacional de Infraestruturas de Investigação, apresenta-se como a infraestrutura experimental de referência, em Portugal, no domínio das tecnologias e aplicações da energia solar a média e alta temperatura. Liderada pela Universidade de Évora e desenvolvida em parceria com o Laboratório Nacional de Energia e Geologia, I.P., a infraestrutura conta com dois pólos: Évora e Lisboa. Visando investigação que promove uma potenciação do contributo da energia solar na descarbonização de diferentes sectores da economia – geração eléctrica, transportes, gestão do sistema energético, comunidades energeticamente independentes, processos industriais – as actividades da INIESC abarcam tópicos que incluem, e.g., o desenvolvimento de tecnologias de colectores, o armazenamento de energia, a produção de combustíveis por via solar e a durabilidade de materiais. Neste artigo apresenta-se o estado actual de desenvolvimento da infraestrutura, assim como um resumo das actividades de I&D nela desenvolvidas até ao presente

Projeto ENBRAIN: transferência de capacidades na área das energias renováveis para a Líbia

PROJECTO ENBRAIN: TRANSFERÊNCIA DE CAPACIDADES NA ÁREA DAS ENERGIAS RENOVÁVEIS PARA A LÍBIAO projeto ENBRAIN é cofinanciado pelo programa Erasmus+ Capacity Building in Higher Education da União Europeia (Grant Reference 2017 - 3484 / 001 - 001)

Simultaneous multiple surface method for the design of new parabolic dish-type concentrator using a Cassegranian approach

Parabolic Dish concentrators are a well-known solution for many applications such as Concentrated Solar Power (CSP), solar metallurgical processes, solar reactors for fuel production, etc. Nevertheless, this technology is facing a tremendous challenge to become more efficient and competitive (especially within CSP field) in comparison with other technologies, namely Central Tower Receivers. A possible path to achieve this goal is to use a Cassegranian approach which enables a top-down design, placing the receiver closer to the ground and with potential higher concentration. In this paper, the theoretical limit of such configurations and a practical solution is presented with a discussion of its advantages and possible drawbacks

A cumulative risk model of child physical maltreatment potential: findings from a community-based study

"Published online before print November 20, 2015"Previous studies have identified the predictive risk factors of child physical maltreatment (CPM). However, a significant number of these studies assessed risk factors in isolation. The cumulative risk hypothesis postulates that health problems are caused by the accumulation of risk factors, independently of the presence or absence of specific risk indicators. Few studies examined the effect of cumulative risk on CPM potential. This study aimed to test two concurrent models of cumulative risk of CPM potential by investigating whether CPM potential was better predicted by a threshold cumulative risk model or a linear cumulative risk model. Data from the National Representative Study of Psychosocial Context of Child Abuse and Neglect in Portugal were used. Parents of school-age children (N = 796) answered to self-report measures regarding sociodemographic variables, history of child maltreatment, psychological distress, and CPM potential. A cumulative risk index was computed, comprising 10 dichotomized risk factors. Evidence for a threshold cumulative effect was found. Additional bivariate logistic regressions revealed that the odds for high-potential CPM were dramatically higher for those parents with six or more risk factors when compared with parents with any one risk factor. By testing and confirming a threshold cumulative effect on CPM potential, it was possible to find a "trigger point" from which a dramatic increase in child physical maltreatment potential occurs.This study was supported by the Portuguese Foundation of Science and Technology through a research grant to the second author (POCTI/PSI/14276/1998