A COMPARISON OF METROBUS SYSTEM AND TROLLEYBUS SYSTEM CONSIDERING ENERGY COSTS AND CO 2 EMISSION: A CASE STUDY FOR ISTANBUL

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1 SET211, 1 th International Conference on Sustainable Energy Technologies, İstanbul, TÜRKİYE, 4-7 Sep. 211 A COMPARISON OF METROBUS SYSTEM AND TROLLEYBUS SYSTEM CONSIDERING ENERGY COSTS AND CO 2 EMISSION: A CASE STUDY FOR ISTANBUL R. Ayaz 1 *, İ. Nakir 1, A. Durusu 1, H. Akca 1, M. Tanrioven 1 1 Yildiz Technical University, Electrical & Electronic Faculty, İstanbul Abstract Recently, alternative energy based vehicles have drawn the attention of engineers specifically on the production of fully electric powered vehicles due to increased environmental awareness and fuel cost. As a result of difficulties in commercializing the vehicles, electric powered cars find an application area in public transportation. One of the solutions for public transportation is to use trolleybus system. This paper gives a comparison of Trolleybus system and existing Metrobus system in Istanbul, Turkey in terms of energy costs and CO 2 emissions. The simulation results show that using Trolleybus system instead of Metrobus is much more economical based on the current prices. As for the emissions, the amount of CO 2 for city centers and overall environment is evaluated. Keywords: Metrobus, Trolleybus, Energy cost, CO 2 Emission 1. Introduction CO 2 emissions, which are harmful to human health and the environment, are released out of fossil fuel based internal combustion engines (ICE). Most of the public transportation system which also uses ICE is a major contributor to urban traffic. The use of fossil fuels as an energy source in public transportation increases CO 2 emissions significantly. The demand for electric vehicles (EV) is increasing every day because of these harmful emissions and decreasing fossil fuels. Using the applications of electric vehicle systems in the urban traffic is an effective way to minimize the CO 2 emissions in city centers. Therefore, it is a good thing to have the electrically powered public transportation system. In the literature, the emissions from ICE based vehicles and electric vehicles are discussed in many studies. These studies have shown that electric vehicles produce less CO 2 emissions. For example, a study by National Defense Council reported that 49-66% CO 2 emissions decreased in case of electric vehicles use in Southern California, where the majority of electrical generation are obtained from natural gas and 21% of the electricity from coal only [1]. The Electric Power Research Institute has performed a study for U.S. Department of Energy. This study has shown that 22-87% CO 2 emissions decreased depending on EV efficiency, geographical location and source of the electric power [1]. The other study have indicated that according to the 3D simulation, 44 ton/day CO 2 emissions are decreased in case of super energy-efficient electric vehicle use instead of diesel vehicle in Tokyo [2]. This paper gives a comparison of Trolleybus system and existing Metrobus system in Istanbul, Turkey in terms of energy costs and CO 2 emissions. 2. Background and Notations Environmentally-conscious vehicle technology has developed because of increasing oil prices and harmful components of fossil energy sources. Current vehicle technologies can be listed as ICE, hybrid and fully electric vehicle. Nowadays, one of the usage areas of fully electric vehicles is public transportation systems. One of the fully electric vehicles that are used in public transportation is Trolleybus. Trolleybuses are vehicles that works just like electric trams with rubber wheel, drawing its power from overhead cables along its way. The difference of this system from electric tram is the use of rubber wheels rather than rail system; so feeding by two cables instead one [3]. * ayaz@yildiz.edu.tr 1

2 SET211, 1 th International Conference on Sustainable Energy Technologies, İstanbul, TÜRKİYE, 4-7 Sep. 211 The engines used in Trolleybuses are more efficient than regular ICEs. Additionally, since some of drivetrains do not exist in electric motors, they have relatively less weight. In transportation systems where start and stop cycles are seen very often, the electric engines are more suitable because of the high torque that is necessary on start moment. 3. The Modeling of Public Transportation Vehicles (Trolleybuses) To model the instantaneous power demand of trolleybus at each step of the simulation, calculations are used on the basis of Newton's second law. (1) In equation (1) and (2), stands for the potential energy of the vehicle and is used for kinetic energy. is the mass of the vehicle with respect to time, and g is the acceleration of gravity. h(t) is the change of height from sea level with respect to time and is change of speed of the vehicle with respect to time. In equation (3) and (4), is the drag force, is the road slope, is the drag coefficient, is the air density, A is the front surface of the vehicle, is the rolling force and is the rolling coefficient [4]. The technical properties of the busses that works on metrobus line are given in the Table 1 below [4][5]. Table 1. The data of busses work on metrobus line Empty weight of the vehicle kg Front surface of the vehicle(a) 6 m 2 Drag coefficient( ),75 Rolling coefficient( ),15 Drivetrain efficiency,8 Taking the derivative of energies obtained from equation (1) and (2), multiplying the speed with the forces obtained from equation (3) and (4), the total power with respect to time are obtained which is given in equation (6). (2) (3) (4) (5) (6) The motion equations given for above vehicle are modeled in MATLAB/Simulink. The simulink model of the vehicle is given in Figure 1. Model input variables are speed, mass, height and slope for every second and output variable is the mechanical power of vehicle which changes with time. 2

3 SET211, 1 th International Conference on Sustainable Energy Technologies, İstanbul, TÜRKİYE, 4-7 Sep. 211 M_power Speed To Workspace2 E_power Mass Height M_Power E_Power To Workspace P_electrical Slope Saturation 1 s M_Power E_electrical Integrator -K- E_energy Figure 1. Simulink model of Trolleybus To Workspace Gain The electrical equivalent of mechanical power is found in system where Trolleybus is used instead of Metrobus. For this purpose, the efficiency of electric engine and line loss are considered. The vehicle subsystem model is given in Figure 1 mass 2 g height speed 1.5 u 2 potential energy kinetic energy ro A Cx u 2 1 mechanical power du/dt Falfa drag force 4 slope atan.8 Drivetrain efficiency Cr.15 g cos Figure 2. Subsystem model of Trolleybus Fr rolling force 3.1. Case Study In this study, Zincirlikuyu-Avcilar route of Metrobus system which is a part of public transportation in Istanbul is used. In this route, there are 26 stops in total. Two of them were ignored in this study since they were not actively used. The route-length is 29.6 km. The time-spent of the vehicle in this distance is 327 seconds. This study is conducted between 18:-19: when the buses are most crowded. Using the rates of number of passengers take off on each stop and the ones take on each stop, the change in total weight of vehicle along its route is given in Table 2 below [6]. The weight of each passenger was considered as 7kg. 3

4 Speed(m/sec) SET211, 1 th International Conference on Sustainable Energy Technologies, İstanbul, TÜRKİYE, 4-7 Sep. 211 Table 2. The change in total weight of the vehicle along its route Stops Average Average number of Actual number number of passengers of passenger in passengers that that take on the bus take off the bus Weight (kg) Distance (m) 1 Zincirlikuyu the 86 bus Mecidiyekoy Caglayan SSK Hastane Perpa Okmeydani Halicioglu Ayvansaray Edirnekapi Vatan Maltepe Topkapi Cevizlibag Merter Zeytinburnu Incirli-Omur Bahcelievler Sirinevler Kuleli-Yenibosna Sefakoy Florya Cennet Mahallesi Kücük Cekmece I.E.T.T. Kampi Sükrübey Avcilar Along this route, the change of the speed of the vehicle and the height from sea-level of vehicle for each second is determined via Gps Datalogger located inside vehicle Figure 3. The speed change of vehicle The speed change of the vehicle is given in Figure 3. The vehicle can reach maximum speed of 25.89m/sec on this route. 4

5 Mechanical Power(W) Height From Sea Level SET211, 1 th International Conference on Sustainable Energy Technologies, İstanbul, TÜRKİYE, 4-7 Sep. 211 In Figure 4 the distance change of the vehicle from sea level is given Figure 4. The change of distance from sea level Entering input parameters that we obtained to our simulink model, we get a metrobus driving cycle. The power requirement of vehicle is changing with respect to the slope of the road, total weight and the speed of the vehicle as it's shown in Figure 5. 5 x Figure 5. The mechanical power requirement of vehicle along its driving cycle Since the necessary mechanical power is provided by electrical system, efficiency of electric engine and line-loss are taken into account. Electrical energy change is shown in Figure 6. 5

6 Electrical Energy(kWh) SET211, 1 th International Conference on Sustainable Energy Technologies, İstanbul, TÜRKİYE, 4-7 Sep Case Study Results Metrobus Case Figure 6. The amount of energy exerted along driving cycle The fuel consumption of vehicles used in Metrobus line is determined in monthly basis. This fuel consumption is found as.5997 lt/km [6]. The fuel consumption along one driving cycle which is 29.6 km is calculated as lt. The energy equivalent of 1 lt diesel fuel is 1.56 kwh. The total energy consumption after one driving cycle is kwh. If we take the cost of fuel as 3.54 TL/lt for Istanbul, the total cost of fuel consumption along one driving cycle is found as TL. Trolleybus Case The total electrical energy need is found as kwh after simulation. If we take the cost of electricity as.16 TL/kWh for Istanbul, the total energy cost is calculated as TL along one driving cycle. 4. Conclusion After this study conducted for Istanbul Metrobus line, it can be concluded that the energy saving for one driving cycle will be kwh if the Metrobus System is transformed into Trolleybus. The energy cost will be 3.15 times less expensive than the current Metrobus system for Istanbul. Thanks to the usage of electric engine instead of diesel engine, Trolleybus System is more efficient than Metrobus System. As a result of the analysis with COPERT which is computer program to calculate emissions from road transport, the amount of CO 2 emission is emitted t/year along one driving cycle by a vehicle on the Metrobus line. The electric engine used Trolleybus will prevent CO 2 emission which is emitted 286,41 t/year by a vehicle. 6

7 SET211, 1 th International Conference on Sustainable Energy Technologies, İstanbul, TÜRKİYE, 4-7 Sep. 211 References [1] Lindly, J.K., Haskew, T.A., "Impact of electric vehicles on electric power generation and global environmental change", Advances in Environmental Research, USA(22). [2] Takeo, S.S., Noboru, Y., Daigo, A., Kazuyoshi, K., "A grand design of future electric vehicle to reduce urban warming and CO2 emissions in urban area", Renewable Energy, Japan(25). [3] Leeds Tbus, Modern Electric Transport For Leeds, 211, on 25/4/211) [4] Alexandre, R., Nicolas, W., Benjamin, B., Abdellatif, M., "Energy sources sizing for hybrid fuel cell vehicles based on statistical description of driving cycles", Vehicle Power and Propulsion Conference (VPPC), Lille(21) [5] Mercedes-Benz Capacity, Standard Introductory Booklet C , 21 [6] Istanbul Electric Tramway and Tunnel Establishments(IETT),(21) 7