Solar Concentration Ratio Research Articles

Building Integrated Heliostats

Heliostats offer a means of improving solar access in densely populated cities. Ocular and skin health considerations recommend control of UV radiation from heliostats in the urban environment. Lessons from integration of polycarbonate filter systems for UV control with building integrated heliostats are discussed, including the impact of solar concentration ratios, thermal stresses, material properties and fatigue. Options for further increasing solar concentration ratios in building integrated heliostat systems are proposed.

Efficiency limits of concentrated solar thermophotonic converters under realistic conditions: The impact of nonradiative recombination and temperature dependence

A concentrated solar thermophotonic converter (CSTC) that efficiently harvests the entire solar spectrum under non-ideal conditions is proposed. This device includes an optical concentrator, a solar absorber, a GaAs light-emitting diode (LED) on the hot side, and an InP photovoltaic (PV) cell on the cold side. The electric power generated by the PV cell is utilized to positively bias the heated LED, resulting in a substantial increase in LED emission power. A comprehensive theoretical model is developed to accurately predict the output electrical performance and overall energy conversion efficiency of the CSTC device, especially considering the impact of the nonradiative recombination and temperature dependence. The calculated results show that when the solar concentrating factor is 30, and the LED and PV cell voltages are 0.989 V and 1.13 V, respectively, the overall peak efficiency can reach 12.8% and the corresponding output power density is 384 mW cm−2, achieving performance metrics nearly 4 orders of magnitude higher than solar thermophotovoltaics (TPV). Additionally, increasing the solar concentration ratio and decreasing the thickness of the semiconductor materials can further improve the overall output performance. This work reveals that CSTC offers several advantages over solar TPV, including more efficient conversion of narrow-spectrum electroluminescence, higher radiated power from the LED emitter, and the ability to operate at lower solar concentrations and lower costs.

Optically manipulated nitrate-salt-based direct absorption solar collectors for a photothermal energy harvesting system

This study introduces a nitrate-salt-based direct absorption solar collector (DASC) for a photothermal energy harvesting system with efficient solar energy harvesting and the reduction of thermal radiation loss. Investigations of the optical properties of snow-like solid-state binary nitrate salt in solar and thermal infrared (IR) spectral regions were first conducted in this study. Research revealed that the solid-state binary nitrate salt showcases high solar reflectivity (>90 %) and infrared emissivity (∼0.85), leading to a cooling power of 36.4 W m−2. This implies pure solid salt cannot gain energy from solar illumination. To tackle this, the proposed system incorporated nano graphite and a hot mirror. Consequently, the absorbed solar energy increased from 67.6 W m−2 to 898.7 W m−2, resulting in a heating power of 794.0 W m−2 under AM 1.5G solar irradiance. With the proposed approaches, melting the salt with lowest solar concentration ratio of 15 (∼12.5 kW m−2) was achieved.

Bayesian neural networks for solar power forecasts in advanced thermoelectric systems

This study presents a Bayesian neural network for the comprehensive performance forecast of an advanced thermoelectric system featuring segmented thermocouples with variable area shape for optimal solar energy conversion. The training data is obtained from a three-dimensional numerical model developed in ANSYS software to account for the energy, exergy, and entropy flows in the thermoelectric module to maximize the power output, energy, and exergy efficiencies while minimizing the entropy generation and system irreversibilities. The thermodynamic model optimizes key parameters, including geometry (height, cross-section, and percentage skutterudite content) across realistic diverse heat fluxes and cooling coefficients. To facilitate a faster and more efficient optimization pipeline, various neural networks, leveraging algorithms like Levenberg-Marquardt, scaled conjugate gradient, and Bayesian regularization, are utilized for efficient data management and accurate performance prediction. The Bayesian neural network emerges as the most accurate and efficient model providing the lowest training and testing loss of ∼10−9. Furthermore, key findings highlight the importance of skutterudite content and solar concentration ratio. For instance, an optimal skutterudite content of 6.2 % at 25 Suns produces maximum power of 29.7 W, while 37 % skutterudite at 75 Suns minimizes exergy destruction. This study's methodology and findings contribute to designing more efficient clean energy systems and advancing sustainable energy goals.

Prediction of Solar Concentration Flux Distribution for a Heliostat Based on Lunar Concentration Image and Generative Adversarial Networks

ABSTRACT The predictive analysis of solar flux distribution on the receiver surface is critical in optimizing the concentration processes of concentrating solar power (CSP) plants. Due to the difficulties of directly measuring the solar flux distribution of the heliostat field, tracking the Moon and measuring the lunar concentration ratio distribution become a promising option. However, many factors affect the flux distribution of a heliostat field. To obtain an accurate predictive model for the solar flux distribution, we propose a deep-learning method using conditional generative adversarial networks (cGAN) and lunar concentration images. The method can take account of tracking errors of individual heliostats, defects of reflecting surfaces, as well as atmospheric attenuation effects, and has the potential to give a reliable prediction of solar flux distribution. Mathematical relations between the solar flux distribution and the solar concentration ratio distribution are discussed in the paper. Experiments have been designed and carried out with an ordinary heliostat at the Beijing Badaling solar concentrating power station. Experimental results show that the AI-generated solar concentration ratio distributions are very close to the actual solar concentration ratio distributions, demonstrating the feasibility of AI models for the prediction of solar flux distribution.

Processing and optical behavior of dense (Hf,Zr)B2 solid solutions for solar energy receivers

While individual borides and, more recently, quinary High Entropy Transition Metal Borides have been investigated, the fabrication and characterization of bulk binary to quaternary solid solutions are barely explored. In this work, dense (Hf0.5Zr0.5)B2 is produced by Spark Plasma Sintering (SPS) from powders prepared by Self-propagating High-temperature (SHS). SHS produced a multiphase product, whose secondary phases are fully converted into the desired diborides during the subsequent SPS step. Optical properties of (Hf0.5Zr0.5)B2 are evaluated for the first time with focus on the possible use as novel high-temperature solar thermal absorber, by hemispherical reflectance measurements and calculation of solar absorptance, temperature-dependent spectral selectivity and absorber opto-thermal efficiency at various solar concentration ratios. To optimize the material, a chemically etched surface texture was realized to modify the optical properties. The etched sample showed a higher solar absorptance (0.71) and a lower spectral selectivity than the unetched one, with consequent higher opto-thermal efficiency at all temperatures for solar concentration ratios 1000 ÷ 3000, while at lower concentration ratios and temperatures >1400 ÷ 1600 K, the unetched sample shows the highest efficiency. These results show the promising properties of binary diborides for solar thermal applications.

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.

An Optical-Electronic-Catalytic Coupled Multi-Physical Simulation for Sunlight-Driven CO2 Reduction Device Based on Light Absorbers Patterned with Island Electrocatalysts

Photoelectrochemical (PEC) reduction of CO2 to value-added chemicals is a promising approach to convert solar energy but it is often suffered from sluggish kinetics and photocorrosion at the semiconductor-electrolyte interface.1, 2 In general, there are two requirements for a good performing solar-driven CO2 reduction: i) effective catalysts for a fast surface redox reaction and ii) an effective semiconductor/catalyst interface for rapid charge transfer across interfaces.3 The deposit of a continuous electrocatalyst layer on the photoabsorber surface can reduce kinetic overpotentials for CO evolution reaction (COER) and can enhance the photoelectrode stability. However, the optical obscuration significantly attenuates the magnitude of the incident illumination. Reducing the coverage (f c) of the catalyst on the photoabsorber surface can reduce the optical obscuration but worsen the reaction kinetics. Moreover, the pinch-off effect occurs as the size of the catalyst is small enough to provide a facile path for carriers to transport across interfaces. The PEC CO2 reduction with the utilization of the pinch-off effects could potentially be advantageous to balance the kinetics and the optical absorption. Understanding the trade-offs between the reduction in photocurrent density due to optical obscuration and the decrease in kinetic overpotentials due to improved active area is important in optimizing PEC CO2 reduction devices.To elucidate the effects of the optical performance, interfacial carrier transport, and electrochemical activity for the PEC CO2 reduction, three possible interfacial configurations in PEC were considered in this study: i) Bare p-Si photocathode case. The bare p-Si photocathode immersed in aqueous electrolyte and CO2R occurs at the semiconductor-electrolyte (SC/E) interface; ii) Layered catalyst case. The continuous layer catalyst is deposited on the surface of p-Si photocathode and forms a semiconductor-metal (SC/M) interface; iii) Patterned catalyst case. Producing a patterned catalyst with a low geometric coverage fraction on the surface of p-Si photocathode. The Schottky junctions with a low barrier height formed by the SC/M are surrounded by the Schottky junctions with a high barrier height formed by the SC/E. We developed a multiphysics model based on the finite element method, including electromagnetic wave propagation, charge transport in bulk semiconductor, species transport in the electrolyte, and charge-transfer kinetics of surface redox reactions.The optical performance and electrochemical performance of CO2R reduction were compared in the three cases. Under the bare p-Si case, the saturation photocurrent densities (J sa) and the onset potential (V on) were -13.40 mA/cm2 and -0.80 V vs. RHE at -1 mA/cm2, respectively. Under the layered catalyst case, the J sa and the V on were -0.84 mA/cm2 and -0.50 V vs. RHE at -0.10 mA/cm2, respectively. Under the patterned catalysts case (f c is 0.1 in this case), the J sa is -12.30 mA/cm2 and V on is -0.69 V vs. RHE at -1 mA/cm2. The magnitude of J sa is influenced by the extent of light obscuration and the magnitude of V on is influenced by the photoelectrode activity and the pinch-off effects. The V on for the patterned case is higher than that of the bare p-Si case due to the improved electrode activity combined with the pinch-off effects. In the bare p-Si case and the patterned catalyst case, the CO2 mass transfer limits the CO partial current density (J CO) to further increase due to high J sa while CO2 mass transfer is not the limitation for COER at high overpotentials for the layered catalyst case due to significant light obscuration. The pinch-off effect also increased the applied voltage corresponding to the maximum J CO for the patterned case (-1.21 V vs. RHE) compared to that for the bare p-Si case (-1.35 V vs. RHE) due to the deceased transport resistance of electrons.The influence of different interfacial configurations, solar concentration ratio, different coverage of catalysts, and different sizes of catalysts for optical loss, pinch-off effect, CO2 mass transfer, current distribution at interfaces, and electrochemical performance are discussed in detail for the optimal design photoelectrode. This framework allows us to provide design guidelines for PEC CO2 reduction devices.

Solar concentrators filled with liquid for enhancement of photocurrent generation and angular responses of light incidence

Design and manufacturing of solar concentrator materials and structures for external light trapping have been widely explored for decades to enhance solar cell performances in various photovoltaic (PV) devices such as silicon, organic, and perovskite ones. Among them, remarkable progress in development of the concentrators has been made to improve the solar concentration ratio of power conversion efficiency (PCE). However, only some studies were carried out to enhance the angular responses of light incidence (AOI). This paper reports a simple liquid-filled solar concentrator (LFSC) that can be effectively implemented by incorporating optical reflection with total internal refraction (TIR). Using the fused deposition modeling (FDM) method in the 3D printing process, the hollow compound concentrators in a parabolic shape were efficiently produced at a low cost. With liquid water and silicone oil, the simulation and experimental results illustrated that the PCE and AOI were increased for the concentrator solar cells composed of bulk heterojunction structure. In particular, it was found that all the AOI exhibited an exponential decay as a Gaussian distribution. Hence, it provided the capability of control over concentrator material and geometry in design and fabrication. In this manner, various such simple devices fabricated by the present method can be further applied in future applications such as PV cell modules and systems.

Energy and exergy analysis of a novel solar-based system merged with power cycle

Parabolic Trough Solar Collector (PTC) is a power generation unit that works based on solar energy. This system provides a considerable amount of thermal power but no electrical energy. Hence, the current investigation attempts to boost the outputs of the PTC system by merging this unit with the Photovoltaic (PV) module and Organic Rankine Cycle (ORC). In this regard, the outputs of the conventional PTC system under multiple operating conditions are compared with those of PTC-PV, PTC-ORC, and PTC-PV-ORC systems. These systems are three-dimensionally simulated using the steady-state approach and the influences of variation in the solar flux and concentration ratio on the energy and exergy efficiencies are scrutinized. According to the obtained data, at the base case condition, the overall energy efficiencies of the conventional PTC, PTC-PV, PTC-ORC, and PTC-PV-ORC systems are 42.75%, 47.20%, 13.43%, and 21.46%, respectively. The performance of these systems from the exergy viewpoints is 5.51%, 14.31%, 4.19%, and 13.33%, respectively. Based on the simulations, from the electrical energy and exergy viewpoints, the PTC-PV-ORC system has the highest performance followed by PTC-PV and PTC-ORC systems. Nonetheless, the thermal exergy of the ORC-based systems is remarkably lower than that of single solar units. This study shows the integration of the PTC system with the PV module and ORC boosts the output of this conventional unit.

THEORETICAL ANALYSIS OF SOLAR THERMOELECTRIC GENERATORS INTEGRATED WITH RADIATIVE COOLER

A comprehensive analysis of solar thermoelectric generators integrated with radiative cooling technology (STEG-RC) is presented in this study. Basically, the STEG-RC operates outdoors; therefore, the effects of various weather parameters on the output performance of the STEG-RC are determined. The results reveal that the most efficient way of enhancing the output performance of the STEG-RC is by concentrating solar energy. The radiative cooling power increases linearly with the ambient temperature achieving the maximum cooling power of 135 W/m2 and 232 W/m2 at solar concentration ratios of C = 1 and C = 5, respectively. The maximum output power of 1.5 mW and 459.6 mW at the optimum wind speeds of 3 m/s and 2 m/s are obtained for C = 1 and C = 5, respectively. There were no significant changes in the power output and radiative cooling power when relative humidity was varied. The cooling power is linearly proportional to solar irradiance for both concentrated and unconcentrated cases.

Experimental study on a concentrating solar photovoltaic/thermal system using different fluid spectral beam filters

Spectral splitting photovoltaic/thermal technology is the leading field in the area of extremely efficient utilization of solar energy. Due to its complexity, experimental research on spectral splitting photovoltaic/thermal devices is relatively limited, mainly focusing on the laboratory scale energy efficiency test or calculation process verification. These studies do not provide intuitionistic guidance for the actual operation of engineering systems. In this paper, a fluid filter-based compound parabolic concentrator solar photovoltaic/thermal system with engineering application dimensions is designed and experimentally studied under actual outdoor environments. Different fluid filters are prepared and used to regulate the spectral splitting characteristics of the proposed system, including the deionized water, silver/water nanofluids and silver-cobalt sulfate/water nanofluids. When the environmental parameters are relatively stable, the method of adjusting the composition of the fluid filter is used to obtain the dynamic operating characteristics of the system. The results show that silver nanoparticles and cobalt sulfate can improve the spectral absorptivity of the deionized water. Compared with the deionized water, when the silver/water nanofluids is used as the fluid filter, the thermal efficiency of the system increases, the electric efficiency and overall exergy efficiency of the system both decrease, and the three efficiencies are 56.0%, 8.5% and 19.6%, while for the silver-cobalt sulfate/water nanofluids, the efficiencies are 58.0% 8.0% and 20.0%. Moreover, the results reveal that for the photovoltaic/thermal system with a low solar concentration ratio, by enhancing the absorptivity of the fluid filter, the fill factor of the photovoltaic module can increase, but the output electric power will decrease. When the silver-cobalt sulfate/water nanofluids is used, the fill factor and maximum output power of the proposed system are 0.633 and 69.2 W. For a unit consisting of four sets of the proposed photovoltaic/thermal systems, the emission reductions of CO2, NOx, SO2 and dust for the whole lifetime are approximately 7794.19 kg, 181.48 kg, 191.95 kg and 111.68 kg, respectively.

Geometric characteristics and design optimization of parabolic trough concentrators with a flat mirror as the secondary reflector designed based on two components of a solar source

Parabolic trough concentrators with a tubular receiver (PTCs) are widely used for the production of solar thermal power. However, the geometric concentration ratio (CR) of PTCs falls short of thermodynamic concentration limit (C0) by a factor larger than π, and restricted by the angle subtended by solar sources (Δs = 2θa). To increase CR, a novel idea by dividing a solar source into two components in the open angle is proposed for the design of PTC equipped with a secondary reflector (SR), and PTC with a flat mirror (FM) is designed as a trial of the idea. For such design idea, rays incident at rims of primary parabolic reflector (PR) from one component (S1) are required to directly redirect onto on the absorber tube (AT) and those from another component (S2) are required to arrive on the AT after reflections from PR first then from FM. To investigate effects of the angular division factor (k) of solar sources (Δs2 = kΔs) and rim angle (ϕe) of PR on the effective CR (Cg), a mathematical procedure to characterize the geometry is suggested and examined by ray-tracing technique. The analysis shows that the geometry of PTC-FM is dependent on k, ϕe and θa, and a set of optimal k and ϕe for maximizing Cg can be obtained when θa is given. Calculation results show that the optimal k for maximizing Cg is 0.5 regardless of θa, but the optimal ϕe of PTC-FM for maximizing Cg, is sensitive to θa. As compared to conventional PTCs, the Cg of optimized PTC-FM is increased more than 80%, larger than 56.5% of C0, for k = 0.5 and θa < 1.0°. Empirical expressions for a quick estimation of optimal ϕe are also proposed based on numerical calculations. Results by ray-tracing analysis indicate that the optimal ϕe for maximizing CR and average solar concentration ratio are almost identical when the reflectivity of PR and FM is higher than 0.8. In principle, the novel idea is applicable for the design of other solar concentrators, therefore a further increase of Cg of PTCs is possible by using other imaging and non-imaging optics as the SR.

Numerical investigation on radiative heat loss of a direct absorption solar collector using the discrete ordinates method

Direct-absorption solar collectors have the potential to be highly efficient and exhibit a uniform temperature distribution. However, the standard numerical model simplifies radiation and heat loss, which require further consideration at high temperatures. Thus, a novel self-programming model for photothermal conversion in a direct-absorption solar collector was developed based on the discrete ordinates method. This novel model contains further details on radiative transfer and specular reflection boundary conditions. This study compared the results of the two models at high temperatures. With an inlet temperature of 500℃ and a solar concentration ratio of 100, the standard model overestimated outlet temperature and conversion efficiency by 27.6 ℃ and 18.9%, respectively. This study investigated radiative heat loss at different temperatures, solar concentration ratios, and incident angles. The results showed that radiative heat loss will exceed 5% with a fluid temperature exceeding 600 ℃. Furthermore, efficiency decreases significantly at incident angles exceeding 30°. The proposed model expands the range of applications of numerical models of solar collectors to high temperatures. These results provide a reference for improving the conversion efficiency of solar collectors at high temperatures, which is regarded as an urgent problem.

Water liquid compatibility as a spectral splitting optical filtration fluid to six types of photovoltaic solar cells under high solar concentrations

The spectral-splitting optical filtration (SSOF) technique has attracted a lot of attention as a solution to the unnecessary portion of solar irradiation that can be stored as heat in the cells of conventional photovoltaic (PV) and photovoltaic/thermal (PV/T) systems. Transmitting the effective portion according to the SSOF fluid optical range and the spectral response of the integrated cell was the key solution proposed by this technique. The present study investigates the numerical feasibility of using liquid water, under six distinct solar concentration ratios, as a SSOF fluid for incident radiation on six types of PV cells with different spectral response ranges. For the 36 cases, the performance of PV and hybrid PV/T systems, represented as PV/Cooling fluid (PV/CF), with SSOF was evaluated and compared to their original performance without SSOF. In mid-July in Dhahran, Saudi Arabia, the functionality of each system was determined by analyzing the generated electrical and thermal energy over the course of a full day. In addition, the electrical efficiency and average PV temperature of the systems were estimated. In terms of spectral compatibility, the water SSOF was more compatible with three PV cells, out of the examined cells. At specified solar concentrations, depending on the engaged PV cell, the results demonstrated that integrating SSOF into the conventional PV and hybrid PV/CF systems produced more electricity at reduced PV temperatures, compared to the corresponding conventional system. In addition, the functionality was extended to increased solar concentrations. Due to the discrepancy in their spectral responses, the electrical energy and efficiency outputs of each cell type varied. When conventional systems were combined with SSOF, the spectral transmittance range of the liquid and the distinct spectral response ranges of the cells increased the number of possible combinations. p-Si and CIGS cells performed comparably in standalone PV and hybrid PV/CF systems, while CIGS and Perovskite cells performed comparably with SSOF. The m-Si and p-Si cells provided the most electrical energy and efficiency, while the a-Si cells were the least efficient, which thereafter influenced the selection of the highly functional system suitable for the PV cell type. At 8.2 suns and above, the hybrid SSOF/PV/CF system had the highest overall energy output and electrical efficiency, for all the examined cells, due to enhanced cooling and reduced solar radiation exposure.

A passive evaporative cooling strategy to enhance the electricity production of hybrid PV-STEG system

The dependable and efficient thermal regulation technology for combined photovoltaic-solar thermoelectric generator (PV-STEG) system is of great importance to ensure output performance. To enhance the electrical behavior of PV-STEG system, a passive evaporative cooling (PEC) technique was presented in this work. Some critical parameters such as solar concentration ratio, ambient temperature, relative humidity, air velocity, and water layer thickness were discussed in detail for a comprehensive assessment of the influence on system temperature, electricity production, and energy conversion efficiency. The obtained findings suggested that adopting PEC technology may greatly lower the operating temperature of the PV-STEG system when compared to the uncooled PV-STEG system. At the solar concentration ratio of 5, the maximum temperature reduction of 92.09 K can be achieved with the assistance of PEC technology. Furthermore, the system performance is greatly influenced by ambient conditions. For example, if the system is exposed to lower ambient temperature, lower relative humidity, and higher air velocity, it produces more electrical power. In addition, compared with other factors, the impact of the water layer thickness is quite gentle, and the temperature difference is less than 1 K. However, there also exists an optimal water layer thickness, and the specific value is 1 mm when the solar concentration ratio is 3. Moreover, compared to traditional passive fin cooling technology, this system demonstrates superior performance.

Direct solar-thermal scalable-decomposition of methanol flowing through a nanoparticle-packed bed reactor under outdoor environment

Using nanoparticles to absorb sunlight and drive methanol decomposition is a potential approach of solar energy utilization, which can convert solar energy into chemical energy of syngas. But a challenge of nanoparticle solar methanol decomposition is how to design concise and efficient large-scale application method. Focusing on the key issues of energy conversion and reaction system optimization, this work analyzes the sunlight capture, flow heat transfer and catalytic reaction in the nanoparticle volumetric absorption solar methanol decomposition system by theoretical and experimental studies. And the applied scalable solar-chemical system is constructed. The results show that the reaction bed constructed by nanoparticles has advanced solar energy capture performance, and can effectively drive the methanol decomposition. Compared with the traditional system, it has the lower solar concentration ratio of 17.5 and the higher energy conversion efficiency of 35.5%, and the reaction can be started up at the temperature of 136 °C. The cumulative solar-to-fuel energy conversion in this work can reach 1.3 × 1011 J/m2 in one year of operation in Nanjing, China. This work can further guide the construction of solar-driven thermochemical systems of splitting methanol into syngas and storing solar energy.

Environmental and energetic behavior of a Beam-down linear Fresnel solar field for low-grade thermal energy applications

Solar concentrators can be used to provide low-grade thermal energy in industry for improving overall efficiency and targeting the emissions reduction goals. In this context, to develop an effective Concentrated Solar Technology for utilizing low-grade thermal energy, different configurations of a beam-down Fresnel solar field are analyzed in terms of thermal energy production and environmental impacts as Global Warming Potential (GWP), Ozone Depletion Potential (ODP) and Particulate Matter (PM). Once the geometry of the solar field is defined, the yearly incoming energy at the solar receiver is obtained. Subsequently, the GWP, ODP and PM are calculated with the Life Cycle Assessment methodology for construction and operation phase. Those environmentally lighter designs in the construction phase are not those that obtain lower results when the energy they provide is analyzed. The GWP and ODP results showed that producing low grade thermal energy with all but two of those beam-down configurations obtained better results than the conventional heat from natural gas. The case study with lowest carbon footprint represents 34.2 % reduction compared to natural gas and 41 % reduction in ODP. However, PM obtained better results for conventional heat than for the proposed solar fields. Configurations with C = 24 as solar concentration ratio achieved the optimal configuration with a good balance between energy production and the analyzed environmental impacts.

New hybrid concentrated photovoltaic/membrane distillation unit for simultaneous freshwater and electricity production

Traditional photovoltaic-thermal desalination systems often rely on electricity to power pumps which can reduce the amount of electricity available for other practices. The current work presents an integrated system combining a concentrator photovoltaic (CPV) with a direct contact membrane distillation (DCMD) in a single unit. Hence, it is possible to use the thermal energy generated by the CPV unit to power the DCMD unit and produce both fresh water and electricity simultaneously. A comprehensive numerical model of the proposed system is developed and validated to investigate the effects of different operating conditions on the system's performance, such as the solar concentration ratio (CR), feed Reynolds number, and feed channel aspect ratio (AR), on the system's productivity. Furthermore, a modified design is introduced in which the length of the DCMD is enlarged beyond the CPV to benefit from the excess energy within the feed water. The predicted produced flux reached ∼33.2 kg/m2 h at CR = 300, Re = 175, and AR = 2400. The modified method produced a higher flux than the original design within the same CR values. The optimum length ratio values were calculated, which were found to be 1.7, while the counter configuration was nearly 1.5.

Passive thermal control of a triple-junction solar cell at high concentrations using various finned heat sink configurations

Designing an effective heat sink that is light, inexpensive, and simple to manufacture and install, is crucial in developing a heat control strategy for high concentrated triple-junction (TJ) solar cells to maintain the cell operating temperature below the maximum allowed limit. Such heat sinks ensure better electrical output power and efficiency at a cheaper cost. Thus, the present research focuses on the passive thermal regulation of a triple-junction solar cell utilizing four different finned heat sink configurations; (A) flat plate, (B) straight fins, (C) pin fins, and (D) flared fins heat sink. A comprehensive 3D thermal and electrical model is developed and computationally simulated, incorporating the cell module layers coupled with the aluminium heat sink. The performance of the proposed system with different heat sink designs is investigated at various concentration ratios (CR) of the solar irradiance ranging from 50 suns to 1250 suns, air temperatures ranging from 25 °C to 40 °C, and wind speeds ranging from 1 m/s to 5 m/s. In hot climatic conditions (40 °C and 1 m/s), the integration of the proposed heat sink configurations A, B, C, and D enables the cell to operate safely (below 110 °C) at high concentration ratios of 440 suns, 1435 suns, 1250 suns, and 1775 suns, respectively, and produce large electric power of 15.2 W/cm2, 49.7 W/cm2, 43.3 W/cm2, and 61.4 W/cm2. In contrast, the maximum permissible concentration ratio of an uncooled cell operating in the same conditions is limited to 77 suns with an electrical output of 2.7 W/cm2. Although the flared fins heat sink is the heaviest, weighing about 0.6 kg, and the flat plate one is the lightest with 0.05 kg, the environmental analysis revealed that utilizing the former for cooling concentrated photovoltaic systems could reduce annual CO2 emissions by 1475.2 tons/m2 compared to 364.5 tons/m2 for the latter if both are operated at the maximum permissible solar concentration ratio.