Spectral Beam Splitting Research Articles

Design and optimization of spectral beamsplitter for hybrid thermoelectric-photovoltaic concentrated solar energy devices

The design and optimization of a thin-film multilayer spectral beamsplitter for hybrid thermoelectric-photovoltaic (TE-PV) solar energy devices are considered. In the configuration being studied the concentrated solar radiation is either transmitted through the beamsplitter onto a thermoelectric generator, or reflected onto a photovoltaic cell. The role of the beamsplitter is to reflect (transmit) those parts of the solar spectrum that can be converted most efficiently in the PV cell (TE generator). Beamsplitters are designed for maximizing the output of the hybrid system taking into account the spectral efficiency of realistic solar cells based on amorphous or microcrystalline silicon, efficiencies of the thermoelectric generator of either 4% or 8%, and the AM1.5 solar spectrum. The beamsplitter is constructed using thin-film layers of SiO2 and Si3N4 deposited on N-BK7 glass. The layer thicknesses are optimized for maximizing the efficiency of the hybrid system. The total achievable efficiency versus the number of layers used in the beamsplitter is studied considering from app. 20 to app. 200 layers. For an amorphous solar cell the relative increase in hybrid system efficiency above the single solar cell efficiency is 21.4%. Designs are made assuming that solar radiation is incident on the beamsplitter at an angle of 45°. However, the efficiency is found to only change slightly if the angle is varied from 35° to 55°. Finally, it is also found that efficient beamsplitters cannot be constructed for the reverse configuration with the TE and PV elements interchanged since efficient reflection of the long-wavelength radiation relevant for the TE generator is not possible without also having reflection of shorter-wavelength radiation that would be converted more efficiently in the PV cell.

A spectral-splitting PV–thermal volumetric solar receiver

Spectral beam splitting of sunlight can improve the efficiency of solar receivers. Hybrid photovoltaic–thermal receivers designed for the concurrent generation of high grade heat and electricity can benefit considerably from this approach. In this paper, we introduce a novel method for filtering sunlight for high temperature hybrid solar receivers employed in linear solar concentrators. In this method, semiconductor doped glass is combined with propylene glycol to act simultaneously as the heat transfer fluid and a band pass filter for the optimal wavelength band, 700–1100nm, required by silicon (Si) solar cells. Ray tracing and experimental analysis of the proposed design has shown that this filtering method directs 29% of the incoming concentrated solar spectrum to the silicon cells in the receiver with the remainder absorbed as heat. This means that 77% of the light in the optimal spectral band is effectively collected by the solar cells. The cell efficiency under this band can reach 26% in theory. The results demonstrate the potential for a simpler spectral filtering mechanism that is suitable for concentrating hybrid solar receivers.

Performance testing of a spectral beam splitting hybrid PVT solar receiver for linear concentrators

A novel spectral beam splitting photovoltaic/thermal (PVT) solar receiver for linear concentrators has been developed capable of generating high-grade thermal energy concurrently with electricity. This paper evaluates the initial field testing of this receiver which combines a selective absorption heat transfer fluid (Propylene Glycol) with a band pass optical filter to achieve efficient spectral splitting. Wavelengths of light between 700nm and 1100nm are directed to the silicon PV cells, with the remaining wavelengths absorbed directly as heat. A prototype has been constructed and mounted to a parabolic trough concentrator with 42× geometrical concentration ratio. Results demonstrated considerable promise for this technique. High grade heat thermal efficiencies of 31% relative to the thermal beam splitting fraction were achieved at a receiver temperature of 120°C, with a total system efficiency of 50%. Electrical yields of approximately 3.8% relative to the total incident power were measured. While lower than expected we expect with minor modifications system efficiencies beyond 75% will be achievable.

Exergoeconomic analysis of a novel concentrated solar energy for lighting-power generation combined system based on spectral beam splitting

Lighting-power generation combined system (LIPGECOS) based on the approach of spectral beam splitting of concentrating solar radiation was introduced and performed exergoeconomic analysis by well-known the Specific Exergy Costing (SPECO) method. From the experimental data, the average energy and exergy efficiencies of the LIPGECOS were calculated as 0.15 and 0.09 respectively. The cost flows for concentrating dish, fibre optic bundle (FOB), cold mirror and Stirling engine were calculated as $0.016, $0.055, $0.040 and $0.018 in daily basis, respectively. The maximum exergetic cost coefficient belongs to the FOB component, while the minimum exergetic cost coefficient was calculated for the concentrating dish. Exergetic cost coefficients for the products of the dish, the mirror, the FOB and the Stirling engine are calculated as 1.07; 65.12; 199.47; 71.01 $/GJ, respectively. The maximum exergetic cost effectiveness (ECE) value is calculated for the dish as 0.1234; while the minimum one is for the mirror as 0.0000002.

Design of broadband multilayer dichroic coating for a high-efficiency solar energy harvesting system.

We report on the design and performance of a broadband dichroic coating for a solar energy conversion system. As a spectral beam splitter, the coating facilitates a hybrid system that combines a photovoltaic cell with a thermal collector. When positioned at a 45° angle with respect to incident light, the coating provides high reflectance in the 40-1100nm and high transmission in the 1200-2000nm ranges for a photovoltaic cell and a thermal collector, respectively. Numerical simulations show that our design leads to a sharp transition between the reflection and transmission bands, low ripples in both bands, and slight polarization dependence.

Vacuum ultraviolet spectropolarimeter design for precise polarization measurements.

Precise polarization measurements in the vacuum ultraviolet (VUV) region provide a new means for inferring weak magnetic fields in the upper atmosphere of the Sun and stars. We propose a VUV spectropolarimeter design ideally suited for this purpose. This design is proposed and adopted for the NASA-JAXA chromospheric lyman-alpha spectropolarimeter (CLASP), which will record the linear polarization (Stokes Q and U) of the hydrogen Lyman-α line (121.567nm) profile. The expected degree of polarization is on the order of 0.1%. Our spectropolarimeter has two optically symmetric channels to simultaneously measure orthogonal linear polarization states with a single concave diffraction grating that serves both as the spectral dispersion element and beam splitter. This design has a minimal number of reflective components with a high VUV throughput. Consequently, these design features allow us to minimize the polarization errors caused by possible time variation of the VUV flux during the polarization modulation and by statistical photon noise.

Experimental testing of SiNx/SiO2 thin film filters for a concentrating solar hybrid PV/T collector

Achieving high temperature thermal outputs from concentrating photovoltaic/thermal (PV/T) systems presents a challenge in that the performance of the PV cells declines with increasing temperature. Spectral beam splitting is an attractive approach to address this conflict by thermally decoupling the PV and thermal receivers, allowing the PV cells to operate at low temperature and the thermal receiver to operate at high temperature. In this study, SiNx/SiO2 multilayer thin film filters were designed and fabricated to act as beam splitting devices in a 10 sun, linear Fresnel mirror-based, concentrating PV/T solar collector. In this collector, reflected light is directed to a silicon PV cell whilst the transmitted light is directed to a thermal receiver. Plasma-enhanced chemical vapor deposition (PECVD) was used to fabricate the filters which were designed to obtain maximum hybrid output. The resulting devices have high reflectance (greater than 95%) for light between 713 and 1067 nm and high transmittance (greater than 90%) for sunlight outside that reflection window. The concentration of process gases in the PECVD reactor was varied in order to reduce undesired absorption at short wavelengths –lower than 650 nm– by the SiNx layers. Indoor testing was carried out for the filters in a system which consists of a Si PV cell, a thermal sensor, and a solid-state plasma light source (6500 K black body spectrum). This study tested filter performance for various angles of incidence (AOI) between 20 and 45°. The experimental results indicate that the PV cells, illuminated with the reflected light from the filters, operate on average at 9.2% absolute higher efficiency than the same cells without the filter. Furthermore, for the best filter, in terms of relative percentage, the measured hybrid output (weighted by a worth factor of electrical vs. thermal energy) is ∼9% higher than the electrical output of a PV cell stand-alone system exposed to the same light source. This paper represents the first study of a hybrid PV/T solar collector using SiNx/SiO2 thin film filters and demonstrates the feasibility of such systems. This study also indicates that this type of system can utilize 85.6% of the incoming solar spectrum based on the measured optical properties of the filters.

Spectrally Splitting Hybrid Photovoltaic/thermal Receiver Design for a Linear Concentrator

A new spectrally splitting photovoltaic-thermal hybrid receiver has been proposed and optimised for use in a linear concentrator with 10 to 20 suns concentration level. This hybrid system can produce high temperature thermal energy along with electrical output. Since photovoltaic cells cannot operate efficiently at high temperatures, they have been thermally decoupled from the thermal sub-module through spectral beam splitting, to avoid excessive heating of the cells. The proposed configuration incorporates a combination of dichroic filtering and selective volumetric absorption to divide the spectrum between the cells and the thermal sub-modules. The optics of the system has been studied using ray tracing and its performance has been compared against an ideal spectrally splitting system showing promising results.

High-Efficiency Broadband Anomalous Reflection by Gradient Meta-Surfaces

We combine theory and experiment to demonstrate that a carefully designed gradient meta-surface supports high-efficiency anomalous reflections for near-infrared light following the generalized Snell's law, and the reflected wave becomes a bounded surface wave as the incident angle exceeds a critical value. Compared to previously fabricated gradient meta-surfaces in infrared regime, our samples work in a shorter wavelength regime with a broad bandwidth (750-900 nm), exhibit a much higher conversion efficiency (∼80%) to the anomalous reflection mode at normal incidence, and keep light polarization unchanged after the anomalous reflection. Finite-difference-time-domain (FDTD) simulations are in excellent agreement with experiments. Our findings may lead to many interesting applications, such as antireflection coating, polarization and spectral beam splitters, high-efficiency light absorbers, and surface plasmon couplers.

Design of diffractive phase element for modulating the electric field at the out-of-focus plane in a lens system

We demonstrate an efficient method to design the diffractive phase element for modulating the electric field at the out-of-focus plane of a lens system by using an equivalent Fresnel diffraction in free space. In the monochromatic illumination, we show an example to certify the validity of our method experimentally. In the nonmonochromatic illumination, we theoretically display that the spectral beam splitting and highly confined intensity can be obtained simultaneously at the out-of-focus plane, which has the potential in the solar concentrating system and optical encryption.

1-D photonic crystals for photovoltaics

The paper presents the theoretical analysis of photonic structures with 1-D photonic crystals on both sides of the slab glass and the results of experimental research. Within the scope of theoretical analysis, using the 2x2 transfer matrix method, we have determined the spectral reflectivity and transmittance characteristics, and basing on the said characteristics, we have determined the influence of the number of bilayers on the maximum reflectivity and on the width of the main reflectivity peak. For the structure with four bilayers (SiO2/TiO2) we have obtained the maximum reflectivity of 0.933 for the wavelength λr = 505nm and full width at half maximum of the main reflectivity peak of FWHM=185nm.   Full Text: PDF References T.M.Razykov, C.S.Ferekides, D.Morel, E.Stefanakos, H.S.Ullal, H.M.Upadhyaya,"Solar photovoltaic electricity: Current status and future prospects", Sol. Energy 85, 1580 (2011)[CrossRef] B. Parida, S. Iniyanb, R. Goic,"A review of solar photovoltaic technologies", [CrossRef] Organic electronics, edited by Hagen Klauk, (Weinheim, WILEY-VCH Verlag GmbH & Co.KGaA,. 2006) E. Gondek, I.V.Kityk, A.Danel,"Some anthracene derivatives with N,N-dimethylamine moieties as materials for photovoltaic devices", [CrossRef] E.Gondek, Y.Djaoued, J.Robichaud, P.Karasiński, I.V.Kityk, A.Danel, K.J.Plucinski,"Influence of TiO2 nanoparticles on the photovoltaic efficiency of the ITO/PEDOT:PSS/fluorine copolymers/polythiophene: TiO2/Al architecture", J. Mater. Sci.: Mater Electron[CrossRef] R.Signerski, G.Jarosz,"Effect of buffer layers on performance of organic photovoltaic devices based on copper phthalocyanine-perylene dye heterojunction", Opto-Electron. Rev. 19, 468 (2011)[CrossRef] A.G.Imenes, D.R.Mills,"Spectral beam splitting technology for increased conversion efficiency in solar concentrating systems: a review", Sol. Energy Mater. Sol. Cells 84, 19 (2004)[CrossRef] A.Zhedi,"Review of modelling details in relation to low-concentration solar concentrating photovoltaic", Ren. Sust. Energy Rev 15, 1609 (2011)[CrossRef] B.C.Rowan, L.R.Wilson, B.S.Richards,"Advanced Material Concepts for Luminescent Solar Concentrators", [CrossRef] R.M.Almeida, L.M.Fortes, M.C.Gonçalves,"Sol–gel derived photonic bandgap coatings for solar control", Opt. Mater. 33, 1867 (2011)[CrossRef] E. Yablonovitch,"Inhibited Spontaneous Emission in Solid-State Physics and Electronics", Phys. Rev. Lett. 58, 2059 (1987)[CrossRef] G.V.Morozov, F.Placido, D.W.L.Sprung,"Absorptive photonic crystals in 1D", J. Opt. 13, 035102 (2011)[CrossRef] P.Karasiński, "Influence of aging and annealing on the properties of silica films produced with sol-gel method", Opt. Appl. 36, 389 (2006) P.Karasiński, E.Gondek, S.Drewniak, I.V.Kityk,"Nano-sized blue spectral shift in sol–gel derived mesoporous titania films", J. Sol Gel Sci. Techn. 61, 355 (2012)[CrossRef]

Design and analysis of two-stage transmitted-reflected concentration PV/thermal system with spectral beam splitter

For the traditional photovoltaic (PV) system which is under a full spectral concentrating condition, only a part of solar energy can be used by solar cells for PV power generation, the other part is not effective for the PV power generation and can result in temperature of solar cells increasing. High temperature can reduce the PV transformation efficiency of solar cells. In this study, a concentration PV/thermal system with beam splitter is proposed, which is composed of a linear Fresnel lens, a concave lens, a beam splitter, solar cells and a thermal receiver. The selective transmission coating on the splitter is designed to improve the incident condition of the sunlight on the surface of solar cells and reflect the noneffective part of sunlight to the thermal receiver for recycling. Theoretical analysis of the PV/thermal system is made and the results show that compared with the traditional concentration PV system, the two-stage transmitted- reflected concentration spectral beam splitting PV/thermal system has a high efficiency.

Concentrating PV/T Hybrid System for Simultaneous Electricity and Usable Heat Generation: A Review

Photovoltaic (PV) power generation is one of the attractive choices for efficient utilization of solar energy. Considering that the efficiency and cost of PV cells cannot be significantly improved in near future, a relatively cheap concentrator to replace part of the expensive solar cells could be used. The photovoltaic thermal hybrid system (PV/T), combining active cooling with thermal electricity and providing both electricity and usable heat, can enhance the total efficiency of the system with reduced cell area. The effect of nonuniform light distribution and the heat dissipation on the performance of concentrating PV/T was discussed. Total utilization of solar light by spectral beam splitting technology was also introduced. In the last part, we proposed an integrated compound parabolic collector (CPC) plate with low precision solar tracking, ensuring effective collection of solar light with a significantly lowered cost. With the combination of beam splitting of solar spectrum, use of film solar cell, and active liquid cooling, efficient and full spectrum conversion of solar light to electricity and heat, in a low cost way, might be realized. The paper may offer a general guide to those who are interested in the development of low cost concentrating PV/T hybrid system.

Optical modeling for a two-stage parabolic trough concentrating photovoltaic/thermal system using spectral beam splitting technology

A two-stage parabolic trough concentrating photovoltaic/thermal (PV/T) system is described, which contains a concentrator, a spectral beam splitting filter, an evacuated collector tube and the solar cell components. The nondimensional optical model with the focal length of the concentrator as the characteristic length has been developed to analyze the properties of the concentrating system using the beam splitting filter. The geometry concentration ratio and the size of solar image at different structure parameters have been obtained. Based on the ray tracing algorithms, a detailed three-dimensional model is set up to evaluate the local radiation flux density distribution on the elements’ surfaces. And the effects of the solar brightness distribution and optical errors (e.g., alignment error and tracking error) are also involved. Furthermore, the spectral distribution of the solar radiation is illustrated with the beam splitting filter, which has been specially designed using the needle optimization method. It is shown that using the filter the heat load of the cell can be reduced by 20.7%, up to 10.5% of the total incident solar energy can be recovery by the receiver, and the overall optical efficiency in theory is about 0.764.

Flat-topped broadband rugate filters

A method of creating rugate interference filters that have flat-topped reflectance across an extended spectral region is presented. The method applies known relations from the classical coupled wave theory to develop a set of equations that gives the spatial frequency distribution of rugate cycles to achieve constant reflectance across a given spectral region. Two examples of the application of this method are discussed: a highly reflective coating for eye protection against harmful laser radiation incident from normal to 45 degrees , and a spectral beam splitter for efficient solar power conversion.

The design of broadband, wide-angle interference filters for solar concentrating systems

The optical performance of spectrally selective interference filters for wide-angle solar applications is addressed. A radially variable interference filter is proposed that can maintain acceptable efficiency over its entire surface in solar concentrating systems with a wide field of view. By applying ray tracing methods and a mapping technique, the angle at which the greatest proportion of energy is incident can be determined at as a function of position on the filter surface. The resulting angular distribution is used to design the interference filter with a tapered thickness profile for optimum performance according to the changing mean angle. The method has been applied for the optimisation of a spectral beam splitter in a hybrid photovoltaic/thermal central receiver system. Two types of interference filters are compared: the discrete multilayer and the rugate filter. Results for bandpass and bandstop configurations are presented, and the performance and practical issues associated with each solution are discussed.

05/02198 Spectral beam splitting technology for increased conversion efficiency in solar concentrating systems: a review

05/02198 Spectral beam splitting technology for increased conversion efficiency in solar concentrating systems: a review

Spectral beam splitting technology for increased conversion efficiency in solar concentrating systems: a review

Solar concentrating systems that employ one or more quantum receivers may realize improved energy utilization and higher electric conversion efficiency by incorporating spectral beam splitting technology. Such techniques were investigated in thermophotovoltaic conversion, introduced in the early 1960s, and in concentrating PV devices using cells of different band-gap materials, proposed as early as 1955. One major application was found in systems combining quantum and thermal receivers. This article presents a review of the various solar hybrid beam splitting systems proposed in the literature and the different spectrum splitting strategies employed.

Mirrors and spectral beamsplitters for lasers in the visible and near-IR ranges

Mirrors and spectral beamsplitters for lasers in the visible and near-IR ranges

Fabricating micro-Bragg reflectors in 3-D photorefractive waveguides

Bragg reflectors as small as optical waveguides can be used at the intersections of waveguides as spectral filters, beam splitters, or beam combiners. We present the concept of fabricating small Bragg reflectors in photorefractive waveguides and show the spectral selectivity of these micro-Bragg reflectors fabricated in a lithium niobate crystal. We also show that we can fabricate waveguide structures simultaneously with the micro-Bragg reflector, by using a crystal whose c-axis is directed 45 degree off the optical axis of the fabrication beam. The reflectivity of the micro-Bragg reflector was smaller than 0.01 and was not large enough for the immediate use.