Concentrator Photovoltaic Cells Research Articles

Study of automotive radiator cooling system for dense-array concentration photovoltaic system

An automotive radiator is proposed for the heat rejection of the dense-array concentrator photovoltaic (CPV) system. Theoretical modeling on the integration of automotive radiator into the cooling system with a specially designed cooling block has been carried out in details. To verify the feasibility of new proposal, the automotive radiator cooling system has been constructed and tested to effectively lower down the temperature of CPV module in a non-imaging planar concentrator prototype with total reflective area of 4.16m2 at solar concentration ratio of 377suns. During the on-site measurement, it has been observed that the conversion efficiency of CPV module has successfully improved from 22.39% to 26.85% when the CPV cell temperature is reduced from 59.4°C to 37.1°C.

Bifacial Growth InGaP/GaAs/InGaAs Concentrator Solar Cells

A three-junction concentrator photovoltaic (CPV) cell with 1.9-eV InGaP top and 1.42-eV GaAs middle cells on one side of an infrared-transparent N-GaAs wafer and a 0.94-eV InGaAs bottom cell on the opposite wafer side (backside) is described. This architecture isolates the upper lattice-matched subcells from threading dislocations generated during the growth of the lattice-mismatched bottom subcell. The cell uses a unique epitaxial bifacial growth technique with only a simple water rinse and spin dry between growths on opposite wafer sides. The best independently verified efficiency for a 1-cm $^2$ cell is 42.3% at 406-suns AM1.5D at 25 °C (V $_{\rm oc}$ 3.452 V, 87.1% FF, and 1-sun J $_{\rm sc}$ of 14.07 mA/cm $^2$ ). We give data on single-junction subcells and tunnel junctions in the tandem, quantum efficiency, and temperature coefficient data, discuss use of a thin pseudomorphic layer at the back of the GaAs middle subcell to extend the wavelength response, and discuss the benefit of graded doping layers in increasing subcell 1-sun J $_{\rm sc}$ at the top and bottom subcells.

Investigation on Cooling System of High-Concentration Photovoltaic with Oscillating Heat Pipe

Cooling of concentration photovoltaic (CPV) cells with oscillating heat pipe was investigated numerically and experimentally. Based on Reynolds-averaged Navier-Stokes approach, a turbulent model was proposed in present work. Numerical study presented the temperature distribution under different heat flux and various outdoor conditions. CPV (with 12 suns concentration) system was experimentally studied, and the results show that the oscillating heat pipe begin operation at about 62°C, and CPV system could enhance electric power with a good cooling system under a high concentration light. The oscillating heat pipe cooling system, without air fan or pump, no power consumption, gives a uniform, reliable, simple and costless cooling method, oscillating heat pipe cooling is suitable for the high-CPV system.

Numerical and experimental study on cooling high-concentration photovoltaic cells with oscillating heat pipe

Both numerical and experimental methods are used to investigate the cooling of concentration photovoltaic (CPV) cells. A numerical study presents the temperature distribution under different heat flux and some other outdoor conditions. The CPV (12 suns) system was experimentally studied, and the results show that the CPV could enhance electric power with a good cooling system. A heat pipe gives a uniform, reliable, simple and costless cooling method. The oscillating heat pipe, without an air fan or a pump, and no power consumption, is suitable for the higher CPV system.

Understanding MOCVD Gas Chemistry to Reduce the Cost of Ownership for GaN LED and AsP CPV Technologies

ABSTRACTAs compound semiconductors continue to make inroads into common electronic devices, it is critically important to lower the cost of the primary metal-organic chemical vapor deposition (MOCVD) epitaxial process, which creates the foundation for the devices. Both GaN-based light-emitting diode (LED) and AsP-based concentrator photovoltaic (CPV) markets have been focused on simultaneous cost-reduction, cycle time reductions, and device efficiency improvements, which can be realized utilizing higher growth rates and operating pressures. To achieve these goals, it has become increasingly important to understand the underlying growth mechanisms that drive the chemistry within the MOCVD process.Higher growth rates and higher operating pressures both result in parasitic gas-phase particle formation, which degrades the physical, electrical and optical properties of the deposited layers. In extreme cases, it can reduce the deposition efficiency to the point where increasing the reactant constituents results in reduced growth rates. In this paper, we will examine the tradeoffs that need to be made to achieve good crystal quality with abrupt interfaces, smooth surface morphology, and good minority carrier properties for films deposited at high growth rates and high pressure. While exceptional device performance has been achieved for both GaN-based LEDs and AsP-based CPV cells, it is primarily cost that is limiting full-scale adoption of compound semiconductors into these potentially enormous markets.

Fabrication and Characterization of Optic Fiber-Based Poly(3-hexylthiophene) Micro Concentrator Photovoltaic Cell

Fabrication and Characterization of Optic Fiber-Based Poly(3-hexylthiophene) Micro Concentrator Photovoltaic Cell

Modeling Thermal Fatigue in CPV Cell Assemblies

A finite-element (FEM) model has been created to quantify the thermal fatigue damage of the concentrating photovoltaic (CPV) die attach. Simulations are used to compare the results of empirical thermal fatigue equations that have originally been developed for accelerated chamber cycling. While the empirical equations show promise when extrapolated to the lower temperature cycles characteristic of weather-induced temperature changes in the CPV die attach, it is demonstrated that their damage does not accumulate linearly: The damage that a particular cycle contributes depends on the preceding cycles. Direct comparison of the FEM with empirical methods and calculation of equivalent times for standard accelerated test sequences were made using CPV cell temperature histories.

Electrical and thermal performance of silicon concentrator solar cells immersed in dielectric liquids

Direct liquid-immersion cooling of concentrator solar cells was proposed as a solution for receiver thermal management of concentrating photovoltaic (CPV) and hybrid concentrating photovoltaic thermal (CPV-T) systems. De-ionized (DI) water, isopropyl alcohol (IPA), ethyl acetate, and dimethyl silicon oil were selected as potential immersion liquids based on optical transmittance measurement results. Improvements to the electrical performance of silicon CPV cells were observed under a range of concentrations in the candidate dielectric liquids, arising from improved light collection and reduced cell surface recombination losses from surface adsorption of polar molecules. Three-dimensional numerical simulations with the four candidate liquids as the working fluids, exploring the thermal performance of a silicon CPV cell array in a liquid immersion prototype receiver, have been performed. Simulation results show that the direct-immersion cooling approach can maintain low and uniform cell temperature in the designed liquid immersion receiver. The fluid inlet velocity and flow mode, along with the fluid thermal properties, all have a significant influence on the cell array temperature.

Design analysis of a Fresnel lens concentrating PV cell

Concentrating photovoltaic (PV) systems provide an effective way to reduce the cost of electricity production by reducing the amount of silicon required. The use of a Fresnel lens is one of the typical design options for the concentrating PV systems. Compared with a parabolic mirror, a Fresnel lens has its focus behind the lens surface. This gives a convenience for installation of PV cells and also there is no matter of shading caused by the PV cells. However, both Fresnel lens and parabolic dish concentrating PV systems need to be accompanied by a high accuracy sun-tracking system. This study presents the design analysis of a Fresnel lens concentrating PV cell which consists of a small linear Fresnel lens and a strip PV cell. A number of cells may form a modular large concentrating PV system using a single sun-tracking system. Based on the analysis of the ray path through the Fresnel lens and a current density distribution model for the PV cell, a computer program has been produced to predict the irradiance distribution on the PV cell and the distribution of current density. The results are used to determine the effect of sun-tracking deviation and PV cell position on the PV current distribution. The calculated and experimental short-circuit current and open-circuit voltage of the designed Fresnel lens concentrating PV cell are also given. Copyright , Oxford University Press.

Instrumentation for accelerated life tests of concentrator solar cells

Concentrator photovoltaic is an emergent technology that may be a good economical and efficient alternative for the generation of electricity at a competitive cost. However, the reliability of these new solar cells and systems is still an open issue due to the high-irradiation level they are subjected to as well as the electrical and thermal stresses that they are expected to endure. To evaluate the reliability in a short period of time, accelerated aging tests are essential. Thermal aging tests for concentrator photovoltaic solar cells and systems under illumination are not available because no technical solution to the problem of reaching the working concentration inside a climatic chamber has been available. This work presents an automatic instrumentation system that overcomes the aforementioned limitation. Working conditions have been simulated by forward biasing the solar cells to the current they would handle at the working concentration (in this case, 700 and 1050 times the irradiance at one standard sun). The instrumentation system has been deployed for more than 10 000 h in a thermal aging test for III-V concentrator solar cells, in which the generated power evolution at different temperatures has been monitored. As a result of this test, the acceleration factor has been calculated, thus allowing for the degradation evolution at any temperature in addition to normal working conditions to be obtained.

Band gap‐voltage offset and energy production in next‐generation multijunction solar cells

AbstractThe potential for new 4‐, 5‐, and 6‐junction solar cell architectures to reach 50% efficiency is highly leveraging for the economics of concentrator photovoltaic (CPV) systems.The theoretical performance of such next‐generation cells, and experimental results for 3‐ and 4‐junction CPV cells, are examined here to evaluate their impact for real‐world solar electricity generation. Semiconductor device physics equations are formulated in terms of the band gap‐voltage offset Woc  (Eg/q) − Voc, to give a clearer physical understanding and more general analysis of the multiple subcell band gaps in multijunction cells. Band gap‐voltage offset is shown experimentally to be largely independent of band gap Eg for a wide range of metamorphic and lattice‐matched semiconductors from 0.67 to 2.1 eV. Its theoretical Eg dependence is calculated from that of the radiative recombination coefficient, and at a more fundamental level using the Shockley‐Queisser detailed balance model, bearing out experimental observations. Energy production of 4‐, 5‐, and 6‐junction CPV cells, calculated for changing air mass and spectrum over the course of the day, is found to be significantly greater than for conventional 3‐junction cells. The spectral sensitivity of these next‐generation cell designs is fairly low, and is outweighed by their higher efficiency. Lattice‐matched GaInP/GaInAs/Ge cells have reached an independently confirmed efficiency of 41.6%, the highest efficiency yet demonstrated for any type of solar cell. Light I‐V measurements of this record 41.6% cell, of next‐generation upright metamorphic 3‐junction cells with 40% target production efficiency, and of experimental 4‐junction CPV cells are presented. Copyright © 2010 John Wiley & Sons, Ltd.

Characterization of a pulsed solar simulator for concentrator photovoltaic cell calibration

The upgrade of a large area xenon lamp pulsed solar simulator to a 1500X pulsed solar simulator is presented in detail. Spectral match, spatial non-uniformity and temporal instability are analyzed according to the existing international standards, resulting in a Class CAA solar simulator: ongoing improvements to meet Class AAA requirements are discussed. The procedure for the calibration of a set of c-Si reference cells equipped with neutral density filters for calibrated measurements at high intensity is also presented. The paper finally highlights the importance of the spectral match to the standard AM1.5d (direct beam) spectrum over a wider range than described in the available standards for solar simulator classification.

Impact of the Peltier effect on concentrating photovoltaic cells

Photovoltaic cells convert most of the absorbed photon energy to heat. Removal of the heat by thermal conduction creates a heat flux that is significant in concentrating photovoltaic (CPV) cells subject to high incident radiation flux. The Peltier effect interaction of this heat flux and the electrical current in the cell can either increase or decrease the temperature gradient within the cell. Here we show that the Peltier effect contributes to a measurable change in the temperature gradient in Ge-based CPV cells and therefore this effect should be considered in cell modelling. The effect may also have an impact on the temperature gradient of other photovoltaic cells and of other high power optoelectronic devices.

Novel accelerated testing method for III–V concentrator solar cells

Accelerated testing is a necessary tool in order to demonstrate the reliability of concentration photovoltaic solar cells, devices which is expected to be working not less than 25 years. Many problems arise when implementing high temperature accelerated testing in this kind of solar cells, because the high light irradiation level, at which they work, is very difficult to achieve inside a climatic chamber. This paper presents a novel accelerated testing method for concentrator solar cells, under simulated electrical working conditions (i.e. forward biasing the solar cells at the equivalent current they would handle at 700 suns), that overcomes some of the limitations found in test these devices inside the chamber. The tracked power of the solar cells to 700×, experiences a degradation of 1.69% after 4232 h, in the 130 °C test, and of 2.20% after 2000 h in the 150 °C one. An additional test has been carried out at 150 °C, increasing the current to that equivalent to 1050 suns. This last test shows a power degradation of 4% for the same time.

Local device parameter extraction of a concentrator photovoltaic cell under solar spot illumination

Focused sunlight can act as a localized source of excess minority carriers in a solar cell. Current signal generated by these carriers gives considerable information about the electrical properties of the cell's material. Point by point current–voltage data were measured for a back point-contact concentrator photovoltaic cell when illuminated by focused sunlight. Two numerical curve fitting procedures: a non-linear two-point interval division and particle swarm optimization algorithm were then applied to extract local parameters (i.e. as function of position) from the current–voltage data at each measurement point. Extracted parameters plotted yields relative spatial information about the electrical properties of a solar cell in a two or three dimensional mapping. The curve fitting routines applied to current–voltage data reveal that performance parameters: short circuit current, open circuit voltage, maximum power and fill factor show distinct variations in the vicinity of the observed current reducing feature. The relative values of the diode ideality factors, series resistance, shunt resistance and reverse saturation currents from both methods showed no significant measurable features that could be distinguished. This shows that the observed reduction in photo-induced current was due to severe recombination in the bulk or around the highly diffused point contacts and not the quality of the multiple p–n junctions of the cell. These approaches allow one to obtain a set of parameters at each local point on the cell which are reasonable and representative of the physical system.

Impact of the Thomson effect on concentrating photovoltaic cells

Photovoltaic cells convert most of the absorbed photon energy to heat. Removal of the heat by thermal conduction creates a temperature gradient that is significant in concentrating photovoltaic (CPV) cells subject to high incident radiation flux. The Thomson effect interaction between this temperature gradient and the electrical current in the cell can either increase or decrease the electrical power output of the cell. Here we show that the Thomson effect has a non-negligible impact on the conversion efficiency of Ge-based CPV cells, which is comparable to the impact of typical series resistance, and therefore this effect should be considered in cell modeling. The effect may also have a significant impact on the performance of other high power optoelectronic devices.

Operating characteristics of multijunction solar cells

Multijunction solar cells produced by Spectrolab are the most efficient solar cells in the world, with a record efficiency of over 40%. Cell designs have been modified for high performance in concentrator photovoltaic (CPV) systems with the potential for low-cost, high-volume manufacturing. High-performance CPV cells have been designed, tested, and entered into production for field testing in CPV systems. Performance under variable concentrations and temperatures has been characterized and compared to semiconductor theory. The cell response has been applied to a spectral irradiance model to predict field performance at reference locations. Cell qualification has been completed for the current-generation C1MJ design.

Thermal Stress Analysis/Life Prediction of Concentrating Photovoltaic Module

Aiming at understanding the structural integrity of two representative concentrating photovoltaic (CPV) module configurations, finite element thermal stress analysis is carried out in this investigation. This study covers the nominal and extreme operating conditions, including system startup and shutdown. While the first CPV module is bonded by epoxy-type material, the bonding material for the second CPV module is lead-free solder. The analysis of the first module confirms that this CPV module can endure the thermal stress under steady-state operation. However, residual stress analysis shows that the epoxy holding together the PV cell/aluminum nitride and aluminum nitride/heat sink pairs will likely break, first at some sporadic spots, and then in a good part of the bond causing the failure of the CPV module, as the cell temperature drops from 100°Cto0°C. Nonlinear viscoplastic analysis using the temperature profile of CPV cell fatigue test ongoing at United Technologies Research Center (UTRC) is performed to evaluate the structure strength and subsequently predict the life of the second CPV module. The result reveals that the maximum characteristic stresses of the PV cell components and heat sink are below the strength allowable for the corresponding materials under both the steady-state and overnight idle conditions. Critical locations on the solder that are potentially susceptible to structural failure after a few thousand thermal cycles due to the excessive shear stress are identified. A rough estimation of the module life is provided and compared with the fatigue test. This investigation provides firsthand understanding of the structural integrity of CPV modules and is thus beneficial for the solar energy community.

04/02805 Point-to-point HVdc systems using 36-pulseoperation: Villablanca, M. et al. Electric Power Systems Research, 2004, 69, (1), 43–50

The option to use the beam down optics of a solar tower system for large-scale and grid-connected concentrated photovoltaic (PV) cells is examined. The rationale is to use this system to split the solar spectrum. Part of the spectrum can be utilized for PV cells. For instance, but not limited to, mono-crystalline silicon cells can convert the 600–900 nm band to electricity at an efficiency of 55–60%. The rest of the spectrum remains concentrated and it can be used thermally to generate electricity in Rankine–Brayton cycles or to operate chemical processes. Two optical approaches for a large-scale system are described and analyzed. In the first concept, the hyperboloid-shaped tower reflector is used as the spectrum splitter. Its mirrors can be made of transparent fused silica glass, coated with a dielectric layer, functioning as a band-pass filter. The transmitted band reaches the upper focal zone, where an array of PV modules is placed. The location of these modules and their interconnections depend on the desirable concentration level and the uniformity of the flux distribution. The reflected band is directed to the second focal zone near the ground, where a compound parabolic concentrator is required to recover and enhance the concentration to a level depending on the operating temperature at this target. In the second approach, the total solar spectrum is reflected down by the tower reflector. Before reaching the lower focal plane, the spectrum is split and filtered. One band can be reflected and directed horizontally to a PV array and, in this case, the rest of the spectrum is transmitted to the lower focal plane. To illustrate the feasibility of these options, commercial silicon cells with antireflective coating, intended to operate under concentrated solar radiation in the range of 200–800 suns, were chosen. The results show that 6.5 MWe from the PV array and 11.1 MWe from a combined cycle can be generated starting from a solar heat input of 55.6 MW.

Hybrid concentrated photovoltaic and thermal power conversion at different spectral bands

The option to use the beam down optics of a solar tower system for large-scale and grid-connected concentrated photovoltaic (PV) cells is examined. The rationale is to use this system to split the solar spectrum. Part of the spectrum can be utilized for PV cells. For instance, but not limited to, mono-crystalline silicon cells can convert the 600–900 nm band to electricity at an efficiency of 55–60%. The rest of the spectrum remains concentrated and it can be used thermally to generate electricity in Rankine–Brayton cycles or to operate chemical processes. Two optical approaches for a large-scale system are described and analyzed. In the first concept, the hyperboloid-shaped tower reflector is used as the spectrum splitter. Its mirrors can be made of transparent fused silica glass, coated with a dielectric layer, functioning as a band-pass filter. The transmitted band reaches the upper focal zone, where an array of PV modules is placed. The location of these modules and their interconnections depend on the desirable concentration level and the uniformity of the flux distribution. The reflected band is directed to the second focal zone near the ground, where a compound parabolic concentrator is required to recover and enhance the concentration to a level depending on the operating temperature at this target. In the second approach, the total solar spectrum is reflected down by the tower reflector. Before reaching the lower focal plane, the spectrum is split and filtered. One band can be reflected and directed horizontally to a PV array and, in this case, the rest of the spectrum is transmitted to the lower focal plane. To illustrate the feasibility of these options, commercial silicon cells with antireflective coating, intended to operate under concentrated solar radiation in the range of 200–800 suns, were chosen. The results show that 6.5 MWe from the PV array and 11.1 MWe from a combined cycle can be generated starting from a solar heat input of 55.6 MW.