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Concept Electric Hybrid SOFC/Battery Transit Bus

  1. Mar 19, 2010 #1
    Good afternoon from England!

    I am sure this is not a homework, rather an engineering project.

    I am interested in an alternative way of electrically propelling a transit bus using a combination of solid oxide fuel cell and battery, focussing on its powertrain.

    Two powertrain configurations arise;

    1. A battery-dominant powertrain =>>> a bigger battery is the prime mover, having a smaller solid oxide fuel cell which constantly and continuously feeds the generated electricity to the battery. SOFC is also used to feed auxiliary devices. A re-gen brake is also used. Here, the SOFC acts as a range extender, extending the driving range. An example is the ABSOLUTE project proposed by Imperial College researchers in London.

    2. A fuel cell-dominant powertrain =>>> having an SOFC as a prime mover and it also powers auxiliary electrical devices. Transient power requirement is provided by a smaller battery. Again, a re-gen brake is also to be used. The example is a Mercedes-Citaro fuel cell bus - however, it uses a PEM fuel cell. Such the buses are operating for a CUTE project.

    I wonder if anybody could comment on the pros and cons of these two arrangement?

    Which one is more practical and better in terms of a transit bus application?

    The only drawback I can see so far with the first layout is the weight and size of the battery since it needs to be big enough to provide sufficient energy.

    The problem with the second layout is that I am not sure if we can rely on a long start-up time of SOFC. It may take several minutes? Will this make the layout impractical even though the only fuel cell vehicle does exist?

    Another problem is the energy required to heat up the fuel cell stack. The energy could be obtained from the stored energy from a battery when we start the bus, but will it turn out to be a waste of having a battery since all stored energy might be used up. And there won't be enough energy from a battery to compliment the prime mover (SOFC) when required during a trip. Does anyone know how the fuel cell Citaro bus actually work in this arrangement?

    Please share your opinion, every single opinion or knowledge from you guys is so valuable to me. Thank you so much.

    PS - Sorry if I make you confused with my poor English.

    PS2 - Do we use "a" or "an" in front of the acronyms, example SOFC, PEMFC

    PS3 - I have also attached my current idea, using a SOFC as a range extender. It feeds the battery as well as power on-board electrical devices

    Attached Files:

  2. jcsd
  3. Mar 19, 2010 #2
    Situation 2 isn't going to work as SOFC really can not do transient operation. This is why PEMFCs are targeted for mobile applications. SOFCs also have a very high start up time, usually around ~1-3hours.

    Situation 1 will work just fine assuming as long as you have a method for heating the cell during start up. Once at operating temperature, SOFCs don't really have trouble remaining at that temperature as long as they are properly insulated and loaded. With this configuration you have a "series" hybrid type of design, basically the same thing as the Chevy Volt but minus the engine and add the fuel cell. Your battery on the other hand doesn't need to be so large that it can power the bus for long periods of time, it only has to be large enough to act as a sufficient "buffer" between the SOFC and the power train. In short, you want your SOFC operating at a constant X load always, and you let the battery do all the transient operation. To do this your battery may only need to power the bus for 20-30 miles or so.

    Delphi and Boeing have done a lot of work in developing SOFC APUs. Delphi plans to release a SOFC APU in the next few years for large trucks and heavy vehicles. I see no reason why APU technology could not be adapted to your application.

    PS: Your english is pretty good, better than many who native language is english.

    PS2: You put an "a" before SOFC or PEMFC as they do not start with vowels.
  4. Mar 19, 2010 #3

    Really appreciated your answers, they even clarify some more questions I am about to ask!!!

    Yeah, I was not so convinced when choosing the 1st one, but now I am pretty sure with the 1st layout with your fact "SOFC is not good at transient power requirement".

    May I ask you guys a bit more detail regarding the SOFC?

    So in this case, a battery only works as a prime mover but deals with the transient power requirement also, not supplying any energy to run electrical devices. A SOFC, on the other hand, only continuously recharges the battery and powers electrical devices. Is this correct? If I am to use a SOFC to both recharge the battery and also power the electrical devices, will this be practical? Would a 10 kW SOFC be sufficient to do a job? (Assuming a conventional deisel bus required total power of 170 kW)

    Ideally, how should I power the APU? >>> by SOFC or by a battery?

    Thank you very much.
  5. Mar 19, 2010 #4

    I don't know. That depends on the characteristics of the system. To figure that out you would have to model the bus and the system which powers it.

    Just have the SOFC power everything except the electric motor. In other words, have the SOFC power all electronics and the recharger for the battery at the same time. Basically, anything that doesn't require transient operation can and should be powered by the SOFC.

    Have you thought about what fuel you are going to use? SOFCs can run on a variety of fuels, even CO. In this case, natural gas (CH4 or similar) or hydrogen would probably be my choice since storage space isn't much of an issue with buses. You can also run them on diesel and really almost any hydrocarbon based fuel.
  6. Mar 19, 2010 #5
    Yes, since this project is specifically aimed at my country, Thailand-specific objective.

    I have decided that a natural gas, NGV will be used. From what I have researhed through literatures, seems like it a good fuel, isn't it? It is cleaner than dielsel or petrol, gives more hydrogen-to-carbon ratio and most importantly, lowest price.

    Thank you very much for your reply.
  7. Mar 19, 2010 #6
    Natural gas is a good choice. Usually the only issue with it is storage since its a gas and not a liquid. Since buses have lots of space, storage isn't really an issue.
  8. Mar 20, 2010 #7
    Hello again, Topher925

    I know this sounds really stupid, but could you please guide me what it means by "MODEL" or "SIMULATION"?

    I have heard of these words many times but no one can actually clarify what they mean exactly.

    So, in terms of modelling a bus or any sub-system, what text should I look at? Are there any GENERIC procedures on MODELLING or SIMULATION.

    Is it possible to give me an example so I can see the picture of what we really do when model a bus (or some other things?).

    Also, what is the output of the simulation? What do we get?

    Thank you very much.
  9. Mar 27, 2010 #8
    Hi again,

    Can anyone give me a clue on what the simulation or modelling actually mean?

    As the above thread, I do not understand what I am supposed to do in the simulation, what would I get from it?

    Thank you very much
  10. Mar 28, 2010 #9
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