A hardware field simulator for photovoltaic materials applications.

2006/2007Il presente lavoro riguarda la descrizione di un simulatore di campo fotovoltaico (in seguito simulatore). Il simulatore è un convertitore elettronico di potenza che, alimentato dalla rete elettrica, riproduce la caratteristica tensione corrente di un campo fotovoltaico (insieme di moduli fotovoltaici connessi in serie e in parallelo) operante in condizioni climatiche di temperatura e irraggiamento arbitrarie. Il nuovo dispositivo verrà impiegato nell’ambito del laboratorio fotovoltaico cui fa riferimento l’impianto in via di realizzazione sul tetto dell’edificio che ospita il Dipartimento dei Materiali e delle Risorse Naturali dell’Università di Trieste. Il simulatore viene proposto come utile strumento per i progettisti di dispositivi solari funzionanti in sistemi fotovoltaici connessi in rete. In particolare, il simulatore permetterà di prevedere il funzionamento di nuovi moduli fotovoltaici operanti in condizioni di ombreggiamento arbitrario e inseriti in un sistema fotovoltaico reale. L’uso del simulatore sarà particolarmente efficace nel caso di simulazioni di tecnologie in film sottile come, ad esempio, il silicio amorfo, il tellururo di cadmio, ecc. Il simulatore sarà anche necessario per testare i componenti che fanno parte di un sistema fotovoltaico connesso in rete, con particolare riferimento ai sistemi di condizionamento della potenza (detti anche inverter). Tali sistemi, oltre a convertire la tensione continua prodotta dai moduli fotovoltaici in una tensione compatibile e sincronizzata con quella della rete, devono garantire istante per istante l’inseguimento del punto di massima potenza estraibile dal campo fotovoltaico cui sono connessi. Il lavoro è stato suddiviso in cinque capitoli. Il primo capitolo fornisce una breve descrizione dello stato dell’arte e di alcune aspetti economici relativi alla tecnologia fotovoltaica. Nel secondo capitolo vengono richiamati il modello classico di una cella solare e le definizioni riguardo le sue caratteristiche principali (punto di massima potenza, efficienza, fill factor, ecc.). Nello stesso capitolo un’overview sui materiali e sulle tecnologie utilizzate nella realizzazione dei dispositivi fotovoltaici divide, come suggerito da Martin Green, le celle solari in tre diverse generazioni: la prima comprende i dispositivi realizzati in silicio cristallino (mono e policrisallino), la seconda quelli in film sottile (in silicio amorfo, tellururo di cadmio CdTe, diseleniuro di rame e indio CIS, diseleniuro di rame, indio e gallio CIGS, diseleniuro di rame, indio, gallio e zolfo CIGSS) e le celle di Graetzel, e la terza le celle multigiunzione, a banda intermedia e quelle organiche. Nel capitolo tre viene fornita una descrizione dei componenti costituenti un sistema fotovoltaico connesso in rete e viene proposto un nuovo metodo per la determinazione delle caratteristiche corrente tensione e potenza tensione prodotte da dispositivi fotovoltaici. Il metodo risulta efficace in quanto non necessita di misure sperimentali da effetture sui diversi dispositivi. I dati forniti nei comuni data sheet che vengono forniti a corredo dei moduli fotovoltaici sono sufficienti a determinarne il comportamento al variare della temperatura di funzionamento e del livello di radiazione solare. L’efficienza di un sistema fotovoltaico (Balance Of the System, BOS) viene calcolata nel capitolo quattro. Particolare enfasi viene data all’effetto di mismatching che è tanto più importante quanto più è elevato il livello di ombreggiamento presente sul piano dei moduli fotovoltaici costituenti l’impianto. Infine, l’ultimo capitolo riguarda la descrizione del simulatore e delle sue applicazioni.The subject of this work is a power electronic device, hereafter named photovoltaic field simulator, which converts the grid voltage into a current voltage characteristic. This characteristic replicates the behavior of a real photovoltaic field working in arbitrary conditions of irradiance and temperature. After building, the photovoltaic field simulator will be used in the photovoltaic laboratory which is connected to the experimental photovoltaic plant which will be installed on the roof top of the Materials and Natural Resources Department of Trieste University. The photovoltaic field simulator will be used for photovoltaic module parameters design with particular reference to its behavior when inserted in a photovoltaic field operating under shaded conditions. The use of the simulator will be particularly effective when simulating thin-film technologies as, for example, amorphous silicon, cadmium telluride, and etc. The photovoltaic field simulator will also be used for testing the components of grid connected photovoltaic systems with particular reference to the power conditioning units (also named inverters). These systems, which convert the direct current produced by the photovoltaic modules into a utility grade current (typically alternate and sinusoidal at a frequency of 50-60Hz), must extract maximum power from the photovoltaic field. The work is divided into five chapters. In the first a brief description of photovoltaic technology and its economic aspects is given. Chapter two is on classic solar cell modelling basics and on the definition of the parameters of photovoltaic technology (maximum power point, efficiency, fill factor, and etc.). In the same chapter a materials and technologies overview splits, as suggested by Martin Green, solar cells in three different generations: the first comprises crystalline silicon (mono and polycrystalline) devices, the second thin-film devices (amorphous silicon, cadmium telluride CdTe, copper indium diselenide CIS, copper indium gallium diselenide CIGS, copper indium gallium sulphur diselenide CIGSS), and the Graetzel cells, while the third multi-junction, intermediate band and organic photovoltaic devices. The third chapter briefly describes photovoltaic grid connected system components. In particular a new model for plotting photovoltaic current voltage and power voltage characteristics is provided. The method is original because only module data sheet parameters are used and experimental measurements are not needed in order to determine the photovoltaic modules behavior with reference to irradiance and working temperatures changes. In chapter four the Balance of a photovoltaic System (BOS) is calculated. In particular the importance of the mismatching effect of photovoltaic modules due to shaded conditions is shown. The last chapter is on simulator description and its applications.XX Ciclo197

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Contrastare gli effetti negativi dei cambiamenti climatici rappresenta una sfida chiave del 21° secolo. L’uso di combustibili fossili per la produzione di energia, il riscaldamento e i trasporti, è la causa principale delle grandi quantità di gas serra rilasciati nell’atmosfera, responsabili dell’attuale riscaldamento globale. Per limitare le conseguenze dannose dei cambiamenti climatici, il mondo ha urgente bisogno di utilizzare l’energia in modo efficiente, utilizzando fonti di energia pulite. Il contributo descrive l’attuale transizione energetica, in cui l’elettrificazione sta emergendo come una soluzione chiave per ridurre le emissioni, ma solo quando accompagnata da energia pulita, sempre più prodotta a costi minori da fonti rinnovabili. Il contributo illustra i principali trend che stanno guidando il boom delle rinnovabili, con il fotovoltaico che funge da portabandiera. Grid-parity e fuel-parity rappresentano un passo fondamentale nel percorso di crescita (a livello globale a tassi record) di questa tecnologia solare. Il contributo introduce poi le microreti come un sistema in grado di bilanciare la produzione variabile di energia rinnovabile con le attività di generazione tradizionali, contribuendo anche a integrare queste energie rinnovabili nel mix energetico. Esse forniscono energia pulita, efficiente, a basso costo, migliorano la resilienza locale ed il funzionamento e la stabilità della rete elettrica regionale.Mitigation and adaptation to climate change are key challenges of the 21st century. Combustion of fossil fuels for energy production, heating and transport, is the main cause of the large amounts of greenhouse gases released into the atmosphere, responsible of the current global warming. To limit the damaging consequences of the climate change, the world urgently needs to use energy efficiently, making use of clean energy sources. The paper describes the current energy transition, where electrification is emerging as a key solution for reducing emissions, but paired with clean electricity, increasingly sourced at the lowest cost from renewable energy. The paper illustrates the main trends that are driving the rapid deployment of renewables, with the photovoltaics as the standard bearer. Grid-parity and fuel-parity represent a fundamental step in the growth path (globally at record rates) of this solar technology. The paper then introduces microgrids as systems able to balance the variable output of renewable energy with traditional generation assets, also contributing to integrate these renewables into the energy mix. They provide efficient, low-cost, clean energy, enhances local resiliency, and improves the operation and stability of the regional electric grid.Mitigation and adaptation to climate change are key challenges of the 21st century. Combustion of fossil fuels for energy production, heating and transport, is the main cause of the large amounts of greenhouse gases released into the atmosphere, responsible of the current global warming. To limit the damaging consequences of the climate change, the world urgently needs to use energy efficiently, making use of clean energy sources. The paper describes the current energy transition, where electrification is emerging as a key solution for reducing emissions, but paired with clean electricity, increasingly sourced at the lowest cost from renewable energy. The paper illustrates the main trends that are driving the rapid deployment of renewables, with the photovoltaics as the standard bearer. Grid-parity and fuel-parity represent a fundamental step in the growth path (globally at record rates) of this solar technology. The paper then introduces microgrids as systems able to balance the variable output of renewable energy with traditional generation assets, also contributing to integrate these renewables into the energy mix. They provide efficient, low-cost, clean energy, enhances local resiliency, and improves the operation and stability of the regional electric grid

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