EXECUTIVE REPORT (first 18 months)

Transcription

1 EXECUTIVE REPORT (first 18 months) NEW TECHNOLOGIES (SUPERCAPACITORS) FOR ENERGY STORAGE AND ENERGY RECUPERATION FOR A HIGHER ENERGY EFFICIENCY OF THE BRUSSELS PUBLIC TRANSPORTATION COMPANY VEHICLES Researchers: (VUB) (ULB) Promoters: Prof. Joeri VAN MIERLO (VUB) Prof. Bernard LEDUC (ULB)

2 1. PARTNERS AND CONTRIBUTION UNIVERSITY: RESEARCHER: (ULB) Service d Aéro-Thermo-Mécanique (ATM) was born in Brussels, Belgium, in He obtained a Master Degree in Business Administration from ICHEC in Brussels in 2002 and a Master Degree in Transport Management from CIEM in Brussels in He has been working as Deputy Director of the Centre Interuniversitaire d Etude de la Mobilité (CIEM) since September 2003 and is currently pursuing the Ph.D. degree in the department of aero-thermo-mechanics, at the Université Libre de Bruxelles, Belgium. His research interests include the economical and environmental analyses of transport projects as well as the policies in mobility concerns. Contact: xtackoen@ulb.ac.be PROMOTER: Bernard LEDUC was born in Brussels, Belgium, in He obtained the M.S. in Electrotechnics and Mechanics from the Université Libre de Bruxelles in 1973 and the Ph.D. degree in Applied Sciences from the in He is Professor at the Université Libre de Bruxelles in the Applied Sciences Faculty since 1988 and Director of the aero-thermo-mechanics department. His research and teaching interests include the optimization of internal combustion engines, biofuels, energy recuperation and mechanical hydraulics. Contact : sma@ulb.ac.be UNIVERSITY: RESEARCHER: (VUB) Department of Electrical Engineering and Energy Technology (ETEC) was born in Pamplona, Spain, in He obtained the M.S. degree in electronics and industrial automation engineering from the Universidad Pública de Navarra, Spain in He is currently pursuing the Ph.D. degree in the department of electrical engineering and energy technology (ETEC), at the Vrije Universiteit Brussel, Belgium. His research interests include applications of supercapacitors in HEVs and public transportation. Contact : rbarrero@vub.ac.be PROMOTER: Joeri VAN MIERLO obtained his PhD in Engineering Sciences from the. He is now a full-time lecturer at this university, where he leads the ETEC research team on transport technology. His research interests include vehicle and drive train simulation, as well as the environmental impact of transportation. Contact : jvmierlo@vub.ac.be

3 The cooperation between the two partners within this project, VUB-ETEC and ULB-ATM, is based on their common and complimentary expertise and earlier collaboration. Both partners have previously worked on several projects of clean transportation technologies. Joining efforts will on one hand avoid duplicated tasks and thus save time and resources and on the other hand reinforce mutual experience gained so far. Within the framework of this multi-actor project, VUB-ETEC will deal mainly with the technical aspects and ULB-ATM will cover the economic aspects. However, some parts of the study, such as the state of the art or the environmental aspects, are carried out together since the methodology requires a multi-disciplinary approach. 2. INTRODUCTION Man-made emissions and increasing levels of carbon dioxide are altering the natural climate cycles bringing extremes in weather all over the world. The extent of the impact and how reversible these effects are may still be unknown, but the direct and indirect consequences of the changes that we are already experiencing present risks that should not be ignored. The Stern Review published in October 2006 estimates that the overall costs and risks of climate change will be equivalent to losing at least 5% of global GDP each year, now and forever if strong corrective action is not taken now. If a wider range of risks and impacts is taken into account, the estimates of damage could rise to 20% of GDP or more. In contrast, the costs of action reducing greenhouse gas emissions to avoid the worst impacts of climate change can be limited to around 1% of global GDP each year. The investment that takes place in the next years will have a profound effect on the climate in the second half of this century and in the next. Actions now and over the coming decades could create risks of major disruption to economic and social activity, on a scale similar to those associated with the great wars and the economic depression of the first half of the 20th century. And worse it will be difficult or impossible to reverse these changes [i]. As urban areas increase, emissions from transport now contribute significantly to the overall greenhouse effect. However, dense urban areas are exactly where rail and public transport perform best and, by forming the backbone of any sustainable transport network, can thus reduce the carbon footprint of these fast growing metropolitan areas. There is a joint responsibility for all transport actors to play a role in reducing their carbon imprint. Public transport authorities and operators must therefore increase their commitment to energy-efficiency and lowering emissions. Systems that operate from the electricity supply grid (most rail-based transport plus trolley buses) should work towards the increased use of power generated from non-polluting and renewable sources. Other systems (predominantly buses and marine transport) must focus on improving the efficiency of present-day energy sources and, in the longer term, working towards more advanced forms of propulsion such as hybrid drives, fuel cells, electrical storage, induction systems and so on [i]. 3. SCOPE OF THE STUDY Although growing pollution levels and traffic congestion are becoming a delicate issue in major cities, they surely could be eased by efficient public transportation systems. In many cities an important part of the public transportation fleets is composed of electric traction vehicles such as metros, trams or trolleybuses. These vehicles present the advantage of being zero-emission vehicles, at least locally. Their well-to-wheel environmental impact is only due to the amount of electricity they use and on the way this electricity is produced. On the other hand, almost all cities keep on using internal combustion engine urban buses

4 and/or minibuses as well to obtain a close-linking of their network and to provide an adequate service to all of their customers [ii]. Although electric vehicles enable large reductions of the emissions, their energy efficiency could be significantly improved by hybridizing the power system with the inclusion of an energy storage system for energy recovery purposes. Recent studies have shown that up to 40 % of the energy supplied to electrical rail guided vehicles could be recovered through regenerative braking [ iii ]. Furthermore, the nature of city driving, where low speeds, frequent acceleration and sudden braking occur, implies that the public transportation sector is an ideal candidate to benefit from an enhanced Energy Storage System (ESS). In some cases, supercapacitors form the optimal option for this purpose. They can accept high power peaks from regenerative braking, have a long lifetime, need no maintenance and work at a wide temperature range without suffering from a negative effect on their lifetime. The use of supercapacitors in public transportation applications has not been deployed for a long time, but in recent years, several pilot projects have been developed around the world. Countries like Germany, France, Sweden, Switzerland, China, Japan or the U.S. have already experienced the benefits of using supercapacitors for various applications. They are especially suited for the recovery of the breaking kinetic energy of trams, buses or metro trains but they can also attain functions such as voltage stabilization in weak distribution networks, operation without overhead lines, start/stop system in city buses, etc. 4. OBJECTIVES This multidisciplinary project aims to assess the cost and benefits of using supercapacitor based peak power units and energy storage systems in public transportation. Buses, trams, metro trains and the electric distribution network applications will be assessed from economic, environmental (air pollution, climate change, noise, vibrations, ) and technical criteria. Supercapacitors are light weight and high power energy storage devices which have an operational life typical equal to that of a vehicle. Supercapacitors allow storing energy while breaking the vehicle or driving downhill. They can be used in buses or in railway applications. In the latter case they can also avoid the use of overhead power lines in certain parts of the route as well as to act as voltage drop compensation in weak distribution electricity networks. The objective of this project is to assess these different applications, to define the required specifications for the supercapacitors modules, in terms of energy capacity and power, for each application and to assess the potential energy savings and reduction of the impacts of air pollution. Economic considerations will also be vital to estimate whether the technology is mature and whether it is worth investing in supercapacitive solutions for the Brussels public transport company. The project contains seven work packages (WP) as showed in Figure 1 The WP1 encompasses a deep analysis of the state of the art in the field of innovative vehicle technologies and especially the use of supercapacitor based energy storage systems for public transportation vehicles. The WP2 consists of identifying the most suitable applications for the STIB both in vehicle use (bus, tram, metro) or connected to the electricity grid and this for: - current applications: integrated alternator-starter for conventional diesel buses, energy storage for the diesel-electric buses, energy storage in trams and metro, energy storage connected to the power grid - future applications: peak power unit in full series hybrid buses and/or fuel cell buses

5 In WP3 the required specifications of the supercapacitors cells for these applications will be assessed, taking into account: - supercapacitors cells particularities: energy, power, voltage, weight, size, costs (unit, series, adaptation, ) - external elements: vehicle features, drive cycles, available braking energy, temperature, altitude differences In WP4 an assessment of the potential energy savings will be carried-out for the different identified applications. An integrated impacts assessment will be made in WP5 taking into account the direct and indirect emissions having an impact on the following elements: global change, ecosystems, biodiversity, human health, noise, vibrations, buildings. Both a Cost-Benefit Analysis (CBA) and Multicriteria Analysis (MCA) will be carried out in the WP6 to evaluate the most promising applications and technologies for the STIB fleet. The WP7 encompasses the dissemination of the results of the study via publishable reports, technical notes, articles in scientific journals and congress presentations as well as putting forth recommendations for the Brussels-Capital Region. Figure 1 EVEREST project structure in work packages

6 ULB will be responsible for WP1 (task 1), WP2 (task 2), WP5 (task 3), WP6 (task 4) and WP7 (task 5). The Figure 2 shows the proposed timetable for the project. 5. RESULTS Figure 2 Timetable of the EVEREST project During the first months of the project, a state of the art research was done in cooperation with project partner X. TACKOEN [ULB]. Electrochemical double layer capacitors technology, their potential applications and actual existing projects of supercapacitors in public transportation across the world have been presented. Contacts have been made with all actors working in this field (supercapacitors manufacturers and resellers, public transport vehicle manufacturers, public transport operators, research institutes, etc.). A Simulation program able to simulate the power flow in the bus fleet has been developed in a Matlab/Simulink environment. The program approach consists on the effect-cause method, which calculates the power flow and energy consumption of the vehicle following a specific driving cycle (e.g. ECE 15, SORT, DUBC, etc.). This program can thus, calculate the differences in energy consumption between the conventional vehicle and the supercapacitors hybridized version. It can also help to size the supercapacitor module in terms of energy content, voltage variations, losses and power requirements. A specific model for rail vehicles has been developed as well. Its purpose is to simulate the tram and metro network in real conditions with several vehicles running on the line and exchanging the regenerated braking energy. The model is able to calculate the vehicles and network power flow, currents, voltages and losses starting from a specific built-in speed cycle that considers the route altitude. Based on the simulations of a tram network, different supercapacitor-based ESSs, ranging from 0.9 kwh to 1.56 kwh, suitable for a 30 m long tram currently in revenue service in Brussels, have been proposed. Results obtained in energy savings at substation level vary from 23.4% to 27.6% under the same driving profile and auxiliaries consumption. Results vary depending on the supercapacitor based Energy Storage Systems (ESS) used and vehicle load. At the end-of-life of supercapacitors, the range varies from 18.1% to 25.1%. Results show the influence of not only the energy size but also on the configuration of the

7 module. Depending on it, the supercapacitor module will have a different efficiency and it will lead to significant differences on energy savings. Using the same methodology, the metro network (Brussels line 2) has been analyzed under different traffic conditions. The high energy exchange ratio between vehicles, requested a more complex study. The line has been studied under different traffic scenarios: peak time, off-peak and night & weekend periods. In these conditions, two options have been evaluated: stationary and on-board the vehicle ESS, each of them with their particular advantages and limitations. Results show that stationary ESSs modules with usable energy content between 2.2kWh and 4.5 kwh, distributed every m are the most reasonable option. With these modules installed on the line, the energy savings vary from 6% to 12% at peak time; from 10% to 17% at off-peak time; and from 22 to 25% at night and weekend periods. The variation of savings corresponds to the size and distribution of ESS on the line. These results will be refined and further analyzed on the second phase of the project. For the on-board ESS, several configurations varying in energy capacity from 0.73kWh to 1.76kWh per metro car have been modelled. Preliminary results show that a size of 1.2 kwh per car is a good commitment between size and energy savings provided, that vary from 19% at peak time 28% at night and weekend periods utilizing the mentioned size. The research also focused on the development of a cost-benefit analysis methodology for assessing the energy storage systems. Based on the results of the technical simulations, three types of energy storage solutions for railway applications have been investigated. Focusing on the selected scenarios, we could estimate the benefits of the use of ESSs on the STIB rail transport network. Despite the many uncertainties and assumptions, we have demonstrated that the supercapacitive technology could help reducing the company s energy bill (direct benefits) and limit the air pollutants and greenhouse gases emissions associated to the generation of electricity (indirect benefits). However, the technology remains regrettably very expensive due to high development costs and a lack of standardization in the public transport sector. Mobile solutions have proved unaffordable for the tram network since the initial investment cannot be surmounted by the lifetime benefits. The ESSs perform better on the metro trains. Mobile applications could possibly open a window for investment although the main limitation, in this case, consists in the installation of the devices aboard the vehicles. On the opposite, stationary systems have shown univocal results and offer a good return. Moreover, this option does not require retrofitting the existing vehicles and could be implemented directly by the company without negotiating with the vehicle manufacturers. Table 1 compares the different applications. The price range and benefits range columns give the extreme values. The time of investment recovery (TIR) refers to the number of years required for the benefits to overcome the costs. The stationary application for the metro network is by far the most attractive. Even in the worst case, the TIR is lower than the lifetime expectancy of the ESS. The smallest configuration with an ESS spread every 2000 meters appears as the best option. Concerning the mobile applications, the system aboard the metro is beneficial except in the worst scenarios where the TIR exceeds 15 years. Again, the smallest configuration gives better results. The system aboard the tram is less convincing as the TIR goes below the 15 years exclusively in the most optimistic situations.

8 Application System description Configuration Total energy content (kwh) Price range ( ) Benefits range ( ) Time of investment recovery (years) METRO TRAM Stationary pessimistic average optimistic Mobile Mobile 4 small-size modules 4 medium-size modules 6 small-size modules 6 medium-size modules Medium-size module Small-size module Medium-size module Small-size module 4 x 10 x 232 BCAP x 10 x 232 BCAP x 10 x 232 BCAP x 10 x 232 BCAP x 300 BCAP x 250 BCAP x 232 BCAP x 234 BCAP kwh kwh kwh 27,18 kwh 1.17 kwh 0.73 kwh 1.2 kwh 0.91 kwh Table 1 Comparative table of ESSs for STIB railway applications 9,31 5,91 3,67 9,77 6,13 3,74 11,47 7,26 4,49 12,16 7,62 4,64 18,28 8,71 4,52 15,58 7,68 4,14 33,00 15,47 7,50 33,33 15,26 7,13 6. CONCLUSION Transport is the essential link between the individuals and their activities or needs. The mobility of goods and people has been constantly increasing to respond to the economic growth. Private cars have the best answered to the citizens requirements of flexibility and velocity but are now confronted to congestion and growing environmental issues. In this context, public transport has a clear role to play for moving to a more sustainable transport system. However, public transport has its own challenges and must fight against the considerable rise in the energy prices without downgrading the quality of service. Faced to this situation, transport operators must find ways to reduce their energy consumption and achieve a better energy efficiency of their vehicles. Hybridising the vehicles is one solution for reducing the use of fuels or electricity and limiting their carbon footprint. This study has extensively presented how storage solutions could improve the energy efficiency of STIB rail vehicles. They offer interesting opportunities to reduce the energy bill of the company and lower the emissions generated by the power plants. Among the findings, one can highlight the fact that supercapacitors seem a suitable technology for energy recovery in heavy transport due to their high power capability, high efficiency and long lifetime. Stationary and mobile energy storage systems have been thoroughly studied and assessed. A simulation tool has been developed to carry out a representative study of the real operational conditions. Despite the uncertainties and unavoidable assumptions, both applications have shown interesting results in terms of energy savings and air pollutants reductions. The technology remains regrettably very expensive due to high development costs and a lack of standardization in the public transport sector. Mobile solutions have proved unaffordable for the tram network since the initial investment cannot be surmounted by the lifetime benefits. The ESSs perform better on the metro trains. Mobile applications could possibly open a window for investment opportunities although the main limitation, in this case, consists in the installation of the devices aboard the vehicles. On the opposite,

9 stationary systems have shown univocal results and offer a good return. Moreover, this option does not require retrofitting the existing vehicles and could be implemented directly by the company without negotiating with the vehicle manufacturers. Considering that the cost of energy is more than likely to follow the upward trend of the previous years and that the environmental concerns will be strengthened, some scenarios should retain the attention of the Brussels-Capital Region and STIB authorities. The Region has clearly expressed its will to promote a cleaner mobility and reduce its transport-related emissions and this would allow Brussels to take up its national and European capital position by ensuring the highest quality of life for its residents. This project is a clear step in this direction as it presents a considerable added value and gives prospective opportunities. This investigation has in addition the originality of involving a multidisciplinary research team from two Brussels universities with a complimentary expertise and a strong collaboration. 7. ADDED VALUE FOR THE BRUSSELS-CAPITAL REGION Issues related to energy consumption are timely. The permanent increase in fuel prices is linked to the gradual depletion of oil reserves and armed conflicts in certain areas of production. This makes us ever more conscious of the need to find alternatives in terms of energy resources supply and use. In this context, the Brussels-Capital Region has initiated various policies to reduce energy consumption in the field of housing, industry or transport. Transportation activities should minimise their impact on the urban environment in order to preserve the quality of life in the city. At this moment, the most current vehicle technologies induce a heavy burden on the environment and contribute significantly to fossil fuel depletion. The transport sector is responsible for a large share of pollutant emissions in the atmosphere, which have direct and indirect effects on the environment and on global warming. The promotion of sustainable transport modes is undoubtedly one of the main runways and this project fits in perfectly with the objectives of the Region aiming at preserving the air quality and limiting the greenhouse gases. It is clear that the Brussels- Capital Region needs to implement the best available technology in its transportation system in order to ensure its future. Similarly to other cities investing massively in green technologies, this will allow the Region to take up its regional, national and European capital position and ensure the highest quality of life for its residents. The proposed project is a clear step in this direction and thus presents a considerable added value for Brussels. Similar developments are taking place in other cities worldwide, which are confronted with the same mobility and environmental problems. The growing interest for cleaner buses on one hand, and the renewed development of tram and light-rail networks, which are in many cases reintroduced in cities that formerly abandoned them (such as the French cities of Bordeaux, Montpellier, Nantes, Nice, Valenciennes) give this project a global appeal, with the particular benefit of the European capital, Brussels, acting as a showcase. This research will enable a prospective analysis on opportunities for STIB to reduce the energy consumption of its vehicles through the use of advanced technologies. The study aims to demonstrate whether the use of supercapacitors-based technology can have a positive impact for the STIB in terms of energy consumption, reduction of pollutant emissions, lower operating costs and even brand image. The results obtained in the framework of this research will undoubtedly help regional authorities to better assess the benefits of investing in promising technologies to reduce the energy consumption and environmental pressure of public transport vehicles and see if this can lead to this virtuous circle:

10 New energy storage solutions for the vehicles Reduction of the energy consumption and associated emissions Decrease of the operational costs Increase in the financial resources of the transport operator New investments in the public transport services Higher usage of the public transport Trafic reduction due to a modal shift and decrease in the associated emissions REFERENCES [ i ] UITP, A low Carbon future with Public Transport, UITP Position paper, January 2007 [ii] Henson, R. and Essex, S. (2003). The development, design and evaluation of sustainable local transport networks. International Social Science Journal 176, p [ iii ] Gunselmann W, Technologies for Increased Energy Efficiency in Railway Systems, ISBN , Proceedings of EPE 2005, Dresden.