Concentrator Photovoltaic Cells Research Articles

Simulation and Model Validation of a Multi-Concentration Points Concentrated Photovoltaic Thermal System

In this study, the transient behavior of a concentrated photovoltaic thermal (CPV/T) system is assessed using one-dimensional mathematical model. The model is based on the heat balance of the concentrated photovoltaic (CPV) solar cells, receiver pipe, thermal fluid, insulation, and the storage tank attached to PV/T system via insulated pipes. The mathematical model was developed and solved using ordinary differential equation solvers in MATLAB® computer program. The interdependence thermo-electric dynamic responses of the CPV/T system were modeled and analyzed by considering two cases such as with and without glass enclosure around the receiver. The electrical and thermal efficiencies are evaluated as the function of enclosure effect, beam solar radiation, and circulating fluid flow rate. For the purpose of model validation, experimental measurements of the CPV/T system were performed. Satisfactory agreements were found between the experimental data and the predicted results. The developed dynamic model is most suitable to predict and evaluate the performance of a point-focused CPV/T system.

An integrated concentrated solar fuel generator utilizing a tubular solid oxide electrolysis cell as solar absorber

We numerically assessed the potential of a solar reactor concept for efficient fuel processing under concentrated solar irradiation. This design integrates a cavity receiver, a tubular solid oxide electrolyzer, and the concentrated photovoltaic cells into a single reactor. The tubular electrolyzer simultaneously acts as the solar absorber (for reactant heating) and as the electrochemical device (for water and carbon dioxide splitting). A multi-physics axisymmetric model was developed, considering charge transfer in the membrane-electrolyte assembly, electrochemical and thermochemical reactions at the electrodes' reaction sites, species and fluid flow in the fluid channels and electrodes, and heat transfer for the whole reactor. A high solar-to-fuel efficiency was predicted (18.6% and 12.3% for indirectly and directly connected approaches, respectively, both at CPV = 385 and Cap = 1273). For synthesis gas production, the upper current density threshold to avoid carbon deposition was found to be 8725 A/m2 at reference conditions. A continuous range of H2/CO molar ratios of the synthesis gas was achieved by varying the inlet H2O/CO2 ratio, the irradiation concentration, and the operation current density. Efficiency-optimized operating conditions and design guidelines are presented. Our novel and integrated solar reactor concept for the solar-driven high-temperature electrolysis of H2O and CO2 has the potential to provide a simple, high solar-to-fuel efficiency reactor at reduced cost, all given by the reduced transmission losses of the integrated reactor design.

Performance analysis of a new concentrator photovoltaic system integrated with phase change material and water jacket

A new integrated concentrator photovoltaic (CPV) system using phase change material (PCM), and a water jacket is developed to increase the thermal regulation period during the daytime and enhance heat removal from the liquid PCM during the nighttime. The system integrates a CPV cell with three different designs of the PCM heat sink: a single-cavity, a three-parallel cavity, and five-parallel cavity configurations. To evaluate the electrical and thermal performance of the integrated CPV-PCM-water jacket system, a comprehensive 2-D mathematical model for CPV layers combined with PCM, and water jacket flow is developed. The full model couples’ thermal models for CPV layers and thermo-fluid models that consider the phase-change phenomenon and water jacket flow. Numerical simulation of the comprehensive model is performed to estimate the transient temperature variation of the employed PCM during melting and solidification processes along with the local and average temperatures of the silicon solar cell. Results reveal that the integrated CPV-PCM-water jacket system attains a significant reduction in the average solar cell temperature throughout the daytime. By using a single cavity configuration at a concentration ratio (CR) of 20, a noticeable decrease in solar cell temperature of around 124 °C is achieved in comparison to the conventional CPV-PCM system. Moreover, at the end of the nighttime, about 55% of the liquid phase changed to solid phase, compared to the conventional CPV-PCM system, where about 10% of the liquid phase transformed to solid phase. By using a five-cavity configuration, the solar cell temperature is maintained below 72 °C during the full day and the average electrical efficiency throughout the daytime is about 17.7%. Furthermore, the liquid phase has completely transformed to solid phase at the beginning of a new cycle of insolation. The present findings can open doors for further research into merging the advantages of passive and active thermal regulation for CPV systems.

A new approach for evaluating flux uniformity for dense array concentrator photovoltaic cells

In this paper, we present two statistical methods to quantify the heterogeneity of the irradiance flux distribution, in a Concentrator Photovoltaic (CPV) dense-array, based on its operation and the optimization of current-matching. Preventing non-uniform flux distribution from design avoids the generation of hot spots, current mismatch and increases the overall efficiency of the system. This new approach considers the effects of the lowest irradiance values in the performance of the complete array, and its performance was corroborated by the simulations of a CPV array modelled in Matlab/Simulink; the irradiance distribution data as an input parameter was obtained from the images taken in a homogenization experiment, in the HoSIER, an 18,000 X solar furnace. The results are interpreted through the new concept of photovoltaic homogeneity, proven that the methodology successfully predicts the flux distributions, which enhances the efficiency of a series connected CPV array. Additionally, we found that the proposed methodology can also be used to optimize the electrical performance of dense-array CPV systems, working under the effects of non-uniformity illumination by rewiring the series connections into series-parallel configurations.

Experimental and numerical investigation of hybrid concentrated photovoltaic – Thermoelectric module under low solar concentration

The quick progress in solar energy technology has made it one of the most promising alternatives to conventional energy systems in recent years. In this work, in order to make efficient use of the solar energy, a hybrid system composed of the concentrated photovoltaic cell and thermoelectric generator (CPV-TEG) is studied using both experimental and numerical approaches. The experimental study is carried out under concentrated radiation of a solar simulator, and the numerical simulation is accomplished using finite volume method. The results are presented for various solar concentration (SC) values ranging from 8 suns to 37 suns. The variation of the temperatures, open circuit voltage, and short circuit current are discussed. I-V-P curves for both CPV and TEG are obtained and evaluated experimentally and numerically. The results show that contribution of the TEG in the total electrical power produced by the hybrid system enhances with increasing the solar radiation. Furthermore, the experimental results indicate that the maximum and minimum efficiency of the CPV is reached to 35.33% and 23.02%, while these values for the TEG are 1.20% and 0.63%, respectively.

Design and characterization of hybrid III–V concentrator photovoltaic–thermoelectric receivers under primary and secondary optical elements

Lattice-matched monolithic triple-junction Concentrator Photovoltaic cells (InGa(0.495)P/GaIn(0.012)As/Ge) were electrically and thermally interfaced to two Thermoelectric Peltier module designs. An electrical and thermal model of the hybrid receivers was modelled in COMSOL Multiphysics software v5.3 to optimize cell cooling whilst increasing photon energy conversion efficiency. The receivers were measured for current–voltage characteristics with the cell only (with sylguard encapsulant), under single secondary optical element at x2.5 optical concentration, and under Fresnel lens primary optical element concentration between x313 and x480. Measurements were taken in solar simulators at Cardiff and Jaén Universities, and on-sun with dual-axis tracking at Jaén University. The hybrid receivers were electrically, thermally and theoretically investigated. The electrical performance data for the cells under variable irradiance and cell temperature conditions were measured using the integrated thermoelectric module as both a temperature sensor and as a solid-state heat pump. The performance of six hybrid devices were evaluated within two 3-receiver strings under primary optical concentration with measured acceptance angles of 1.00° and 0.89°, similar to commercially sourced Concentrator Photovoltaic modules. A six-parameter one-diode equivalent electrical model was developed for the multi-junction cells under both primary and secondary optical concentration. This was applied to extract six model parameters with the experimental current–voltage curves of type A receiver at 1, 3 and 500 concentration ratios. Standard test conditions (1000 W/m2, 25 °C and Air Mass 1.5 Global spectrum) were assumed based on trust-region-reflective least squares algorithm in MATLAB. The model fitted the experimental current–voltage curves satisfactorily with a mean error of 4.44%. The combined primary and secondary optical intensity gain coefficient is as high as 0.92, in comparison with 0.50–0.86 for crossed compound parabolic concentrators. The determined values of diode reverse saturation current, combined series resistance and shunt resistance were similar to those of monocrystalline PV cell/modules in our previous publications. The model may be applicable to performance prediction of multi-junction CPV cells in the future.

Behavior of hybrid concentrated photovoltaic-thermoelectric generator under variable solar radiation

Transient response of a hybrid system composed of concentrated photovoltaic (CPV) cell and thermoelectric generator (TEG) is investigated in this study. This research is carried out by using a numerical simulation approach thermally coupled between the CPV and TEG. A transient model is established and solved by finite volume algorithm. In spite of temperatures profile in the hybrid CPV-TEG module, as results of variation of solar irradiation, power generation and efficiency of the CPV and TEG under the transient condition are presented. The results show that efficiency of the TEG and CPV varies diversely versus changing the solar radiation and module temperature. Moreover, the thermal response of the TEG stabilizes temperature fluctuation of the hybrid module when the solar radiation rapidly changes. In this work, impact of the thermal contact resistance on the temperature profile and system efficiency is investigated. The model presented in this study provides a fundamental understanding of the thermal and electrical effect of the TEG in hybrid CPV-TEG module under transient conditions.

Experimental characterization and multi-physics simulation of a triple-junction cell in a novel hybrid III:V concentrator photovoltaic–thermoelectric receiver design with secondary optical element

A lattice-matched monolithic triple-junction Concentrator Photovoltaic cell (InGa(0.495)P/GaIn(0.012)As/Ge) was electrically and thermally interfaced to a Thermoelectric Peltier module. A single optical design secondary lens was bonded to the CPV-TE receiver. The hybrid SILO-CPV-TE solar energy harvesting device was electrically, thermally and theoretically investigated. The electrical performance data for the cell under variable irradiance and cell temperature conditions were measured using the integrated thermoelectric module as both a temperature sensor and as a solid-state heat pump. The cell was electrically characterised under standard test conditions (1000 W/m2 irradiance, 25°C temperature and AM1.5G spectrum) for comparison with literature data. Transient multiphysics simulations in ANSYS CFX 15.0 were carried out to calculate cell temperatures and to determine the short circuit current and temperature coefficient in a scaling law. The optimization was used to determine 15 model parameters for the component sub-cells within the triple-junction cell at STC with a MATLAB scaling law. The root-mean-square error in electrical currents between measurement and simulations was 0.66%.

Optical Design and Validation of an Infrared Transmissive Spectrum Splitting Concentrator Photovoltaic Module

A new modular, hybrid solar power system is designed to generate both electrical and thermal energy by utilizing the full solar spectrum. The key element, an infrared-transparent concentrator photovoltaic (CPV) module, acts as a spectrum splitter, dividing solar radiation into two parts. The ultraviolet and visible light (“in-band”) are converted to electricity with high efficiency in CPV cells, while the infrared light (“out-of-band”) is transmitted directly to a thermal receiver, where thermal power may be converted to electricity by a suitable heat engine or used directly for industrial process heat applications whenever needed. Here, we describe the optical design, modeling, fabrication, and performance validation of this novel spectrum splitting CPV module. A transfer matrix style approach, cumulative transmission model, is built to study the reflection, absorption, and transmission in each layer of the CPV module. To optimize the optical performance, different materials for module superstrate/substrate, encapsulant, cell substrate, and cooling fluids are compared in order to enhance the transmission of out-of-band light through the CPV module by minimizing absorption. Six antireflection coatings along with front and backside electrical contact grids are designed to maximize transmittance of in-band light to the cell and out-of-band light to the thermal receiver. The final design, currently being prototyped, predicts out-of-band light transmission to the thermal receiver of 74.1% (for the passively cooled version) and 65.3% (for the actively cooled version). When epitaxial liftoff technology is applied, the transmission will change to 80.8% (passively cooled) and 71.9% (actively cooled). Experimental prototypes show good agreement with modeled optical performance.

Thermal Management of Concentrated Multi-Junction Solar Cells with Graphene-Enhanced Thermal Interface Materials

We report results of experimental investigation of temperature rise in concentrated multi-junction photovoltaic solar cells with graphene-enhanced thermal interface materials. Graphene and few-layer graphene fillers, produced by a scalable environmentally-friendly liquid-phase exfoliation technique, were incorporated into conventional thermal interface materials. Graphene-enhanced thermal interface materials have been applied between a solar cell and heat sink to improve heat dissipation. The performance of the multi-junction solar cells has been tested using an industry-standard solar simulator under a light concentration of up to 2000 suns. It was found that the application of graphene-enhanced thermal interface materials allows one to reduce the solar cell temperature and increase the open-circuit voltage. We demonstrated that the use of graphene helps in recovering a significant amount of the power loss due to solar cell overheating. The obtained results are important for the development of new technologies for thermal management of concentrated photovoltaic solar cells.

A highly-efficient, concentrating-photovoltaic/thermoelectric hybrid generator

A concentrating photovoltaic (CPV) cell exhibits the highest conversion efficiency among any solar cells. However, the further enhancement of the CPV efficiency is strongly limited by the heat generation at high solar concentrations. Here, we demonstrate a concentrating photovoltaic/thermoelectric hybrid generator using a single-junction, GaAs-based solar cell and a conventional thermoelectric module as a model system. Our hybrid generator gives rise to the conversion efficiency larger than the single CPV cell by ~3% at the solar concentration of 50 suns. Controlling thermal flow in the hybrid generator and the Peltier cooling effect is the key to achieving high efficiency. Our result provides a framework for designing a highly-efficient hybrid generator using both photo-electric and photo-thermal effects for the clean-energy production.

Performance study of water-cooled multiple-channel heat sinks in the application of ultra-high concentrator photovoltaic system

For achieving cost effectiveness in solar power generation, ultra-high concentrator photovoltaic (UHCPV) system operating at 1800 suns is highly recommended in order to minimize the usage of semiconductor material. Although sunlight focusing can be accomplished via two-stage concentrator consisted of non-imaging dish concentrator and an array of crossed compound parabolic concentrator lenses, the thermal management of concentrator photovoltaic (CPV) cells remains as a crucial problem. The objective of this study is to optimize the configuration of multiple-channel heat sink with the best design in thermal performance so that the temperatures of CPV cells are below 100°C even operating under ultra-high concentrated sunlight. Comprehensive analysis has been carried out via computational fluid dynamics (CFD) simulation to study thermal performance of heat sinks for different configurations with various fin thicknesses and fin heights. To emulate the real case, optical analysis has been carried out via ray-tracing method to simulate the solar flux distribution and input solar power illuminated on receiver so that the results can be fed into the CFD modeling. The heat sink with configuration of 1mm fin thickness×20mm fin height (1×20) was found to be the most optimized design in which the CFD simulation has shown the lowest values for both average temperature of CPV cells and maximum temperature difference between CPV cells. By optimizing the average water velocity at 0.6m/s, the heat sink with the configuration of 1×20 can maintain the CPV cells operating at 91.4°C under solar concentrator ratio of 1800 suns and direct normal irradiance of 1000W/m2. Through the optimization of the thermal performance, the UHCPV system can produce the net electrical output power of 4064W at power conversion efficiency of 31.8%.

Coupled natural convection and radiation heat transfer of hybrid solar energy conversion system

A hybrid solar energy conversion system described in this study is designed to exceed the efficiency of each type of technology alone by combining advantages of concentrated solar power (CSP) technology and high performance concentrated photovoltaic (CPV) cells. This hybrid system can be tilted at different inclination angles to track the solar power at different latitudes and different time zones. Thermal management is important to CPV cells, as 1000× concentrated solar radiation onto CPV not only leads to higher performance but also generates more waste heat flux. In this work, the effects of natural convection with and without the interaction of surface radiation in the system consisting of PV cells, optical funnels and a heatsink were numerically investigated with an experimentally validated model. The influence of inclination on the overall flow structure and heat transfer was examined. Under the effect of these funnels, the heat transfer was enhanced when the heat was transferred through PV cells to funnels. At the same time, the separation flow between the spaces of funnels would take the heat to the ambient. The minimum average temperature of surrogate PV cells occurred at the inclination angle of 60°. When the inclination angle varied from 0° to 90°, the stagnation point moved from the downward surface of the heat sink towards the edge of heat sink. From 0° to 60°, the stagnation point was at the downward surface of heat sink and there was a dramatic decrease in the average temperature of the surrogate PV cells. When inclination angles were less than 60°, except that there was a separation region above substrate, the side flow could flow in and out freely between adjacent funnels and then formed a pair of separation bubble, or spiral node, on top of the funnels. At these inclination angles, flow velocity was found to be the dominant factor influencing heat transfer because the flow pattern (separation bubble) was the same on top of the funnels. However, at inclination angles of 60° to 90° the stagnation point occurred at the edge of the heat sink, and the surrogate PV temperature increased. When the inclination angle reached 90°, the flow was trapped and recirculated among funnels, and the vortical wake on top of the funnel disappeared. It can be concluded that from 60° to 90°, the dominant factor influencing heat transfer is funnel effect because the flow velocity stayed almost constant.

Cooling design and evaluation for photovoltaic cells within constrained space in a CPV/CSP hybrid solar system

A hybrid solar energy system has been designed by combining the advantages of concentrated solar power (CSP) technology and high performance concentrated photovoltaic (CPV) cells which outperforms either single technology. Thermal management is crucial to CPV cells in this hybrid solar system, as concentrated solar radiation onto the PV cells leads to higher heat flux. If the heat is not dissipated effectively, it can cause obvious temperature rise and efficiency reduction in the cell. In addition, the constrained space available for PV cell cooling in such hybrid solar systems presents more challenges. In this study both passive cooling and active cooling techniques were systematically investigated in both numerical and experimental ways. For the passive cooling method, two different designs from off-the-shelf heat pipes with radial fins or annular fins were proposed and studied under various heat rejection requirements. Results shows that heat pipes with radial fins exhibited narrow capability of dumping the heat, while heat pipes with annular fins presented better performances under the same conditions. Numerical optimal designs of annular fin numbers and fin gaps were then carried out and experimentally validated, indicating a capability of dumping moderate waste heat (∼45W). For active cooling technique, a comprehensive study of designing plate fin heatsinks were conducted corresponding to high Ingress Protection (IP) rated off-the-shelf fans. Results show that with a less than 2W fan power consumption, this active cooling method can control the average PV cell temperature below our target temperature of 75°C even under 45°C ambient. To evaluate the overall performance in a year round life cycle, the enhancement in the annual electricity output of the PV cells was estimated according to the cooling effects subjected to the climate of Tucson, Arizona. Finally, taking into consideration of both the temperature control results and net gain/loss analysis, an active cooling design was chosen for our system to dissipate a maximum waste heat of 84W (21.8W/cm2) due to its lower cost, lower CPV temperature, and higher net energy efficiency gain. It is also demonstrated that passive cooling will become more attractive when the heat dissipation requirement is less than 50W (13.0W/cm2).

Small-Volume Fabrication of a 144-Cell Assembly for High-Concentrating Photovoltaic Receivers

Concentrating photovoltaic (CPV) is a solution that is gaining attention worldwide as a potential global player in the future energy market. Despite the impressive development in terms of CPV cell efficiency recorded in the last few years, a lack of information on the module's manufacturing is still registered among the documents available in literature. This work describes the challenges faced to fabricate a densely packed cell assembly for 500× CPV applications. The reasons behind the choice of components, materials, and processes are highlighted, and all the solutions applied to overtake the problems experienced after the prototype's production are reported. This article explains all the stages required to achieve a successful fabrication, proven by the results of quality tests and experimental investigations conducted on the prototype. The reliability of the components and the interconnectors is successfully assessed through standard mechanical destructive tests, and an indoor characterization is conducted to investigate the electrical performance. The fabricated cell assembly shows a fill factor as high as 84%, which proves the low series resistance and the lack of mismatches. The outputs are compared with those of commercial assemblies. A cost breakdown is reported and commented: a cost of $0.79/Wp has been required to fabricate each of the cell assembly described in this paper. This value has been found to be positively affected by the economy of scale: a larger number of assemblies produced would have reduced it by 17%.

Up-conversion luminescence from single vanadate through blackbody radiation harvesting broadband near-infrared photons for photovoltaic cells

Up-conversion (UC) is a promising route to harvest near-infrared (NIR) sunlight and enhance the power conversion efficiency (PCE) of photovoltaic (PV) cells. However, most of the UC materials have some bottleneck problems associated with them, such as own only narrower excitation band matching with the sun spectrum, lower UC luminescence efficiency, and considerable heat losses. Thus, it is essential to design and find a UC material that can absorb broadband NIR photons through an attractive route named thermal radiation for photon energy UC. In this work, we investigated the UC luminescence properties of single CeVO4 materials, in which the excitation bands can be augmented at least a range of 808–1064 nm. We also confirmed that this kind of UC emission is triggered by the thermal absorption of VO43−, which might be expanded to other single vanadate materials. The UC luminescence mechanisms were analyzed by power dependence and temperature modeling, and interpreted in terms of blackbody radiation theory. We demonstrated the possibility of photocurrent response in thin-film-hydrogenated amorphous silicon solar cell modified with CeVO4 powders through blackbody radiation for harvesting NIR photons. Such single vanadate materials can absorb broader NIR photons for UC luminescence through blackbody radiation, will open a new door for the enhancement of the PCE in the next-generation concentrated PV cells.

Low-Frequency Noise Diagnostic of Silicon Concentrator Photovoltaic Cell with Very High Efficiency

In this paper we present the comparisons of noise spectroscopy, I-V characteristic and microplasma detection of silicon concentrator photovoltaic (CPV) cell with very high efficiency. Efficiency reaches to 38 %. We studied two groups with different technologies (A and B). Each group had 6 samples. The samples were quality screened using noise analysis. From the measurement results it follows that the noise spectral density related to defects is of 1/f or generation-recombination types. G-R noise and burst noise is not fundamental noise and therefore can by use as a quality indicator.

Concentrator Photovoltaic Cells in Practice – Family House Heating

In concentrator cells, light is concentrated using lens to fall on solar cell to deliver a maximum possible energy. By using concentrator cells light intensity is increased by targeting on certain area, which in result increases electricity production. Design and optimization of cooling equipment for heating concentrator solar cells is realized by ANSYS Fluent system. The device is analyzed on the utilization of waste heat.

A Cell-Level Differential Power Processing IC for Concentrating-PV Systems With Bidirectional Hysteretic Current-Mode Control and Closed-Loop Frequency Regulation

This paper describes an integrated power management IC with bidirectional current capability, aimed at compensating differences in output current between series-connected cells in concentrating photovoltaic (CPV) systems. The integrated 3.6-MHz power stage allows building a small-form-factor converter per cell. A hysteretic current-mode controller regulates the bidirectional converter's current to equalize neighboring cell voltages. A phase-locked loop controls the inductor current ripple around the average value to stabilize the switching frequency. The use of hysteretic current-mode control with a novel bidirectional senseFET scheme provides inherent current protection and high reliability. The converter can operate from an input voltage as low as 1.8 V and with an inductor current up to $\pm$ 1.5 A, while achieving a system efficiency above 90% for current mismatches between cells up to 60%. Measurement results show that the converter maximizes the output power of series-connected CPV cells with mismatched output currents.

Pushing the limits of concentrated photovoltaic solar cell tunnel junctions in novel high‐efficiency GaAs phototransducers based on a vertical epitaxial heterostructure architecture

AbstractA monolithic compound semiconductor phototransducer optimized for narrow‐band light sources was designed for achieving conversion efficiencies exceeding 50%. The III‐V heterostructure was grown by metal‐organic chemical vapor deposition, based on the vertical stacking of 5 partially absorbing GaAs n/p junctions connected in series with tunnel junctions. The thicknesses of the p‐type base layers of the diodes were engineered for optimal absorption and current matching for an optical input with wavelengths centered near 830 nm. Devices with active areas of ~3.4 mm2 were fabricated and tested with different emitter gridline spacings. The open circuit voltage (Voc) of the electrical output is five times or more than that of a single GaAs n/p junction under similar illumination. The device architecture allows for improved Voc generation in the individual base segments because of efficient carrier extraction while simultaneously maintaining a complete absorption of the input photons with no needs for complicated fabrication processes or reflecting layers. With illumination powers in the range of a few 100 mW, the measured fill factor (FF) varied between 88 and 89%, and the Voc reached over 5.75 V. The data also demonstrated that a proper combination of highly doped emitter and window layers without gridlines is adequate for sustaining such FF values for optical input powers of several hundred milliwatts. As the optical input power is further increased and approaches 2 W (intensities ~58 W/cm2), the multiple tunnel junctions sequentially exceed their peak current densities in the case for which typical (n++)GaInP/ (p++)AlGaAs concentrated photovoltaic tunnel junctions are used. Lower bandgap tunnel junctions designed with improved peak current densities result in phototransducer devices having high FF and conversion efficiencies for up to 5 W optical input powers (intensities ~144 W/cm2). Measurements at different temperatures revealed a Voc reduction of −6 mV/°C at ~59 W/cm2. Copyright © 2015 John Wiley & Sons, Ltd.