Primary Optical Element Research Articles

Cassegrain-based concentrator with a high uniformity and acceptance angle

In this study, we improved a Cassegrain concentrator [Appl. Opt. 59, 8603 [2020)APOPAI0003-693510.1364/AO.400756] by redesigning the secondary optical element (SOE) with a freeform design, including geometrically mapped and tilted steps, to replace the design of the primary optical element (POE). This modification increased the acceptance angle and formed a more uniform irradiance distribution in the system without a homogenizer while maintaining the same level of efficiency. The result is a 1236× geometric concentration ratio, 1035× concentration ratio, 83.73% optical efficiency, ±0.40∘ acceptance angle, 8.96 uniformity, and 0.254 aspect ratio.

Simulation and experimental validation in outdoor conditions of a CPV system based on both pyramid and cone secondary optical elements

• Design, simulation and experimental validation of three FL based CPV concentrators. • Highest η opt and η elec reaching 81% and 30% respectively. • Large acceptance angle for the pyramid-based concentrator, reaching 1.35°. • Possibility of upscaling the system This work deals with real conditions testing of two Fresnel lens-based optical concentrators for concentrator photovoltaic systems (CPV). Particular attention is paid to validate the performances of the secondary optical elements (SOEs), namely pyramid and cone, both made from highly transparent fused silica and mounted with a poly methyl methacrylate (PMMA) Fresnel lens as a primary optical element (POE). The effet of the focal distance of the POE on the main optical characteristics is analyzed by simulation and the corresponding results and behavior are discussed in details. Prototypes based on Fresnel lens having 75 and 100mm in diameter and pyramid- and cone-based secondary optical elements have been simulated, fabricated and tested. Optical and electrical characterization procedures are described in details. The optical efficiency, acceptance angle, spatial homogeneity of the output power and electrical performances of the fabricated CPV units are measured and are in a good agreement with simulation data. Results show that the pyramid-type concentrator gives the best optical and electrical performances. The electric efficiency achieved by the pyramid-based concentrators reaches 30% which make it able to reach the highest standards of CPV technology performances. A large acceptance angle of 1.35° is measured as one of the highest value reported in the literature for systems with pyramid as a SOE. A good agreement between simulation and experiment results has been obtained, confirming the performance expected from a CPV system having the same secondary optical element with a larger primary optical element

Performance analysis of a ball lens as secondary optical element for a micro photovoltaic concentrator

Concentrated Photovoltaic (CPV) is a promising technology for higher efficiency power generation than other photovoltaic power generating technologies. However, the lack of demand and its failure in the commercial field is mainly due to its long-term reliability issues as well as its cost, which is an order of magnitude higher than the other technologies. Therefore, several measures have been taken to minimize the cost, improve the reliability as well as improve the performance of these concentrators. In this approach, Micro photovoltaic concentrators have been introduced as an outstanding alternative to shed light on all these challenges while keeping the same principle as the CPV modules. This paper presents a theoretical analysis of a micro photovoltaic concentrator system with a geometrical concentration ratio of 100x consisting of a Plano-convex lens as a primary optical element, a ball lens as a secondary optical element, and a solar cell. The aim is to present a compact module with high optical efficiency, low thermal stress, and high mechanical tolerance to keep the optimum optical alignment between the submillimeter cell and the small-sized optics.

Design of Primary Optical Element with Multiple Sublenses to Improve Irradiance Uniformity over the Receiver of Concentrator Photovoltaic System

Design of Primary Optical Element with Multiple Sublenses to Improve Irradiance Uniformity over the Receiver of Concentrator Photovoltaic System

PERFORMANCE ANALYSIS AND OPTIMIZATION OF A CONCENTRATED PHOTOVOLTAIC SYSTEM WITH DOUBLE FRESNEL LENSES

Bu çalışmada, yoğunlaştırıcı optik eleman olarak nokta odaklı Fresnel lens kullanılan çift optik elemanlı bir CPV sistemin performansı deneysel olarak incelenmiştir. Bu kapsamda, birincil ve ikincil optik eleman yoğunlaşma oranları (C_1, C_2), f sayıları (f_1, f_2) ve lensler arası mesafenin (L_D) CPV sistem performansı üzerindeki etkileri tek ve çift Fresnel lensli farklı konfigürasyonlar için araştırılmıştır. Genel olarak, lensler arası mesafe belirli bir kritik değere (L_(D,crit)) ulaşıncaya kadar, L_D artışı ile CPV sistem performansının iyileşmekte olduğu ancak L_D’nin kritik değerin üzerine çıktığında sistem performansının kötüleşmeye başladığı gözlenmiştir. Ayrıca, L_(D,crit)’in önemli ölçüde Fresnel lens çiftinin optik özelliklerine bağlı olduğu not edilmiştir. Bunun yanı sıra, yüksek f_1 değerine sahip çift Fresnel lensli CPV sistemlerinin, tekli Fresnel lens uygulamalarına göre daha iyi performans sergilediği görülmüştür. f_1>0.5 olduğunda CPV sisteminin performansının ikincil bir Fresnel lens kullanılarak iyileştirilebileceği tespit edilmiştir. Bunların ötesinde, Fresnel lens çiftlerinin optik özelliklerinin CPV sistem performansına etki oranını karşılaştırmak için deneysel veriler kullanılarak ANOVA analizleri yapılmıştır. ANOVA analizi sonuçları, birincil optik eleman özellikleri C_1 ve f_1’in çift Fresnel lensli CPV sistem performansı üzerinde ağırlıklı olarak etkili olduğunu işaret etmiştir. Öte yandan, diğer parametrelerle karşılaştırıldığında f_2'nin CPV sistem performansı üzerinde en az etkiye sahip olduğu da görülmüştür. Son olarak, genetik algoritma ve yapay sinir ağı temelli çalışmalar ile optimum C_1, C_2, f_1, f_2 and L_(D,crit) tahmin edilmiştir.

Solar collector tube as secondary concentrator for significantly enhanced optical performance of LCPV/T system

Improving efficiency, controlling cost and reducing the temperature of solar cells are great challenges for linear concentrated photovoltaic/thermal systems (LCPV/T). In this work, we report a new design with a linear Fresnel lens as the primary optical element and an additional multi-functioned solar collector tube as the secondary optical element. With such design, the low-cost solar collector tube acts multiple roles simultaneously, i.e., lens, spectral beam-splitting filter and heat collector. It was demonstrated that the addition of such multi-functional solar collector tube in LCPV/T system can significantly increase the irradiation uniformity and decrease the average temperature of photovoltaic (PV) module under the same thermal condition, which results in the improved electricity output performance of PV module. Under the solar irradiance and ambient temperature for a typical daytime, the average electrical, thermal and total energy efficiencies of the proposed system are 11.39%, 64.72% and 76.11%, respectively. Our work should be of guidance for the design of LCPV/T system with high efficiency, long-life and low cost.

Optical Performance of Single Point-Focus Fresnel Lens Concentrator System for Multiple Multi-Junction Solar Cells—A Numerical Study

This paper investigates the potential of a new integrated solar concentrated photovoltaic (CPV) system that uses a solo point focus Fresnel lens for multiple multi-junction solar cells (MJSCs). The proposed system comprises of an FL concentrator as the primary optical element, a multi-leg homogeniser as the secondary optical element (SOE), a plano-concave lens, and four MJSCs. A three-dimensional model of this system was developed using the ray tracing method to predict the influence of aperture width, height, and position with respect to MJSCs of different reflective and refractive SOE on the overall optical efficiency of the system and the irradiance uniformity achieved on the MJSCs’ surfaces. The results show that the refractive homogeniser using N-BK7 glass can achieve higher optical efficiency (79%) compared to the reflective homogeniser (57.5%). In addition, the peak to average ratio of illumination at MJSCs for the reflective homogeniser ranges from 1.07 to 1.14, while for the refractive homogeniser, it ranges from 1.06 to 1.34, causing minimum effects on the electrical performance of the MJSCs. The novelty of this paper is the development of a high concentration CPV system that integrates multiple MJSCs with a uniform distribution of rays, unlike the conventional CPV systems that utilise a single concentrator onto a single MJSC. The optical efficiency of the CPV system was also examined using both the types of homogeniser (reflective and refractive).

Cassegrain-based concentrator with tailored mirrors.

In this study, we design a Cassegrain-based concentrator with tailored mirrors. The proposed concentrator comprises a primary optical element (POE) and a secondary optical element (SOE). The POE is a parabolic concave mirror and the SOE is a hyperbolic convex mirror. In order to achieve uniform irradiance distribution without a homogenizer, the POE is tailored and tilted to generate a uniform distribution by overlapping the energy well. The Cassegrain-based concentrator with tailored mirrors can achieve a geometric concentration ratio of 1236×, a concentration ratio of 1034×, an optical efficiency of 83.66%, an acceptance angle of ±0.38∘, a uniformity of 7.87, and an aspect ratio of 0.254.

Увеличение КПД концентраторных фотоэлектрических модулей при использовании фоконов в качестве вторичных оптических концентраторов

Concentrator photovoltaic module with Fresnel lenses as primary optical elements and focons made of sheet aluminum as the secondary optical concentrators has been developed. To enhance the efficiency of conversion of solar energy into electrical the optimal focon design have been determined and the photoelectric characteristics of a module with such focons investigated. Implementation of focons in module design allowed to increase acceptance angle of the latter from ±0.45% (without focons) up to ±0.85% (with focons) and to increase the efficiency from 29% to 32.8%.

Algorithmically Optimized Hemispherical Dome as a Secondary Optical Element for the Fresnel Lens Solar Concentrator

The significance of this work lies in the development of a novel code-based, detailed, and deterministic geometrical approach that couples the optimization of the Fresnel lens primary optical element (POE) and the dome-shaped secondary optical element (SOE). The objective was to maximize the concentration acceptance product (CAP), while using the minimum SOE and receiver geometry at a given f-number and incidence angle (also referred to as the tracking error angle). The laws of polychromatic light refraction along with trigonometry and spherical geometry were utilized to optimize the POE grooves, SOE radius, receiver size, and SOE–receiver spacing. Two literature case studies were analyzed to verify this work’s optimization, both with a spot Fresnel lens POE and a spherical dome SOE. Case 1 had a 625 cm2 POE at an f-number of 1.5, and Case 2 had a 314.2 cm2 POE at an f-number of 1.34. The equivalent POE designed by this work, with optimized SOE radiuses of 13.6 and 11.4 mm, respectively, enhanced the CAP value of Case 1 by 52% to 0.426 and that of Case 2 by 32.4% to 0.45. The SOE’s analytical optimization of Case 1 was checked by a simulated comparative analysis to ensure the validity of the results. Fine-tuning this design for thermal applications and concentrated photovoltaics is also discussed in this paper. The algorithm can be further improved for more optimization parameters and other SOE shapes.

Novel Design of Primary Optical Elements Based on a Linear Fresnel Lens for Concentrator Photovoltaic Technology

In this paper, we present a design and optical simulation of a novel linear Fresnel lens. The lens can be applied to a concentrator photovoltaic (CPV) system as a primary optical element (POE) to increase the concentration ratio and improve the uniformity of irradiance distribution over the receiver. In addition, the CPV system can use the proposed lens as a concentrator without involving a secondary optical element (SOE). The designed lens, which is a combination of two linear Fresnel lenses placed perpendicular to each other, can collect and distribute the direct sunlight on two dimensions. The lens is first designed in the MATLAB program, based on the edge ray theorem, Snell’s law, and the conservation of the optical path length, and then drawn in three dimensions (3D) by using LightToolsTM. Furthermore, in order to optimize the structure and investigate the performance of the lens, the ray tracing and the simulation are also performed in LightToolsTM. The results show that the newly designed lens can achieve a high concentration ratio of 576 times, a high optical efficiency of 82.4%, an acceptable tolerance of 0.84°, and high uniform irradiance of around 77% for both horizontal and vertical investigation lines over the receiver.

Nine-sector three-stage Fresnel lens concentrator.

In this paper, we design a three-stage Fresnel lens concentrator with a low f number. The proposed concentrator consists of a primary optical element (POE) and a second optical element (SOE). The nine-sector three-stage Fresnel lens is composed of three types of triangular prisms: the refractive triangular prism, single total internal reflection triangular prism, and double total internal reflection triangular prism. In order to increase the uniformity and acceptance angle of the POE coupled to the SOE, the SOE is also divided into nine sectors. Finally, it is found that this nine-sector three-stage Fresnel lens concentrator can achieve a concentration ratio of 1000×; the uniformity is 25.8, optical efficiency is 81.8%, f number is 0.46, and acceptance angle is ±0.73°.

Design and characterization of hybrid III–V concentrator photovoltaic–thermoelectric receivers under primary and secondary optical elements

Lattice-matched monolithic triple-junction Concentrator Photovoltaic cells (InGa(0.495)P/GaIn(0.012)As/Ge) were electrically and thermally interfaced to two Thermoelectric Peltier module designs. An electrical and thermal model of the hybrid receivers was modelled in COMSOL Multiphysics software v5.3 to optimize cell cooling whilst increasing photon energy conversion efficiency. The receivers were measured for current–voltage characteristics with the cell only (with sylguard encapsulant), under single secondary optical element at x2.5 optical concentration, and under Fresnel lens primary optical element concentration between x313 and x480. Measurements were taken in solar simulators at Cardiff and Jaén Universities, and on-sun with dual-axis tracking at Jaén University. The hybrid receivers were electrically, thermally and theoretically investigated. The electrical performance data for the cells under variable irradiance and cell temperature conditions were measured using the integrated thermoelectric module as both a temperature sensor and as a solid-state heat pump. The performance of six hybrid devices were evaluated within two 3-receiver strings under primary optical concentration with measured acceptance angles of 1.00° and 0.89°, similar to commercially sourced Concentrator Photovoltaic modules. A six-parameter one-diode equivalent electrical model was developed for the multi-junction cells under both primary and secondary optical concentration. This was applied to extract six model parameters with the experimental current–voltage curves of type A receiver at 1, 3 and 500 concentration ratios. Standard test conditions (1000 W/m2, 25 °C and Air Mass 1.5 Global spectrum) were assumed based on trust-region-reflective least squares algorithm in MATLAB. The model fitted the experimental current–voltage curves satisfactorily with a mean error of 4.44%. The combined primary and secondary optical intensity gain coefficient is as high as 0.92, in comparison with 0.50–0.86 for crossed compound parabolic concentrators. The determined values of diode reverse saturation current, combined series resistance and shunt resistance were similar to those of monocrystalline PV cell/modules in our previous publications. The model may be applicable to performance prediction of multi-junction CPV cells in the future.

Performance analysis of non-imaging Fresnel lens as a primary stage for CPV units

Fresnel lens is widely used in concentrating photovoltaic (CPV) systems as a primary optical element. It focuses sunlight on small solar cells or on the entrance apertures of secondary optical elements. In this work, we present a performance analysis of a non-imaging Fresnel lens as a primary optical element for different values of focal length. Results show, among others, the necessary use a secondary stage of concentration in order to achieve good performances in terms of the uniformity of the flux and a large acceptance angle compared with those of a Fresnel lens used alone.

Design and preliminary experiments of truncated ball lens as secondary optical element for CPV system

The Concentrated Photovoltaic (CPV) technology based on the use of high-efficiency multi-junction solar cells has higher power generation efficiency than other photovoltaic power generating technology. However, the cost and reliability of CPV technology are the primary reasons that restrict its progress. A truncated ball lens as a secondary optical element for CPV optical system is proposed in this paper to reduce the cost and improve the reliability. Theoretical analysis and experimental investigations were conducted on a concentrator with geometrical concentration ratio of 625×, a flat Fresnel lens as primary optical element and a truncated ball lens as secondary optical element. Test results show that the concentrator with power generation efficiency of 30.1% and acceptance angle of 0.73° can be obtained. Additionally, temperature effects of SOG lens on power generation are also studied.

Design optimization of ultra-high concentrator photovoltaic system using two-stage non-imaging solar concentrator

This paper presents a systematic approach for optimizing the design of ultra-high concentrator photovoltaic (UHCPV) system comprised of non-imaging dish concentrator (primary optical element) and crossed compound parabolic concentrator (secondary optical element). The optimization process includes the design of primary and secondary optics by considering the focal distance, spillage losses and rim angle of the dish concentrator. The imperfection factors, i.e. mirror reflectivity of 93%, lens’ optical efficiency of 85%, circumsolar ratio of 0.2 and mirror surface slope error of 2 mrad, were considered in the simulation to avoid the overestimation of output power. The proposed UHCPV system is capable of attaining effective ultra-high solar concentration ratio of 1475 suns and DC system efficiency of 31.8%.

Analysis of a novel design of uniformly illumination for Fresnel lens-based optical fiber daylighting system

Recently, advanced daylighting has become an important part of sustainable architecture design to increase visual comfort and illuminate deep interior spaces. Daylighting systems based on solar concentrators and fiber optical transmission have attracted a lot of research attention. In this paper, the authors propose a daylight collection and transmission design to transmit the concentrated light more uniformly into the optical fibers employing two optical elements: an eight-fold Fresnel lens as the primary optical element (POE) and an octagonal spherical fiber connector as the secondary optical element (SOE). In addition, a bi-layer prismatic optical panel acting as a diffuser is proposed in order to distribute light more uniformly in the interior space. The proposed designs of those optical elements are verified by ray-tracing simulation for achieving the required illumination level. The simulation results have shown that the combination of the proposed POE and SOE transmits light more uniformly into the bundle of optical fibers, and meanwhile the light diffuser provides relatively even illuminance distribution on a working plane. This shows a considerable advancement to the optical fiber daylighting designs. A case study shows the transmission efficiency of the proposed design is about 10% better than other common designs.

Ball lens as secondary optical element for CPV system

Various measures should be taken to optimize the performance, minimize the cost and improve the reliability of CPV concentrator. This paper presents theoretical analysis and experimental verification on a concentrator optical system with geometrical concentration ratio of 625× consisting of a Fresnel lens as primary optical element, a ball lens as secondary optical element and a solar receiver. The solar cell and the ball lens are separated by a small air gap in this proposed CPV system and the ball lens is mounted mechanically on the receiver to enhance the reliability of the CPV system. Test results show that a power generation efficiency of 30.3% and acceptance angle of 0.72° can be obtained for a CPV device with Fresnel lens, ball lens with AR coatings and solar cell with efficiency of 40%.

Deep-brain imaging via epi-fluorescence Computational Cannula Microscopy

Here we demonstrate widefield (field diameter = 200 μm) fluorescence microscopy and video imaging inside the rodent brain at a depth of 2 mm using a simple surgical glass needle (cannula) of diameter 0.22 mm as the primary optical element. The cannula guides excitation light into the brain and the fluorescence signal out of the brain. Concomitant image-processing algorithms are utilized to convert the spatially scrambled images into fluorescent images and video. The small size of the cannula enables minimally invasive imaging, while the long length (>2 mm) allow for deep-brain imaging with no additional complexity in the optical system. Since no scanning is involved, widefield fluorescence video at the native frame rate of the camera can be achieved.

Comparative study of two CPV optical concentrators, using a Fresnel lens as primary optical element

In this work, the performances of two optimized reflective secondary optics elements a CPC (Compound Parabolic Concentrator) and a Cone for use in a CPV concentrator system are studied using ray-tracing simulation for the same primary optical element: a Fresnel lens. These optical elements are compared in terms of concentration, acceptance angle, exit angle and output light distribution. Our results show that the power distribution at the end of the concentrator is more uniform in the case of the cone. The optical efficiency is higher when the secondary element is placed at a distance with f the focal length; R the input radius of the secondary optical element and θ the acceptance angle of the secondary optical element. Also, we found that the length and the input radius of each optical element decrease when the Fresnel lens diameter increases but the input radius of the CPC stills the larger. Finally, our calculation show that the CPC is longer than the cone while the Fresnel lens diameter is less than 200 mm and beyond this value both the cone and the CPC mostly present the same length.