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Electric car question

  1. Aug 11, 2009 #1

    Wax

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    There's a lot of hype about saving money by buying a hybrid but what I want to know is if you save money in general and not just gas? I understand that you can get 100 or 200 extra miles per gallon but you still have to plug your hybrid into a power outlet. Are you saving money by paying more for your electric bill then using gas?
     
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  3. Aug 11, 2009 #2

    mgb_phys

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    Generally a hybrid (at least the current generation) isn't a plugin - it uses the gasoline engine to charge it's batteries. The next generation (including the Volt) can also be pre-charged from an outlet. They both only have a limited range on battery (30-40mi).

    How economic it is depends on your driving, if you do a lot of stop start in-town driving they are fantastic. Taxi drivers love them - the claims here are that they are spending $20/day on gas instead of $100.
    If you do >50miles/day on freeways you are likely to do better with a diesel or any small hatchback that does 50mpg.

    Once plugin electric vehicles become available it is likely that the cost of running them on off-peak electric will be much lower than gasoline (unless the tax man comes up with a 'solution')
     
  4. Aug 11, 2009 #3

    Wax

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    I think you missed my question. Let me try to rephrase it with an example. What I'm trying to figure out is if you are really saving money, not gas.


    Lets try and use your example.
    Lets say I spend 100$ on gas for a regular car and it gives me a total of 400 miles. If I decide to buy a hybrid, will i have to spend 20$ on gas and 80$ on electricity to get 400 miles?
     
  5. Aug 11, 2009 #4
    He did answer the question, it depends on what driving. Electricity is cheaper than petrol per mile, so you could potentially save money.

    40 miles of stop start low speed city driving works perfectly with an electric motor as you never ue the engine.

    Endless long range driving at motorway speeds and you'll be spending much more on fuel as you are using both the engine and the electric motor and would be better with a small diesel.

    So in general yes a hybrid will save you money, but is it the best/cheapest option?

    400 miles of town driving != 400 miles motorway driving.
     
  6. Aug 11, 2009 #5

    Wax

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    Ah.. nice nice.

    Thanks.
     
  7. Aug 11, 2009 #6
    The average cost of electricity is $0.11 per kWh.

    The Volt is expected to use 25 kilowatt hours per 100 m. This means that for the first 40 miles, it will use 10 kwh, which costs $1.1. So, your cost per mile is 2.75 cents per mile.

    After that, you switch over to gasoline at 50 mpg. The cost of gaslone is...lets say. $4.60, so your cost per mile is then 9.2 cents per mile.

    In other words, the first 40 miles are about 3 times cheaper than later miles. Only 3x?
     
  8. Aug 11, 2009 #7

    mgb_phys

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    Rough figures, the chevy volt has a 16 kWh battery but apparently is only used 85%, so assuming the manufacturer's figures of 40mile/charge are correct - you are doing 40miles/9kWh = 4.5 miles / unit of electricity.
    Depending on location and off-peak deals you are probably paying around 10c/unit for electricity - so if you can just use the plugin range it is very very cheap
     
  9. Aug 11, 2009 #8
    Do the Volt's batteries last longer when recharged more often for the same usage?
     
  10. Aug 11, 2009 #9
    This is surely the draw from the batteries. Converting the AC line to battery charge should lose 25% in converter and batteries. So the cost should be 3.66c per mile.

    The volt will sell for $50K. Is this number correct? If my $5K scrapyard SUV gets 15 miles per gallon, what is the break even mileage? Shall we use $3 per gallon?
     
    Last edited: Aug 11, 2009
  11. Aug 11, 2009 #10
    50,000 = 5000 + 4.6/15*miles
    miles = 146,739

    So if you sold your SUV and bought a Volt, the break even point would be after you put 150k miles on your Volt.
     
  12. Aug 11, 2009 #11

    Pengwuino

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    A few things to note, gasoline in the US is only about $2.5/gallon on average. Also, the Volt is extremely expensive (around $42,500 after government rebates) and the batteries only have a 10 year life span which works against people who would use the car in the ideal situation of short trips back and forth between work seeing as how the batteries are expensive. Other hybrid cars are pretty much cheaper in any case though. Even if you use the car almost exclusively for long cross country trips... they run on pretty efficient engines so that's good no matter what.
     
  13. Aug 11, 2009 #12
    That's another thing...I have a hard time trusting these lithium ion batteries. They never seem to work as advertised. A lithium ion battery loses charge faster when in warm weather (when not in use). If you ever stop charging a lithium battery before it is fully charged, it suffers permanent memory loss. If you ever let a lithium ion battery fall close to zero charge, it is permanently whacked.

    When I had an IPod, that damn battery kept dying after about 25 minutes. I even got a replacement battery. My laptop which originally lasted 7.5 - 8 hours on a charge now only lasts about 2.5 hours -- and I am pretty anal retentive about good battery manage. Heck, I used to even store the battery in the freezer when not in use for long periods of time.

    Oh and another thing...if the Volt runs on battery until the battery runs down, then you turn off the car before the batter can be recharged, you might have trouble turning it back on!!!
     
  14. Aug 11, 2009 #13

    Pengwuino

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    From what I read, it charges to 85% and allows drainage until 30%. Then the engine takes over.
     
  15. Aug 11, 2009 #14
    Battery life is tricky and dependent on battery technology, which is why I didn't bring it up. If you use very little off the top of the battery charge you get disproportionately more discharge cycles than if you take it down further. More simply, the deeper the discharge the less total energy output you get before the batteries die.
     
  16. Aug 11, 2009 #15

    Pengwuino

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    Yes it sure is. Also, an article I read claimed that the engine would turn on if the batteries weren't at the proper temperature range. Considering the temperature dependent properties of batteries, is there going to be problems running this vehicle in the various climates you see around the US?
     
  17. Aug 11, 2009 #16
    Yeah. I have little doubt they are using anything other than Lithium Polymer batteries. There aren't any other battery techologies that can compete at this time. They can't run cold. Optimum is 50C internal temp(?). If they are too hot,usually through self heating to get this hot, they become dangerous. So hot weather is probably not a problem, but in the northern states in winter they won't do well. Actually, what's the problem? If you can run the engine and batteries in parallel, the high resistance of the cold batteries would let them heat up, but at a premium in heating current. ---Obviously I don't know enough to comment on temperature stuff, so nevermind, :blushing: but these sort of issues are what you should be looking for if you wish to investigage.
     
    Last edited: Aug 11, 2009
  18. Aug 11, 2009 #17

    mgb_phys

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    IIRC They don't suffer damage in cold but don't work very well - specifically they can't efficiently be charged when cold so they have a heater system that keeps them above 0C while charging.

    No the Volt isn't the ultimate perfect cheap electric car, this is from a company (and a country!) that can't make a small economical gas/diesel hatchback that can do 60mpg.
    It's expensive and limited, it's going to be sold to people who would have bought a BMW but like the green image (plus a lot of taxi drivers) you will get your 100mi range cheap reliable PHEV from the Japanese (and Chinese) in a few years.
     
  19. Aug 11, 2009 #18

    Pengwuino

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    Yah it's definitely a PR stunt hoping to get a government push with the EPA rating. I'm just waiting for another company to come out and do it three times as well. I don't really get the taxi driver thing though considering the tremendous cost (and I don't see how the battery will help since they cant charge up during their work day).
     
  20. Aug 11, 2009 #19

    mgb_phys

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    It's a hybrid, the engine charges the battery on the longer stretches where you get above 20mph on the way to the airport or the suburbs.
    The hour you are sitting in traffic or at walking pace in downtown is free. Conventional taxis probably get only half the makers 'city' mileage because of the stop -tart congested driving.

    If you are doing 50-100,000 miles/year the capital cost of the car is irrelevant - reliability and fuel economy are all that matter, that's why most taxis in europe are E class mercedes.

    If I were Toyota I would have made sure that the first years production of the Prius went to taxi drivers and tracked the repair/fault rate very carefully.
     
    Last edited: Aug 11, 2009
  21. Aug 11, 2009 #20

    Pengwuino

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    Oh yah, I keep forgetting the Volt has regenerative braking too :rofl:. It does make me wonder how much do the batteries cost? With a 10 year battery life on normal use, I would hope you arent replacing all those batteries every year or so.
     
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