Supercapacitors for trolleybuses: an effective technology

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1 Promoting clean public transport Supercapacitors for trolleybuses: an effective technology map by (2010) data2map.at Daniele Balestrazzi TUM München TROLLEY Summer University

2 What are supercapacitors? Supercapacitors or supercaps, technically known as electric double-layer capacitors, are electrochemical capacitors with an energy density hundreds of times greater than electrolytic capacitors. They are used for energy storage in various applications such as vehicles, medical and low-power devices, alternative energy appliances and as complement for batteries. In the field of public transport, supercaps have been installed on: -trolleybuses -hybrid and electric buses -light and heavy rail vehicles. 2

3 Structure and properties Supercaps are made by two layers of the same material (usually activated carbon) connected with an electrode and divided by a thin separator. The porosity of the material allows the storage of high quantities of charge in a realtively small volume. PROPERTIES Capacitance up to 5 kf Voltage in operation a few Volts (need of series-connections) Specific energy up to 30 Wh/kg Mass to volume ratio 0.33 to 3.89 kg/l 3

4 Supercaps for trolleybuses The use of supercaps for trolleybus vehicles has been developed over a few years. They have proved to be energy-saving and reliable. Supercap modules are usually placed on the roof beside the trolley poles 4

5 Supercaps cities Solingen Eberswalde Milano Parma 5

6 Operational advantages Reduced risk of electric arcs Reduction of overloads in substations Improved reliability of on-board devices Regained energy from braking system: more than 90% Overall operational energy saving: more than 25% Energy saving on brakes resistance 6

7 Supercaps charge Overhead 600 V BNU DPU HTS Brake Resist M 3~ ESM Supercap Air conditioning 7

8 Supercaps discharge Overhead 600 V BNU DPU HTS Brake Resist M 3~ ESM Supercap Air conditioning 8

9 Design of a supercap system A supercap system must be sized according to the characteristics of the trolleybus network. There is always a number of modules that represents the most efficient solution. MORE ENERGY SAVED MORE MODULES mean MORE ENERGY USED to carry their additional weight The perfect number of modules depends on: CURVES SLOPE SPEED of each trolleybus route. 9

10 Design of a supercap system Example: PARMA Trolleybus route 5 Flat route Frequent stops City route (speed limit 50 km/h) 4 modules on each trolleybus Energy stored max kwh equivalent to a 40 to 0 km/h or a 50 to 30 km/h slowing down 10

11 Supercap simulators Supercaps performance is simulated through specific softwares. This complicated process can be simplified into four steps. 1. Definition of a basic circuit model 2. Test of supercaps behaviour in various conditions (e.g. voltage, temperature) 3. Improvement of the circuit model through test results 4. Simulation of supercaps performance through differential computing applied to the new model 11

12 Supercap simulators Example of a supercap circuit model used for simulation after the modelling phase (from P.Johannson, B.Andersson, Comparison of Simulation Programs for Supercapacitor Modelling, Chalmers University of Technology, Gothenburg) 12

13 Diagnostic help Road tests on the performance of supercaps are supported by the data registered by the diagnostic help unit of the trolleybus. Similar data are also recorded in everyday operation for the convenience of transport companies. They are usually revised with specific softwares such as Mathcad. 13

14 Diagnostic help Key to colours Overhead voltage Acceleration and braking moment Line current IST couple Supercap voltage Speed Distance 14

15 Contacts Daniele Balestrazzi 15