Concentrated Solar Thermal Systems Research Articles

Comparative Analysis of Solar Tower and Parabolic Trough Systems for Solar Heat in a Steel Industry

Concentrated Solar Thermal (CST) systems emerge as a promising alternative to replace fossil fuels used in industrial thermal processes due to their high energy density and dispatchability. In this study, a comparative analysis of two CST systems, Solar Tower (ST) and Parabolic Trough Collector (PTC), has been made to replace natural gas used in the steam generation process in Türkiye's largest steel production plant, located in the Mediterranean Region of Türkiye. Both the ST and PTC systems were placed in a field area of approximately 0.4 km2. The results have shown that, on a monthly basis, the PTC system could exceed the plant's thermal energy for two-thirds of the year, while the ST system could meet the plant's energy requirements for one-third of the year. This could reduce CO2 by about 12.7 and 19.1 kilo-tones for ST and PTC at LCOH of about 68.9 and 36.9 EUR/MWh, respectively.

Integration of solar receiver and thermal energy storage into a single unit in concentrating solar plants

Abstract Integrating solar receivers and thermal energy storage in a concentrating solar thermal plant helps to enhance plant efficiency and cost-effectiveness. Here, we provide an overview of the technology to unify solar receivers and thermal energy storage into a single system. We discuss the advantages, challenges, and prospects associated with this innovative approach. This emerging technology has the potential to improve overall thermal performance and facilitate operation of high-temperature dispatchable concentrating solar thermal systems.

Simulation for impact of nanofluid spectral splitter on efficiency of concentrated solar photovoltaic thermal system

Nanofluid filter has been applied in current research to boost the efficiency of a concentrated photovoltaic thermal (CPVT) module. Owing to tunable optical features of nanofluid and its greater thermal characteristics, it was utilized as spectral filter and cooling fluid in the present proposed solar system. The mixture of silver and water has been utilized as working fluid and its concentration within the filter and cooling duct are 0.005 and 0.05, respectively. Three dimensional models have been proposed involving spectral distribution of solar irradiation. Also, transmissivity of nanofluid filter has been derived according to empirical models. Two structures have been applied for cooling duct: 1) straight bottom wall; 2) wall with triangular obstacles (semi-wavy wall). As velocity of nanofluid within the filter (Vf) section enhances, the electrical performance increases about 3.4 %. For case 4, with augment of concentration ratio (CR) from 3 to 30, the electrical performance reduces about 13.57 % while thermal performance augments about 5.68 %. When CR=10, utilizing case 4 makes electrical and thermal performance to enhance about 25.09 % and 22.36 % in comparison to case 1. Also, cell temperature decreases about 47.82 % with applying the filter within the second structure of the cooling duct.

The effect of HelioPod™ mobility on concentrated solar thermal project economics

The production of heat for industrial processes is one of the significant contributors to greenhouse gas emissions, with the mining and minerals processing industry in South Africa as a substantial user of high-temperature process heat. South Africa produces 80 % of the world's manganese. The sintering of manganese in South Africa is fossil fuel intensive and emits nearly a million and a half tons of CO2 per year. Concentrating Solar Thermal (CST) produces heat that can be utilised at a significantly lower cost than diesel firing, which is currently used for sintering. However, with CST being a nascent technology, most mining operations are reluctant to commit to its use. These risks can be minimised for the customer using an Energy Supply Company (ESCo or energy-as-a-service company) to provide heat to the mine.For the ESCo, one of the most significant risks is the potential for the mining customer to terminate the contract before the end of the life of the CST energy supply asset. Using a solar field based on heliostats, such as the HelioPod™, that can be redeployed presents a level of insurance against this risk. In this analysis, the economic advantage of the HelioPod™ solar field-based CST system is compared to that of a conventional permanent pedestal-based heliostat field. The comparison was made assuming early termination of the contract and scenarios where the CST facility was redeployed once or twice during the nominal life of the facility. The discounted cash flow analysis shows that reusing the heliostat field leads to significant economic improvements. The study shows that the conventional permanent heliostat system reduces the project NPV@7 % by up to 28 % compared to the HelioPod™ system with one move in the project's life.

Thermodynamic analysis of a sorption-enhanced gasification process of municipal solid waste, integrated with concentrated solar power and thermal energy storage systems for co-generation of power and hydrogen

A system of coupled CO2 capture and gasification has led to a new concept entitled sorption-enhanced gasification (SEG) which can increase H2 concentration in the syngas composition. This study proposed a novel configuration of the SEG system comprising concentrated solar power and thermal energy storage systems. Calcium looping (CaL) is utilized as the CO2 capture process. Unlike conventional SEG systems in which calcination heat demand is supplied by an oxy-combustion process, this study considers a heliostat field to provide heat for sorbent regeneration. The solar and thermal energy storage systems are simulated dynamically to achieve accurate results. A steam Rankine cycle is also designed to recover the released heat sources through the SEG system. The overall system performance is explored through energy and exergy analyses. Based on the results, the proposed system managed to produce 0.58 kg/s pure hydrogen in addition to 13.96 MW of net electrical power. Meanwhile, CO2 is captured from syngas composition with capturing efficiency of 95%. The energy analysis shows cold gas efficiency and the annual total energy efficiency of 87.76 and 70.74%, respectively. Based on exergy analysis results, the carbonator reactor exhibits the highest permeance compared to the gasifier and calciner reactors, with an exergy efficiency of 88.74%. Parametric study results show an increase in the cold gas efficiency, hydrogen production rate, and electrical energy efficiency with enhancing steam-to-biomass ratio. An increase in CO2 capture efficiency also improves both the electrical energy efficiency and H2 concentration of the syngas composition. CO2 capture efficiency and S/B ratio are inversely related to the exergy efficiency of the system.

Energy saving in industrial buildings using advanced concentrated solar thermal systems

Saving energy in industrial buildings is one of the ten pillars of the European Green Deal. The application of renewable energy technologies in industrial processes and their buildings is an appropriate way to support the European energy goals. The paper presents an innovative solar heating method for industrial buildings that focuses on overcoming the current limitations of these systems. The method is based on the modular and flexible integration of two innovative technologies for the solar collector (SunDial technology – parabolic collectors) and thermal energy storage (based on phase change materials, PCM) which, through a control system, allow flexible operation to maintain continuous use against the unpredictable nature of the solar source and partly even during the night. The method can cover a significant percentage of the heat demand in industrial processes that use temperatures above 150°C. At the same time, there is the possibility of meeting cooling needs using an absorption chiller.The work describes the technologies of centralized solar collectors and the connection, operation, control and monitoring systems as well as the possibilities of covering thermal and cooling loads in an industrial building. This technology can be applied to both commercial and residential buildings. The purpose of this application is to contribute to the reduction of the requirements for heating and cooling in industrial buildings of the European Union which is estimated at approximately 72TWh per year.

TiN-based metasurface absorber for efficient solar energy harvesting

Solar absorber, which is widely used in concentrated solar thermal systems and solar photovoltaics, has attracted great attention in recent years. Concentrated solar irradiation not only saves production costs, but also effectively improves the photothermal conversion efficiency of the system. However, the huge radiative heat flux will cause the system temperature to rise rapidly, which poses significant challenges for designing solar absorbers. Here, a metasurface absorber based on cylinder array structure is proposed for efficient solar energy harvesting, using the high-temperature resistant materials TiN and SiO2. The total solar absorption of the absorber is up to 0.94 at wavelengths of 300–2500 nm. The high absorption performance of the metasurface absorber can be explained as the coupling effect of surface plasmon resonance and Fabry-Pérot resonance, which is confirmed by the electric field distribution. Moreover, the effect of geometric parameters on absorption performance is analyzed. Finally, we discuss the influence of incident angle on the solar absorber. We believe this work could deepen the understanding of coupling resonance mode and guide the design of high-temperature solar absorbers.

Techno-economic and GHG mitigation assessment of concentrated solar thermal and PV systems for different climate zones

In this study, energy production by two solar energy technologies, namely concentrated solar power (CSP) and photovoltaic (PV) power, is compared from a technical, economic and environmental perspective. Initially, a 50 MW CSP plant is modeled and simulated at four selected sites in Pakistan. Then, the most feasible location of the CSP plant is compared with the solar PV plant of the same capacity. The effect of the solar thermal storage size and cooling system of the CSP system is investigated, while the photovoltaic tracking system is investigated to evaluate the technical and economic performance of the power plants. Technical performance is evaluated based on energy generation and capacity factors metrics, while economic performance is evaluated with respect to levelized cost, payback period and net present value. In addition, environmental criteria such as reducing greenhouse gas emissions (GHG), saving fossil fuels, and life-cycle water consumption are evaluated. From the results, it was concluded that the CSP plant located in Quetta is technically and economically viable. The capacity factor of the CSP plant is 36.6% compared to 19.8% for the PV plant, while the solar-to-electrical efficiency of the CSP plant is 14.2% compared to 20.8% for the PV plant. The required land area is 2.77 acres/GWh for the CSP plant and 2.33 acres/GWh for the PV plant, while the net capital cost of the CSP plant is five times higher than that of the PV plant. Various design parameters are optimized to obtain the minimum levelized cost of energy (LCOE) for both CSP and PV plants. The results of CSP and PV plants indicate that the LCOE can be reduced to 11.57 cents/kWh and 4.69 cents/kWh, respectively. Thus, the CSP plant performs better from the technical point of view while the PV plant performs better from the economic perspective.

Photothermal conversion potential of full-band solar spectrum based on beam splitting technology in concentrated solar thermal utilization

It is still a great challenge for the concentrated solar thermal (CST) technology to promote the utmost out of solar energy further because the CST's receiver generally discards the longer wavelength spectra to prevent radiative heat loss due to high temperatures. Spectrum splitting is a well-known technology generally used in multi-energy cogeneration devices, such as Photovoltaic/thermal (PV/T) systems, aiming to improve photoelectrical efficiency. In this study, the solar spectrum splitting technology is employed in the CST system to take full advantage of solar radiation through enhanced absorptions and conversions of piecewise solar radiation. The exergy efficiency of a beam-splitting photothermal (BSPT) system is used to evaluate its effectiveness. Here, the mechanisms of beam splitting under different splitting wavelengths (λsp) and concentration ratios (Cr) are investigated. Furthermore, the influence of the split number is evaluated, and the performance of the dual-segment BSPT system is compared with traditional photothermal systems with real and assumed coatings. It shows that beam splitting can play an excellent role in improving exergy performance. The exergy efficiency improvement ratio of the BSPT stabilizes at around 9% when λsp is 1300 nm, and the proposed dual-segment BSPT system can maintain an excellent performance even under off-design working conditions.

Cobalt-rich spinel oxide-based wide angular spectral selective absorber coatings for solar thermal conversion applications

Solar energy conversion technologies attain enormous attention to create more efficient energy production sources to meet the current world's demand. The solar thermal conversion system converts solar energy to heat, and the receiver tube is crucial for achieving high photo-thermal conversion efficiency. The absorber coatings with high solar absorptance at normal and wide incidence angles of solar radiation improve the performance of concentrated and non-concentrated solar thermal systems. To achieve high photo-thermal conversion efficiency in the solar thermal conversion system, a novel spinel structured cobalt-rich transition metal oxide-based absorber coating was developed by a cost-effective wet chemical route. The developed absorber coatings with sub-micron scaled surface protrusions with porous structure (size 0.75 μm) exhibit an excellent spectral selectivity (α/ε = 0.91/0.13). In addition, the coatings show an excellent wide angular solar absorptance of 0.97–0.96 at incidence angles of 10°–40°. Extensive characterization has been carried out to analyze the structural properties of the absorber coatings and correlated to the spectral selectivity and wide angular solar absorptance property. The stability of the absorber coating at 400 °C for 100 h in an open-air atmosphere assessed by the performance criteria (PC) function value of 0.015 indicates the ability of the optimized absorber coatings to employ in solar thermal systems.

On the compatibility of liquid sodium as heat transfer fluid for advanced concentrated solar thermal energy systems

The use of liquid sodium as a heat transfer fluid has shown great promise and application in nuclear power generation and it is now being utilized in concentrated solar thermal power (CSP) applications, owing to its favorable thermodynamic properties. Its implementation, however, comes with a unique array of technical issues in CSP applications, primarily the incompatibility of structural materials with liquid sodium in these operational environments. In this review, major damage mechanisms will be discussed, with a focus on their relevance to advanced CSP plants. Such mechanisms include corrosion, liquid metal embrittlement, carburization/de-carburization, erosion, creep, and thermal fatigue. The degradation factors such as impurities in the sodium (e.g. oxygen) and the dissolution of the structural material's alloying elements (Cr, Mn, Ni and Si, etc.) are also discussed. This review presents a holistic overview of these inter-connected mechanisms, and most importantly explores potential solutions to mitigate these issues, including better structural material candidates, robust plant operational parameters/design, better service life predictions, and improved purification and monitoring methods for stringent control of impurities. The future directions of research are also discussed to ensure the successful use of liquid sodium in the next generation of CSP technology.

Optical and thermal performance simulation of a micro-mirror solar collector

Concentrating solar thermal systems are widely used for industrial heat production. The state-of-the-art methods use different concepts among which tracking Fresnel mirrors or parabolic troughs. In the market however there are very few devices operating at intermediate to medium temperatures. In order to fill this gap, an innovative concentrating solar thermal system is studied in the frame of the Hellenic — German cooperation project “SCoSCo”. The proposed device concentrates the solar radiation to the receiver using a micro-mirror array. The scope of this paper is to present the optical simulation results of this innovative reflector, and compare the results obtained by different software packages. The optical performance assessed using Solstice ray-tracing software, yields a theoretical optical efficiency from 0.7 to 0.9. In order to evaluate the annual energy yield of the prototype, solar radiation data measurements in Patras, Greece for 2016 and were used as input. A three dimensional thermal model is developed in the COMSOL software to estimate the temperature distribution at the receiver. It was found that temperatures , ranged from 115 to 225 °C. The annual energy yield, calculated using the CARNOT toolbox ranges from 683 to 729 kWh.

Techno-economic assessment of application of particle-based concentrated solar thermal systems in Australian industry

Australia has significant areas with high quality solar resources, but the requirement for large scale solar thermal plants to be financially competitive in the electricity market appears to have hindered uptake. Industrial use of heat provides an alternative route to market where the technology is not impacted by poor efficiencies in converting heat to electricity and an appropriate scale can be applied to the demands of a specific site. A re-examination of prior industrial energy use studies in Australia was used in combination with solar data and published data on industrial sites to identify three specific industrial sites for case studies. These sites were selected to cover applications in three industries with varying scale and temperature requirements. The primary solar technology selected utilizes a particle receiver on a tower with associated storage and heat exchanger for hot water/steam production or heating a gas reactor. The wide range of temperatures possible with this technology appears to be desirable for development of a general-purpose industrial heat system. Comparison with parabolic trough systems that are commercially available was conducted for cases where the required temperatures were appropriate. In all assessments, the optimized solar plant designs approach cost competitiveness with the estimated cost of natural gas purchase for the relevant locations and industrial scales. In smaller and lower temperature applications, parabolic trough systems are likely to be appropriate conventional choices, but the particle system exhibited a high degree of flexibility across multiple sites and applications, which is encouraging to future commercial application.

De-Risking Solar Receivers to Achieve SunShot Targets

Concentrating solar thermal (CST) systems are unique among renewable energy options for the ease of integration with thermal energy storage (TES). This enables dispatchable (or continuous) production of electricity, process heat, solar fuels, or other chemical products. The solar receiver in a CST system converts concentrated sunlight to transportable thermal energy. In solar power towers, the solar receiver’s physical limitations are often the constraining conditions for the system; they restrict maximum temperature, maximum solar concentration, or controllable chemical production. It is also a uniquely challenging component to prototype and test at sizes beyond the laboratory scale. Transitioning exceptional research innovations into viable components for an integrated system and ultimately leading to CST market adoption requires a multiscale vision for component de-risking and development. Technical requirements for holistic novel receiver development are reviewed based on learnings from the US Department of Energy’s (USDOE) SunShot Initiative, its active Third Generation of Concentrating Solar Power Systems (Gen3 CSP) program, and anticipation of requirements for future high value applications for CST. Context and learnings from the Gen3 CSP program are provided to exemplify successful receiver risk-reduction paradigms.

Experimental Study of Eutectic Molten Salts NaCl/KCl/ZnCl2 Heat Transfer Inside a Smooth Tube for High-Temperature Application

AbstractEutectic salts NaCl-KCl-ZnCl2 and NaCl-KCl-MgCl2 are two of the chloride salt systems that are promising for being used as high-temperature heat transfer fluid (HTF) and thermal energy storage (TES) materials in a wide range of temperatures from 230 °C to 750 °C in concentrated solar thermal power systems. To conduct measurement of the heat transfer coefficient of the molten salt at high temperatures, a circulation system and instrumentation of flow and heat transfer was constructed. Experimental measurement of the convective heat transfer coefficients of NaCl-KCl-ZnCl2 (molar fraction: 13.8–41.9–44.3%) inside tubes has been accomplished to find the most suitable heat transfer correlations. Experience of salt processing and operation of the high-temperature heat transfer test system was obtained. Two correlations, Dittus-Boelter equation and Gnielinski’s correlation for Nusselt number against Reynolds number and Prandtl number, are evaluated using the test results, and the latter correlation is recommended due to its better agreement of prediction against tested data.

Solar parabolic dish collector for concentrated solar thermal systems: a review and recommendations.

Energy demand in the present scenario is rising to meet the increasing demands of energy usage. On the other hand, the use for renewable energy sources now becomes essential to mitigate the climate change as well as to reduce gradual depletion of fossil fuels. Among these renewable energy sources, solar energy particularly solar thermal systems have phenomenal scope in present and future research. In solar thermal systems, concentrators are used to extract the energy from solar irradiation and convert it into useful form. Among different types of solar concentrators, the parabolic dish solar concentrator is preferred as it has high efficiency, high power density, low maintenance, and potential for long durability. In this paper, a detailed review has been carried out on the design parameters like focal length, concentration ratio, and rim angle of the parabolic dish solar concentrator system for achieving higher overall efficiency. The effects of different geometrical shapes of receivers on the overall heat transfer rates are discussed in this paper. Conical shaped receiver is having high overall optical and thermal efficiency comparing with other shapes of receivers. This study also shows that how the thermal performance of the receiver gets enhanced by 10-13% using nanofluids in place of general heat transfer fluids. The paper highlights different models using ray-tracing method for estimation and evaluation of the solar irradiation distribution on the receiver surface. The empirical relations for the design of parabolic dish solar concentrator system are derived for estimating overall concentrator efficiency and heat available at the receiver are given in this review. From the literature, the thermal performance of the receiver affecting the overall performance of the system is observed. Thermal losses due to geometrical properties and ordination of the receiver are explained in the observation section.

Minimizing the Computational Effort to Optimize Solar Concentrators with the Open-Source Tools SunPATH and Tonatiuh++

Integrals that are of interest in the analysis, design, and optimization of concentrating solar thermal systems (CST), such as the annual optical efficiency of the light collection and concentration (LCC) subsystem, can be accurately computed or estimated in two distinct ways: on the time domain and on the spatial domain. This article explores these two ways, using a case study that is highly representative of the commercial CST systems being deployed worldwide. In the time domain, the computation of these integrals are explored using 1-min, 10-min, and 1-h solar DNI input data and using The Cyprus Institute (CyI)’s High-Performance Computing (HPC) system and an open-source ray tracer, Tonatiuh++, being actively developed at CyI. In the spatial domain, the computation of these integrals is explored using SunPATH, another open-source software tool being actively developed at CyI, in tandem with Tonatiuh++. The comparison between the time and spatial domain approach clearly indicate that the spatial domain approach using SunPATH is dramatically more computationally efficient than the time domain approach. According to the results obtained, at least for the case study analyzed in this article, to compute the annual energy delivered by the LCC subsystem with a relative error less than 0.1%, it is enough to provide SunPATH with 1-h DNI data as input, request from SunPATH the sun position and weights of just 30 points in the celestial sphere, and run Tonatiuh++ to simulate these 30 points using 15 million rays per run. As the test case is highly representative, it is expected that this approach will yield similar results for most CST systems of interest.

Optimal Sizing of Cylindrical Receivers for Surround Heliostat Fields Using fluxtracer

Abstract This article presents an innovative approach for optimizing the dimensions of cylindrical receivers for solar tower systems. In this approach, a single set of rays, representative of a complete annual ray-tracing simulation of the solar tower system, is used and processed to evaluate numerous receiver designs simultaneously and to select the optimum. The simultaneous evaluation of receiver designs is achieved by exploiting the geometrical properties of the intersection between a ray and a cylinder, which allows estimating the annual energy intercepted by receivers of different heights without the need for processing the annual set of rays more than one time. Once the annual intercepted energy is known for each receiver, the application of a costing function estimating the receiver cost as a function of its surface area allows to estimate their cost and, therefore, to select the receiver dimensions that will yield a minimum surface area for a given annual energy interception factor. The overall workflow to carry out the mentioned receiver optimization approach has been implemented by adapting several open-source tools that The Cyprus Institute (CyI) is developing in collaboration with the Australian National University (ANU) to assist in the modeling, analysis, design, and optimization of concentrated solar thermal (CST) systems. This article also presents a detailed overview of the overall simulation workflow as well as a case study demonstrating the capabilities of the approach.

FEM analysis of novel Fresnel sheet solar concentrating system for TEG

The expensive manufacturing process and low efficiency at the high working temperature of photovoltaic cells necessitate the need for an alternate solar energy generation system. In this study, a concentrated solar thermal system that works on the principle of the Seebeck effect has been selected for electical energy conversion. Standard Thermal Electric Generator (TEG) of material Bismuth Telluride is considered for harvesting energy from concentrated solar irradiance. In this research work, a Fresnel sheet concentrator has been used as the concentrating medium due to its low weight and easy installation. The solar simulator experiment is carried out on the Bismuth Telluride TEG module (type TEP1-12656-0.6) to find out its output characteristics curve with respect to irradiance. In this connection, high temperature is maintained at the top of the TEG by using fresnel concentrator and low temperature is maintained at the bottom by utilising the Flow Channel concept. Analysis of the flow channel is done in detail using ANSYS version 15. Results are discussed. Based on this result, the water flow rate has been optimised and it is found that the high temperature at the top of the TEG is not constant due to solar irradient uncertainity. A complete cost analysis is performed and the payback period of the proposed model is found out to be considerably less compared to the conventional solar panel system. Hence, in this manner, the most abundant renewable energy like solar energy is made use efficiently as well as economically, without causing any harm to the environmental well-being.

Numerical and experimental study of a concentrated solar thermal receiver for a solar heating system with seasonal storage

Solar heating systems are promising, reliable solutions for meeting heating demands, and reducing greenhouse gas emissions. Due to the temporal fluctuations of solar energy and the mismatch between solar energy availability and heating loads, the application of seasonal thermal storage for solar space heating has drawn much attention. Due to the significant reduction of the collection efficiency of flat plate collectors in the temperature range of 70-95°C, the expansion of the application of concentrated solar thermal (CST) systems has aroused a strong interest. This study describes a demonstration project with a CST receiver designed for a solar heating system with seasonal storage. This work is to reveal the performance of the receiver in the middle and low-temperature operation through experimental-numerical approach using a one-dimensional transient model with a non-uniform flux distribution. The simulation results agreed well with experimental data for various operating conditions. The receiver had a collection efficiency of about 82% on a typical day. Meanwhile, the heat losses were mainly reflection losses followed by convection (about 5.6%) and radiation (about 2.1%). Additionally, the model was also used to investigate the effect of various operating parameters such as the inlet temperature, outlet temperature, and incident power on the collection efficiency and heat losses. Ultimately, the developed model and on-site operating data are valuable for broadening the applications of CST receivers and further system simulation and optimization.