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The development of the photovoltaic (PV) sector in the last decade was spurred by the implementation of various support strategies aimed at reducing the gap between PV energy cost and the energy price for conventional generation. The deployment of support policies has pushed the reduction of PV energy costs, but despite this PV is still not very competitive and its development still requires adequate support mechanisms, simple grid connection procedures, and so on. This chapter provides a technical-economic analysis of investments in PV systems, evaluating the positioning of the main European markets (Germany and Italy), with the purpose of highlighting the main differences in the implementation of support policies in the two top countries. Several case studies are examined, differentiated in relation to the rated power (from 3 kW to 1 MW) and the type of plant (ground-mounted and rooftop PV systems). The profitability indexes in terms of the payback period (PBP), net present value (NPV) and the internal rate of return (IRR) are evaluated throughout the reference period. The chapter is expected to be very useful for policy makers, energy producing industries and national Governments to estimate the profitability of PV investments in the two selected countries, predicting how the PV sector will evolve in each of the two EU states.

In this paper, the problem of minimum losses reconfiguration in weakly meshed medium voltage (MV) distribution systems is dealt with. The presence of meshes can either be a cause of the presence of particular loads, favoured customer (FC) nodes, requiring a double supply path or of distributed generation (DG) nodes, that cannot work in islanded mode. The problem has been brought back to the more general problem of radial networks reconfiguration with the major aim of minimising power losses subject to constraints on voltage drops at load nodes and current in branches as well as on the partition of power generated among supply nodes in the network. The problem is non-linear and combinatorial considering the objective function, the constraints and the unknowns; for its solution, the authors have used a genetic algorithm. For the creation of the first generation as well as of the subsequent generations, a set of new generation and perturbation operators have been set up. They guarantee that all solutions represent a radial structure while supplying all the loads. In this way, the generation of unfeasible solutions is avoided and the verification step afterwards is no longer necessary. The applications show that such operators allow a wider exploration of the search space, while their implementation is quite easy and does not require a particular computational effort.

Today, photovoltaic (PV) attracts considerable interest among renewable energy sources (RES), because of its potential to significantly contribute to the future of clean energies. However, PV development is strongly related to the support policies introduced by national governments. The modification or fading out of such support schemes can strongly influence the development of the PV market in any given country. Although the PV market in European developing countries is still quite small, it has been growing rapidly in recent years. Until 2006, the installation of small off-grid PV plants prevailed in eastern EU countries. Starting from 2008, large-scale on-grid PV plants have been put into effect. Today on-grid installations constitute more than 95% of the total installed PV plants. The large increase of PV market in the last two years is a consequence of the enormous development of PV sector in the Czech market, stimulated by effective support mechanisms. Other developing member states, such as Slovakia and Bulgaria, have adequate PV support schemes including, in particular, effective Feed-in Tariff (FIT) systems. Other support mechanisms are tradable green certificates (TGCs), capital subsidies, tax credit and net metering. In this paper, after a brief review of national support policies in PV technology in the considered EU developing countries, the authors perform an economic analysis of the main support mechanisms that are implemented in these countries. The comparative analysis is based on the calculation of the cash flow, the Net Present Value (NPV) and the Internal Rate of Return (IRR) indices. The analysis shows that in some situations, support policies can be inconvenient for the owner of the PV system and that, in many cases, the differences between the implementation of the same support policy in different countries, can give rise to significantly different results. The comparative analysis carried out in this work could help: to evaluate the impact of the PV energy measures in eastern EU member states; to gain an insight into green energy companies by identifying potential PV markets and investigating the policy landscape across eastern EU countries.

Alla luce del meccanismo incentivante vigente in Italia a favore degli impianti fotovoltaici e dei risultati raggiunti in termini di numero di impianti e potenza installata, si riporta un’analisi di sensitività degli indici di redditività dell’investimento e le prospettive di sviluppo potenziale del fotovoltaico in Italia sino al 2020.

In this paper, a methodology to solve radial distribution networks, with constant current and/or impedance loads, is proposed. The techniques currently available to solve such systems are based either on iterative methods or on the bus impedance matrix. The method developed is the extension of a technique that is valid to solve networks made of impedances with one supply point. The methodology can be applied to directly and rapidly solve large distribution systems in which the loads are modeled as constant current/impedance. It is also able to solve meshed systems having voltage-dependent loads, inside an iterative backward/forward method.

L’utilizzo di strutture di sostegno ad inseguimento, nella realizzazione di impianti fotovoltaici, permette di ottenere un considerevole aumento dell’energia elettrica prodotta dagli stessi impianti. L’incremento di producibilità dipende dalla tipologia di inseguitore considerata (monoassiale o biassiale) ed, in misura minore, dalla località del sito d’installazione dell’impianto fotovoltaico. Nel presente testo, dopo aver preso in rassegna le diverse tipologie di strutture ad inseguimento, descrivendone le configurazioni strutturali, le tipologie di comando ed i meccanismi di movimentazione, viene svolta un’analisi di producibilità in funzione della latitudine del sito d’installazione dell’impianto fotovoltaico. I valori di producibilità vengono infine utilizzati per effettuare una valutazione tecnico-economica delle diverse tipologie di inseguitori, tenendo conto del sistema di incentivazione attualmente vigente nel territorio italiano.

Distributed Generation demonstrates to be able to significantly influence the electric power system, bringing considerable benefits to the quality of service and improving the energetic efficiency of the distribution network. In particular, in the last few years, Distributed Generation from renewable energy sources is considerably increased thanks to the many support policies promoted worldwide with the aim of facing the environmental issue and the problem of the permanent rise of prices of the fossil energy. In this contest, after a brief review on the financing strategies carried out in Europe in the last decade for promoting the recourse to renewable energy, the paper presents a comparison among the main support strategies for Wind Farms (Feed-in tariffs and Green Tags), taking into account the situation in some European Countries.

In the last two decades an increasing amount of electricity has been generated from renewable sources in order to mitigate the environmental impact of the conventional power plants. In the next future wind turbines may affect the behaviour of electrical power system. This paper describes the model of a typical fixed speed wind turbine connected to the grid; the model is developed in the simulation tool Matlab/Simulink. It’s composed by the aerodynamic system, the shaft model (two-mass system), the induction generator (fifth order model) and the stall control system of the wind turbine rotor. The validation of the wind turbine model is made in steady-state operation, and the results are verified by field measurements made on an Italian wind farm. The model is sufficiently accurate to be used for transient stability investigation. Dynamic simulations will be carried out for evaluating the dynamic operation of the wind turbine when a disturbance occurs in the grid and for studying the participation of wind farm to system regulations.

The single-line equivalent model is commonly used for voltage stability studies in both distribution and transmission systems. Referring to a single-line system, in the companion paper [1] the authors presented the theoretical aspects of voltage stability related to the load characteristics. In particular, expressions of the stability index for constant power, constant impedance and constant current loads, singularly and in all the possible combinations have been obtained. This index indicates how far the load node is from its voltage collapse point, allowing the maximum load power beyond which voltage collapse takes place to be evaluated. In this paper a simple method to evaluate the parameters which define the single-line equivalent system of a radial distribution network is presented, allowing to extent to it the expressions of the stability index previously found. Finally, the results of a detailed analysis of the influence of load models on the voltage stability of a realistic network, obtained with different methodologies, are reported for comparison and discussed.

The two-bus equivalent model is commonly used for voltage stability studies in both distribution and transmission systems. The paper presents a simple method to evaluate, for each bus, the parameters which define the equivalent circuit of a radial distribution network. In particular, a straightforward way for determining the Thévenin equivalent impedance behind a load node is proposed, which allows to better identify the maximum loading point beyond which the voltage collapse takes place in the network. Simulation results show that the proposed method is significantly more accurate than other existing methods on evaluating the critical power at a particular node (i.e. the weak node of the network) starting from any operating point.

In the paper, after having presented the general backward/forward methodology for radial systems analysis, a new b/f procedure showing some interesting features that improve its performance in terms of convergence speed and calculation effort is presented. The features that fundamentally are responsible for such improvements concern the main steps of the b/f procedure. The starting voltage profile solution is different from the flat profile and is suitably modified. In the backward phase and starting from the second iteration, the branch currents variations due to the loads changes are evaluated; the latter variations are calculated on the basis of the difference of nodal voltages at the beginning and at the end of each iteration. Finally, the adopted convergence criterion is based on the entity of the difference between each load node current in two subsequent iterations. The results of the applications of the proposed methodology to a set of networks taken from the literature on the topic are reported. In this way, the performance of the proposed methodology has been evaluated in terms of computational efficiency. The results of other tests have evidenced the influence of each feature of the modified b/f methodology over its performances.

L’obiettivo che questo articolo si propone di perseguire è di valutare la fattibilità tecnica e le implicazioni conseguenti alla sostituzione, in un gruppo di continuità statico, delle batterie tradizionali con le celle a combustibile, quali sorgenti di energia in corrente continua. La configurazione circuitale proposta, denominata fuel cell in configurazione range extender, presenta una struttura estremamente versatile e modulare sotto almeno due punti di vista. In primo luogo il sistema si integra perfettamente con i gruppi di continuità statici tradizionali, per i quali è sufficiente sostituire i pacchi batteria con uno stack di celle a combustibile. In secondo luogo per modificare le caratteristiche del sistema in termini di potenze erogabili, affidabilità, autonomia di esercizio, ecc., in relazione alle esigenze ed alle necessità dell’utenza che possono evolvere e mutare nel tempo, è sufficiente modificare le caratteristiche dei dispositivi di potenza. Le conclusioni dedotte dalle analisi sperimentali sono state particolarizzate per un sistema UPS passive stand-by; tuttavia esse sono immediatamente estendibili a tutte le altre architetture circuitali. Naturalmente i costi della configurazione proposta sono, ad oggi, non competitivi nel breve e medio termine con i gruppi di continuità tradizionali, ma con la riduzione dei costi dovuta al consolidamento di un’economia di scala delle celle a combustibile, il sistema fuel cell in configurazione range extender potrà costituire un’alternativa valida sia tecnicamente che economicamente. A tutto ciò vanno aggiunti gli ineluttabili vantaggi connessi allo sfruttamento del vettore energetico idrogeno.

This paper shows a technical-economical analysis of a novel Uninterruptible Power Systems (UPS) configuration, in which the backup batteries would be replaced by a photovoltaic (PV) system. Many interesting technical and economical issues concerning the proposed configuration are discussed against the traditional UPS and backup batteries solution. Moreover the technical solutions concerning the proposed integrated system realized using a double conversion UPS are motivated. Finally the operating costs of the proposed integrated PV-UPS system and the classical system with UPS and batteries with different sizes, and as the back-up time varies, are also compared and interesting results have been observed. Of course, the costs estimation for systems including renewables is not easy and cannot be precise, especially on the mid and long term, but still the analysis carried out shows that the proposed system seems to be an economically convenient choice at present in many cases and in the near future almost in all cases.

The interconnection of grounding systems of HV-MV stations via the armors of medium voltage cables, is herein analyzed to verify the effects on touch voltages in ground-fault conditions. The major contributions of this paper are two: the analysis of the impact of an HV ground-fault on a global grounding system (GGS), and the analysis of the parameters that may affect safety due to the interconnection between HV-MV stations and the GGS. The authors have analyzed cases when the connection of an HV-MV station to a GGS improves safety, and then may introduce hazards under ground-fault conditions. Two main issues are herein discussed: 1) the transfer of dangerous voltages to substations, due to ground-faults occurring at the HV-MV station; and 2) the reduction in the magnitude of the ground potential rise caused by ground-fault conditions at substations, due to the connection of their ground grids to the HV-MV station's grounding system. This paper, by examining various grid configurations, demonstrates that in some instances the inclusion of HV-MV stations in the GGS may reduce the level of protection against touch voltages, and that this depends on the following elements: the number of MV lines fed by the faulted station, the number of MV-LV substations per line, the value of the ground resistance of the substations, and the distance between the substations. This paper has practical relevance for both utilities distribution systems and industrial facilities supplied by the MV power grid.

Stationary battery systems are gaining a lot of interest in recent years, mainly because of their ability to balance generation and demand of electricity over time. The intermittent nature of renewable generation connected to the power grid is causing major stability and reliability issues in the power system, that can be solved also using stationary storage systems, able to provide the ancillary services necessary to the proper operation of the power network. Despite the considerable advantages offered by these technologies, the electrochemical storage industry is still in the nascent state and it is important to identify the main trends and prospects in relation to future technical developments, regulatory landscape and future commercial models. This paper is the second of a two-part series, aiming to provide an overview of stationary battery systems in the major world markets, identifying the applications most widely used in each storage market. In this second paper, a country overview is provided for each of the selected markets, in terms of policy regulations, subsidy programs and storage installations. The main trends are also identified, with reference to the viable use cases currently spread in the main world markets. This has been done analyzing the U.S. Department of Energy (DOE) storage database, containing details about electrochemical projects installed in each country. The analysis carried out in this work could help stakeholders to assess the impact of energy storage policies in different countries, identifying the future trends and the most promising markets around the world.

Il presente lavoro di tesi presenta e dimostra una tecnica innovativa e completamente integrata dedita alla rilevazione coerente di radiazioni a frequenze Terahertz (THz), cioè di onde elettromagnetiche il cui contenuto frequenziale cade convenzionalmente nella finestra spettrale compresa tra 0.1-10x1012 Hz. Tale tecnica è stata battezzata col nome di solid-state-biased coherent detection (SSBCD), dal momento che essa sfrutta le proprietà di un mezzo a stato solido e consente di ricostruire simultaneamente l’informazione sulla fase e sull’ampiezza degli impulsi THz, anche nel caso in cui quest’ultimi siano dotati di spettri a banda cosiddetta “ultra larga” (> 10 THz). Tale metodo di rivelazione può essere utilizzato con successo in quei sistemi in cui gli impulsi THz vengono comunemente impiegati come strumento diagnostico o come portanti di segnali a banda stretta, per esempio nelle aree della spettroscopia nel dominio tempo e nell’elaborazione di immagini o segnali, rispettivamente. La tecnica SSBCD si basa su una piattaforma completamente compatibile con il ben noto processo CMOS, cioè una tecnologia di micro fabbricazione comunemente impiegata per la realizzazione di circuiti elettronici miniaturizzati (chips), risultando quindi economicamente conveniente e particolarmente affidabile per la produzione di un gran numero di dispositivi per singolo processo produttivo. Queste caratteristiche rendono il metodo SSBCD particolarmente attraente per un ampio pubblico sia strettamente accademico sia industriale. Infatti, il suo principale vantaggio è rappresentato da una risposta spettrale estremamente larga, così da coprire l’intera gamma del dominio THz (qualora la durata temporale dell’impulso ottico lo consenta), permettendo potenzialmente di risolvere gran parte dei problemi e le limiti che caratterizzano le attuali tecniche di rivelazioni, le quali rappresentano invece il collo di bottiglia di molti sistemi che operano a frequenze THz. Di seguito, dopo una breve panoramica sulla tecnologia THz ed i diversi regimi spettrali di funzionamento, esamineremo le principali tecniche di rilevazione, che sono state recentemente dimostrate per ricostruire nel modo più fedele possibile impulsi THz ultra corti. In particolare, ci concentreremo su quei metodi che consentono di ricostruire la forma di impulsi i cui spettri coprono l'intero dominio THz e anche oltre (vale a dire, il regime ultra-broadband). Vedremo che tutte queste tecniche sono essenzialmente basate sull’impiego di gas, sfruttando sostanzialmente lo stesso fenomeno fisico, dal momento che le configurazioni basate sui materiali a stato solido e che rappresentano lo stato dell'arte nell'area della rivelazione THz, non sono adatte per operare nel regime ultra-broadband, essendo caratterizzate da una limitata risposta in frequenza. Pertanto, passeremo alla descrizione in dettaglio di tre approcci diversi, evidenziandone vantaggi e inconvenienti, concentrando infine l’attenzione su un metodo di rivelazione detto air-biased coherent detection (ABCD). In effetti, mostreremo che il nostro nuovo approccio supera essenzialmente alcune problematiche cruciali della tecnica ABCD, grazie all’utilizzo di materiali alquanto usuali (essenzialmente dei vetri) e un’unica semplice struttura integrata. Infatti, il meccanismo intrinseco nell’ABCD sfrutta la non linearità dell’aria, richiedendo perciò energie ottiche dell'ordine dei microjoule e tensioni di polarizzazione pari a diversi kilovolt. Ciò restringe la sua applicazione da un lato a sistemi laser amplificati, che sono costosi e voluminosi, e dall’altro ad amplificatori ad alta tensione, che funzionano a basse frequenze di modulazione (onde quadre), limitando le prestazioni in termini di rumore, nonché comportando rischi per la sicurezza dell’operatore. Al contrario, mostreremo come il metodo SSBCD consente di ridurre drasticamente non solo il fabbisogno di potenza ottica al livello dei nanojoule, ma anche le dimensioni fisiche della regione di interazione fra impulsi THz ed ottici, rispetto al caso dell’ABCD, permettendo così l’utilizzo di livelli di tensione di polarizzazione paragonabili a quelli utilizzati regolarmente per le antenne fotoconduttrici. Tali risultati spianano la strada alla realizzazione di un dispositivo unico e portatile che può essere potenzialmente pilotato da oscillatori laser (che generano fasci laser di migliore stabilità ma a ben più basse energie) e amplificatori a bassa tensione, operanti a frequenze di modulazione molto più elevate, portando così ad un significativo aumento della dinamica dei segnali rivelati e dei loro rapporti segnale-rumore. In this dissertation, we develop and demonstrate an innovative and fully integrated technique aimed at the coherent detection of terahertz (THz) radiation, i.e., electromagnetic waves whose frequency content conventionally falls in the spectral window ranging between 0.1-10x1012 Hz. We named such a detection technique solid-state biased coherent detection (SSBCD), since it is based on a solid-state medium and allows simultaneously recording both the amplitude and phase information of ultrashort THz pulses, i.e. featuring ultra-broadband spectra (> 10 THz). As such, our technique can be successfully used in those systems where THz pulses are employed as either diagnostic tool or signal carriers, such as in the areas of time-resolved spectroscopy and imaging or signal processing. SSBCD is based on platform fully compatible with the CMOS process, i.e. a microfabrication technology commonly employed for the realization of miniaturized electronics circuits (chips), thus being cost-effective and particularly reliable for the production of a great number of devices. Hence, its affordability makes it attractive for both a broad scientific and industrial audience. Indeed, the fundamental advantage of the technique here presented is the unlimited operating bandwidth in the whole THz range (allowed via interaction with ultrashort pulse durations), thus potentially addressing many of the issues and constraints of those THz solutions where the detection scheme represents a bottleneck in terms of the frequency response of the entire system. Hereinafter, following a brief introduction regarding state-of-the-art of the THz technology and its different spectral regimes of operation, we will mainly review those detection techniques, which have been lately demonstrated to achieve the exact reconstruction of ultrashort THz transients. In particular, we will focus on those methods, which allow the detection of THz radiation whose spectra cover the entire THz domain or even beyond (namely, the ultra-broadband regime). We will see that such particular techniques are essentially gas-based and rely on a similar concept, since the so far available solid-state methods, representing the state-of-the-art in the THz detection area, are not suitable in the ultra-broadband regime, since they suffer a limited frequency response. Then, we will pass to the detailed description of mainly three different approaches, highlighting both advantages and drawbacks or limitations, eventually focusing the attention on the air-biased coherent detection (ABCD) technique. Indeed, we will show that our novel approach essentially overcomes some of the crucial issues of the ABCD method, by adopting particular, yet very common solid-state media (glasses) and plain integrated structures. ABCD exploits the nonlinearity of air and therefore operates at optical probe energies in the order of microjoule and bias voltage as high as several kilovolts. This restricts its application to expensive, bulky amplified ultrafast laser systems, and slow, high voltage amplifiers, which limit the noise performance and imply health hazard (electrical shocks). On the contrary, we show how the employment of CMOS-compatible dielectrics as a nonlinear medium, allows dramatically decreasing not only the requirement of optical energy to the level of nanojoules but also to greatly shrink down the size of the interaction region between the THz and optical pulses, with respect to the case of air. This results in the possibility to perform the THz detection in a compact structure, by using orders of magnitudes lower bias voltage, comparable to those regularly employed for photoconductive antennas. Such results pave the way to the realization of a unique and portable device that can be potentially driven by laser oscillators (featuring very good beam stability) and low-voltage amplifier, operating at much higher repetition rates and modulation frequencies, which will result in the significant increase of both dynamic range and signal-to-noise ratios.