Concentrating Solar Thermal Technologies Research Articles

Impact of ambient temperature on supercritical CO2 recompression Brayton cycle in arid locations: Finding the optimal design conditions

In this paper, we present a new method to determine the optimal design conditions of a supercritical CO2 recompression Brayton cycle with dry cooling based on plant location. These power cycles are gathering high interest in concentrated solar thermal power technologies, which are most likely to be deployed in arid areas where dry cooling is a strategic choice. However, the usual high ambient temperature associated with these locations affects negatively the cycle performance. The key selection of two design parameters, the recompression fraction and the compressor inlet temperature, can minimise this negative effect. The method presented here allows the adjustment of these two parameters maximising the annual generation of electricity and cycle efficiency simultaneously. The optimisation process analyses the drop in the cycle performance due to the yearly variation of ambient temperature at the specific location. To reduce the computational effort required, polynomial regressions extrapolate the results from a reduced set of design-point and off-design cycle simulations in a wide range of ambient and compressor inlet temperatures. As an example, the method is applied to three different locations demonstrating the existence of optimal design conditions and justifying the need to adjust these two key parameters for each specific location.

Application of Solar Thermal Energy for Medium Temperature Heating in Automobile Industry

There is a huge potential to deploy solar thermal energy in process heat applications in industrial sectors. Around 50 % of industrial heat demand is less than 250 °C which can be addressed through solar energy. The heat energy requirement of industries like automobile, auto ancillary, metal processing, food and beverages, textile, chemical, pharmaceuticals, paper and pulp, hospitality, and educational institutes etc. can be partially met with solar hybridization based solutions. The automobile industry is one of the large consumers of fossil fuel energy in the world. The automobile industry is major economic growth driver of India and has its 60 % fuel dependence on electricity and remaining on oil based products. With abundant area available on roof top, and need for medium temperature operation makes this sector most suitable for substitution of fossil fuel with renewable solar energy. Auto sector has requirement of heat in the temperature range of 80-140 oC or steam up to 2 bar pressure for various processes like component washing, degreasing, drying, boiler feed water preheating, LPG vaporization and cooling. This paper discusses use of solar energy through seamless integration with existing heat source for a few processes involved in automobile industries. Integration of the concentrated solar thermal technology (CST) with the existing heating system is discussed with a case study for commonly used processes in auto industry such as component washing, degreasing and phosphating. The present study is undertaken in a leading automobile plant in India. Component cleaning, degreasing and phosphating are important processes which are carried out in multiple water tanks of varying temperatures. Temperatures of tanks are maintained by electrical heaters which consumes substantial amount of electricity. Non-imaging solar collectors, also known as compound parabolic concentrators (CPC) are used for generation of hot water at required process temperature. The CPC are non-tracking collectors which concentrate diffuse and beam radiation to generate hot water at required temperature. The solar heat generation plant consists of CPC collectors, circulation pump and water storage tank with controls. The heat gained by solar collectors is transferred through the storage tank to the process. An electric heater is switched on automatically when the desired temperature cannot be reached during lower radiation level or during non-sunny hours/days. This solar heating system is designed with CPC collectors that generate process heating water as high as 90OC. It also seamlessly integrates with the existing system without compromising on its reliability, while reducing electricity consumption drastically. The system is commissioned in April, 2013 and since then it has saved ~ 1,75,000 units of electricity/year and in turn 164 MT of emission of CO2 annually.

Molten salt composition and composites for improved latent heat thermal energy storage

The growing concern over nonrenewable fuel sources, coupled with the continued increase of global energy demand has incentivised research into numerous new and pre-existing renewable energy sources. Concentrated solar thermal (CST) takes advantage of the high heat capacity of molten salts to provide an alternative solar solution to photovoltaic cells that allows reduced downtime through heat storage for use during suboptimal conditions. This meta-study examines the effectiveness of various eutectic Molten Salt compositions and materials as thermo-physical augmenters, with a focus on improved thermal conductivity when composited with molten salts as a method of enhancing the efficiency of concentrated solar thermal storage technology. The study is based on literature retrieved from scientific databases to investigate information available about enhancing LHTES technology. Research into carbon composites such as Expanded Graphite (EG) exhibits promising results revealing thermal conductivity increases as high as 40% in eutectic salt materials, however inconsistencies in measurements and materials used reveal a need for a greater analysis. Although molten salt thermal storage systems are not optimal in their current state, indication was found that composite storage mediums could potentially solidify their spot as a viable renewable energy source.

EU-SOLARIS: The European Infrastructure for Concentrated Solar Thermal and Solar Chemistry Technologies

EU-SOLARIS project is a European project, co-funded by the 7th framework programme of the European Union. It is a Research Infrastructure (RI) initiative aimed to foster and promote the scientific and technological development of Concentrating Solar Thermal (CST) and Solar Chemistry technologies. EU-SOLARIS aims to create a new legal entity to explore and implement new and improved rules and procedures for the overall coordination and join exploitation of the main European RI for CST and Solar Chemistry technologies, in order to optimize RI development and Research and technology Development (R&D) coordination. It is expected to be the first of its kind, where industrial needs and private funding will play a significant role. The success of the EU-SOLARIS initiative will be the establishment of a new governance body, aided by sustainable financial models for this unique European large and distributed research infrastructure in the CST and Solar Chemistry fields. EU-SOLARIS is expected to be an important tool in consolidating Europe's leadership in these areas. This will be accomplished by linking the research community and the industry involved in the CST sector and providing them the research infrastructures needed to innovate and advance the state of the art of CST and Solar Chemistry technologies. EU-SOLARIS is also expected to increase the efficient use of the economic and human resources required throughout the European research context and to provide efficient resource management to complement research and to avoid unnecessary technological duplication and repetition.This article presents the vision, objectives, activities and current status of the EU-SOLARIS project and discusses the most important - expected to be achieved - outcomes of the project, which is currently at its last year of its preparatory phase.

Comparison of Degradation on Aluminum Reflectors for Solar Collectors due to Outdoor Exposure and Accelerated Aging

Reflectors for concentrated solar thermal technologies need to withstand 20 or even 30 years of outdoor exposure without significant loss of solar specular reflectance. In order to test the durability of innovative reflectors within a shorter period of time, an accelerated aging methodology is required. The problem with accelerated testing is that poor correlation between laboratory and field test results has been achieved in the past. This is mainly because unrealistic degradation mechanisms are accelerated in the weathering chambers. In order to define a realistic testing procedure, a high number of accelerated aging tests have been performed on differently coated aluminum reflectors. The degradation mechanisms of the accelerated tests have been classified and systematically compared to samples that have been exposed at nine different exposure sites outdoors. Besides the standardized aging tests, innovative aging procedures have been developed in such way that the agreement to the degradation pattern observed outdoors is increased. Although degradation depends on materials and location, five generic degradation mechanisms were detected. Standardized tests only reproduced one or two of the five mechanisms detected outdoors. Additionally, several degradation effects that were not observed outdoors appeared. The innovative accelerated aging tests of artificially soiled samples were able to reproduce three of the five mechanisms observed outdoors, presenting a much more realistic overall degradation pattern.

Commercial Readiness of eSolar Next Generation Heliostat

eSolar has been designing small heliostats since the company's founding in 2007. One of the cornerstones of our approach to heliostat design is to deploy many factory-built small heliostats in high density fields. The fields are replicated and thus aggregated into solar plants supporting steam and molten salt electric power, integrated solar combined cycle (ISCC), and process heat applications, such as enhanced oil recovery and desalination. The small heliostat approach has been used in several pilot projects and was previously evolved into a commercially available product presented in 2011 at SolarPACES. In this paper we discuss the ground up redesign of our small heliostat hardware, with a focus of leveraging the proven approach into a higher reliability, globally applicable, more industrial, simple to source and most importantly total installed cost reduced solar collector product. During the redesign we discovered methods to simplify the design and confirmed that small, factory-built, affordable heliostats provide a compelling concentrated solar thermal technology. We discuss details on system optimization, concept selection and prototype development, including some results from design validation testing. Finally, we discuss how this new solar collector system (SCS5) performs and meets economic requirements. eSolar's SCS5 product will be commercially released early in 2014, and is currently available to quote for CSP projects.

Potential Applications of Concentrated Solar Thermal Technologies in the Australian Minerals Processing and Extractive Metallurgical Industry

The Australian minerals processing and extractive metallurgy industries are responsible for about 20% of Australia’s total greenhouse gas (GHG) emissions. This article reviews the potential applications of concentrated solar thermal (CST) energy in the Australian minerals processing industry to reduce this impact. Integrating CST energy into these industries would reduce their reliance upon conventional fossil fuels and reduce GHG emissions. As CST technologies become more widely deployed and cheaper, and as fuel prices rise, CST energy will progressively become more competitive with conventional energy sources. Some of the applications identified in this article are expected to become commercially competitive provided the costs for pollution abatement and GHG mitigation are internalized. The areas of potential for CST integration identified in this study can be classed as either medium/low-temperature or high-temperature applications. The most promising medium/low-grade applications are electricity generation and low grade heating of liquids. Electricity generation with CST energy—also known as concentrated solar power—has the greatest potential to reduce GHG emissions out of all the potential applications identified because of the 24/7 dispatchability when integrated with thermal storage. High-temperature applications identified include the thermal decomposition of alumina and the calcination of limestone to lime in solar kilns, as well as the production of syngas from natural gas and carbonaceous materials for various metallurgical processes including nickel and direct reduced iron production. Hybridization and integration with thermal storage could enable CST to sustain these energy-intensive metallurgical processes continuously. High-temperature applications are the focus of this paper.

Basic Principles for Rational Design of High‐Performance Nanostructured Silicon‐Based Thermoelectric Materials

Recently, nanostructured silicon-based thermoelectric materials have drawn great attention owing to their excellent thermoelectric performance in the temperature range around 450 °C, which is eminently applicable for concentrated solar thermal technology. In this work, a unified nanothermodynamic model is developed to investigate the predominant factors that determine the lattice thermal conductivity of nanocrystalline, nanoporous, and nanostructured bulk Si. A systematic study shows that the thermoelectric performance of these materials can be substantially enhanced by the following three basic principles: 1) artificial manipulation and optimization of roughness with surface/interface patterning/engineering; 2) grain-size reduction with innovative fabrication techniques in a controllable fashion; and 3) optimization of material parameters, such as bulk solid-vapor transition entropy, bulk vibrational entropy, dimensionality, and porosity, to decrease the lattice thermal conductivity. These principles may be used to rationally design novel nanostructured Si-based thermoelectric materials for renewable energy applications.

Multi-criteria decision aid to assess concentrated solar thermal technologies

There are now several concentrated solar thermal technologies (CSP), such as parabolic troughs and central receivers using various heat transfer media, that have reached the phase of initial commercial deployment for large-scale power production. Information about cost, performance and impact on the environment of the systems being analyzed is currently affected by uncertainty. In many cases, traditional evaluation methods such as cost-benefit analysis and the main economic and financial indicators (LEC, NPV, ROI, IRR,- etc.) are unable to deal with all the components involved in a valid energy project. Multi-criteria methods provide a flexible tool that is able to handle and bring together a wide range of variables appraised in different ways and thus offer useful assistance to the decision maker in mapping out the problem. This paper sets out the application of a multi-criteria method to make a preliminary assessment of CSP technologies. As this work demonstrates, multi-criteria analysis can provide a technical-scientific decision making support tool that is able to justify its choices clearly and consistently, especially in the renewable energy sector.

State of the nation

This paper discusses about solar power. In solar power, 4,000MW of utility scale projects are planned, contracted or under construction using concentrated solar thermal (CST) technology. CST is currently seen as a cheaper generation technology than PV. However, PV is thought likely to become more cost effective as it takes greater advantage of semiconductor-based cost-down economics.

US decarbonization options

The quest to reduce reliance on energy generating technologies releasing global warming pollutants such as carbon dioxide and methane has been a target of concern across the world. An analysis of a map of actions leading to decarbonization in the US has recently been described. Carbon rich fossil fuels are 85% of the United States energy sources. This new analysis identifies concentrated solar thermal energy, nuclear energy, geothermal and hydrothermal energy, wind, solar cells, and biomass as candidate alternative energy sources. Over the last twenty years, concentrated solar thermal technology has been demonstrated in a 354 MW plant located in the Mojave Desert. Nuclear energy deserves to be aggressively reevaluated in the context of current energy needs but significant issues such as reprocessing and storage of waste loom as major detracting elements. Nuclear energy currently accounts for 40% of the US electricity requirements. The contribution of wind and geothermal/hydrothermal energy is expected to be limited. Solar cells are limited by storage capacity and the time of daily solar radiance useful to the technology. Biomass has promising prospects but will not be able to completely replace petrochemical fuel stock to meet transportation demands. Prospects of hydrogen production derived from biomass are significantly limited when considering the available conversion technology. This analysis makes a case that alternative energy sources could replace 70% of the US demand for fossil fuels at a cost of $200 billion per year. (Science 2006, 313: 1234–1244)