Triple-junction Photovoltaic Cells Research Articles

Thermal management of PV cell in HCPV/T system: Cooling by mini-channel with pin-fin and jet impingement

This study examines the effects of two novel arrangements of circular pin-fins, inline and staggered, radial distance between the pin-fins and number of water outlets of a heat sink on temperature reduction of a triple-junction photovoltaic cell in a highly concentrated photovoltaic/thermal (HCP V/T) system under concentration ratio of 450 Suns with jet impingement. Results indicate the case of staggered arrangement which includes four flow outlets and passes 0.001 kg/s, proposes about 2.32% photovoltaic temperature reduction and 15.57% improvement in Nusselt number. It is also shown that for this case, as the distance increases and when the mass flow of the fluid rises from 0.001 kg/s to 0.0013 kg/s, 4.88% improvement in the electrical efficiency is obtained. Regardless of mass flow rate, the cases of staggered arrangement lead to a lower cell temperature in comparison with its inline counterpart. Besides, the cell temperature and electrical efficiency are improved 0.277% and 0.215% in two-outlet configuration.

A new Concentrated Photovoltaic Thermal-Hydrogen system with photocatalyst suspension as optical liquid filter

Although typical Concentrated Photovoltaic-Thermal systems can overcome high cell temperatures, the low-level heat generated not only increases the irreversible energy loss but also narrows the application scope of the system. Here, we established a new Concentrated Photovoltaic Thermal-Hydrogen system coupling the Pt loaded TiO2 nanoparticle suspension, serving as both a photothermal hydrogen catalyst and an optical liquid filter for spectrum beam splitting, with a GaInP/GaAs/Ge triple-junction photovoltaic cell connected to an electrolytic cell to achieve full-spectrum solar energy to hydrogen storage conversion. Besides the additional hydrogen production, the Concentrated Photovoltaic Thermal-Hydrogen system with spectral beam splitting of TiO2 suspension can reduce the cell temperature by 32.8%, increase the electrical power by 65.7%, and save 49% of the cell area at most, compared to the case without spectral beam splitting. Thermalization loss was also reduced, which, in turn, increased the photovoltaic electrical performance. The proposed system can produce hydrogen at a maximum solar-to-hydrogen efficiency of 14% when the TiO2 loading amount is 150 ppm. It is expected to provide a guiding reference for achieving full-spectrum and high-efficiency solar energy conversion.

Gold-like activity copper-like selectivity of heteroatomic transition metal carbides for electrocatalytic carbon dioxide reduction reaction

An overarching challenge of the electrochemical carbon dioxide reduction reaction (eCO2RR) is finding an earth-abundant, highly active catalyst that selectively produces hydrocarbons at relatively low overpotentials. Here, we report the eCO2RR performance of two-dimensional transition metal carbide class of materials. Our results indicate a maximum methane (CH4) current density of −421.63 mA/cm2 and a CH4 faradic efficiency of 82.7% ± 2% for di-tungsten carbide (W2C) nanoflakes in a hybrid electrolyte of 3 M potassium hydroxide and 2 M choline-chloride. Powered by a triple junction photovoltaic cell, we demonstrate a flow electrolyzer that uses humidified CO2 to produce CH4 in a 700-h process under one sun illumination with a CO2RR energy efficiency of about 62.3% and a solar-to-fuel efficiency of 20.7%. Density functional theory calculations reveal that dissociation of water, chemisorption of CO2 and cleavage of the C-O bond—the most energy consuming elementary steps in other catalysts such as copper—become nearly spontaneous at the W2C surface. This results in instantaneous formation of adsorbed CO—an important reaction intermediate—and an unlimited source of protons near the tungsten surface sites that are the main reasons for the observed superior activity, selectivity, and small potential.

A transmissive concentrator photovoltaic module with cells directly cooled by silicone oil for solar cogeneration systems

Hybrid concentrator photovoltaic-thermal systems can cogenerate electricity and heat by beam-splitting incoming concentrated light onto photovoltaic cells and a thermal receiver to increase total conversion efficiency and potentially reduce system cost. To demonstrate this, we have designed and prototyped a transmissive spectrum-splitting concentrator photovoltaic module that maximizes solar energy conversion by utilizing the entire solar spectrum. Visible light is collected using infrared-transmissive triple-junction photovoltaic cells to achieve an in-band module efficiency of 43.3% for light of wavelength λ < 873 nm, while 44.2% of out-of-band light with λ > 873 nm is transmitted through for collection by a thermal receiver. During testing on a dual-axis tracked parabolic concentrator dish at up to 166 suns, cell temperatures were maintained at 119 °C or below via a novel active cooling method. This cooling system strictly flows silicone oil directly across both sides of the cells, without inhibiting optical transmission, as verified through experimentation and simulation. The module was validated outdoors for 572 sun·hrs, and achieved a maximum thermal receiver temperature of 180 °C. 86.1% of incident solar power is collected at 166 suns average concentration collectively among the electrical, cooling, and thermal receiver subsystems. The remaining 13.9% is lost to mirror reflectivity, dish shadowing, receiver reflection, and thermal losses. The ability to directly cool the cells with an inert silicone oil offers the potential for reduced system cost relative to previous transmissive hybrid concentrator photovoltaic-thermal systems, including microfluidic-cooled designs. This solar cogeneration capability is valuable in a wide range of commercial and industrial applications.

COVID-19 lockdown air quality change implications for solar energy generation over China

We exploit changes in air quality seen during the COVID-19 lockdown over China to show how a cleaner atmosphere has notable co-benefits for solar concentrator photovoltaic energy generation. We use satellite observations and analyses of the atmospheric state to simulate surface broadband and spectrally resolved direct normal irradiance (DNI). Over Wuhan, the first city placed under lockdown, we show how the atmospheric changes not only lead to a 19.8% increase in broadband DNI but also induce a significant blue-shift in the DNI spectrum. Feeding these changes into a solar cell simulator results in a 29.7% increase in the power output for a typical triple-junction photovoltaic cell, with around one-third of the increase arising from enhanced cell efficiency due to improved spectral matching. Our estimates imply that these increases in power and cell efficiency would have been realised over many parts of China during the lockdown period. This study thus demonstrates how a cleaner atmosphere may enable more efficient large scale solar energy generation. We conclude by setting our results in the context of future climate change mitigation and air pollution policies.

A Photovoltaic-Thermochemical Hybrid Solar Power Generator

High penetration of photovoltaic (PV) power into the energy system could be challenged by its limited dispatchability related to fluctuations and intermittency of solar illumination. We demonstrate an integrated PV-thermochemical (PVTC) device that backs up PV output with dispatchable power generated by solar-thermal enriched fuel. The H2-rich fuel as derived from PV-thermal-driven endothermic chemical reaction enables an overall experimental solar-to-power efficiency of 43.7%, among which more than 40% is contributed by solar thermal energy. This represents a 9.2 percentage points advance over all prior solar PV-thermal power efficiencies reported to date. A modular PVTC prototype based on a triple-junction PV cell and methanol reforming reaction was demonstrated with 24 h continuous operation at a sustained power output of 27.4 W. Cost analysis indicates levelized cost of electricity (LCOE) ranges of 0.173 – 0.273 $ kWh-1 and 0.097 – 0.197 $ kWh-1 for 5 kW and 100 kW PVTC systems, respectively, which are considerably lower than that of PV-battery combination (0.578 – 0.802 $ kWh-1).

Spectrally robust series/parallel-connected triple-junction photovoltaic cells used for artificial photosynthesis

We have overcome two drawbacks involved in series-connected double-junction (S-2J) and triple-junction (S-3J) photovoltaic cells to compose monolithic modules of artificial photosynthesis consisting of directly connected photovoltaic cells and electrolyzers of the same size. One is current mismatching among the subcells under solar spectrum variation. The other is inefficient utilization of high-energy photons that can generate sufficiently high voltage to promote the target reaction, caused by consumption of two or three photons for extracting a single electron regardless of the photon energies. This arises from the predetermined operating voltage, contrasting to no restriction of the output voltage for solar cells combined with power conditioners. In a series/parallel-connected triple-junction (S/P-3J) photovoltaic cell, the series-connected middle and bottom cells are connected with the top cell in parallel. High-energy photons absorbed in the top cell are efficiently utilized because the photoexcited electrons are directly extracted. Although relative intensities of high-energy photons in the measured solar spectra changes remarkably, the top cell is free from the current matching restriction. On the other hand, current matching between the middle and bottom cells approximately holds, because solar spectrum in the relevant range changes only slightly. Consequently, the S/P-3J significantly improves solar-to-chemical conversion efficiency (ηSTC) and is more advantageous on overcast days owing to the spectral robustness. Using the state-of-the-art electrolyzers, ηSTC = 32%−26% of H2 production by water splitting is estimated on fine and overcast days. CO2 reduction to CO proceeds with ηSTC = 30%−25%. These values are higher than those for the S-2J by 3%−9%.

Field testing of a spectrum-splitting transmissive concentrator photovoltaic module

Hybrid photovoltaic-thermal systems can decouple IR light from visible light, allowing it to be collected separately by spectrum-optimized mechanisms for increased total efficiency. To demonstrate this, we have designed and prototyped a transmissive spectrum-splitting concentrator photovoltaic module that maximizes solar energy conversion by utilizing the entire solar spectrum. The system first collects visible light using IR-transmissive triple-junction photovoltaic cells to achieve an in-band module efficiency of ηmIB = 34.7% for light of wavelengths λ < 870 nm. Simultaneously, 58.8% of light with λ > 870 nm is transmitted through the cells for collection by a thermal receiver. By combining electrical and thermal power collection, 75% of incident solar power is collected, far surpassing the collection capability of only photovoltaics. The module was tested on a dual-axis tracked parabolic concentrator dish at up to 160 suns for 60 cumulative on-sun hours while maintaining photovoltaic cell temperatures at an average of 50 °C via active cooling. The system performed as expected based on modeled values, and represents a cost-effective path forward for dual-generation of electricity and high-temperature heat with increased total efficiency. The capability is valuable in a wide range of commercial and industrial cogeneration applications.

An Earth-Abundant Catalyst-Based Seawater Photoelectrolysis System with 17.9% Solar-to-Hydrogen Efficiency.

The implementation of water splitting systems, powered by sustainable energy resources, appears to be an attractive strategy for producing high-purity H2 in the absence of the release of carbon dioxide (CO2 ). However, the high cost, impractical operating conditions, and unsatisfactory efficiency and stability of conventional methods restrain their large-scale development. Seawater covers 70% of the Earth's surface and is one of the most abundant natural resources on the planet. New research is looking into the possibility of using seawater to produce hydrogen through electrolysis and will provide remarkable insight into sustainable H2 production, if successful. Here, guided by density functional theory (DFT) calculations to predict the selectivity of gas-evolving catalysts, a seawater-splitting device equipped with affordable state-of-the-art electrocatalysts composed of earth-abundant elements (Fe, Co, Ni, and Mo) is demonstrated. This device shows excellent durability and specific selectivity toward the oxygen evolution reaction in seawater with near 100% Faradaic efficiency for the production of H2 and O2 . Powered by a single commercial III-V triple-junction photovoltaic cell, the integrated system achieves spontaneous and efficient generation of high-purity H2 and O2 from seawater at neutral pH with a remarkable 17.9% solar-to-hydrogen efficiency.

A differential spectral responsivity measurement system constructed for determining of the spectral responsivity of a single- and triple-junction photovoltaic cells

A differential spectral responsivity (DSR) measurement system has been designed and constructed at National Metrology Institute of Turkey (TUBITAK UME) to determine the spectral responsivity (SR) of a single- or a multi-junction photovoltaic device (solar cell). The DSR setup contains a broad band light bias source composed of a constructed Solar Simulator based on a 1000 W Xe-arc lamp owning a AM-1.5 filter and 250 W quartz-tungsten-halogen lamp, a designed and constructed LED-based Bias Light Sources, a DC voltage bias circuit, and a probe beam optical power tracking and correction circuit controlled with an ADuC847 microcontroller card together with an embedded C based software, designed and constructed in TUBITAK UME under this project. By using the constructed DSR measurement system, the SR calibration of solar cells, the monolitic triple-junction solar cell GaInP/GaInAs/Ge and its corresponding component cells have been performed within the EURAMET Joint Research Project SolCell.

A scaling law for monocrystalline PV/T modules with CCPC and comparison with triple junction PV cells

Scaling laws serve as a tool to convert the five parameters in a lumped one-diode electrical model of a photovoltaic (PV) cell/module/panel under indoor standard test conditions (STC) into the parameters under any outdoor conditions. By using the transformed parameters, a current-voltage curve can be established under any outdoor conditions to predict the PV cell/module/panel performance. A scaling law is developed for PV modules with and without crossed compound parabolic concentrator (CCPC) based on the experimental current-voltage curves of six flat monocrystalline PV modules collected from literature at variable irradiances and cell temperatures by using nonlinear least squares method. Experiments are performed to validate the model and method on a monocrystalline PV cell at various irradiances and cell temperatures. The proposed scaling law is compared with the existing one, and the former exhibits a much better accuracy when the cell temperature is higher than 40°C. The scaling law of a triple junction flat PV cell is also compared with that of the monocrystalline cell and the CCPC effects on the scaling law are investigated with the monocrystalline PV cell. It is identified that the CCPCs impose a more significant influence on the scaling law for the monocrystalline PV cell in comparison with the triple junction PV cell. The proposed scaling law is applied to predict the electrical performance of PV/thermal modules with CCPC.

Optical Switch of a-IGZO TFT and Triple Junction Photovoltaic Cell

This study presents an optical switch that integrates an indium gallium zinc oxide (IGZO) thin-film transistor (TFT) and a GaInP/GaAs/Ge triple junction (TJ) photovoltaic (PV) cell. The device is driven by a TJ PV cell, which has a steady output voltage and a voltage regulator, to induce current in it. It should be noted TJ solar cell is broadband sensitive and the open circuit voltages are close under different illumination levels and a voltage regulator can assist it has identical working voltages. Moreover, The switch off (dark) and on (illuminated) current values of the optical switch are around 10−8 and 10−5 A, under different simulated test lights, respectively. The test light source is from solar simulator. The stable characteristics and good on/off ratio levels of this device under different light make it practicable in outdoor and indoor environments.

Field Investigation of the Effect of Spectral Response Upon Photovoltaic Energy Yields

The operating efficiencies of multijunction photovoltaic (PV) cells are sensitive to changes in the spectral distribution of solar irradiance. Previous studies suggest that optimizing a cell's spectral response can improve energy yields. To examine how this affects their performance in the field, two sets of triple-junction photovoltaic cells with different spectral responses are being characterized side-by-side outdoors in Nicosia, Cyprus. High-resolution measurements of the solar spectrum are also being recorded at this location, allowing a detailed examination of the cell performances under varying spectral conditions. Using spectral matching ratios to analyze the data has indicated that daily changes in the fill factors of the cells can be attributed to their spectral responses. However, average performance ratios over the period of testing are similar for the two cell types. An in-depth analysis reveals that this is due to a combination of both the spectral responses and the spectral resource at the test site, where both cells operate close to their optimum. This indicates that customizing the spectral response of a cell may only be advantageous for applications under an extreme spectral resource distribution.

Evaluation of optimal dual axis concentrated photovoltaic thermal system with active ventilation using Frog Leap algorithm

In this study, design and optimization of a concentrated photovoltaic thermal (CPVT) system considering electrical, mechanical, and economical aspects is investigated. For this purpose, each section of the system is simulated in MATLAB, in detail. Triple-junction photovoltaic cells, which are the most recent technology, are used in this study. They are more efficient in comparison to conventional photovoltaic cells. Unlike ordinary procedures, in this work active ventilation is used for absorbing the thermal power of radiation, using heat storage tanks, which not only results in increasing the electrical efficiency of the system through decreasing the temperature, but also leads to storing and managing produced thermal energy and increasing the total efficiency of the system up to 85 percent. The operation of the CPVT system is investigated for total hours of the year, considering the needed thermal load, meteorological conditions, and hourly radiation of Khuznin, a city in Qazvin province, Iran. Finally, the collector used for this system is optimized economically, using frog leap algorithm, which resulted in the cost of 13.4$/m2 for a collector with the optimal distance between tubes of 6.34cm.

Laboratory Characterization of Homogeneous Spacecraft Materials

This paper presents laboratory measurements and analysis of optical spectral bidirectional reflectance distribution functions of materials commonly found on the surfaces of spacecraft. A goniospectrometer sensitive to light with wavelengths between 350 and 1100 nm was constructed, and four classes of materials were studied in a variety of illumination and observational geometries: triple-junction photovoltaic cells, aluminum, white-coated metallic surface, and aluminized polyimide films. The measurements were analyzed to study how specific materials could be characterized based on their spectral bidirectional reflectance distribution function and how it varies with changing illumination and observational geometry. In the end, the experiment yielded two significant outcomes. First, the results provide a better understanding of how the spectral energy distribution of light reflected from these materials behaves as the illumination and observational geometry is varied. This result will be particularly useful in the interpretation of spectra and color photometric measurements of artificial objects in Earth orbit. Second, and more important, this experiment convincingly demonstrates that any spectral library of materials commonly found on spacecraft must include measurements taken throughout the widest range of observational geometries. With this in mind, the measurements collected during this experiment now serve as the first entries in an open-access spectral library of spacecraft material.

Analysis of the CanX-1 Engineering Model Spectral Reflectance Measurements

This paper presents a detailed analysis of the CanX-1 engineering model spectral reflectance measurements that were collected during the model’s spectrometric characterization. Over 1000 low-resolution spectra spanning a range between 350 and 2500 nm were gathered over a wide range of observational geometries in a controlled laboratory environment. As part of the data analysis, a physics-based reflectance model was implemented in a numerical computing environment to allow for a better understanding of the measurements. In the end, the experiment led to two unexpected results. First, the spectrometric measurements of the triple-junction photovoltaic cells showed significant interference fringes at wavelengths greater than 800 nm, which, at the time of this experiment, did not correspond to any previously published spectra for this type of material. Second, these empirical results also showed that the spectral reflectance of photovoltaic cells varied significantly as a function of the illumination geometry. The modeling results confirmed this finding and showed that this was also the case for an aluminum surface with an rms surface roughness different from zero. These results invalidate a widely held assumption among those who study the spectrometric characterization of artificial space objects that the spectral reflectance of homogeneous materials is invariant. The outcomes of this study not only serve to improve the laboratory characterization of spacecraft in controlled environments before their launch but also provide new insight in the interpretation of spectrometric measurements of artificial space objects, namely spacecraft and space debris, in Earth orbit.

Experimental and Numerical Study of a Parabolic Trough Linear CPVT System

The electric and thermal performance of a parabolic trough linear concentrating photovoltaic-thermal (CPVT) system operating in Padova (northern Italy) is experimentally investigated. The system moves about two axes and exhibits a geometrical concentration ratio around 130. The receiving module placed on the focus line displays a secondary optics made of two flat mirrors to gather some reflected radiation and to contribute to the concentrated flux on two lines of triple junction photovoltaic cells soldered on a ceramic substrate. The substrate is in thermal contact with a aluminium heat exchanger with water flow channels to cool the PV cells.During the test runs, the inlet water temperature ranges from 20°C to 80°C and the heat yield is obtained from mass flow rate and temperature measurements while a rheostat and a power analyzer are connected to the electric terminals of the module to assess the electrical production. The direct normal irradiation (DNI) is measured by a pyrherliometer mounted on a solar tracker. Experimental results are used to assess a numerical model of the solar receiver and the whole concentrator.

Responses of Thin Film Photovoltaic Cell to Irradiation under Double Laser Beams of Different Wavelength

During the process of Laser beam long-range energy transmission based on the photovoltaic principle, the temperature elevation of the photovoltaic cell under Laser irradiation would greatly affect its photoelectric conversion efficiency. In this work, the heat generation mechanism of thin-film photovoltaic cell under Laser irradiation was analyzed based on the energy conversion relationship between light, electricity and heat. The output voltage characteristic of a thin film GaInP/GaAs/Ge triple-junction photovoltaic cell under irradiation of dual-wavelength Laser beam was investigated, and the results show the dependence of the conversion efficiency on the temperature and the valve effect, which was caused by the long wavelength Laser and would sharply reduce the photovoltaic conversion efficiency of short wavelength Laser. The temperature field of the multi-layer structure subjected to Laser irradiation was analyzed by finite element method, and the results indicate that the temperature elevation pattern depends on the spatial distribution of the light absorption and can be adjusted via optimizing the photovoltaic cell structure.

Carrier Transport and Improved Collection in Thin-Barrier InGaAs/GaAsP Strained Quantum Well Solar Cells

Multiple quantum wells (MQW) lattice matched to GaAs consisting of In0.14Ga0.76As wells balanced with GaAs0.24P0.76 barriers have been used to extend the absorption of GaAs subcells to longer wavelengths for use in an InGaP/GaAs/Ge triple-junction photovoltaic cell. Thin barriers with high-phosphorus composition are capable of balancing the strain from the InGaAs wells; thus, creating conditions to allow for thicker wells and for carrier tunneling to dominate transport across the structure. As a result, a larger percentage of the depletion region is occupied by InGaAs quantum wells that absorb wavelengths beyond 875 nm and the indium composition is not limited by thermionic emission requirements. Measurements at elevated temperatures and reverse bias suggest that a thermally assisted tunneling mechanism is responsible for transport through the barriers.

Efficient solar water oxidation using photovoltaic devices functionalized with earth-abundant oxygen evolving catalysts

Indium tin oxide (ITO) surfaces of triple junction photovoltaic cells were functionalized with oxygen evolving catalysts (OECs) based on amorphous hydrous earth-abundant metal oxides (metal = Fe, Ni, Co), obtained by straightforward Successive Ionic Layer Adsorption and Reaction (SILAR) in an aqueous environment. Functionalization with Fe(iii) oxides gave the best results, leading to photoanodes capable of efficiently splitting water, with photocurrent densities up to 6 ± 1 mA cm(-2) at 0 V vs. the reversible hydrogen electrode (RHE) under AM 1.5 G simulated sunlight illumination. The resulting Solar To Hydrogen (STH) conversion efficiencies, measured in two electrodes configuration, were in the range 3.7-5%, depending on the counter electrode that was employed. Investigations on the stability showed that these photoanodes were able to sustain 120 minutes of continuous illumination with a < 10% photocurrent loss at 0 V vs. RHE. Pristine photoanodic response of the cells could be fully restored by an additional SILAR cycle, evidencing that the observed loss is due to the detachment of the more weakly surface bound catalyst.