Holographic Solar Concentrators Research Articles

Building-Integrated Concentrating Photovoltaics based on a low-toxicity photopolymer

Low-toxicity solar concentrator systems represent an important challenge for outstanding photovoltaic (PV) applications. Particularly, multiplexed holographic lenses (MHL) as Holographic Solar Concentrators (HSC) provide insight into promising possibilities for Building-Integrated Concentrating PVs. This technology does not affect crucial ecosystems, and can convert buildings from energy consumers into energy suppliers. They can be used in windows, roofs, or walls, and a high diffraction efficiency and wide acceptance angle are desired. In this work, we presented several designs of MHL of low spatial frequency 525 lines mm−1, based on a low-toxicity photopolymer and supported on a window glass. The average diffraction efficiency of these HSC was evaluated at 633 nm, whereas the acceptance angle was evaluated by measuring the short-circuit current under solar illumination at different incident angles. Versatile and high-efficiency holographic elements have been used to concentrate sunlight from different relative positions during the day, avoiding the need for expensive tracking systems. To the best of our knowledge, this is the best trade-off between high diffraction efficiency (85 % ) and wide acceptance angle (104∘) in a low-toxicity holographic solar concentrator.

Green and wide acceptance angle solar concentrators.

A low-toxicity photopolymer was employed to prepare holographic solar concentrators (HSCs). The main aim of this study is to obtain a versatile holographic element to concentrate the sunlight from different relative positions of the Sun during the day, avoiding the need of expensive tracking systems. Multiplexed holographic elements that combine symmetric and asymmetric holographic lenses of low frequency (545 l/mm) have been recorded in the same plate to concentrate the sunlight from sunrise to sunset. The holographic behavior of HSCs has been studied by measuring the angular diffraction efficiency at 633 nm (close to the maximum response of silicon cells). The efficiency of the complete system "HSC-solar cell" has been evaluated by measuring the short-circuit current (Isc) under solar illumination at different incident angles. This study overcomes the trade-off between good efficiency and high incident acceptance angle, showing an important breakthrough to obtain wide acceptance angle systems.

Dichromated gelatin, an efficient material for the fabrication of wavelength selective holographic solar concentrators for high-efficiency operation

The use of holographic concentrators for photovoltaic solar concentration is a very attractive proposition as the hologram can be designed to be wavelength selective i.e. it can be designed to disperse, diffract and concentrate specific spectral regions of the solar spectrum with maximum efficiency in a spectrum splitting solar cell system. The practical application of highly efficient holographic solar concentrators requires intensive as well as extensive research work on the choice of the appropriate recording material. Among the available materials for recording holographic concentrators, Dichromated gelatin (DCG) is considered to be one of the best materials because maximum diffraction efficiency and high value of modulation in refractive index (reported value is up to 0.08) can be achievable in DCG film. Also, DCG has high resolution and shows low scattering noise.In present paper theoretical study on refractive index modulation capability of dichromated gelatin (DCG) for same and different thickness of DCG film have been performed to design a holographic concentrator for high-efficiency wavelength selective performance. To validate the theoretical results, holographic concentrators have been recorded in DCG film with different values of index modulation, and the typically recorded holographic concentrators were reconstructed with different wavelengths of the laser source, and corresponding diffracted power is measured. A comparison between experimental results and theoretical results are presented. Experimental and theoretical study reveals that for a constant film thickness low value of modulation in the refractive index gives maximum efficiency in lower wavelength regions and high values of index modulation are desired for maximum efficiency in higher wavelength regions. Further for a constant value of index modulation maximum efficiency gets shifted towards higher wavelength regions with an increase in film thickness. Theoretically simulated curves show that by appropriate selection of index modulation and film thickness, holographic concentrator may be fabricated to use almost entire useful portion of the solar radiation with reasonably high diffraction efficiency.

Holographic Optical Lenses Recorded on a Glassy Matrix-Based Photopolymer for Solar Concentrators

Global warming is a very topical issue, therefore the search for new renewable energy sources is considered of fundamental importance. Among these, solar energy offers great possibilities considering that the amount of sunlight hitting the Earth ‘s surface in an hour and a half is enough to meet the world’s electricity consumption for a complete year. Generally, solar concentrators are used to collect the solar radiation and to concentrate it at a single focal point. These devices consist in a set of mirrors or mechanical structures to reduce the area of a photovoltaic cell, which is typically very expensive. Volume transmission phase holographic optical elements could be opportunely designed and realized to obtain a simple, lightweight, compact and inexpensive planar solar concentrator. With the aim of bringing scientific attention to this still developing topic, in this work we critically report a complete investigation on a new photopolymeric material obtained by sol-gel reactions used as possible recording material for volume holographic solar concentrators; as a proof of concept, both terrestrial and extreme environments, such as space, are considered as potential applications.

Digital holographic method to study stress formation in photopolymer during live recording of holograms

Stress formation during the recording and bleaching of photopolymer holograms results in distortion of the internal diffractive structure and causes many undesirable effects. This is especially important in the case of holographic solar concentrators and similar holographic optical elements that are supposed to meet stringent specifications. We report a new digital holographic method to measure and study stress formation in photopolymers during hologram recording. A glass substrate, with one of its sides diffusely reflecting, is effectively applied to facilitate the recording of good digital holograms captured using a CMOS camera. A green-sensitive photopolymer is used for the study. Digital holograms recorded in successive time intervals of exposure were overlaid and numerically reconstructed. High-contrast stress fringes were generated, and the preliminary results are presented.

Recording of Holographic Solar Concentrator in Ultra Fine Grain Visible Wavelength Sensitive Silver Halide Emulsion

Recording of Holographic Solar Concentrator in Ultra Fine Grain Visible Wavelength Sensitive Silver Halide Emulsion

Application of Photopolymer Materials in Holographic Technologies.

The possibility of the application of acrylate compositions and Bayfol HX photopolymers in holographic technologies is considered. The holographic characteristics of materials, their advantages, and limitations in relation to the tasks of obtaining holographic elements based on periodic structures are given. The conditions for obtaining controlled two and multichannel diffraction beam splitters are determined with advantages in terms of the simplicity of the fabrication process. The diffraction and selective properties of volume and hybrid periodic structures by radiation incidence in a wide range of angles in three-dimensional space are investigated, and new properties are identified that are of interest for the development of elements of holographic solar concentrators with advantages in the material used and the range of incidence angles. A new application of polymer materials in a new method of holographic 3D printing for polymer objects with arbitrary shape fabrication based on the projection of a holographic image of the object into the volume of photopolymerizable material is proposed, the advantage of which, relative to additive 3D printing technologies, is the elimination of the sequential synthesis of a three-dimensional object. The factors determining the requirements for the material, fabrication conditions, and properties of three-dimensional objects are identified and investigated.

Outdoor performance evaluation of a holographic solar concentrator optimized for building integration

A holographic solar concentrating system with a Silicon photovoltaic (PV) cell is designed, constructed and characterized. The design is based on a previous system and is further optimized. The cylindrical holographic lenses forming the concentrating system are modeled with a ray-tracing algorithm based on Coupled Wave Theory and are recorded on Bayfol® HX photopolymer. Measurements are carried out outdoors with solar illumination and provide a current density of 146 mA/cm2 with a current concentration factor of 3.48, validating the theoretical simulations results (172 mA/cm2 and 3.81, respectively). The effect of the temperature on the performance of the Holographic Optical Elements (HOEs) is studied and taking it into account by assuming a 1.3° tilt of the fringes of the hologram caused by thermal expansion (which is reversible if the HOEs are encapsulated and sealed) provides simulation results closer to the experimental ones (a current density value of 155 mA/cm2 and current concentration of 3.43). The ageing of HOEs recorded in Bayfol® HX photopolymer due to the outdoor environmental conditions is also analyzed, revealing the need of encapsulation and sealing.

Optical design and characterization of holographic solar concentrators for photovoltaic applications

In present work, different possible aspects of holographic PV concentrators like wide acceptance angle, wavelength selectivity and maximum efficiency operation have been investigated by controlling different processing parameters like depth of refractive index modulation, film thickness and fringe spacing. We have discussed and analyzed individual as well as cumulative effect of processing parameters on angular selectivity, wavelength selectivity and efficiency. In addition, we are also reporting optimized value of the processing parameters for designing high efficiency holographic concentrator.

Holographic Solar Energy Concentrator Using Angular Multiplexed and Iterative Recording Method

Holographic optical elements can be fabricated to concentrate the solar energy with no sun tracking system. Concentrated diffraction efficiency (CDE) for the holographic solar concentrator is suggested as a new efficiency calculation method. The exposure response of a monochromatic hologram recorded in photopolymer film is presented. The iterative exposure schedules at three different angles are chosen to optimize the uniformity of the CDE using angular multiplexed technique. The experimental results confirm that the angular multiplexing method and newly proposed iterative recording scheduling are appropriate for fabricating the holographic solar concentrator.

One-axis tracking holographic planar concentrator systems

A design methodology for low-concentration ratio holographic solar concentrators with one-axis tracking is investigated. This methodology maximizes the energy collected by cascaded holographic gratings and reduces diffracted beam cross talk between gratings. Several types of transmission gratings, optimized to work with single-axis tracking systems, are used in a cascaded configuration to concentrate a large fraction of the useable solar spectrum on the surface of photovoltaic cells. A model is developed that determines the energy yield of the holographic planar concentrator (HPC). Good agreement is found between simulation and measurement of a prototype system. Simulation of an optimized HPC design shows that 80% optical efficiency at 2X geometric concentration ratio is possible. The acceptance angle in the nontracking direction is ±65 deg, and a ±16-deg tracking tolerance is sufficient to maintain 80% of the maximum optical efficiency. Simulation also shows that the single-axis tracking HPC system has a 43.8% increase in energy yield compared to a nontracking holographic solar concentrator.

Energy collection efficiency of holographic planar solar concentrators

We analyze the energy collection properties of holographic planar concentrator systems. The effects of solar variation on daily and annual energy collection are evaluated. Hologram diffraction efficiency, polarization, crosstalk in cascaded elements, and constraints imposed by the radiance theorem, as well as solar illumination characteristics, are considered. A planar holographic solar concentrator configuration is designed and modeled to maximize energy collection efficiency during the course of a year without the need for tracking. Results indicated that nearly 50% of the available energy illuminating hologram areas can be collected by photovoltaic cells without the need of tracking.

Design and Fabrication of a Holographic Solar Concentrator

The main purpose of this paper is to present the potential of photovoltaic systems using holographic solar concentrators. A hologram used here focuses light, spectrally splits it and diverts unwanted infrared heat away from the solar cell. The output of the hologram appears as a perpendicular thin spectral line and is displaced to solar cells on both sides. To obtain optimum design conditions we used the coupled wave theory and the vector ray tracing method. The measured data showed that the diffraction efficiency was 75 ％ and the spectral bandwidth was 350 nm.

Holographic solar concentrator

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Jacques E. Ludman, "Holographic solar concentrator," Appl. Opt. 21, 3057-3058 (1982) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article