ENERGY STORAGE SOLUTIONS FOR IMPROVING THE ENERGY EFFICIENCY OF PUBLIC TRANSPORT VEHICLES

ENERGY STORAGE SOLUTIONS FOR IMPROVING THE ENERGY EFFICIENCY OF PUBLIC TRANSPORT VEHICLES R. BARRERO (VUB) - X. TACKOEN (ULB) STIB - Brussels - 5th of February 2009

Plan of the presentation The EVEREST project The supercapacitors technology and market overview Potential solutions for STIB rail vehicles - On-board application for the tram network - Stationary application for the metro network Conclusion and project perspectives Lunch & talk

The EVEREST project OBJECTIVES Define the most efficient energy storage applications for the Brussels public transport company (STIB/MIVB) Estimate the potential energy savings of each application Measure the associated air pollution reduction Assess the costs and benefits of the identified configurations

The EVEREST project AKNOWLEDGEMENTS Project supported by the Institute for the Encouragement of Scientific Research and Innovation of Brussels (IRSIB/IWOIB) Multi-actor project involving the VUB for the technical aspects and the ULB for the economic aspects, both partners working on the environmental issues 4 years project started in January 2007

THE SUPERCAPACITORS TECHNOLOGY AND MARKET OVERVIEW

SUPERCAPACITORS BRIDGE THE GAP BETWEEN BATTERIES AND CONVENTIONAL CAPACITORS Source : Wikipedia

TECHNOLOGY Based on conventional capacitor principle, make use of battery technology Electrical energy stored in an electric field (capacitors)

TECHNOLOGY Based on conventional capacitor principle, make use of battery technology Electrical energy stored in an electric field (capacitors) Special electrodes soaked in electrolyte (batteries) Charge separation occurs in the interface electrode-electrolyte Capacitance No chemical reaction involved

ADVANTAGES High power density High efficiency Low internal resistance Long lifetime, there is very little wear induced by cycling Easy to determine the state of charge by measuring the cell voltage Rapid charge and discharge Wide range of temperature operation SHORTCOMINGS Low energy density High price in energy terms Low cell voltage requires many cells in series for certain applications Voltage balancing needed

MARKET OVERVIEW Telecommunications Industrial electronics Energy generation Transportation & automobile industry

MARKET OVERVIEW Annual growth rate of 15% Slow market entry due to high manufacturing costs Source : Maxwell Thanks to more automated techniques, costs should come down to +/- 0,005 per Farad by 2010

POTENTIAL APPLICATIONS FOR THE BRUSSELS NETWORK

ENERGY STORAGE SYSTEMS On-board application for the tram network

CONVENTIONAL TRAM ARCHITECTURE DC OVERHEAD LINE 700 V Power train Low pass filter Motor - Drive Electric Motor Gearbox and Wheels

HYBRID TRAM ARCHITECTURE DC OVERHEAD LINE 700 V Power train Low pass filter Motor - Drive Electric Motor Gearbox and Wheels Supercapacitor ESS DC/DC converter Hybrid Electric Power System

MITRAC ENERGY SAVER IN MANNHEIM (GERMANY) In commercial service after a 4 years trial phase Very good regularity Around 20% total energy savings

MITRAC ENERGY SAVER IN MANNHEIM (GERMANY) In commercial service after a 4 years trial phase Very good regularity Around 20% total energy savings 2 modules of 0,85 kwh each = 1,7 kwh 270.000 per vehicle

TECHNICAL METHODOLOGY Assess the potential energy savings related to hybrid vehicles following a city route Simulation software needed to do a sensitivity analysis of several parameters Simulation tool: - Determination of power flow and energy consumption - effect-cause method - Relatively simple vehicle models - Fast simulation times

CASE STUDY: TRAM LINE 23 IN BRUSSELS Former 23 line from Heysel to Gare du Midi Real distances between stops - Total length: 20.4 km Max speed - 60 km/h in tunnel sections - 50 km/h in surface (30 km/h for short distances between stops) Traffic conditions and altitude differences are not considered Each tram stop is set to 20 seconds

SYSTEM MODEL

ENERGY STORAGE SYSTEM CONFIGURATIONS Option A. Middle size Cells: C=2000F, Vmax= 2.5V Configuration: 4 strings x 232 cells in series Usable energy: 1.2 kwh Max Voltage: 580 V Cells weight: 371kg Option C. Large size Cells: C=3000F, Vmax= 2.5V Configuration: 4 strings x 200 cells in series Usable energy: 1.56 kwh Max Voltage: 500 V Cells weight: 440 kg Option B. Middle size alternative Built-in modules: C=63F, Vmax= 125 V. Configuration: 3 strings X 4 modules in series Usable energy: 1.23 kwh Max Voltage: 500V Modules weight: 696 kg* Option D. Small size Cells: C=1500F, Vmax= 2.5V Configuration: 4 strings x 234 cells in series Usable energy: 0.91 kwh Max Voltage: 585 V Cells weight: 300 kg *including cells, connections, packaging and cooling

Energy savings range from 23% up to 26% and increase with supercapacitors size ENERGY SAVINGS Savings are higher when the vehicle is loaded with passengers Energy savings decrease at the end of life of the supercapacitors Voltage drops are significantly reduced

Energy savings range from 23% up to 26% and increase with supercapacitors size VOLTAGE DROPS Savings are higher when the vehicle is loaded with passengers Energy savings decrease at the end of life of the supercapacitors Voltage drops are significantly reduced

BENEFITS VS COSTS Insurance Maintenance Less infrastructure Emissions reduction Energy savings Installation Investment

PARAMETERS AND SCENARIOS Parameters - Annual mileage: 50.000 kilometers - Average vehicle occupancy: 2 passengers/m 2 - Vehicle weight: 45,2 tons - Lifetime of the system: 15 years Scenario 1 (medium size) - Module A configuration - Energy content: 1,2 kwh Scenario 2 (small size) - Module D configuration - Energy content: 0,91 kwh

Energy savings LIFETIME BENEFITS ANALYSIS Lifetime results show a consumption reduction of 960 MWh for scenario 1 and 890 MWH for scenario 2 The price of eletricity for large consumers almost doubled in 5 years between 2002 and 2007 Source : Essenscia

LIFETIME BENEFITS ANALYSIS Considering a 50% price increase in 15 years, lifetime benefits amount to +/- 80.000 A higher price increase would allow substantial benefits Energy savings benefits for a T3000 (lifecycle approach) Energy savings benefits 200 000,00 180 000,00 160 000,00 140 000,00 120 000,00 100 000,00 80 000,00 60 000,00 40 000,00 20 000,00 0,00 0% 50% 100% 200% Energy price increase (baseline=74 ) Scenario 1 (Module A - 1,2 kwh) Scenario 2 (Module D - 0,91kWh)

Air pollutants reduction LIFETIME BENEFITS ANALYSIS Unlike cars or conventional buses using fuel, electric vehicles do not exhaust pollutants locally However, the production of electricity generates various air pollutants: CO2, CH4, N2O, NOx, SO2, particulate matters, volatile organic compounds The STIB network is exclusively supplied by ELECTRABEL

LIFETIME BENEFIT ANALYSIS Air pollutants reduction CO2 tons could be cut annually by 15 tons for both scenarios Other harmful emissions could also be reduced

Air pollutants reduction LIFETIME BENEFIT ANALYSIS By attributing a valuation price to each pollutant, we can estimate the cost of the externalities associated to the production of one MWh by the ELECTRABEL facilities (figures from 2007)

Air pollutants reduction LIFETIME BENEFIT ANALYSIS The valuation price of a CO2 ton is expected to increase in the future Source: Handbook on external costs

Air pollutants reduction LIFETIME BENEFIT ANALYSIS The valuation price of a CO2 ton is expected to increase in the future Valuation of environmental benefits (lifecycle approach) Environmental benefits monetization 50 000,00 45 000,00 40 000,00 35 000,00 30 000,00 25 000,00 20 000,00 15 000,00 10 000,00 5 000,00 0,00 Scenario 1 (Module A - 1,2 kwh) Scenario 2 (Module D - 0,91kWh) Source: Handbook on external costs 11,65 18,66 29,18 47,87 Environmental effects monetary values ( /MWh)

LIFETIME COSTS ANALYSIS Costs have been estimated using cost functions with many uncertainties and assumptions Determining the cost of an energy storage system is difficult due to : - influence of development costs - the absence of standardized products for the public transport sector

BENEFITS VS COSTS Energy savings + environmental benefits 300 000,00 Scenario 1 (Module A - 1,2 kwh) 250 000,00 Scenario 2 (Module D - 0,91kWh) Total benefits 200 000,00 150 000,00 100 000,00 ESS cost (Mannheim - 1,7kWh) ESS cost (prototype - 1,2 kwh) ESS cost (large-scale - 1,2 kwh) 50 000,00 ESS cost (prototype - 0,91 kwh) 0,00 Pessimistic Average low Average high Optimistic ESS cost (large-scale - 0,91 kwh) Scenarios

COST-BENEFIT APPROACH (CBA) In order to determine if investing in energy storage solutions is socially desirable, a cost-benefit analysis has been carried out. The approach consists in calculating the Net Present Value (NPV) of the various scenarios (prototype and large-scale). The NPV is defined as the net present value of future cash flows. When the NPV is higher than 0, the project is acceptable. We considered a discount rate of 4% showing that much attention is given to the future generations.

MOBILE ESS FOR A TRAM (PROTOTYPE) - SCENARIO 2

CBA: SENSITIVITY ANALYSIS Energy price increase External costs valuation increase

MOBILE ESS FOR A TRAM: CONCLUSION The use of the ESS has proved that substantial energy savings (around 25%) and emissions reduction could be achieved However, even in the most optimistic cases, investing in mobile energy storage solutions for the Brussels tram network seems not profitable due to the high costs of the technology and the lack of standardization in the public transport sector We estimate that the cost per vehicle should not exceed 100.000 to become attractive Other benefits such as reducing the number of substations or operate without overhead lines could influence the analysis and will have to be assessed in the next steps of the project

ENERGY STORAGE SYSTEMS Stationary application for the metro network

On the Brussels metro network, conventional energy transfers between vehicles can go up to 35% at peak time. But the energy regeneration could be significantly improved by storing the energy in supercapacitors (time differentiation)

STATIONARY SYSTEM ARCHITECTURE

SITRAS SES IN COLOGNE (GERMANY) In operation in cities including Bochum, Cologne and Dresden (Germany), Madrid (Spain) and Peking (China) 300-500 MWh saved annually Around 300 CO2 tons avoided annually

CASE STUDY: METRO LINE 2 High traffic density network (metro every 3 minutes at peak-time) High speeds achieved (70 km/h) before the introduction of the Eco-Drive program Significant altitude differences High vehicle mass (compared to trams)

ASSUMPTIONS Vehicles auxiliaries consumption 20 kw/car Unidirectional line simulated Altitude differences considered Substations installed every 1000 m Trafic scenarios: Cars per metro train Occupancy rate [p/m 2 ] Time delay between trains [min] Peak Time 5 4 3 Off-Peak 5 2 4 Night & WE 4 Only Seats 10

Effect-cause model of vehicles, network and stationary ESS MODEL DESCRIPTION

MODEL DESCRIPTION Effect-cause model of vehicles, network and stationary ESS Vehicles driving cycle

MODEL DESCRIPTION Effect-cause model of vehicles, network and stationary ESS Vehicles driving cycle Vehicles power

MODEL DESCRIPTION Effect-cause model of vehicles, network and stationary ESS Vehicles driving cycle Vehicles power Substations power

MODEL DESCRIPTION Effect-cause model of vehicles, network and stationary ESS Vehicles driving cycle Vehicles power Substations power Network voltage

MODEL DESCRIPTION Effect-cause model of vehicles, network and stationary ESS Vehicles driving cycle Vehicles power ESS SoC ESS power Substations power Network voltage

SIMULATION RESULTS: CONVENTIONAL VEHICLES Peak time Substations delivered energy [kwh] 1080 Traction energy (vehicles) [kwh] 1333 Braking energy regenerated (vehicles) [kwh] 336 Line losses [kwh] 82 Max. available braking energy (vehicles) [kwh] 615 Energy recuperation (E regen./ E traction) [%] 25 Night and Weekend Substation delivered energy [kwh] 235 Traction energy (vehicles) [kwh] 246 Braking energy regenerated (vehicles) [kwh] 18 Off-peak Substation delivered energy [kwh] 744 Traction energy (vehicles) [kwh] 859 Braking energy regenerated (vehicles) [kwh] 159 Line losses [kwh] 43 Max. available braking power (vehicles) [kwh] 392 Energy recuperation (E regen./ E traction) [%] 18 Line losses [kwh] 7 Max. available braking power (vehicles) [kwh] 115 Energy recuperation (E regen./ E traction) [%] 7

ENERGY STORAGE SYSTEM CONFIGURATIONS Small Cells: C=1500F, V max = 2.5V Configuration: 10 strings x 232 cells in series Usable energy: 2.26 kwh Max Voltage: 580 V Cells weight: 742kg Large Cells: C=3000F, V max = 2.7V Configuration: 15 strings x 232 cells in series Usable energy: 6.79 kwh Max Voltage: 580 V Cells weight: 1914 kg Medium Cells: C=3000F, V max = 2.7V Configuration: 10 strings x 232 cells in series Usable energy: 4.53 kwh Max Voltage: 580 V Cells weight: 1275 kg Extra large Cells: C=3000F, V max = 2.7V Configuration: 20 strings x 232 cells in series Usable energy: 9,06 kwh Max Voltage: 580 V Cells weight: 2552 kg

ENERGY SAVINGS AT PEAK TIME

ENERGY SAVINGS AT OFF-PEAK TIME

ENERGY SAVINGS AT NIGHT AND WEEK-END

ENERGY SAVINGS CONCLUSION High impact of ESS size and line positionning Savings up to 11% and 25% depending on trafic scenarios ESS size around 2-4 kwh and distribution every 1500-2000m seems to be the best trade-off solution for this case study Line losses remain unaltered The chosen strategy focuses on energy savings and does not produce any benefits for the network voltage (voltage drops avoidance)

BENEFITS VS COSTS Insurance Maintenance Less infrastructure Emissions reduction Energy savings Installation Investment

PARAMETERS AND SCENARIOS Scenario 1-4 ESS on the line spread every 2000 meters - small-size modules Scenario 2-4 ESS on the line spread every 2000 meters - medium-size modules Scenario 3-6 ESS on the line spread every 1500 meters - small-size modules Scenario 4-6 ESS on the line spread every 1500 meters - medium-size modules

LIFETIME BENEFIT ANALYSIS Energy savings In this case, energy savings are measured on an hourly basis (kwh/h) For each traffic condition, the number of operating hours during one year were calculated based on the timetables

LIFETIME BENEFIT ANALYSIS Energy savings Results show a reduction of 1.800 MWh up to 2.800 MWh annually for the whole metro line depending on the chosen scenarios

LIFETIME BENEFIT ANALYSIS Energy savings Results show a reduction of 1.800 MWh up to 2.800 MWh annually for the whole metro line depending on the chosen scenarios Energy savings benefits (lifecycle approach) 8 000 000,00 Energy savings benefits 7 000 000,00 6 000 000,00 5 000 000,00 4 000 000,00 3 000 000,00 2 000 000,00 1 000 000,00 Scenario 1 (4 small-size ESS every 2000m) Scenario 2 (4 medium-size ESS every 2000m) Scenario 3 (6 small-size ESS every 1500m) Scenario 4 (6 medium-size ESS every 1500m) 0,00 0% 50% 100% 200% Energy price increase (baseline=74 )

Air pollutants reduction LIFETIME BENEFIT ANALYSIS Results show a cut of 423 up to 666 tons of CO2 annually and important reduction of the other air pollutants

Air pollutants reduction LIFETIME BENEFIT ANALYSIS Results show a cut of 423 up to 666 tons of CO2 annually and important reduction of the other air pollutants Valuation of environmental benefits (lifecycle approach) 2 500 000,00 Environmental benefits monetization 2 000 000,00 1 500 000,00 1 000 000,00 500 000,00 Scenario 1 (4 small-size ESS every 2000m) Scenario 2 (4 medium-size ESS every 2000m) Scenario 3 (6 small-size ESS every 1500m) Scenario 4 (6 medium-size ESS every 1500m) 0,00 11,65 18,66 29,18 47,87 Environmental effects monetary values ( /MWh)

LIFETIME COSTS ANALYSIS This table shows the price only for one system but several systems must be installed along the line

BENEFITS VS COSTS Energy savings + environmental benefits 10 000 000,00 9 000 000,00 8 000 000,00 7 000 000,00 6 000 000,00 5 000 000,00 4 000 000,00 3 000 000,00 2 000 000,00 Scenario 1 (4 small-size ESS every 2000m) Scenario 2 (4 medium-size ESS every 2000m) Scenario 3 (6 small-size ESS every 1500m) Scenario 4 (6 medium-size ESS every 1500m) Scenario 1 (prototype) Scenario 2 (prototype) Scenario 3 (prototype) Scenario 4 (prototype) 1 000 000,00 0,00 Pessimistic Average low Average high Optimistic Scenarios

COST-BENEFIT ANALYSIS: SCENARIO 2 (PROTOTYPE)

CBA: SENSITIVITY ANALYSIS The Net Present Value appears positive in most cases which indicates that benefits overcome the costs

STATIONARY ESS FOR THE METRO NETWORK: CONCLUSION The use of stationary energy storage systems on the metro network offers consequent energy savings and emissions reduction Even in the case of an energy prices stabilization, investing in stationary energy storage solutions for the Brussels metro network seems profitable Scenario 2 seems the best option and consists in installing a medium-size module in four substations spread every 2000 metres. The main advantage of the stationary application compared to the on-board is that the vehicles must not be retrofitted which is easier to implement by the transport company.

CONCLUSION

ADVANTAGES OF ENERGY STORAGE SYSTEMS Significant energy consumption reduction Voltage drop compensation in weak distribution networks Potential investment reduction in infrastructure: substations, overhead lines,... A good way to fight against the energy price increase OBSTACLES FOR A WIDE USE OF THE TECHNOLOGY High development costs due to a lack of standardization in the public transport network Difficult to retrofit existing vehicles

PROJECT PERSPECTIVES A mobile system for the metro has been assessed and shows interesting results but seem almost impossible to implement on the vehicles due to the lack of room (more info on request) Information requested from STIB to consider: - the benefits of having more vehicles without adding new substations - the economic impact of driving without overhead lines on small sections - the influence of reducing the electricity demand at peak time and benefit from better tariffs (avoid to go beyond some thresholds)

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