Optical Concentration Ratio Research Articles

Optimally Splitting Solar Spectrums by Concentrating Solar Spectrums Splitter for Hydrogen Production via Solid Oxide Electrolysis Cell

The concentrating solar spectrums splitter (CSSS)-driven solid oxide electrolysis cell (SOEC) is an attractive technology for green hydrogen production. The CSSS mainly comprises a concentrating photovoltaic (CPV), which converts sunlight with shorter wavelengths into electricity, and a concentrating solar collector (CSC), which converts the remaining sunlight into heat. However, the optimal splitting of the solar spectrums is a critical challenge that directly impacts the efficiency and normal operation of the SOEC. To address this challenge, a mathematical model integrating the CSSS with the SOEC is developed based on principles from thermodynamics and electrochemistry. By analyzing the requirements of electricity and heat for the SOEC, the model determines the optimal configuration and operational parameters. The results show that the anode-supported type, higher operating temperature, larger inlet flow rate of water, higher operating pressure of the SOEC, higher operating temperature of the CSC, and larger electric current of the CPV contribute to allocating more solar spectrums to the CSC for heat generation. However, the greater effectiveness of the heat exchangers, higher operating temperature, and larger optical concentration ratio of the CPV exhibit contrasting effects on the spectrum allocation. The obtained results provide valuable theoretical guidance for designing and running the CSSS for hydrogen production through SOEC.

Heat pipe-cooled highly-concentrated multi-junction solar cell

Concentrator photovoltaic (CPV) systems have proven the capability of competing with traditional photovoltaic (PV) systems due to their high efficiency and low area occupancy. Such CPV systems require efficient heat removal auxiliary systems, especially for medium and high optical concentration ratios. Operating a CPV system under a high optical concentration (ratio > 200 X) might require active cooling techniques, which have high operating costs and maintenance. On the other hand, heat pipes (HPs) are widely used in electronic devices for cooling purposes. This work discusses the possibility of operating a CPV system coupled with HPs as a passive cooling technique. Two different HPs with different lengths are used to compare cooling efficiency. Each HP length was tested either in a single or double configuration. Long HPs showed better heat removal compared to a traditional fin-cooling system. CVP cooling with HP systems enhanced the entire electrical output of the cell, mainly at high optical concentration ratios.

Design and Optical Performance Evaluation of the Three-Dimensional Solar Concentrators with Multiple Compound Parabolic Profiles and Elliptical and Rectangular Receiver Shapes

The compound parabolic concentrator (CPC) is a core technology in the field of solar concentration. Nevertheless, it only has one degree of freedom in the choice of its half-acceptance angle. In this study, extending the idea of the three-dimensional CPC, a design method for new kinds of concentrators having a CPC shape at each profile with various acceptance angles in all directions is proposed. The feature of this method is that the receiver can take any shape. Here, elliptical and rectangular receivers are assumed, and the shape and concentration performance of the concentrators with multiple CPC profiles and an elliptical receiver (MultiPro-ECPCs) and the concentrators with multiple CPC profiles and a rectangular receiver (MultiPro-RCPCs) are derived. The new designs are compared to the conventional CPC and a mirrorless flat receiver through ray-tracing simulations in terms of energy distribution on the receiver, optical efficiency, and optical concentration ratio based on axial and solar angles. The results show that in terms of optical efficiency, the MultiPro-RCPCs cover a wider range of incident angles after the 3DCPC. In terms of the optical concentration ratio, the MultiPro-ECPC with a longitudinal half-acceptance angle of 15° has the highest peak value of 19.5, followed by the MultiPro-RCPC. This study enlightens that with the concentration system settings adapted to the acceptance range of the proposed concentrators, a higher concentration can be achieved with the MultiPro-ECPC and MultiPro-RCPC compared to the conventional CPC.

Performance Potential of a Concentrated Photovoltaic-Electrochemical Hybrid System

A novel hybrid system model, combining a concentrated photovoltaic cell (CPC) with a thermally regenerative electrochemical cycle (TREC), is proposed. This innovative setup allows the TREC to convert heat from the CPC into electricity. The model incorporates mathematical equations that explicitly define power output, energy efficiency, and exergy efficiency for both the CPC and the TREC individually, as well as for the hybrid system as a whole. The outcomes of the computations reveal that the hybrid system surpasses the performance metrics of the CPC alone. Specifically, the hybrid system achieves a notably higher maximum power density (MPD), maximum energy efficiency (MEE), and maximum exergy efficiency (MMEE) compared to the standalone CPC, with improvements of 392.68 W m−2, 10.33%, and 11.11%, respectively. Through thorough parametric analyses, it was observed that specific factors positively impact the hybrid system’s performance. These factors include higher operating temperatures, increased solar irradiation, specific concentration ratios, and alterations in the internal resistance or temperature coefficient of the TREC. However, it was noted that elevating the operating temperature of the CPC adversely affects the hybrid system’s performance. Furthermore, augmenting solar irradiation and optical concentration ratios amplifies the limiting electric current. Conversely, reducing the internal resistance of the TREC enhances the overall performance of the hybrid system. These discoveries have practical implications for optimizing the design and operation of a functional CPC-TREC hybrid system, providing valuable insights into maximizing its efficiency and effectiveness.

Transient numerical simulations in innovative thermoelectric power: A comprehensive study on material segmentation and cross-section design for multi-facetted excellence

In the pursuit of sustainable energy innovations, this study investigates the transformative potential of material segmentation and non-uniform cross-sections in the field of thermoelectric power generation. By analyzing four distinct thermoelectric models under varying optical concentration ratios (OCRs), our research is dedicated to optimizing exergy efficiency, economic viability, and thermo-mechanical performance. Model 3, representing a uniform cross-section segmented thermoelectric generator (TEG), emerges as the frontrunner in our study. The significance of this research lies in its potential to revolutionize thermoelectric power generation, offering a fresh perspective on sustainable energy production. Our primary aim is to elucidate the impact of innovative design strategies on thermoelectric performance. To achieve this, we employ numerical simulations and transient analyses to explore the dynamic behavior of these models under changing OCRs. Our key findings reveal the remarkable superiority of Model 3, which achieves a peak power output of 624.60 mW, exergy efficiency of 10.27 %, and CO2 savings of 1.08 kgyr−1, all under an OCR of 700. Notably, Model 3 outperforms conventional systems by 300.45 % in power output and 75.76 % in CO2 savings. Conclusively, our research provides valuable insights into the capacity of material segmentation and non-uniform cross-sections to reshape the realm of thermoelectric power generation, highlighting their potential in propelling sustainable energy solutions.

A New Two-Foci V-Trough Concentrator for Small-Scale Linear Fresnel Reflectors

We present the design of an original secondary cavity for use in Small-Scale Fresnel Reflectors in photovoltaic applications. The cavity is similar to the classical V-trough, but the primary reflector system is configured so that there are two focal points on the aperture. The rays coming from each side of the primary system reach the opposite side of the cavity, producing a non-symmetrical distribution of the irradiance. This modifies the acceptance half-angle and allows us to break the maximum limit for the concentration ratio of ideal symmetric concentrators. Our study is analytic, and we provide formulas for any number of reflections. Numerical simulations with a ray-tracing program based on MATLAB are included. We provide a comparison of optical concentration ratio, height and cost parameter between our system and two classical designs with a single focal point: the V-trough and the Compound Parabolic concentrators. This way, we verify that our design yields better concentration ratios while keeping the ray acceptance rate at one. Our solution proves to be better than both the classical one-focus V-trough and the Compound Parabolic concentrator. Specifically, the proposed solution is significantly better than the classical one-focus V-trough in optical concentration ratio, with an increase between 15.02 and 35.95%. As regards the compound parabolic concentrator, the optical concentration ratio is always slightly better (around 4%). The height of the cavity, however, is notably less in this design (around 54.33%).

Optical concentration ratio of a parabolic trough collector with flat receiver and concentrator with surface irregularities

Optical concentration ratio of a parabolic trough collector with flat receiver and concentrator with surface irregularities

Optical performance and alignment characterization of a parabolic trough collector using a multi-junction CPV solar cell

Parabolic trough collectors are widely used to generate thermal and/or electrical energy from direct solar irradiation. These collectors use parabolic mirrors to precisely focus sunlight onto so-called absorber tubes. The optimal design and geometric alignment of all necessary components is essential in order to achieve a high degree of efficiency and a high energy yield. However, this optical fine-tuning process can be quite challenging and is in many cases avoided by using absorber tubes with larger diameters, which in turn cause greater thermal losses and a higher material effort. This paper describes a simple, yet reliable and quantifiable way to measure the optical performance of a parabolic trough collector using a commercial multi-junction solar cell (CPV). The presented measurement system allows for convenient adjustment of the parabolic mirror and the effective optimization of the overall collector design. The theoretical background is discussed and the test setup is described in detail. Measurement results are presented, ranging from the determination of the actual optical concentration ratio, the optimal centering and height adjustment of the absorber tube to the measurement of the contribution of the individual mirror segments, revealing that the investigated industrial parabolic trough collector can be improved in terms of optical accuracy. Finally, an optical surveillance of the mirror using a line laser was performed to validate the results.

Exergy analysis of a novel concentrated photovoltaic-thermoelectric system

Exergy analysis of a thermodynamic system is carried out to identify sources, causes and magnitude of both reversible and irreversible losses and its usefulness as a tool in improving the performance of a system. Herein, an exergy analysis of a novel concentrated photovoltaic-thermoelectric system is presented. Results showed that losses increase with increase in the optical concentration ratio and at high optical concentration ratio; it is more beneficial to lower the efficiency temperature coefficient than to increase the energy conversion efficiency of the photovoltaic system.

Flux profile at focal area of concentrating solar dishes

We analytically, experimentally and computationally explore the solar radiation flux distribution in the interior region of a spherical mirror and compare it to that of a paraboloidal one with the same aperture area. Our investigation has been performed in the framework of geometrical optics. It is shown that despite one can assign a quasi focus, at half the radius, to a spherical mirror, the light concentration occurs as well on an extended line region which starts at half-radius on the optical axis. In contrast to a paraboloidal concentrator, a spherical mirror can concentrate the radiation parallel to its optical axis both in a point-focus and in a line-focus manner. The envelope of the reflected rays is also obtained. It is shown that the flux distribution has an axial symmetry. The radial dependence of the flux on a flat circular receiver is obtained. The flux longitudinal dependence is shown to exhibit three distinctive regions in the interval [0, R] (R is mirror radius). We obtain the radiational (optical) concentration ratio characteristics and find the optimal location of the flat receiver of a given size at which the concentration ratio is maximised. In contrast to a parabolic mirror, it is shown that this location depends on the receiver size. Our findings offers that in spherical mirrors one can alternatively use a line receiver and gains a considerable thermal energy harvest. Our results are supported by Monte Carlo ray tracing performed by Zemax optical software. Experimental validation has been performed in lab with a silver-coated lens as the spherical mirror.

Optical component analysis for ultrahigh concentrated photovoltaic system (UHCPV)

This article investigates the discrepancy between the theoretical and the experimental optical characterisation results of a Fresnel Lens - silicon on glass (SOG), as a primary optical component toward UHCPV of >3000 suns design (Shanks et al., 2018). All the equations were elaborated for single- and multi-junction solar cells, emphasising the performance when the focal spot area is larger or lesser than the solar cell area. This simple prediction approach of optical characterisation has shown a strong agreement between the theoretical and experimental results of the multi-junction solar cell with a discrepancy of 2% at 7.7 W (77 suns) and 6% on the average cross a solar irradiance on the cell from 3.1 W to 7.7 W corresponding to 31 suns – 77 suns in concentration ratio. A theoretical analysis of the optical performance for a 1/4 of the system grouping three optical interfaces is performed to estimate the optical loss and its influence on the optical efficiency and optical concentration ratio.

Performance Analysis and Comparison of a Concentrated Photovoltaic System with Different Phase Change Materials

In this work, temperature regulation and electrical output of a concentrated photovoltaic system coupled with a phase change material (CPVPCM) system is investigated and compared with a single sun crystalline photovoltaic (PV) system. A fully coupled thermal-optical-electrical model has been developed in-house to conduct the simulation studies for actual weather conditions of Doha (Qatar) and selected phase change materials (PCMs). The selected PCMs are lauric acid, RT47, S-series salt, STL47, ClimSelTM C48, RT54, RT60, RT62, and RT64. An optical concentration ratio of 20× is considered on a 15 mm wide crystalline silicon cell. The temperature evolution, thermal energy storage and electrical output of the CPVPCM system are obtained for 48-hour simulations with representative weather conditions for each month of a typical meteorological year (TMY). Results and overall thermal and electrical efficiency are compared for each PCM. In brief, the CPVPCM system with S-series salt performs better than all other PCM with an overall efficiency of 54.4%. Furthermore, this system consistently produces more power than a PV system with an equal footprint (1 m2) for each month of the TMY.

Overall performance optimisation of tapered leg geometry based solar thermoelectric generators under isoflux conditions

The performance of thermoelectric devices improves either by changing the thermoelectric material properties or the geometry of the thermoelectric leg. Many research papers show that the tapered leg geometry improves the performance of thermoelectric generators (TEGs). However, they assume isothermal conditions across the hot and cold junctions of both variable area and rectangular area leg-based TEGs. This is rather inaccurate and unrealistic, because when exposed to same heat flux, temperatures vary across the hot and cold junctions of these devices. Scarcely has anything been said pertaining the performance evaluation and optimisation of variable area leg TEGs using realistic isoflux conditions. Therefore, this study presents a thermo-mechanical analysis of variable area and rectangular area leg TEGs, using ANSYS 2020 R2 software, with realistic isoflux boundary conditions instead of previous unrealistic isothermal ones. The leg height, area, external load resistance and optical concentration ratio are optimised. Results indicate that short legs are crucial for maximum power while long legs improve the device efficiencies. Also, although tapered thermoelectric leg TEGs improve the electrical performance of conventional rectangular leg TEGs, they decrease the device mechanical performance and thermodynamic stability. Finally, the optimum ranges in which tapered leg TEG outperforms the conventional device are obtained.

A New Approach for Design Optimization and Parametric Analysis of Symmetric Compound Parabolic Concentrator for Photovoltaic Applications

A compound parabolic concentrator (CPC) is a non-imaging device generally used in PV, thermal, or PV/thermal hybrid systems for the concentration of solar radiation on the target surface. This paper presents the geometric design, statistical modeling, parametric analysis, and geometric optimization of a two-dimensional low concentration symmetric compound parabolic concentrator for potential use in building-integrated and rooftop photovoltaic applications. The CPC was initially designed for a concentration ratio of “2×” and an acceptance half-angle of 30°. A MATLAB code was developed in house to provoke the CPC reflector’s profile. The height, aperture width, and concentration ratios were computed for different acceptance half-angles and receiver widths. The interdependence of optical concentration ratio and acceptance half-angle was demonstrated for a wide span of acceptance half-angles. The impact of the truncation ratio on the geometric parameters was investigated to identify the optimum truncation position. The profile of truncated CPC for different truncation positions was compared with full CPC. A detailed statistical analysis was performed to analyze the synergistic effects of independent design parameters on the responses using the response surface modeling approach. A set of optimized design parameters was obtained by establishing specified optimization criteria. A 50% truncated CPC with an acceptance half-angle of 21.58° and receiver width of 193.98 mm resulted in optimum geometric dimensions.

Optical Design of a Novel Polygonal Trough Collector for Solar Concentrating Photovoltaic Applications

This paper presents a methodology for the optical design of a novel solar concentrating photovoltaic trough collector, consisting of several flat reflecting segments, joined together in an open polygonal shape. The concentrator reflects the incident solar radiation to a flat receiver, thus forming a photovoltaic module. The system of analytical design equations modeled in this work accounts for the number of segments and their tilt angles, focal length, optical concentration ratio, concentration fraction, height, width and the rim-angle of the collector. The effects of angular deviation between the incoming radiation and tilt angles of the segments, as well as the incidence angle at the receiver, are also accounted for in this work. In order to generalize the results, the parameters are normalized with respect to the receiver’s length. The model is validated by comparing a developed design with measurements taken in a 2D drafting program. The effects on various design parameters of changing the focal length are presented and discussed in detail. A visual and tabular tool comprising eight different designs is illustrated, which can be used to quickly select a design according to the desired application.

Performance optimization and thermodynamic analysis of irreversibility in a contemporary solar thermoelectric generator

In this paper, a model based on the first and second laws of thermodynamics is developed in MATLAB R2020a Simulink software and is utilized in thermodynamically optimizing a bismuth telluride based solar thermoelectric generator (STEG) while estimating all system irreversibilities. This study aims at presenting a cheaper and simpler method of optimizing the performance of traditional STEGs without using segmentation or cascading. This is achieved by studying the effects of operating thermal and electric parameters such as load-resistance ratio (LRR), optical concentration ratio (OCR), thermal concentration ratio (TCR), hot junction temperature (Th), cold junction temperature, current and voltage on STEG power output, energy and exergy efficiencies, respectively. The results obtained are validated with experimental and numerical data from previous studies. Results indicate that for an OCR of 30, a STEG exergy efficiency of about 6.5% is obtained from a conventional bismuth-telluride single-stage module. Also, a means of maximising STEG performance while reducing system irreversibilities to the barest minimum is presented. The results obtained herein will provide useful information in the maximisation of conventional and complex STEG systems employing segmentation or cascading.

Optimization and feasibility analysis of a microscale pin‐fins heat sink of an ultrahigh concentrating photovoltaic system

Nowadays, the most recent optical configuration based on Cassegrain and Fresnel lens designs of concentrator photovoltaic(CPV) has shown a race to achieve the ultrahigh concentration ratio. Still, none of those has experimentally shown an optical concentration ratio (GC) beyond 2000 suns. This is because their energy concentration ratios are challenged by the excessive temperature raised throughout the optical stages, which diminishes the efficiency of the solar cell. In this context, this research work aims to numerically investigate a microscale pin-fins heat sink configuration to enhance the thermal performance and the cost-competitivity of ultrahigh CPV thermal receiver. The impacts of the solar cell area, cell efficiency, and heat sink's material have been analyzed and discussed. The results showed that a circular pin-fins heat sink could accomplish a drop of 23.28% in the maximum operating cell temperature at 10 000 suns for cell area of 1 × 1 mm2 relatively compared to the conventional flat-plate heat sink. Furthermore, for a circular pin-fins heat sink with a cell area of 2 × 2 mm2, the cell temperature started exceeding the safe operating range of temperature (80°C) at 8000 suns with an average temperature of 96.1°C and reaching a maximum of 113.91°C at 10 000 suns. A gradient temperature on the planar direction of the aluminum circular pin-fins heat sink was about 1.187°C at 10 000 suns whereas 0.703°C was recorded in the case of a copper circular pin-fins heat sink. The circular pin-fins heat sink showed the highest thermal performance resulting in maintaining the solar cell temperature within its safe operating range even beyond 10 000 suns. From an economic point of view, aluminum circular pin-fins heat sink has been found to be less costly than the copper one. Finally, it was found that at 8000 suns, the flat-plate heat sink cost is more expensive than the traditional pin-fins heat sink by 14.7%, where the flat-plate heat sink becomes the worst economic configuration at 10 000 suns. At that concentration ratio, the cost has increased by 43.38%, 5.75%, and 10.61% compared to the traditional pin-fins heat sink, cylindrical pin-fins heat sink, and circular pin-fins heat sink, respectively.

Performance assessment of a heat pump and a concentrated photovoltaic thermal system during the wood drying process

Wood drying is an unavoidable step to bring to the market products with higher added value. Achieving drying under certain economic conditions requires calculating the drying cost with great precision while minimizing energy consumption. Conventional dryers with very high heating power are useful, but their energy consumption and greenhouse gas emissions remain too high. This work aims to propose a water/air heat pump powered by a concentrated photovoltaic thermal as a new hybrid solution for carrying out the drying process of softwood. The drying system consists of four main units, a drying chamber, a Closed Feed Air Heater, a water/air heat pump and a concentrated photovoltaic thermal. The study is based on the establishment of energy and mass balances in the drying system. The governing equations of the drying model are solved using the finite difference method. A perfect agreement is obtained between experimental and numerical results. The results show that the electrical energy consumption ratio using a heat pump as the main heater device fluctuates between 29 and 52 kWh.m−3. The coefficient of performance also ranges from 3.91 to 7.2. The results show that a decrease of the heat pump set temperature from 75 to 65 °C improves the coefficient of performance at least 17%. The combined use of heat pump and concentrated photovoltaic thermal system has the effect of reducing the energy consumption ratio up to 86%. The effect of parameters such as optical efficiency, concentration ratio and evaporator air temperature on drying performance is investigated. The results show that the heat recovered at the Closed Feed Air Heater increases as the temperature of air leaving the dryer increases. A decrease in optical efficiency from 0.9 to 0.65 increases the electrical energy consumption ratio by 73%. An increase in the aperture area from 100 to 150 m2 also improves electricity production and drying capacity by 45 and 27%, respectively. The drying capacity has known an increase of about 43% by increasing the mass flow rate from 0.6 to 1 kg.s−1. Finally, the combined use of a heat pump and a concentrated photovoltaic thermal can reduce significantly the electrical energy consumption and improve thermal performance of drying systems throughout the year.

Construction strategy and performance analysis of large-scale spherical solar concentrator for the space solar power station

The space solar power station is a gigantic power satellite to provide the earth with continuous energy. The front-end system of space solar power station, solar concentrator, has significant influences on the optical performance. Regarding the proposed orb-shaped membrane energy gathering array scheme, this paper deals with the construction strategy of its large-scale spherical concentrator to reduce the complexity of manufacturing and improve the optical properties. The optical principle of the spherical concentrator is described and the spatial motion characteristic is presented. A novel construction strategy for the large-scale concentrator is proposed via partitioning octahedron on the sphere and polygonal partition. This paper evaluates the optical performance of the concentrator constructed by the novel strategy using ray tracing method. Performance parameters such as optical concentration ratio and collection efficiency are obtained. Comparison with the other strategies are also implemented. In addition, influence factors such as the sun's non-parallelism, the tracking precision, the orbital periodic motion, and the potential blockage effects of microwave transmitting antenna and supporting structure are mathematically discussed and evaluated. The numerical results indicate that the proposed strategy achieves a high collection rate, a small efficiency fluctuation, appropriate energy distribution, and relatively small splicing modules, which is conducive to improve optical performance and decrease difficulty in manufacturing.

Design of leak-free sawtooth planar solar concentrator for daylighting system

Daylighting system installed on the roofs of commercial buildings is an effective measure for low-carbon green buildings. In order to further improve the efficiency and uniformity of daylighting system, this paper proposes an indoor daylighting system based on the design method of the solar concentrator with leak-free sawtooth lightguide. The mathematical model of the total internal reflection (TIR) lens array and lightguide is established. A plate of beam splitter plate is added to separate visible and non-visible light, and daylight and artificial light are used to provide indoor lighting. The factors affecting the optical concentration ratio and the concentration-acceptance product (CAP) value of solar concentrator are analyzed, which is helpful to design better daylighting system. When the optical concentrations ratio are 300, 800, and 1800, the acceptance angles are greater than ±0.17°, ±0.31° and ±0.45°, respectively. Simulation software is used to track the light. The results shows that the illumination uniformity of the system in the working plane reached 0.3, and the total efficiency of the daylighting system reached 65.36%. This design provides a new idea for commercial building lighting and greenhouse lighting applications, which has promising potential applications in the clean production.