Optical Concentration Ratio Research Articles

Bench-scale evaluation of water disinfection by visible-to-UVC upconversion under high-intensity irradiation

The feasibility of applying visible-to-UVC upconversion (UC) luminescence to enhance the kinetics of solar water disinfection was evaluated using Lu7O5F9:Pr3+ ceramics incorporated into a solar reactor containing E. coli suspensions. Inactivation was assessed in batch conditions using both laser and lens-concentrated sunlight excitation conditions. Under 840-mW argon laser excitation, the UC efficiency was estimated to be 1 order of magnitude greater than previously reported under lamp excitation and UVC emitted by the reactors resulted in 3.6-log inactivation in 20min. However, experiments using ~1500mW of concentrated natural sunlight showed no additional inactivation that could be attributed to UC within the timescale studied. Due to the fundamental and practical limitations of solar focusing, the optical concentration ratio employed herein prevented the excitation beam from achieving the power densities required to attain UC efficiencies comparable to the laser experiments. We also observed that the high intensity of both the laser and sunlight induced rapid photoreactivation by the bacteria, which detracted from net disinfection performance. The results suggest that current UC materials perform inadequately for environmental application; nonetheless, valuable qualitative and quantitative insight was gained that more explicitly defines materials development goals and considerations for application of UC to environmental technology.

Solar concentrator with a toroidal relay module.

III-V multijunction solar cells require solar concentrators with a high concentration ratio to reduce per watt cost and to increase solar energy transforming efficiency. This paper discusses a novel solar concentrator design that features a high concentration ratio, high transfer efficiency, thin profile design, and a high solar acceptance angle. The optical design of the concentrator utilizes a toroidal relay module, which includes both the off-axis relay lens and field lens design in a single concentric toroidal lens shape. The optical design concept of the concentrator is discussed and the simulation results are shown. The given exemplary design has an aspect ratio of 0.24, a high averaged optical concentration ratio 1230×, a maximum efficiency of 76.8%, and the solar acceptance angle of ±0.9°.

Coupled Simulation of Performance of a Crossed Compound Parabolic Concentrator with Solar Cell

An optimal installation of a compound parabolic concentrator (CCPC) into a scalable solar thermoelectrics and photovoltaics system is desirable by applying analytical tools to improve the optical and thermal performance of a CCPC with a solar cell. In this paper, the optical and thermal performances of an isolated CCPC with solar cell are investigated by employing commercial software ‘ANSYS CFX 15.0’ with a coupled optical grey and multiphysics model. Numerical results are validated against the experimental data at various incidence angles, especially for the optical concentration ratio and optical efficiency. Results confirm that ‘ANSYS CFX’ is an effective numerical tool for determining correctly both the optical and thermal behaviour of CCPC. The very important finding is a highest temperature core in the silicon layer of solar cell which may be responsible for a solar cell to work properly. The limitation of the work is that the electric performance of the solar cell is not involved and the simulations are steady.

A Theoretical Comparison of Optically Concentrating, Solar Water-Splitting Devices

The use of optically concentrating lenses provides a mechanism to reduce the cost and energy input required to manufacture solar fuels-producing devices. The direct production of hydrogen via water splitting could thereby be realized in a cost-competitive, low carbon fashion. In this work, a modeling approach is used to assess which concentrator architectures are appropriate for integration with wireless photoelectrochemical cells. The model captures optical, heat transfer, photoelectrochemical and climactic phenomena. The variation of design parameters such as lens type, optical concentration ratio, deployment location, cell dimensions and tracking schemes are explored. It is found that the devices that perform most efficiently employ modest concentration ratios, continuous tracking of the sun, and maintain sufficiently small photovoltaic cell size in order to reduce potential losses in the electrolyte. However, designs that exhibit the lowest cost and energy input per unit of produced fuel have somewhat higher concentration ratios and simpler tracking mechanisms. Employing passive cooling to maintain sufficiently low cell temperature during extreme ambient conditions becomes difficult as the photovoltaic cell size and optical concentration ratio increase. Figure 1

Multiple dyes containing luminescent solar concentrators with enhanced absorption and efficiency

The fabrication and characterization of luminescent solar concentrators (LSCs) that contain multiple dyes are reported. LSCs were fabricated using one, two, or three dyes doped in a poly(methyl methacrylate) (PMMA) waveguide, and their performance was characterized. The three-dye LSC had a power conversion efficiency of 1.40% with an optical concentration ratio of 1.2. This efficiency is 16.7% greater than the maximum value of the single-dye LSCs. The external quantum efficiency of the three-dye LSC was greater than the single-dye LSCs.

Design and study of Fresnel lens for an antenna in indoor visible light communication system

Indoor visible light communication is a novel wireless communication based on white LED technology. For its application needs, equal-pitch flat Fresnel lens is designed. Compared with traditional lens, Fresnel lens has several advantages including strong focus ability, short focal length, thin thickness, light weight, low cost, etc. The optical concentration ratio, the optical efficiency and the spot size of these Fresnel lenses are analyzed respectively with different parameters by means of Trace pro. Furthermore, the concentration performance is discussed at different incident angles. The results indicate that this kind of Fresnel lens could be used as an antenna of high-gain and small field, and the optical efficiency could be obtained to be 92.1%.

Model Development and Performance Studies of a Concentrating Direct Absorption Solar Collector

A detailed three-dimensional (3D) computational fluid dynamics (CFD) model of a direct absorption solar collector (DAC) is presented. Radiative transfer equation (RTE) is coupled with Navier–Stokes equations and solved numerically to predict the collector efficiency. The spectral properties of absorbing liquids are captured using a band-averaged absorption model. This numerical model is validated with experimental data for two different types of absorbing fluids viz., gray (graphite particles in water) and nongray (copper sulfate) fluids. The validated model is used for parametric studies to determine the right design choices for an improved collector. Impact of optical concentration ratio (CR), optical density of the fluid, mass flowrate, and thermal insulation on the collector efficiency were studied. Increase in collector efficiency of up to 28% is seen due to higher optical CRs, which is attributable to good absorption characteristics of the receiver and reduced area for losses. The collector efficiency does not improve with absorption coefficient of the fluid beyond a certain value for a given thickness of the fluid layer. The range of mass flow rates considered in the study was found to have no impact on collector efficiency. Thermal insulation is found to be very effective in minimizing the overall thermal losses and enhancing the collector efficiency. The numerical model presented here may be used to identify optimum CR, absorption coefficient of liquid for a direct absorption concentrating collector.

Optical performance of dichroic spectrum-splitting filters

We investigate the optical performance of dichroic filters used in solar spectrum-splitting applications. Photovoltaic (PV) systems utilizing spectrum splitting have higher theoretical conversion efficiency than single-bandgap PV modules. Dichroic filters have been used in several spectrum-splitting optical system designs with success. However, dichroic filters only achieve ideal performance under collimated incident light. With an incident angle constraint the optical concentration ratio is limited. A high-concentration ratio helps to achieve high-conversion efficiency and control cost by reducing the PV cell area. In a dual-junction spectrum-splitting PV configuration with a gallium arsenide (GaAs) PV cell and a 2.1-eV bandgap PV cell, the experimental dichroic filter can provide 86.3% of the ideal designed performance. The filter nonideal performance under focused incident light is simulated with ZEMAX. System efficiency under different F-number and filter refractive index is simulated for dual-junction and three-junction systems to show the performance of dichroic filters. We have found that for a dual-bandgap spectrum-splitting system there is a 0.32% system efficiency gain associated with a filter refractive index increased from 1.5 to 1.95. An efficiency gain of 0.41% is associated with an aperture size reduction from F2.0 to F3.0. In a three-junction configuration, simulation shows that a 0.57% system efficiency gain is possible when the filter refractive index is increased from 1.5 to 1.95. An efficiency gain of 0.63% is associated with an aperture size reduction from F2.0 to F3.0.

Smart windows: Thermal modelling and evaluation

A numerical investigation of the performance of a multi paned smart window integrated with water-cooled high efficiency third generation GaAsP/InGaAs QWSC (∼32% efficiency) solar cells illuminated by two-axis tracking solar concentrators at 500× in the inter pane space is presented. Optimising system parameters such as optical concentration ratio and coolant (water) flow rate is essential in order to avoid degradation in system performance due to high cell temperatures and thermal stresses. Detailed modelling of the thermo-fluid characteristics of the smart windows system was undertaken using a finite volume CFD package. Results of this analysis which considered the conductive, convective and radiative heat exchange processes taking place in the interior of the smart window system as well as the heat exchange to the internal and external ambient environment are presented.

Luminescent Solar Concentrators Fabricated by Dispersing Rare Earth Particles in PMMA Waveguide

Luminescent solar concentrators (LSCs) were fabricated by dispersing CaAlSiN3 : Eu2+particles in a PMMA waveguide. A series of LSCs (dimension 5.0 cm × 5.0 cm × 0.5 cm) with different CaAlSiN3 : Eu2+particle concentration were obtained and their performance was evaluated. The maximum optical concentration ratio is 1.23 with a power conversion efficiency of 1.44% for the LSC containing 0.5 wt% CaAlSiN3 : Eu2+particles concentration. This strategy of dispersing rare earth particles in PMMA waveguide represents an alternative approach to producing highly durable LSCs.

Nonimaging achromatic shaped Fresnel lenses for ultrahigh solar concentration

The maximum concentration ratio achievable with a solar concentrator made of a single refractive primary optics is much more limited by the chromatic aberration than by any other aberration. Therefore achromatic doublets made with poly(methyl methacrylate) and polycarbonate are of great interest to enhance the concentration ratio and to achieve a spectrally uniform flux on the receiver. In this Letter, shaped achromatic Fresnel lenses are investigated. One lossless design is of high interest since it provides spectrally and spatially uniform flux without being affected by soiling problems. With this design an optical concentration ratio of about 8500× can be achieved.

Optical Analysis of a Heliostat Array With Linked Tracking

The optical performance of a novel solar concentrator consisting of a 400 spherical heliostat array and a linked two-axis tracking system is analyzed using the Monte Carlo ray-tracing technique. The optical efficiency and concentration ratio are compared for four different heliostat linkage configurations, including linkages of 1 × 1, 1 × 2, 2 × 2, 4 × 4, and 5 × 5 heliostats for 7-hour operation and the selected months of June and December. The optical performance of the concentrator decreases with the increasing number of heliostats in the individual groups due to increasing optical inaccuracies. In June, the best-performing linked configuration, in which 1 heliostat in the east-west direction and 2 heliostats in the north-south direction are linked, provides a monthly-averaged 7-hour optical efficiency and average concentration ratio of 79% and 511 suns, respectively. In December, the optical efficiency and the average concentration ratio decreases to 61% and 315 suns, respectively.

Optical characterisation and optimisation of a static Window Integrated Concentrating Photovoltaic system

In this work, three different geometrical properties have been considered to develop a new solar concentrator design for Window Integrated Concentrating Photovoltaic (WICPV). They are (i) elliptical entry aperture; (ii) hyperbolic profile section and (iii) square exit aperture. Due to the increasing demands for stationary solar concentrators for building integrated photovoltaic (BIPV), this new design focuses on the use as a stationary solar concentrator. The complete optical analysis of the concentrator is carried out via 3-D ray trace technique. The analysis is based on all necessary design parameters, i.e., elliptical entry axis, concentrator height and the exit aperture geometry, in order to obtain the optimal overall optical performance of the new 3-D solar concentrator. Four different geometrical low concentration ratios were investigated: 4×, 6×, 8× and 10×. Results of the computer simulation show that the designed concentrator of 4× concentration ratio gives the higher optical efficiency of 68% compared to the other low concentration ratios. The 6×, however, gives a higher optical concentration ratio, despite having a lower optical efficiency (55%) than the 4×. A prototype of the designed concentrator was manufactured and tested under indoors conditions. The experimental results have shown an agreement by a difference of 5% with the simulation results. These results highlight how different factors need to be taken into consideration when carrying out optimisation studies. Overall, the proposed concentrator looks promising with sound results to confirm its performance and validate it as a stationary solar concentrator and thereby promote its use in WICPV.

Performance Evaluation of Parabolic Solar Disc for Indoor Cooking

In present energy crisis scenario, it has become necessary to exploit new energy sources. Among these sources solar energy has an infinite potential and available at free of cost. For efficient utilization of solar energy, focusing type paraboloidal solar collector was designed and fabricated having aperture area 0.628 m 2 , focal length 0.8 m, receiver area 0.015m 2 and optical concentration ratio 40.Bi-axial manual tracking mechanism is developed which can be operated from the kitchen. It was tested for its thermal performance and cooking abilities. Also comparative analysis with box type solar cooker was done. The system was found useful in cooking a variety of food materials.

406 集光機能を有する太陽集熱器用真空管の設計と性能評価(新エネルギー(2))

The objective of this research is to improve efficiency of conventional evacuated solar collector by simulation. To achieve this, the upper half of vacuum tube consists of Non-imaging Fresnel lens. Non-imaging Fresnel lens consists of many prisms and has acceptable half-angle. The vacuum tube is designed by changing parameters, for example, a position of heat collector, the radius o f the vacuum tube and the number of prisms. The optical efficiency is calculated by ray tracing. As a result, parameters, which affect optical efficiency greatly, are number of prisms and the distance between heat collector and center of vacuum tube. The greatest optical concentration ratio was about 3.0 when parameters of vacuum tube changed.

A Novel Lens-Walled Compound Parabolic Concentrator for Photovoltaic Applications

A compound parabolic concentrator (CPC) is a nonimaging concentrator that can concentrate solar radiation coming within its acceptance angle. A low concentration CPC photovoltaic system has the advantages of reduced Photovoltaics (PVs) cell size, increased efficiency and stationary operation. The acceptance angle of a CPC is associated with its geometrical concentration ratio, by which the size of PV cell could be reduced. Truncation is a way to increase the actual acceptance angle of a mirror CPC, but it also reduces the geometrical concentration ratio. On the other hand, a solid dielectric CPC can have a much larger acceptance angle, but it has a larger weight. To overcome these drawbacks, this study presents a novel lens-walled CPC that has a thin lens attached to the inside of a common mirror CPC or has the lens to be mirror coated on its outside surface. The shape of the lens is formed by rotating the parabolic curves of a CPC by a small degree internally around the top end points of the curves. The refraction of the lens allows the lens-walled CPC to concentrate light from wider incidence angle. The commercial optical analysis software PHOTOPIA is used to verify the principle of the presented lens-walled CPC and examine its optical performance against the common CPCs. As an example, the simulation is aimed to evaluate whether a lens-walled CPC with a geometrical concentration ratio of 4 has any advantage over a common CPC with a geometrical concentration ratio of 2.5 in terms of actual acceptance angle, optical efficiency and optical concentration ratio.

Modeling of concentrating solar thermoelectric generators

The conversion of solar power into electricity is dominated by non-concentrating photovoltaics and concentrating solar thermal systems. Recently, it has been shown that solar thermoelectric generators (STEGs) are a viable alternative in the non-concentrating regime. This paper addresses the possibility of STEGs being used as the power block in concentrating solar power systems. STEG power blocks have no moving parts, they are scalable, and they eliminate the need for an external traditional thermomechanical generator, such as a steam turbine or Stirling engine. Using existing skutterudite and bismuth telluride materials, concentrating STEGs can have efficiencies exceeding 10% based on a geometric optical concentration ratio of 45.

Theoretical efficiency of solar thermoelectric energy generators

This paper investigates the theoretical efficiency of solar thermoelectric generators (STEGs). A model is established including thermal concentration in addition to optical concentration. Based on the model, the maximum efficiency of STEGs is a product of the opto-thermal efficiency and the device efficiency. The device efficiency increases but the opto-thermal efficiency decreases with increasing hot side temperature, leading to an optimal hot-side temperature that maximizes the STEG efficiency. For a given optical concentration ratio, this optimal hot-side temperature depends on the thermoelectric materials’ nondimensional figure-or-merit, the optical properties of wavelength-selective surface and the efficiency of the optical system. Operating in an evacuated environment, STEGs can have attractive efficiency with little or no optical concentration working in the low temperature range (150–250 °C) for which Bi2Te3-based materials are suitable.

Enhancement of photovoltaic cell response due to high-refractive-index encapsulants

This study compares the electrical output of photovoltaic (PV) cells encapsulated with silicones having different refractive indices to unencapsulated PV cells. It is demonstrated that the optical concentration ratio of dome-shaped concentrator PV systems can be increased by using a higher refractive-index encapsulant. The short-circuit photocurrent of the PV cell having high-refractive-index encapsulation (n=1.57) is 71% higher than that of the PV cell having a low-refractive-index encapsulation (n=1.41), and 316% higher than that of the unencapsulated PV cell. These experimental concentration-ratio enhancements are consistent with the theoretical estimates of concentration ratio dependence on the refractive index of the PV concentrator.

Optical performance of fixed east–west aligned CPCs used in China

In this article, a mathematical procedure is developed to estimate the annual collectible radiation captured by fixed compound parabolic concentrators (CPCs, in short) oriented in east-west direction based on the monthly horizontal radiation. Results show that for fixed east–west aligned symmetric CPCs used over the atmosphere, the optimal acceptance half-angle for maximizing its annual energy collection was 25.97°, the yearly optimal tilt-angle of apertures relative to the horizon was equal to the site latitude, and the maximum annual average optical concentration ratio was uniquely related to the site latitude. For CPCs used in China, the optimal acceptance half-angle were in between 25.3° and 26°, the yearly optimal tilt-angle approached the site latitude with a deviation less than 1°, and the maximum annual average optical concentration ratios ranged from 1.45 to 1.74. Results also indicated that CPCs were more favorable to be used in the areas with higher latitude and abundant solar resources. Effects of tilt-angle and azimuth angle of CPCs on its annual solar gain were also presented.