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Thread: electric/hybrid/gas car efficiency

  1. #1 electric/hybrid/gas car efficiency 
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    My highschool physics teacher told us that electric cars (excluding hybrids) are inefficient. He explained when energy transforms from one form to another it is not 100% efficient so some of the energy is "lossed". So there's the electric car route (1) and the gasoline car route (2).

    (1)
    Oil/Gas/Coal/Nuclear/whatever --> converted to electricity in power plant --> charges electric car

    (2)
    Gasoline --> directly powers gasoline car

    So apparently, gas cars are more energy efficient then electric cars.

    He then told us that hybrid vehicles, on the other hand, are the best because they harness energy that would normally be lost in breaking, and use it to help power the car in combination with your typical gasoline engine.

    So basically my questions are,

    How accurate is this interpretation? Is there significant energy loss in electric cars? Is this why electric cars aren't more popular?

    Do hybrid vehicles work by regenerative braking? Are flywheels used in electric cars, and why or why not? Why don't you have to charge hybrid cars like you do only electric cars?


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  3. #2 Re: electric/hybrid/gas car efficiency 
    Reptile Dysfunction drowsy turtle's Avatar
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    Quote Originally Posted by brushman
    (2)
    Gasoline --> directly powers gasoline car
    How about energy to pump the oil out the ground, energy to process and purify the fuel, and energy to move the fuel around the place to fuel stations?

    Compared to:

    sun -> national grid -> car batery

    On this basis, gasoline is much more wasteful.

    Quote Originally Posted by brushman
    How accurate is this interpretation?
    Very inaccurate.

    Quote Originally Posted by brushman
    Is there significant energy loss in electric cars?
    Yes. And also in petrol cars; heat from the engine is wasted, and fuel is not always completely combusted.

    Quote Originally Posted by brushman
    Is this why electric cars aren't more popular?
    No. It is because they are slow, have a much shorter range, and take many hours to refuel.

    Quote Originally Posted by brushman
    Do hybrid vehicles work by regenerative braking?
    Yes.

    Quote Originally Posted by brushman
    Why don't you have to charge hybrid cars like you do only electric cars?
    The batery is charged by regenerating breaking, as you said. The energy comes from gasoline to start with.

    Basically, a hybrid car gives you more miles to the gallon than a normal car.


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  4. #3  
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    How about energy to pump the oil out the ground, energy to process and purify the fuel, and energy to move the fuel around the place to fuel stations?

    Compared to:

    sun -> national grid -> car batery

    On this basis, gasoline is much more wasteful.
    Most of the electric car's energy won't come from solar power. It will be from coal, natural gas, nuclear, oil, etc. like the gasoline car. It's just the way I see it, there's one more energy conversion step for the electric car which seems like it'd waste energy.

    Yes. And also in petrol cars; heat from the engine is wasted, and fuel is not always completely combusted.
    I see what you are talking about here, but what about the energy lost when changing forms (1)?

    basically,

    when the electricity to power the electric car is converted to electricity from other forms, are significant amounts of energy lost?



    sorry if i'm not explaining this well, or i don't know what i'm talking about
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  5. #4  
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    Electric cars are pointless unless you harness the energy to produce electricity from a clean energy source. When you start with something like gasoline, it is inefficient to convert it to electricity. In that way, you could say in this context that gasoline cars are "more efficient". I believe the reason why the Prius uses a gasoline powered engine to convert the energy to electricity is because the wheels are turned by an electric motor. They could have made a mechanism to switch from the gas engines power to the electrics, but maybe that would have been difficult to engineer and expensive. They could have gone with an all electric car, but putting that many batteries into the car is very expensive, and you cannot instantly refill it like you can with gas. So, instead you run off of the batteries for as long as you can, then once you run out you move to fuel. In the end it adds up to save energy when compared to a pure gas car, however they should try to work on a drive shaft diverter so it does not have to convert the gas to electric energy.

    In terms of inefficiency, my computer PSU alone in converting 120V AC to 12V DC (5v, 3v, etc..) is only 82% efficient. I should assume that the gas motor outputs at high voltage AC and has to convert it to low voltage DC, battery voltage. So, even given the highest conversion rates I've seen (around 92%), you will still loose 8% of the energy. And that's just in HV AC conversion, there is also inefficiency in the generator and in charging the batteries themselves (notice that batteries heat up when you charge them, that energy has to come from somewhere). And if you want to get picky, you also have losses from inductive coupling (.1%?) and evanescent wave near field coupling (.0000001%?).

    My classes just got out and I have allot of free time, so ask as many question as you like : )
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  6. #5  
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    i prefer the in-wheel hybrid.
    it takes out the whole mechanical transmission linkage, and instead the power is transmitted directly to the wheels.
    this way, an in-wheel hybrid is 25% more efficient than an all-gasoline car, or hybrid.
    there's also a lot of buzz about hybrid retrofit kits:

    http://www.mira.co.uk/
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  7. #6  
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    Quote Originally Posted by brushman
    Yes. And also in petrol cars; heat from the engine is wasted, and fuel is not always completely combusted.
    I see what you are talking about here, but what about the energy lost when changing forms (1)?
    Energy is 'lost' when it is turned into a form as energy which is not useful in this situation, usually heat.

    In both the electric car and the gas car, energy is lost as heat when the oil/gasoline is burned, and probably at similar percentage efficiencies.

    For instance, a petrol car engine has about 30% efficiency, and a diesel engine around 45%.

    http://en.wikipedia.org/wiki/Fuel_efficiency

    In a power station, electricity will be generated at more like 70% efficiency, but will be reduced during charging of bateries, and lost as heat by the electric motor in the car.
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    Quote Originally Posted by drowsy turtle
    In a power station, electricity will be generated at more like 70% efficiency, but will be reduced during charging of bateries, and lost as heat by the electric motor in the car.
    I think your estimate for the power plant a bit optimistic. Perhaps you were thinking of the theoretical Carnot efficiency.
    Quote Originally Posted by wikipedia
    In practice, because the operating cycles of real engines are nowhere near as efficient as the Carnot cycle, coupled with other irreversibilities such as the combustion process itself and friction, real engines fall far short of the Carnot efficiency. Real automobile engines are only around 25% efficient. Combined cycle power stations efficiencies are higher, approaching 46%, but still fall at least 15 points short of the Carnot value. As Carnot's theorem only applies to heat engines, devices that convert the fuel's energy directly into work without burning it, such as fuel cells, can exceed the Carnot efficiency.
    http://en.wikipedia.org/wiki/Thermodynamic_efficiency
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  9. #8  
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    Quote Originally Posted by Harold14370
    Quote Originally Posted by drowsy turtle
    In a power station, electricity will be generated at more like 70% efficiency, but will be reduced during charging of bateries, and lost as heat by the electric motor in the car.
    I think your estimate for the power plant a bit optimistic.
    Probably. I ran out of time to research a suitable figure; places to be and so on.
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  10. #9 Re: electric/hybrid/gas car efficiency 
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    Quote Originally Posted by brushman
    How accurate is this interpretation? Is there significant energy loss in electric cars? Is this why electric cars aren't more popular?
    Your teacher is full of shit. Fossil fuel plants are usually around 40-50% efficient, mainly because they can take advantage of all sorts of elaborate heat-capturing technology that you don't have room/weight for in a car engine. Add in about 7.5% loss in electrical transmission across the power lines and 8% loss going from the battery to kinetic energy in the motor, and an electric car is around 32-42% efficient. Your car engine, on the other hand, is probably around 18-30% efficient.
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  11. #10  
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    Quote Originally Posted by Cold Fusion
    I believe the reason why the Prius uses a gasoline powered engine to convert the energy to electricity is because the wheels are turned by an electric motor. They could have made a mechanism to switch from the gas engines power to the electrics, but maybe that would have been difficult to engineer and expensive.
    http://www.cleangreencar.co.nz/page/prius-transmission

    The prius is able to blend the power from both power plants or capture power from the wheels to put back in to the batteries in any ratio. We own a 2008, it does everything as advertised. I lean more toward the VW TDI's however.

    I agree electric cars will be a bit of a waste until we have more solar or other clean energy sources. The electric motors themselves are much more efficient then any petrol engine, at least last time I checked.
    Pleased to meet you. Hope you guess my name
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