Photovoltaïque à concentration : optimisation de l'étage secondaire

Concentrating Photovoltaics (CPV) is one of the most promising ways to generate clean energy at potentially reduced costs. The main idea is to use optical elements to concentrate the solar rays on a multi-junction solar cells to take advantage of their high efficiencies. Concentrators for CPV can have very different architectures and optical elements, resulting in a wide variety of possible designs. A typical optical architecture for a CPV concentrator is formed by: a first optical element called the primary optical element (POE) which collects the direct rays of the sun, it can be either refractive or reflective. And a secondary optical element (SOE) that receives light from the primary and sends it to the cell. The main role of this element in a CPV unit is to broaden the angle of acceptance and to homogenize the irradiance distribution on the solar cell. Our research thematic deals with this kind of solar concentrators, it concerns the design, testing and optimization of two-stage CPV units, that use a Fresnel lens as POE. After a detailed bibliographic study, we carried out a comparative study of four solar concentrators dedicated to high concentration photovoltaic systems. These four concentrators are formed from the same Fresnel lens associated to four secondaries: a compound parabolic concentrator (CPC), a crossed compound parabolic concentrator (CCPC), a pyramid and a cone. Four materials with different refractive indices were considered. The Fresnel lens has a diameter d = 350mm and a focal length f = 265mm. Our simulations are performed using the TracePro ray tracing software. The results showed that the pyramid was the best performing SOE. For the experimental test we designed small size prototypes, a parametric analysis was carried out to highlight the main performances of the secondary element, as it is the most critical element in the CPV unit. Experimental set ups have been realized for the indoor and outdoor measurements and characterization of the prototypes. The results show that the measured optical efficiencies and acceptance angles of the CPV units were very close to those obtained by optical simulations. The pyramid gives the best optical efficiency and the widest angle of acceptance. Electrical measurements also confirmed that the best solution for the secondary optic is the pyramid because it shows the higher electrical power and the efficiency. The optical and electrical efficiencies reach respectively 80,81% and 30.77%, these results correspond to the best efficiencies recorded in the literature.Le Photovoltaïque à concentration (CPV) est l’un des moyens les plus prometteurs de générer l’énergie propre à des coûts potentiellement très réduits. Son idée consiste principalement à utiliser des éléments optiques pour concentrer les rayons solaires sur des cellules multi-jonctions de petites tailles pour profiter de leurs rendements élevés. Une architecture optique typique pour un concentrateur CPV est formée par : un premier élément optique appelé élément optique primaire qui recueille les rayons directs du soleil, il peut être soit réfractif ou réfléchissant. Et un élément optique secondaire qui reçoit la lumière du primaire et la renvoie à la cellule, l’ajout de cet élément dans un système CPV aide à élargir l’angle d’acceptance et à homogénéiser la distribution de l’irradiance sur la cellule. C’est dans ce contexte que s’inscrit notre travail de recherche qui porte sur le CPV à deux étages à base des lentilles de Fresnel comme POE et de différentes formes géométriques comme secondaire. Nous avons réalisé une étude comparative de quatre concentrateurs à base de la lentille de Fresnel, dédiés aux systèmes photovoltaïques à haute concentration. Ces quatre concentrateurs sont formés de la même lentille de Fresnel comme élément optique primaire et quatre secondaires : CPC, CCPC, pyramide et cône. Quatre matériaux avec des indices de réfraction différents ont été considérés. La lentille a un diamètre d = 350mm et une distance focale f = 265mm. Nos simulations sont effectuées à l’aide du logiciel de traçage de rayons TracePro. Les résultats ont montré que la pyramide était le SOE le plus performant. Pour les tests expérimentaux nous avons conçu des prototypes de petites tailles, une analyse paramétrique a été réalisée pour mettre en évidence les principales performances de l’élément secondaire. Des bancs de mesure ont été montés pour comparer les efficacités optiques et électriques des différents prototypes. Les résultats montrent que les rendements optiques mesurés et les angles d’acceptance des unités CPV étaient très proches de ceux des simulations optiques. La pyramide offre la meilleure efficacité optique (80,81%) et le plus grand angle d’acceptance (2,03°). Les mesures électriques ont également confirmé que la meilleure solution pour l’optique secondaire est la pyramide car elle accorde une puissance et un rendement électriques plus élevés. Les efficacité optique et électrique obtenues sont respectivement 80,81% et 31%, ces résultats correspondent aux meilleures efficacités enregistrées dans la littérature

Concentrated photovoltaics : optimization of the second stage

Le Photovoltaïque à concentration (CPV) est l’un des moyens les plus prometteurs de générer l’énergie propre à des coûts potentiellement très réduits. Son idée consiste principalement à utiliser des éléments optiques pour concentrer les rayons solaires sur des cellules multi-jonctions de petites tailles pour profiter de leurs rendements élevés. Une architecture optique typique pour un concentrateur CPV est formée par : un premier élément optique appelé élément optique primaire qui recueille les rayons directs du soleil, il peut être soit réfractif ou réfléchissant. Et un élément optique secondaire qui reçoit la lumière du primaire et la renvoie à la cellule, l’ajout de cet élément dans un système CPV aide à élargir l’angle d’acceptance et à homogénéiser la distribution de l’irradiance sur la cellule. C’est dans ce contexte que s’inscrit notre travail de recherche qui porte sur le CPV à deux étages à base des lentilles de Fresnel comme POE et de différentes formes géométriques comme secondaire. Nous avons réalisé une étude comparative de quatre concentrateurs à base de la lentille de Fresnel, dédiés aux systèmes photovoltaïques à haute concentration. Ces quatre concentrateurs sont formés de la même lentille de Fresnel comme élément optique primaire et quatre secondaires : CPC, CCPC, pyramide et cône. Quatre matériaux avec des indices de réfraction différents ont été considérés. La lentille a un diamètre d = 350mm et une distance focale f = 265mm. Nos simulations sont effectuées à l’aide du logiciel de traçage de rayons TracePro. Les résultats ont montré que la pyramide était le SOE le plus performant. Pour les tests expérimentaux nous avons conçu des prototypes de petites tailles, une analyse paramétrique a été réalisée pour mettre en évidence les principales performances de l’élément secondaire. Des bancs de mesure ont été montés pour comparer les efficacités optiques et électriques des différents prototypes. Les résultats montrent que les rendements optiques mesurés et les angles d’acceptance des unités CPV étaient très proches de ceux des simulations optiques. La pyramide offre la meilleure efficacité optique (80,81%) et le plus grand angle d’acceptance (2,03°). Les mesures électriques ont également confirmé que la meilleure solution pour l’optique secondaire est la pyramide car elle accorde une puissance et un rendement électriques plus élevés. Les efficacité optique et électrique obtenues sont respectivement 80,81% et 31%, ces résultats correspondent aux meilleures efficacités enregistrées dans la littérature.Concentrating Photovoltaics (CPV) is one of the most promising ways to generate clean energy at potentially reduced costs. The main idea is to use optical elements to concentrate the solar rays on a multi-junction solar cells to take advantage of their high efficiencies. Concentrators for CPV can have very different architectures and optical elements, resulting in a wide variety of possible designs. A typical optical architecture for a CPV concentrator is formed by: a first optical element called the primary optical element (POE) which collects the direct rays of the sun, it can be either refractive or reflective. And a secondary optical element (SOE) that receives light from the primary and sends it to the cell. The main role of this element in a CPV unit is to broaden the angle of acceptance and to homogenize the irradiance distribution on the solar cell. Our research thematic deals with this kind of solar concentrators, it concerns the design, testing and optimization of two-stage CPV units, that use a Fresnel lens as POE. After a detailed bibliographic study, we carried out a comparative study of four solar concentrators dedicated to high concentration photovoltaic systems. These four concentrators are formed from the same Fresnel lens associated to four secondaries: a compound parabolic concentrator (CPC), a crossed compound parabolic concentrator (CCPC), a pyramid and a cone. Four materials with different refractive indices were considered. The Fresnel lens has a diameter d = 350mm and a focal length f = 265mm. Our simulations are performed using the TracePro ray tracing software. The results showed that the pyramid was the best performing SOE. For the experimental test we designed small size prototypes, a parametric analysis was carried out to highlight the main performances of the secondary element, as it is the most critical element in the CPV unit. Experimental set ups have been realized for the indoor and outdoor measurements and characterization of the prototypes. The results show that the measured optical efficiencies and acceptance angles of the CPV units were very close to those obtained by optical simulations. The pyramid gives the best optical efficiency and the widest angle of acceptance. Electrical measurements also confirmed that the best solution for the secondary optic is the pyramid because it shows the higher electrical power and the efficiency. The optical and electrical efficiencies reach respectively 80,81% and 30.77%, these results correspond to the best efficiencies recorded in the literature

Photovoltaic Concentration: Research and Development

International audienceConcentrator Photovoltaic (CPV) technology, by using efficient optical elements, small sizes and high efficiency multi-junction solar cells, can be seen as a bright energy source to produce more cost-effective electricity. The main and basic idea is to replace the use of expensive solar cells with less expensive optical elements made from different materials. This paper aims to give to the readers a rapid and concise overview of CPV and the main characteristics to be considered when designing a CPV system. It reviews the main optical configurations presented in the literature, their advantages and drawbacks, as well as the recent progress in the concentration ratio and the major performances achieved in the field. The paper considers the more recent works, their optical designs, as well as their optical and electrical performances. It also relates the major achievements on the industrial side with the major milestones in CPV developments

Optimal design of a dielectric totally internally reflecting concentrator for CPV units

International audienceThe aim of the presented work is to determine the optimum height and front surface arc angle of dielectric totally and internally reflecting concentrator associated with a Fresnel lens for solar concentrators used in photovoltaic systems. Ray tracing technique was used to simulate the optical characteristics of this CPV unit with various design parameters. An optimum concentrator was determined by varying sizes of the secondary optic and using two materials: the Fused Silica and the BK7

Indoor characterization of pyramid- and cone-type secondary optics

International audienceTwo stages optical concentrators for concentrated photovoltaic (CPV) are studied both experimentally and theoretically. They are composed of a Fresnel lens made of PMMA and coupled to two different secondary optical elements (SOEs) types: a pyramid and a cone made of fused silica. Results, in terms of optical efficiency and acceptance angle, show that the pyramid-type is the best choice for the secondary optical element

Analyzing the soybean transcriptome during autoregulation of mycorrhization identifies the transcription factors GmNF-YA1a/b as positive regulators of arbuscular mycorrhization

Background: Similarly to the legume-rhizobia symbiosis, the arbuscular mycorrhiza interaction is controlled by autoregulation representing a feedback inhibition involving the CLAVATA1-like receptor kinase NARK in shoots. However, little is known about signals and targets down-stream of NARK. To find NARK-related transcriptional changes in mycorrhizal soybean (Glycine max) plants, we analyzed wild-type and two nark mutant lines interacting with the arbuscular mycorrhiza fungus Rhizophagus irregularis.Results: Affymetrix GeneChip analysis of non-inoculated and partially inoculated plants in a split-root system identified genes with potential regulation by arbuscular mycorrhiza or NARK. Most transcriptional changes occur locally during arbuscular mycorrhiza symbiosis and independently of NARK. RT-qPCR analysis verified nine genes as NARK-dependently regulated. Most of them have lower expression in roots or shoots of wild type compared to nark mutants, including genes encoding the receptor kinase GmSIK1, proteins with putative function as ornithine acetyl transferase, and a DEAD box RNA helicase. A predicted annexin named GmAnnx1a is differentially regulated by NARK and arbuscular mycorrhiza in distinct plant organs. Two putative CCAAT-binding transcription factor genes named GmNF-YA1a and GmNF-YA1b are down-regulated NARK-dependently in non-infected roots of mycorrhizal wild-type plants and functional gene analysis confirmed a positive role for these genes in the development of an arbuscular mycorrhiza symbiosis. Conclusions: Our results indicate GmNF-YA1a/b as positive regulators in arbuscular mycorrhiza establishment, whose expression is down-regulated by NARK in the autoregulated root tissue thereby diminishing subsequent infections. Genes regulated independently of arbuscular mycorrhization by NARK support an additional function of NARK in symbioses-independent mechanisms