Effect of soiling in CPV systems

The effect of soiling in flat PV modules has been already studied, causing a reduction of the electrical output of 4% on average. For CPV's, as far as soiling produces light scattering at the optical collector surface, the scattered rays should be definitively lost because they cannot be focused onto the receivers again. While the theoretical study becomes difficult because soiling is variable at different sites, it becomes easier to begin the monitoring of the real field performance of concentrators and then raise the following question: how much does the soiling affect to PV concentrators in comparison with flat panels?? The answers allow to predict the PV concentrator electrical performance and to establish a pattern of cleaning frequency. Some experiments have been conducted at the IES-UPM and CSES-ANU sites, consisting in linear reflective concentration systems, a point focus refractive concentrator and a flat module. All the systems have been measured when soiled and then after cleaning, achieving different increases of ISC. In general, results show that CPV systems are more sensitive to soiling than flat panels, accumulating losses in ISC of about 14% on average in three different tests conducted at IESUPM and CSES-ANU test sites in Madrid (Spain) and Canberra (Australia). Some concentrators can reach losses up to 26% when the system is soiled for 4 months of exposure.

Second international spectroradiometer intercomparison: preliminary results and impact on PV device calibration

This paper describes the preliminary results of an intercomparison of spectroradiometers for global (GNI) and direct normal incidence (DNI) irradiance in the visible (VIS) and near infrared (NIR) spectral regions together with an assessment of the impact these results may have on the calibration of triple-junction photovoltaic devices and on the relevant spectral mismatch calculation. The intercomparison was conducted by six European scientific laboratories and a Japanese industrial partner. Seven institutions and seven spectroradiometer systems, representing different technologies and manufacturers were involved, representing a good cross section of the todays available instrumentation for solar spectrum measurements.

An open-source simulation tool of grid-connected PV systems.

This paper will present an open-source simulation tool, which is being developed in the frame of an European research project1. The tool, whose final version will be freely available through a website, allows the modelling and the design of different types of grid-connected PV systems, such as large grid-connected plants and building-integrated installations. The tool is based on previous software developed by the IES-UPM2, whose models and energy losses scenarios have been validated in the commissioning of PV projects3 carried out in Spain, Portugal, France and Italy, whose aggregated capacity is nearly 300MW. This link between design and commissioning is one of the key points of tool presented here, which is not usually addressed by present commercial software. The tool provides, among other simulation results, the energy yield, the analysis and breakdown of energy losses, and the estimations of financial returns adapted to the legal and financial frameworks of each European country. Besides, educational facilities will be developed and integrated in the tool, not only devoted to learn how to use this software, but also to train the users on the best design PV systems practices. The tool will also include the recommendation of several PV community experts, which have been invited to identify present necessities in the field of PV systems simulation. For example, the possibility of using meteorological forecasts as input data, or modelling the integration of large energy storage systems, such as vanadium redox or lithium-ion batteries. Finally, it is worth mentioning that during the verification and testing stages of this software development, it will be also open to the suggestions received from the different actors of the PV community, such as promoters, installers, consultants, etc.

Automatic detection of PV systems failures from monitoring validated on 10,000 BIPV systems in Europe

The installers and owners show a growing interest in the follow-up of the performance of their photovoltaic (PV) systems. The owners are requesting reliable sources of information to ensure that their system is functioning properly, and the installers are actively looking for efficient ways of providing them the most useful possible information from the data available. Policy makers are becoming increasingly interested in the knowledge of the real performance of PV systems and the most frequent sources of problems that they suffer to be able to target the identified challenges properly. The scientific and industrial PV community is also requiring an access to massive operational data to pursue the technological improvements further.

Variable impedance LED matrix control system for lamps in PV applications

The interest in LED lighting has been growing recently due to the high efficacy, lifelime and ruggedness that this technology offers. However the key element to guarantee those parameters with these new electronic devices is to keep under control the working temperature of the semiconductor crystal. This paper propases a LED lamp design that fulfils the requ irements of a PV lighting systems, whose main quality criteria is reliability. It uses directly as a power supply a non·stabilized constant voltage source, as batteries. An electronic control architecture is used to regulate the current applied to the LEO matri)( according to their temperature and the voltage output value of the batteries with two pulse modulation signals (PWM) signals. The first one connects and disconnects the LEOs to the power supply and the second one connects and disconnects several emitters to the electric circuit changing its overall impedance. A prototype of the LEO lamp has been implemented and tested at different temperaturas and battery voltages.

A 500-kW pv generator I-V curve

This paper presents the measurement of the I-V curve of a 500-kW PV generator by means of an own-made capacitive load. It is shown that I-V curve analysis can also be applied to big PV generators and that when measuring the operation conditions with reference modules and taking some precautions (especially regarding the operation cell temperature), it is still a useful tool for characterizing them and therefore can be incorporated into maintenance procedures. As far as we know, this is the largest I-V curve measured so far.

Field experiment of 800× off-axis XR-Köhler concentrator module on a carousel tracker

This paper presents the design and preliminary experimental results of a concentrator-type photovoltaic module based on a free-form off-axis 800×XR-Köhler concentrator. The off-axis XR-Köhler concentrator is one of the advanced concentrators that perform high concentration with a large acceptance angle and excellent irradiance uniformity on a solar cell. As a result of on-sun characterization of the unglazed single-cell unit test rig, the temperature-corrected DC module efficiency was 32.2% at 25 °C without an anti-reflective (AR) coating on the secondary optics, and the acceptance angle was more than ±1.0°. In addition, the non-corrected DC efficiency of an individual cell in a glazed 8-cell unit module mounted on a carousel tracking system was measured. The individual efficiency deviated in the range of 24.3-27.4%, owing to the mirror shape and alignment errors. The resultant series-connected efficiency was approximately 25% at direct normal irradiation (DNI) of 770 W/m2.

Light regulates motility, attachment and virulence in the plant pathogen Pseudomonas syringae pv tomato DC3000.

Pseudomonas syringae pv tomato DC3000 (Pto) is the causal agent of the bacterial speck of tomato, which leads to significant economic losses in this crop. Pto inhabits the tomato phyllosphere, where the pathogen is highly exposed to light, among other environmental factors. Light represents a stressful condition and acts as a source of information associated with different plant defence levels. Here, we analysed the presence of both blue and red light photoreceptors in a group of Pseudomonas. In addition, we studied the effect of white, blue and red light on Pto features related to epiphytic fitness. While white and blue light inhibit motility, bacterial attachment to plant leaves is promoted. Moreover, these phenotypes are altered in a blue-light receptor mutant. These light-controlled changes during the epiphytic stage cause a reduction in virulence, highlighting the relevance of motility during the entry process to the plant apoplast. This study demonstrated the key role of light perception in the Pto phenotype switching and its effect on virulence.

Review and Comparison of Step-Up Transformerless Topologies for Photovoltaic AC-Module Application

This paper presents a comprehensive review of stepup single-phase non-isolated inverters suitable for ac-module applications. In order to compare the most feasible solutions of the reviewed topologies, a benchmark is set. This benchmark is based on a typical ac-module application considering the requirements for the solar panels and the grid. The selected solutions are designed and simulated complying with the benchmark obtaining passive and semiconductor components ratings in order to perform a comparison in terms of size and cost. A discussion of the analyzed topologies regarding the obtained ratings as well as ground currents is presented. Recommendations for topological solutions complying with the application benchmark are provided.

Good and bad practices in pv plants

The PVCROPS project (PhotoVolta ic Cost r€duction, Reliability, Operational performance, Prediction and Simulation), cofinanced by European Commission in the frame of Seventh Framework Programme, has compiled in the “Good and bad practices: Manual to improve the quality and reduce the cost of PV systems” a collection of good and bad practices in actual PV plants . All the situations it collects represent the state-of-the-art of existing PV installations all around Europe. They show how the different parts of an installation can be implem ented properly or not. The aim of this manual is to represent a reference text which can help any PV actor (installers, electricians, maintenance operators, owners, etc.) not only to check and improve an already existing installation but will also, and mainly, avoid the previously known bad practices for the construction of a new PV installation. Thus, solving a priori the known errors, new PV installations will be more reliable, efficient and cost-effective and can recover the initial investment in a shorter time. The manual is going to be free available in the PVCROPS website in several languages.

New concepts and techniques for the development of high-efficiency concentrating photovoltaic modules

El interés por los sistemas fotovoltaicos de concentración (CPV) ha resurgido en los últimos años amparado por el desarrollo de células multiunión de muy alta eficiencia basadas en semiconductores de los grupos III-V. Estas células han permitido obtener módulos de concentración con eficiencias que prácticamente duplican las del panel plano y que llegan al 35% en los módulos récord. Esta tesis está dedicada al diseño y la implementación experimental de nuevos conceptos que permitan obtener módulos CPV que no sólo alcancen una eficiencia alta en condiciones estándar sino que, además, sean lo suficientemente tolerantes a errores de montaje, seguimiento, temperatura y variaciones espectrales para que la energía que producen a lo largo del año sea máxima. Una de las primeras cuestiones que se abordan es el diseño de elementos ópticos secundarios para sistemas cuyo primario es una lente de Fresnel y que permiten, para una concentración fija, aumentar el ángulo de aceptancia y la tolerancia del sistema. Varios secundarios reflexivos y refractivos han sido diseñados y analizados mediante trazado de rayos. En particular, utilizando óptica anidólica y basándose en el diseño de una sola etapa conocido como ‘concentrador dieléctrico que funciona por reflexión total interna‘, se ha diseñado, fabricado y caracterizado un secundario con salida cuadrada que, usado junto con una lente de Fresnel, permite alcanzar simultáneamente una elevada eficiencia, concentración y aceptancia. Además, se ha propuesto y prototipado un método alternativo de fabricación para otro de los secundarios, denominado domo, consistente en el sobremoldeo de silicona sobre células solares. Una de las características que impregna todo el trabajo realizado en esta tesis es la aproximación holística en el diseño de módulos CPV, es decir, se ha prestado especial atención al diseño conjunto de la célula y la óptica para garantizar que el sistema total alcance la mayor eficiencia posible. En este sentido muchos sistemas ópticos desarrollados en esta tesis han sido diseñados, caracterizados y optimizados teniendo en cuenta que el ajuste de corriente entre las distintas subcélulas que comprenden la célula multiunión bajo el concentrador sea muy próximo a uno. La capa antirreflectante sobre la célula funciona, en cierto modo, como interfaz entre la óptica y la célula, por lo que se ha diseñado un método de optimización de capas antirreflectantes que considera no sólo el amplio rango de longitudes de onda para el que las células multiunión son sensibles sino también la distribución angular de intensidad sobre la célula creada por la óptica de concentración. Además, la cuestión de la falta de uniformidad también se ha abordado mediante la comparación de las distribuciones espectrales y espaciales de irradiancia que crean diferentes ópticas (simuladas mediante trazado de rayos y fotografiadas) y las pérdidas de eficiencia que experimentan las células iluminadas por dichas ópticas de concentración medidas experimentalmente. El efecto de la temperatura en la óptica de concentración también ha sido objeto de estudio de esta tesis. En particular, mediante simulaciones de elementos finitos se han dado los primeros pasos para el análisis de las deformaciones que sufren los dientes de las lentes de Fresnel híbridas (vidrio-silicona), así como el cambio de índice de refracción con la temperatura y la influencia de ambos efectos sobre el funcionamiento de los sistemas. Se ha implementado un modelo que tiene por objeto considerar las variaciones ambientales, principalmente temperatura y contenido espectral de la radiación directa, así como las sensibilidades térmica y espectral de los sistemas CPV, con el fin de maximizar la energía producida por un módulo de concentración a lo largo de un año en un emplazamiento determinado. Los capítulos 5 y 6 de este libro están dedicados al diseño, fabricación y caracterización de un nuevo concepto de módulo fotovoltaico denominado FluidReflex y basado en una única etapa reflexiva con dieléctrico fluido. En este nuevo concepto la presencia del fluido aporta algunas ventajas significativas como son: un aumento del producto concentración por aceptancia (CAP, en sus siglas en inglés) alcanzable al rodear la célula con un medio cuyo índice de refracción es mayor que uno, una mejora de la eficiencia óptica al disminuir las pérdidas por reflexión de Fresnel en varias interfaces, una mejora de la disipación térmica ya que el calor que se concentra junto a la célula se trasmite por convección natural y conducción en el fluido y un aislamiento eléctrico mejorado. Mediante la construcción y medida de varios prototipos de unidad elemental se ha demostrado que no existe ninguna razón fundamental que impida la implementación práctica del concepto teórico alcanzando una elevada eficiencia. Se ha realizado un análisis de fluidos candidatos probando la existencia de al menos dos de ellos que cumplen todos los requisitos (en particular el de estabilidad bajo condiciones de luz concentrada) para formar parte del sistema de concentración FluidReflex. Por ´ultimo, se han diseñado, fabricado y caracterizado varios prototipos preindustriales de módulos FluidReflex para lo cual ha sido necesario optimizar el proceso de fabricación de la óptica multicavidad a fin de mantener el buen comportamiento óptico obtenido en la fabricación de la unidad elemental. Los distintos prototipos han sido medidos, tanto en el laboratorio como bajo el sol real, analizando el ajuste de corriente de la célula iluminada por el concentrador FluidReflex bajo diferentes distribuciones espectrales de la radiación incidente así como el excelente comportamiento térmico del módulo. ABSTRACT A renewed interest in concentrating photovoltaic (CPV) systems has emerged in recent years encouraged by the development of high-efficiency multijunction solar cells based in IIIV semiconductors that have led to CPV module efficiencies which practically double that of flat panel PV and which reach 35% for record modules. This thesis is devoted to the design and experimental implementation of new concepts for obtaining CPV modules that not only achieve high efficiency under standard conditions but also have such a wide tolerance to assembly errors, tracking, temperature and spectral variations, that the energy generated by them throughout the year is maximized. One of the first addressed issues is the design of secondary optical elements whose primary optics is a Fresnel lens and which, for a fixed concentration, allow an increased acceptance angle and tolerance of the system. Several reflective and refractive secondaries have been designed and analyzed using ray tracing. In particular, using nonimaging optics and based on the single-stage design known as ‘dielectric totally internally reflecting concentrator’, a secondary with square output has been designed, fabricated and characterized. Used together with a Fresnel lens, the secondary can simultaneously achieve high efficiency, concentration and acceptance. Furthermore, an alternative method has been proposed and prototyped for the fabrication of the secondary named dome. The optics is manufactured by direct overmolding of silicone over the solar cells. One characteristic that permeates all the work done in this thesis is the holistic approach in the design of CPV modules, meaning that special attention has been paid to the joint design of the solar cell and the optics to ensure that the total system achieves the highest attainable efficiency. In this regard, many optical systems developed in the thesis have been designed, characterized and optimized considering that the current matching among the subcells within the multijunction solar cell beneath the optics must be close to one. Antireflective coating over the cell acts, somehow, as an interface between the optics and the cell. Consequently, a method has been designed to optimize antireflective coatings that takes into account not only the broad wavelength range that multijunction solar cells are sensitive to but also the angular intensity distribution created by the concentrating optics. In addition, the issue of non-uniformity has also been addressed by comparing the spectral and spatial distributions of irradiance created by different optics (simulated by ray tracing and photographed) and the efficiency losses experienced by cells illuminated by those concentrating optics experimentally determined. The effect of temperature on the concentrating optics has also been studied in this thesis. In particular, finite element simulations have been use to analyze the deformations experienced by the facets of hybrid (silicon-glass) Fresnel lenses, the change of refractive index with temperature and the influence of both effects on the system performance. A model has been implemented which take into consideration atmospheric variations, mainly temperature and spectral content of the direct normal irradiance, as well as thermal and spectral sensitivities of systems, with the aim of maximizing the energy harvested by a CPV module throughout the year in a particular location. Chapters 5 and 6 of this book are devoted to the design, fabrication, and characterization of a new concentrator concept named FluidReflex and based on a single-stage reflective optics with fluid dielectric. In this new concept, the presence of the fluid provides some significant advantages such as: an increased concentration acceptance angle product (CAP) achievable by surrounding the cell with a medium whose refractive index is greater than one, an improvement of the optical efficiency by reducing losses due to Fresnel reflection at several interfaces, an improvement in heat dissipation as the heat concentrated near the cell is transmitted by natural convection and conduction in the fluid, and an improved electrical insulation. By fabricating and characterizing several elementary-unit prototypes it was shown that there is no fundamental reason that prevents the practical implementation of this theoretical concept reaching high efficiency. Several fluid candidates were investigated proving the existence of at least to fluids that meet all the requirements (including the stability under concentrated light) to become part of the FluidReflex concentrator. Finally, several pre-industrial FluidReflex module prototypes have been designed and fabricated. An optimization process for the manufacturing of the multicavity optics was necessary to attain such an optics quality as the one achieved by the single unit. The module prototypes have been measured, both indoors and outdoors, analyzing the current matching of the solar cells beneath the concentrator for different spectral distribution of the incident irradiance. Additionally, the module showed an excellent thermal performance.

Enhancing iDynoMiCS framework with a plasmid conjugation module

Actualmente existen aplicaciones que permiten simular el comportamiento de bacterias en distintos hábitats y los procesos que ocurren en estos para facilitar su estudio y experimentación sin la necesidad de un laboratorio. Una de las aplicaciones de software libre para la simulación de poblaciones bacteriológicas mas usada es iDynoMiCS (individual-based Dynamics of Microbial Communities Simulator), un simulador basado en agentes que permite trabajar con varios modelos computacionales de bacterias en 2D y 3D. Este simulador permite una gran libertad al configurar una numerosa cantidad de variables con respecto al entorno, reacciones químicas y otros detalles importantes. Una característica importante es el poder simular de manera sencilla la conjugación de plásmidos entre bacterias. Los plásmidos son moléculas de ADN diferentes del cromosoma celular, generalmente circularles, que se replican, transcriben y conjugan independientemente del ADN cromosómico. Estas están presentes normalmente en bacterias procariotas, y en algunas ocasiones en eucariotas, sin embargo, en este tipo de células son llamados episomas. Dado el complejo comportamiento de los plásmidos y la gama de posibilidades que estos presentan como mecanismos externos al funcionamiento básico de la célula, en la mayoría de los casos confiriéndole distintas ventajas evolutivas, como por ejemplo: resistencia antibiótica, entre otros, resulta importante su estudio y subsecuente manipulación. Sin embargo, el marco operativo del iDynoMiCS, en cuanto a simulación de plásmidos se refiere, es demasiado sencillo y no permite realizar operaciones más complejas que el análisis de la propagación de un plásmido en la comunidad. El presente trabajo surge para resolver esta deficiencia de iDynomics. Aquí se analizarán, desarrollarán e implementarán las modificaciones necesarias para que iDynomics pueda simular satisfactoriamente y mas apegado a la realidad la conjugación de plásmidos y permita así mismo resolver distintas operaciones lógicas, como lo son los circuitos genéticos, basadas en plásmidos. También se analizarán los resultados obtenidos de acuerdo a distintos estudios relevantes y a la comparación de los resultados obtenidos con el código original de iDynomics. Adicionalmente se analizará un estudio comparando la eficiencia de detección de una sustancia mediante dos circuitos genéticos distintos. Asimismo el presente trabajo puede tener interés para el grupo LIA de la Facultad de Informática de la Universidad Politécnica de Madrid, el cual está participando en el proyecto europeo BACTOCOM que se centra en el estudio de la conjugación de plásmidos y circuitos genéticos. --ABSTRACT--Currently there are applications that simulate the behavior of bacteria in different habitats and the ongoing processes inside them to facilitate their study and experimentation without the need for an actual laboratory. One of the most used open source applications to simulate bacterial populations is iDynoMiCS (individual-based Dynamics of Microbial Communities Simulator), an agent-based simulator that allows working with several computer models of 2D and 3D bacteria in biofilms. This simulator allows great freedom by means of a large number of configurable variables regarding environment, chemical reactions and other important details of the simulation. Within these characteristics there exists a very basic framework to simulate plasmid conjugation. Plasmids are DNA molecules physically different from the cell’s chromosome, commonly found as small circular, double-stranded DNA molecules that are replicated, conjugated and transcribed independently of chromosomal DNA. These bacteria are normally present in prokaryotes and sometimes in eukaryotes, which in this case these cells are called episomes. Plasmids are external mechanisms to the cells basic operations, and as such, in the majority of the cases, confer to the host cell various evolutionary advantages, like antibiotic resistance for example. It is mperative to further study plasmids and the possibilities they present. However, the operational framework of the iDynoMiCS plasmid simulation is too simple, and does not allow more complex operations that the analysis of the spread of a plasmid in the community. This project was conceived to resolve this particular deficiency in iDynomics, moreover, in this paper is discussed, developed and implemented the necessary changes to iDynomics simulation software so it can satisfactorily and realistically simulate plasmid conjugation, and allow the possibility to solve various ogic operations, such as plasmid-based genetic circuits. Moreover the results obtained will be analyzed and compared with other relevant studies and with those obtained with the original iDynomics code. Conjointly, an additional study detailing the sensing of a substance with two different genetic circuits will be presented. This work may also be relevant to the LIA group of the Faculty of Informatics of the Polytechnic University of Madrid, which is participating in the European project BACTOCOM that focuses on the study of the of plasmid conjugation and genetic circuits.

Energy Management Module for Mobile Robots in Hostile Environments

In hostile environments at CERN and other similar scientific facilities, having a reliable mobile robot system is essential for successful execution of robotic missions and to avoid situations of manual recovery of the robots in the event that the robot runs out of energy. Because of environmental constraints, such mobile robots are usually battery-powered and hence energy management and optimization is one of the key challenges in this field. The ability to know beforehand the energy consumed by various elements of the robot (such as locomotion, sensors, controllers, computers and communication) will allow flexibility in planning or managing the tasks to be performed by the robot.

Bankable procedures for the technical quality assurance of large scale PV plants

Strict technical quality assurance procedures are essential for PV plant bankability. When large-scale PV plants are concerned, this is typically accomplished in three consecutive phases: an energy yield forecast, that is performed at the beginning of the project and is typically accomplished by means of a simulation exercise performed with dedicated software; a reception test campaign, that is performed at the end of the commissioning and consists of a set of tests for determining the efficiency and the reliability of the PV plant devices; and a performance analysis of the first years of operation, that consists in comparing the real energy production with the one calculated from the recorded operating conditions and taking into account the maintenance records. In the last six years, IES-UPM has offered both indoor and on-site quality control campaigns for more than 60 PV plants, with an accumulated power of more than 300 MW, in close contact with Engineering, Procurement and Construction Contractors and financial entities. This paper presents the lessons learned from such experience.

Optimizing PV use through active demand side management

With recent technological developments within the field of power conditioning and the progressive decrease of incentives for PV electricity in grid-connected markets, new operation modes for PV systems should be explored beyond the traditional maximization of PV electri city feed-in. An example can be found in the domestic sector, where the use of modern PV hybrid systems combin ed with efficient electrical appliances and demand side management strategies can significantly enhance the PV value for the user. This paper presents an active demand side management system able to displace the consumer’s load curve in response to local (PV hybrid system, user) and external conditions (external grid). In this way, th e consumer becomes an “active consumer” that can also cooperate with others and the grid, increasing even more the PV value for the electrical system.