Innovative Electric Storage Systems And New Prospects For Pubblic Transport Electrification

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1 Innovative Electric Storage Systems And New Prospects For Pubblic Transport Electrification Luca Buzzoni 1, Giovanni Pede 2 (1) Mobility and Public Transport Department, D.G. Infrastructural Networks, Logistics and Mobility Systems, Emilia-Romagna Region, Viale Aldo Moro 30, 40127, Bologna. address: lbuzzoni@regione.emilia-romagna.it (2) ENEA Casaccia Research Center, Via Anguillarese 301, S. Maria di Galeria (Roma). address: giovanni.pede@casaccia.enea.it Abstract - The paper deals with a new class of trolley buses and trams that do not need a catenary (the first nor the rails), but offer the same energy and environmental benefits of traditional electric traction, well above those offered by thermal traction. Starting from the analysis of mission, defines storage characteristics and quick charging specifics, proceeds to a costbenefit analysis. I. INTRODUCTION In order to reduce traffic air pollution, RER (Emilia-Romagna Region) allocates incentives to local public transport (LPT) either by contributing to the bus fleet renewal or supporting researches, meetings and agreements, so collaborating with the Department of Energy, Nuclear and Environmental Protection Engineering (D.I.E.N.C.A.) of University of Bologna, that strives to promote and coordinate basic and applied research relating to the processes of rational usage of energy sources. For this purpose RER works together with national and regional research institutes such as Cnr, Arpa and ENEA. Since many years ENEA is involved in research on technologies for automotive and especially in the development and characterization of electric and hybrid traction systems, first in Italy to propose and test full-scale use for supercapacitors. As a matter of fact, the market success of hybrid cars like Prius and similar Honda models, together with gradual spread of electric vehicles which use lithium batteries with their outstanding performances, demonstrates the feasibility of hybrid-electric propulsion, whose environmental merits are widely recognized. These electric storage systems, lithium batteries and supercapacitors, offer innovative features also in terms of rapid recharging, which have opened them additional potential uses, especially for local public transport (TPL). In TPL, in fact, the typical vehicle mission, regularity of exercise and very frequent stops-and-go, allow you to extend the autonomy to like, as long as the stops are used for charging. The concept (biberonage) is known for a long time, but only new generation of storage systems would make it possible. II. EMILIA-ROMAGNA REGION (REGIONE EMILIA- ROMAGNA - RER) STRATEGY IN TPL RER s strategy aims on one side at progressively creating local public transport fleets made up of eco-compatible vehicles, and on the other side in relationship to urban areas at supporting modal interchange and traffic fluidification on the main access roads to towns centres (by means of reserved bus lanes and telecontrol systems). The low impact technologies on which RER is mainly engaged are CNG, electric, and hybrid vehicles. RER is also interested in researches on the use of hydrogen as energy carrier. With reference to electric and hybrid vehicles, RER has promoted them first of all in urban areas since they help to decrease noise and air pollution (particulate). The European Project ITACA, with reference to the related Emilia-Romagna Region Lead Partner s role, will pay particular emphasis on study of opportunities, synergies and benefits for implantation of mixed fleets of pure batteries electric vehicles, charged when possible from renewable energy facilities, and fuel cell/batteries electric vehicles, using hydrogen from renewable sources, both for private and public use in different regions and cities of Europe, according to population, territory, environment, productive areas qualified as "Ecological Parks", social customs, climatology, etc. In this point, the project is strongly focused on energy efficiency and carbon saving issues, showing new technologies and devices (fuel cells, charging points from RE, etc.) which could facilitate the introduction of electric vehicles not only for the inner cities, but also for metropolitan areas, improving its features through the increase of autonomy and availability of the vehicle A. Air Pollution and Energy Consumption (i.e. CO 2 emissions) All transportation modes consume energy and at present this is mostly derived from the combustion of oil-derived fuels and, in general, of hydrocarbons. Combustion inevitably

2 produces CO 2 and a lot of other substances, depending on specific fuel characteristics, e.g. Nitrogen Oxides, Sulphur Oxides, Lead (Pb), Volatile Organic Compounds (VOCs), Particulate Matter (PM), and Carbon Monoxide (CO) due to incomplete combustion. At certain concentrations, such substances change physical and biological characteristics of the air (mainly of the troposphere) with adverse consequences on health, climate and weather precipitations. Most of the noxious emissions stay in a small range from the source. Some of them spread further such as CO 2, NO x and SO 2, producing effects in other regions. Thanks to electric vehicles with dual mode capacity, in the future it will be possible to achieve urban vehicles with local zero-emissions and no compromise in performance. In the case of greenhouse gases, effects take place at planetary level. It is important to observe that large differences arise in global (well-to-wheel) CO 2 emissions for electric and non electric transport. The table below displays data for public local transport (TPL) in Rome TABLE I Electric Electric Diesel traction traction traction CO2 Emission factor in Average Combined 3,16 t/t (Italy) Cycle CO2 Emission factor in g/kwh Fuel consumption g/km 700 kwh/km 2.2 Emission factor (final, at wheels) in g/km It is apparent a 50% advantage for the electric traction, considering the mean value (400 tco 2 /t) for the emissions of the thermoelectric power-plant. B. Noise Apart from energy consumption and gaseous emissions, vehicle operation is responsible for acoustic emissions. Although noise could represent a very negative feature for quality of life, it stays at a very local level so that effective mitigation devices can be adopted in some cases (such as extraurbanways). Nevertheless, measures must be taken to reduce acoustic emissions at source, particularly from road traffic in urban areas. Therefore, the European Commission has also regulated noise produced from road vehicles. Despite such limits, noise from urban traffic is very often higher than acceptable thresholds. According to WHO estimations (Concerning for Europe s Tomorrow, 1995), more than 72% of European citizens are exposed to noise higher then 65 db(a) and 27% to levels higher than 75 db(a). At over 55 db(a) psychological and nervous disturbances can be observed. Electric drives do not make as much noise as combustion engines. As a matter of fact, during start up, acceleration and in the lower speed range, lower noise emissions are demonstrated for electric vehicles. At higher speeds, where rolling noise predominates, battery electric vehicles derived from conventional vehicles may be slightly louder than comparable models on account of their heavier weight, Fig. 1. Vehicle on stop Gear from: 0 km/h Gear 50 km/h III VW Golf Fig.1 City Stromer db(a) PAST EXPERIENCES AND STATE OF THE ART The late 19th century painting (Fig.2) depicts an electrical drive tram which just started operations in London. It provides a snapshot of the revolutionary impact that electricity provided large cities: light, speed, cleanness and power, a quantum leap ahead of coal and gas, steam tramways and the subsequent smoke in the air. Fig.2 Electric tram in London In the later years after WWII diesel replaced electrical drive which had gained popularity also for extra urban routes, given the undisputed advantages even with traffic situations and public transport demand far inferior to today's level. The presence of the fixed electrical facilities started to be perceived as invasive and anti aesthetic and requires very high investments, not mentioning the maintenance and operating costs. For trolleybus lines in Milan, the investment cost is keuro/km (author's private information source). As a consequence of this in the 60 s trolleybus technology started to be discontinued with subsequent scrap of old vehicles and decommissioning of the power lines.

3 The recent environmental concerns and the need to diversify energy sources from fossil fuels revamped the attractiveness of electrical traction which involves a renowned attention to the trolleybus technology, for which the implications of the external power line still exist. As a matter of fact batteries cannot completely resolve the wire free electrical drive problem, mainly due to limited duration. The most recent answers to this problem which found extensive application are hybrid systems having on board two different energy sources, being one of the two a gen set or electrical drive bi mode systems fed by the electrical grid or by an onboard source (electric energy storage or gen set). Vehicles of such type are made by IVECO (Civis), Bombardier transport (TVR) and Lohr industries (Translhor). The main technical characteristics for advanced intermediate rubber-tyred transport systems are shown below: Such system was not successful (it was decommissioned in the early 60 ) due to the excessive weight of the fly wheel (3 tons) and long stops for recharging, also in the extra urban routes. The system proposed by ENEA is a step forward to the trolley bus, but is also overcoming the defects which sentenced the premature end of Gyrobus. ENEA is the holder of a patent that makes use of these technologies, claiming a series of systemic innovations that make it possible to take full advantage from quick recharging. TABLE II CIVIS TRANSLOHR TVR Size cross-section (m) 2.55 x x x 3.40 length (m) Vehicle capacity (p) Commercial speed (km/h) Traction external twin twin overhead twin supply overhead line line overhead line on-board (optional) dieselelectric batteries dieselelectric bydirectional no yes no An on-board source can be used also on trolley-bus, and typically it is operated in downtown, i.e. in Rome with Trollini, Fig.3, by Ganz Solaris. In this case, the batteries are charged during the march under catenaries. Thanks to recent development of some technologies we are also facing the renowned interest for a bi modal system with recharge stations at the stops along the route. A vehicle of this type, named Gyrobus and manufactured by Oerlikon, was initially operative in Belgium, in the 50. The Gyrobus was an electrically driven vehicle, powered by a simple on-board generator consisting of an electrical machine and a high mass inertial storage device, a flywheel. It was connected to the power grid through a three phase connector that was on during throughout the stops (fig 4). Feed as a normal motor it was accelerated to the nominal design speed in order to store kinetic energy. Once the fly wheel was charged, the connector was withdrawn and the vehicle could re start with having the fly wheel as a generator. The electrical machine through a controlled revolving speed reduction was able to convert kinetic energy into electric energy, feeding the electric motor for several kilometres. There was no need to build the catenaries along as in a trolley-bus line, which was replaced by a power line built in the roadway, feeding the recharge points at the bus stops. IV. Fig. 3 Trollino Filo Bus in Rome THE ZERO FILO BUS The recent progresses in the materials (allowing rotating speed of several thousand rpm, being kinetic energy proportional to square revolving speed) and power electronics (in order to convert power generated at variable frequency and voltage into constant parameters) revamped the interest to fly wheels, which today are available in the kw range, having weight and dimensions compatible with urban transport industry needs. An example of application of fly wheels is offered by a Siemens prototype, derived from the tram-train Avanto, developed within the European projects ULEV-TAP I e ULEV-TAP II. Other electrical storage systems with lower weight than traditional batteries and better modularity features than flywheels better fit the needs of a trolleybus dimensions vehicle. They are supercapacitors and latest generation lythium batteries. Supercapacitors have been recently utilized by Van Hool on the trolleybuses now being delivered to Milan city (Fig 4), where their function is to guaranteed a certain level of energy saving (energy recovery braking) whose magnitude is estimated to about 24%. By redesigning such trolleybuses with enough storage capacity in order to feed the autonomous electrical march between two feed points, Fig.5, such as the old Gyrobus, we

4 have de facto a wire free trolleybus, that ENEA named ZeroFilo-Bus. Fig.4 Van Hool Filo Bus in Milan km/h ZeroFilo-Bus mission: stop & start every 270 m, maximum speed 35 km/h " Fig.5 The choice between supercapacitors and lithium-ion batteries depends on the mission, and more specifically on the relationship between two mission-dependent parameters, pulse discharge power (in the case of a 18 m long class trolleybus, like the Trollino, is about 300 kw, Fig. 8) and requested energy (1,23 kwh, calculated by power integration during the accelerating phase), the so called P/E (Power/Energy ratio), that for such a mission is very high, 260. The same ratio can be calculated for each kind of storage device, by the ratio between its specific power, W/kg, and its specific energy, Wh/kg. For instance, available traction batteries have a P/E ratio of 1-4, good for battery EV, but far too low for start-and stop application. High power storage system (high-power lead-acid battery, Ni-MeH batteries, Lithium-ion batteries) have a more adequate ratio, starting from 10 W/Wh, Fig.6. UCs benefit from a P/E ratio much higher, more than 100 W/Wh (specific power is very high, up to 1000 W/kg and specific energy is less than 5 Wh/kg). A storage system whose P/E ratio reflects the relationship between power and energy requested by the considered hybrid vehicle s typical mission, would have all the power in order to satisfy the cycle power peaks, without having more energy than the necessary one. Fig. 6, from Performance Characteristics of Lithium-ion Batteries of Various Chemistries for Plug-in Hybrid Vehicles, A. Burke,M. Miller, UCD, Institute of Transportation Studies, EVS-24, Stavanger 2009 On top of this physical nature issues, correct management methodology needs to be addressed in order to guarantee sufficient operation security (avoiding stops on the way between two charging points). The calculated electric energy storage specifics, for a 18 m long trolleybus, are as following: Peak power: 300 kw Minimum energy: 1.23 kwh Maximum duty cycle: 50% Maximum voltage: 1000 V Minimum voltage: 500 V Maximum current: 600 A that are satisfied by a bank composed by 2x8 = 16 modules HTM BMOD (63F/125V), manufactured by Maxwell. The maximum operating temperature is 65 C and, considering an operational temperature of 40 C with a 50% duty cycle, the maximum current for such modules (Fig.7) is 300 A (continuous maximum is 150 A). Delta T Delta T vs. I (duty cycle = 50%) Fig. 7. Thermal behaviour for HTM BMOD module I The bank, composed by 2 strings, assures therefore the desired maximum power. The available energy for each module (1/2C (Vnom^2 1/2Vnom^2) /3600) is about 100

5 Wh, therefore total energy is 1.6 kwh, more than maximum need. The single module weighs less than 60 kg and measures 315 mm x 425 mm x 744 mm and is designed to perform reliably through one million deep charge/discharge cycles (Vmax 0.5 Vmax), which equates to more than 15 years of operational life. Production pricing ranges from 3000 $ to 4000 $ per unit, depending on volume. Auxiliary loads are fed by a separated electric energy storage, with different characteristics (high energy/low power), typically a battery system. A limited trial of supercapacitors has been recently experimented in China between 2005 and 2006, Fig. 8, even if such experience is better addressing the 'biberonage' concept, as the recharge was only operated at the terminals of the lines and not at all the stops. supervising the recharge duration at the stops by taking into account the stops schedule and the minimum capacitors storage level required, with longer re charge duration at the line terminals also enabling the lithium batteries recharge; malfunctions diagnoses for storage elements in order to cut them out in order to prevent domino effects and triggering timely maintenance. In such situations an emergency protocol is activated in order to manage the reduced energy availability through longer charge stops, auxiliary facilities cut out, speed reduction, etc.; continuous update of the self learning module for an accurate estimate of consumption in the different legs of the line; real time information to the driver about the charge status, the need to extend recharge stops, the activation of emergency status. Fig. 10. Supercapacitor equipped trolley-bus by Shanghai Aowei Technology Development Company & Sinautec The project wrecked due to the not feasible trade-off between the required dimensions of the super capacitors for such a heavy duty and the dimensions of the bus. Today China operates ordinary trolley buses. The limitations surfaced during this experience could be overcome thanks to the possibility of integrating transport systems with adequate remote management technologies and the capability of uncertainty prediction of charge status of supercapacitors, enabling predictive power flow management. Therefore, the Zero Filobus system will include a remote fleet monitoring station whereas on board the vehicle an intelligent management system will incorporate the following functions: constant evaluation of system storage (voltage measurement) in order to avoid exceeding a preset discharge level; management of energy flows in order to backup the super capacitors with lithium battery storage for very short intervals and emergency (super capacitor charge below a certain value or peak power request) cut off of low priority utilities (such as A/C); management of braking energy dissipation in order to avoid a charge excess that might damage the super capacitors and redirecting energy surplus to auxiliary utilities such heating passengers ambient; V. CONCLUSIONS The proposed system finds ideal application in hystorical city centres, where on one side it is necessary to contain noise and polluting emissions and on the other to limit the growth of aesthetically invasive and expensive infrastructures such as trolleybus power lines and tramways. If latest generation batteries with biberonage at the line terminals seem to just suffice the needs of small buses, electrical vehicles busways having distributed power feed points represents a viable alternative to trams and trolley buses. Such approach proves convenient from functional and any other point of view and requires and integrated perspective between system and vehicle, recharge infrastructure, route management REFERENCES 1. Innovative Technologies for the public transportation in the Urban Mobility Plan of Padova, M. Andriollo, G.Del Torchio, G. Martinelli, A. Morini & A. Tortella, University of Padova, L ibrido e l ambiente nella trazione ferroviaria, R.Cheli, A.Di Donato, A. Laganà, G. Pede, Ingegneria Ferroviaria, Novembre Valutazione tecnica economica del costo del Sistema di accumulo a supercondensatore in applicazioni industriali di recupero energetico: carroponti, E. Tironi, V. Musolino, Dip. Di Elettrotecnica Politecnico Di Milano, 20 Seminario ANAE, Bressanone Comparison of SC and high-power batteries for use in hybrid vehicles, M. Ceraolo, S. Barsali, G. Lutzemberger, M. Marracci, University of Pisa Dipartimento di Sistemi Elettrici ed Automazione, ICE 2009, Capri 5. Development of Contact-Wire/battery Hybrid LRV, Masamichi Ogasa, Railway Technology No.22-23, Life Cycle Cost di un sistema filoviario bimodale a batterie di trazione rapportato al confronto economico con l autobus tradizionale, R. Emili, D. D Agostino, Ingegneria Ferroviaria, Settembre ITACA HANDBOOK Realizing Sustainable Mobility, L. Buzzoni et al., ITACA Project, Power Programme, September 2011.