Authors

Opec had no choice

Giuseppe Artizzu

www.huffingtonpost.it // january 2015

The long-awaited Opec Summit in Vienna on thursday ended with nothing concrete: cartel production in 2015 will remain the current one, despite the collapse of more than 30% of barrel price since this summer. Who has interpreted the decision as a deliberate choice by the Saudis to make a price war on American producers is wrong. Opec had no choice, the financial perspectives are grave for weaker members of the cartel, such as Venezuela and Nigeria, in a context of low oil prices. What determines the excess supply on the international oil market are not the big producers who challenge the hegemony of the Kingdom, but hundreds of small American oil companies, which drill as if there was no tomorrow. For these, the future consequences of petrol supply are not taken into consideration.

Technical Strategies for Voltage Power Regulation in LV Distribution Networks

M. Delfanti, L. Frosio, G. Monfredini, M. Merlo, C. Rosati, D. Rosati, G. Marchegiani

Distributed Generation and Alternative Energy Journal, vol. 30, no.4, pp. 7-14 // 1 January 2015

We report the integration of a novel voltage regulation strategy in the inverter control algorithm for Dispersed Generation (DG) applications. The adoption of a decentralized voltage control based on local curves allows the voltage profile to be controlled at the Point of Common Coupling (PCC) of the generators and, therefore, the capacity of existing distribution networks to host more generation from renewables. The work is focused on a low voltage distribution network and both the reactive power modulation and the real power curtailment are considered in the proposed local strategy. Both numerical and experimental analysis are necessary in order to test and validate the proposed voltage control strategy. Firstly, the performances of the proposed control are tested by a numeral analysis and the impact on both the electrical system and the inverter apparatus is evaluated. Secondly, the benefit of the control strategy is analysed by experimental analysis in a test facility to verify the feasibility of voltage regulation in a real feeder.

Hybrid distributed generation system for a rural village in Africa

M. S. Carmeli, P. Guidetti, M. Mancini, S. Mandelli, M. Mauri, M. Merlo, R. Perini, G. Tomasini, G. Marchegiani, D. Rosati

3rd Renewable Power Generation Conference (RPG 2014), pp. 1-6 // 24-25 September 2014

Nowadays the use of distributed generating systems, which use a renewable energy source, has experienced a fast development. Moreover, their intrinsic intermittent nature can be overcome using hybrid systems which combine more energy sources. This paper proposes the study and design of a hybrid generation system able to cover the energy needs of a school in a rural village in Africa (Tanzania), combining renewable and/or alternative sources and storage systems. The final results consist in the definition of an electric grid architecture suitable to interface renewable and energy needs in the most reliable way, exploiting advanced regulation and control techniques.

Why solar energy has systemic relevance

Giuseppe Artizzu

www.qualenergia.it // june 2014

Photovoltaics has assumed a role, sometimes that is a dominant one in the coverage of daily requirements. Its cost, especially in southern Italy, is competitive with that of fossil fuels. The near future is auto-consumption and accumulation. How can we change the logic of the electricity market? Giuseppe Artizzu’s article published in the latest issue of the magazine QualEnergia. In 2013 photovoltaics covered 7% of Italian electric requirements, a share that has no equal in the world. But due to the seasonal profile and time, this figure is not representative of the actual role that technology has taken. However in winter, there is a tangible impact on the wholesale price of electricity, the weight on the need is still limited, in summer and even more in the late spring technology has transformed the market, arriving to cover in a structural way 15-20% of the working day (significantly more for the holidays).

Harmonic Analysis of Output Filters for Grid Connected Converters in Battery Energy Storage Systems

Alberto Dolara, Giulia Magistrati, Riccardo Zich, Luisa Frosio and Gabriele Marchegiani

16th International Conference on Harmonics and Quality of Power (ICHQP) // 25-28 May 2014

Battery Energy Storage Systems, as well as many distributed generation systems, use voltage source inverter as interface with the grid. These converters require a filtering section to reduce current harmonics injected to the grid. Usually, harmonic filter is a series inductance connected between grid and inverter. Higher order filters can provide better harmonic attenuation at lower switching frequency and reduce filter size, with potential benefits for high power applications. This paper deals with the sizing and the frequency response of three different harmonic filters suitable to reduce the ripple in the grid current waveform. Dynamic simulations of a 100 kW Battery Energy Storage System highlight the better performance of high order filters.

Ho to put an end to dependence on russian gas

Giuseppe Artizzu

www.huffingtonpost.it // may 2014

A couple of weeks ago it was suggested, provocatively but not too much so that the Russian gas taps should be closed to buyers. Provocation or not, the developments of recent days demonstrate that the energy dependence has a political cost which is too high. Now let’s spare ourselves yet another sterile call for a diversification of sources: we need a plan and its concrete and immediate implementation. Who says it takes decades does not know the market or has a conflict of interests. Exiting from this dependance doesn’t mean stopping the import gas from Russia; it simply means reducing imports to a level that could enable, if necessary, alternatives at a tolerable cost.

Electricity market. Is the design really obsolete?

Giuseppe Artizzu

www.qualenergia.it // february 2014

In the Italian electricity system outlined there is the hypothesis that the closure of part of the thermoelectric capacity would compromise system security. It would be better to leave the reserve margin to drop and see if commodity prices return to levels compatible with ensuring the system. An article by Giuseppe Artizzu. Until three years ago, the time profile of the equilibrium price in the market followed the electric load curve faithfully. By 2012 the photovoltaics had brought a gradual but systematic reduction of price in the central hours of the day, preceded and followed by two short spikes in the early morning and late afternoon, also helped by migrating to those times of the programmable power production. In substance the hourly price curve doesn’t follow the load but the residual load, i.e. the portion not covered by intermittent sources at zero marginal cost.

The big bluff of oil companies

Giuseppe Artizzu

www.huffingtonpost.it // february 2014

The Eni media campaign focuses on the emergency of a competitive European industry, penalized by gas and electricity which is much more expensive than in the United States. The problem is real, but there are also real doubts about the sustainability of a model founded on cheap hydrocarbons. Besides this, what is striking is the unscrupulousness with which Eni, alone among the big oil companies, has chosen to play a controversial match. The leaders of the company have taken a position contrary to community strategies of decarbonisation, claiming them to be ineffective, a high cost to the economy and a potential injury to the security of supply. The economical alternative, according to Eni, would be the American choice in favor of shale gas, which means drilling in Europe and renewing the pacts with historical suppliers like Algeria and Russia.

The american energy model is not a model

Giuseppe Artizzu

www.huffingtonpost.it // january 2014

Americans are paying a third of the cost of gas in Europe, and half of that of electricity. The America of Bush and Obama is an enlightened energy model, to be imported to this side of the Atlantic. The numbers are not far from reality, but this conclusion is somewhat hasty. That Scaroni and his colleagues pester the European press with slogans is understandable, however the Ministers of Industry being their sounding board is not. This is a brief recent American history, : in the past decade the soaring prices of oil and gas has made it for the first time economically exploitable, with innovative technologies and known reserves of non-conventional hydrocarbons. Money, skills and infrastructure, combined with private ownership of the subsoil, triggered a typical American rush to deposit: within a few years, the seemingly irreversible decline of gas production has turned into a boom, shortly followed by an oil production boom too.

An OFF-GRID Base Station Powered By Sun Wind, and Water

S. Bian, X. Wang, M. Congiatu

Intelec 2013, Hamburg, Germany // 13 - 17 October 2013

With the fast deployment of mobile network the energy consumption is increasing at the same time. The Radio Access Network may occupy more than 60% total energy consumption of a mobile operator. How to improve the energy efficiency of the Base Stations is vital important. The renewable energy is now widely used to power the Base Stations and usually the Lead Acid Batteries are used to be the energy storage. In this paper a new hybrid pure renewable energy system for BTS is introduced. The Site is powered only by the Sun Wind, and Water. The most innovative technology is that a water electrolyzer and PEM hydrogen fuel cell is integrated together with solar panel and wind turbine as the energy storage system replacing the legacy lead acid batteries. This made the BTS can work totally off-grid and zero carbon emission.

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A novel mechanical hardware in the loop platform for distributed generation systems

M. S. Carmeli, F. Castelli-Dezza, M. Mauri, G. Marchegiani

Distributed Generation and Alternative Energy Journal, vol. 28, no. 3, pp. 7-27 // 24 September 2013

The growing number of distributed generation (DG) plants has emphasized the need to perform tests before the plants begin to operate. DG systems are complex enough that setting up of an experimental phase requires high costs and efforts. Moreover, renewable energy sources are intrinsically intermittent as they vary randomly with the time of day, the season and the weather. Consequently, the possibility of emulating the behavior of the whole renewable generation system in a real time environment, where a part of the real system, the natural energy source, is replaced by a real time computer simulation allows one to test the actual system in all the operating conditions, optimizing the control strategy before its service entrance, overcoming the randomness of renewable energy sources. This article proposes a mechanical hardware in the loop approach applied to a renewable energy generating system, where the whole drive (control, power electronics and electric machine) is tested and the mechanical part is simulated in real time environment. The problem of emulating the inertial torque, which can have a significant high value, is solved through an approach that relaxes the high dynamic requirements of the electrical drive that emulates the mechanical part. The hardware in the loop test bench emulates two energy sources (hydro and wind). In addition, a control strategy that emulates the inertial torque is implemented. An experimental phase in which different energy sources are modeled and emulated in a real time environment is presented as well. The underlying hardware-in-the-loop energy source emulation and experimentation scheme is shown to accurately represent real systems performance, under various control strategies and varying operating conditions.

Dispersed generation to provide ancillary services: AlpStore project

M. Delfanti, L. Frosio, M. Merlo, G. Monfredini, L. Pandolfi, C. Rosati, D. Rosati,

International Conference on Clean Electrical Power (ICCEP), pp. 133-138 // 29 August 2013

In the future, electrical systems should be able to integrate all users at the same time and guarantee power quality, stability and safety over time. The integration of renewable energy sources leads to new issues involving the intermittence of this generation typology. A high penetration of intermittent power plants will reduce the capability of the system to overcome critical events (e.g. frequency oscillations and voltage profile perturbation). This work presents new regulation schemes/functions developed in the AlpStore project framework, devoted to managing dispersed generation in order to provide ancillary services to the main grid. The work developed can be split into two main items: reactive injection regulation and frequency control regulation. The first regulation is devoted to increasing the Hosting Capacity of the distribution grid (i.e. it results to be a local control), whereas the latter aims to guarantee the energy balance of the national electric grid (i.e. it could be classified as a grid control).

Commercial bills are cut with the carbon tax

Giuseppe Artizzu

www.huffingtonpost.it // august 2013

In 2012 the electric bills have been loaded wth 10 and a half billion euros of incentives for renewable energy sources. Who benefits is who works in the green industry, at least indirectly. I do not intend to defend the reasons for incentives, nor stigmatize mistakes. I will look at the facts: the average charge in a bill is over 4 cents per kilowatt hour. Aside from second homes and families with high consumption, users most affected are small and medium-sized enterprises. On the other hand there are a number of exempted consumers like those of railways and a number of big businesses. Cutting bills is a cornerstone of the relaunch of the industrial sector. But the proposals, from a further opening of the gas market, the modification of charges between categories of users, the extension of charges of auto consumption (a blatant stupidity), have limited the short-term impact. If you want to make a big difference then you need to act with a direct cut of the administration part of the bill: the rational way to do this is to transfer the renewable energy incentivation costs , with the introduction of a carbon tax.

Gas bills are falling – thanks to who?

Giuseppe Artizzu

www.huffingtonpost.it // june 2013

“In a scenario of strong contraction of the demand for energy, the new system of balancing introduced by the authorities in December 2011 has contributed -along with other regulatory interventions and recent European rules on transport capacity allocation and congestion management- to lowering the spread in the rest of Europe”. The spread which the energy authority has spoken about is the one that reflects the difference between the price of gas in Italy and across the borders. In recent months the differential has fallen dramatically, until becoming inverted: recently our wholesale price has often been lower than average European prices. The authority, for its part, has implemented a series of measures to reflect this reality in detail, which we have seen in our bills.

Parallel-connected photovoltaic inverters: Zero frequency sequence harmonic analysis and solution

M. S. Carmeli, M. Mauri, L. Frosio, A. Bezzolato, G. Marchegiani

International Journal of Emerging Electric Power Systems, vol. 14, no. 2, pp. 199-2016 // 30 May 2013

High-power photovoltaic (PV) plants are usually constituted of the connection of different PV subfields, each of them with its interface transformer. Different solutions have been studied to improve the efficiency of the whole generation system. In particular, transformerless configurations are the more attractive one from efficiency and costs point of view. This paper focuses on transformerless PV configurations characterised by the parallel connection of interface inverters. The problem of zero sequence current due to both the parallel connection and the presence of undesirable parasitic earth capacitances is considered and a solution, which consists of the synchronisation of pulse-width modulation triangular carrier, is proposed and theoretically analysed. The theoretical analysis has been validated through simulation and experimental results.

Centrali ibride, tecniche di controllo per la gestione di micro reti intelligenti

L. Frosio, C. Rosati, G. Marchegiani, I. Mazzucco

Automazione e Strumentazione, 84-88.pdf // April 2013

Le centrali ibride, elemento chiave per poter realizzare e controllare le microreti ad alta penetrazione di Fonti Energetiche Rinnovabili, richiedono tecniche di controllo specifiche. In questo articolo si presenta una panoramica sulle varie modalità di controllo degli inverter di interfaccia delle centrali ibride e sulle diverse architetture di microrete che si possono realizzare. Si presentano inoltre alcuni risultati sperimentali ottenuti su una microrete a potenza ridotta sulla quale sono state implementate diverse strategie di controllo.

Methods to detect and mitigate catalyst support carbon corrosion in PEM fuel cells

Denis Bona, Francesco Pedrazzo, Ilaria Rosso, Dennis E. Curtin, Elena M. Tresso

International Workshop on characterization and quantification of MEA degradation processes, Grenoble, France // 26 - 27 September 2012

Carbon black based electrodes are generally recognized as state of art for PEM fuel cell technology due to the high performance achieved with relatively low Pt content. However, the catalyst carbon support is prone to carbon oxidation. This leads to loss of catalyst area and overall performance, as well as higher mass transport loss due to an increased flooding tendency. This phenomenon is particularly severe when the fuel cell experiences repetitive start-stop cycles. Therefore, specific countermeasures against catalyst layer carbon oxidation are required, especially for automotive and backup power applications, where the startup/shutdown rate is considerably high. The authors evaluated a basic design that uses a stack shunt. A properly modified control protocol, which includes the stack shunt, is able to avoid high cathode potential peaks, which are known to accelerate catalyst carbon support corrosion and its negative effects. During two separate durability tests, one adopting the shunt design and another using non-protected shutdown, a 24-cell stack was subjected to continuous starts and stops for several months and its performance constantly monitored. Results show that when the shunt is used, there is a 37 percent reduction in the voltage degradation rate for each startup/shutdown cycle, and a two-fold increase in the number of startup/shutdown cycles before an individual cell reached the specified “End of Life” voltage criteria. Furthermore, ex-situ FE-SEM analysis revealed cathode catalyst layer thinning, an indication that the emerging degradation mechanism is the catalyst support carbon corrosion, as expected. This provides further support that the constant voltage degradation rate typically experienced in PEMFCs can be attributed primarily to the catalyst support carbon corrosion rate. The proposed shunt protocol is very cost-effective and does not require any substantial changes in the system. For this reasons, its adoption is recommended as a viable method to decrease the catalyst support carbon corrosion rate and extend the operating life of the PEMFC stack.

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Control strategies and configurations of hybrid distributed generation systems

M. S. Carmeli, F. Castelli-Dezza, M. Mauri, G. Marchegiani, D. Rosati

Renewable Energy, vol. 41, pp. 294-305 // May 2012

Nowadays the use of distributed generating systems, which use a renewable energy source, has experienced a fast development. Moreover, their intrinsic intermittent nature can be overcome using hybrid systems which combine more energy sources. This paper discusses the main topologies which can be adopted for a general hybrid generation system and it focuses on a particular hybrid system which combines two different energy sources, evidencing high level and local level power flow control strategies in both stand-alone and grid connected operation. A full experience in the realization of a hybrid plant which uses an internal combustion engine with cogeneration functionalities and solar source, installed in Delebio, Italy is then presented. System design aspects, with particular attention to the possible topologies and power flow control strategies, are analyzed. After the analysis of the design aspects, experimental results of the real plant are reported.

Reduction of high frequency zero sequence harmonics in parallel connected PV-inverters

A. Bezzolato, M. S. Carmeli, L. Frosio, G. Marchegiani, M. Mauri

Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) // 15 September 2011

High power photovoltaic plants are usually constituted of the connection of different photovoltaic subfields, each of them with its interface transformer. Different solutions have been studied to improve the efficiency of the whole generation system. In particular, transformerless configurations are the more attractive one from efficiency and costs point of view. This paper focuses on transformerless photovoltaic configurations characaterised by the parallel connection of interface inverters. The problem of zero sequence current due to both the parallel connection and to the presence of undesirable parasitic earth capacitances is considered and a solution, which consists on the synchronisation of PWM triangular carrier is proposed and theoretically analysed. The theoretical analysis has been validated through simulation and experimental results.

Reduction of motor overvoltage fed by PWM AC drives using a universal model

A. Bezzolato, M. S. Carmeli, L. Frosio, G. Marchegiani, M. Mauri

Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) // 15 September 2011

High power photovoltaic plants are usually constituted of the connection of different photovoltaic subfields, each of them with its interface transformer. Different solutions have been studied to improve the efficiency of the whole generation system. In particular, transformerless configurations are the more attractive one from efficiency and costs point of view. This paper focuses on transformerless photovoltaic configurations characaterised by the parallel connection of interface inverters. The problem of zero sequence current due to both the parallel connection and to the presence of undesirable parasitic earth capacitances is considered and a solution, which consists on the synchronisation of PWM triangular carrier is proposed and theoretically analysed. The theoretical analysis has been validated through simulation and experimental results.