How do hybrid cars save energy?

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    Oct 08, 2011 7:40 PM GMT
    The way I understand it, while you’re driving along, the gasoline engine in addition to turning your wheels is also cranking a generator that charges a battery, and when the car senses you need less power, it shuts the gasoline engine down and runs the car on electric power. Seems simple enough.

    But, wait – the first law of thermodynamics says you can’t get any more energy out of a system than you put into it. So, charging the battery takes just as much gasoline as if you were using it to run the car during those times when the battery takes over. Otherwise, the battery wouldn’t have enough power to turn the wheels. So, you're using more energy than you need to when the gas engine is running - part of it turns the wheels and the rest is stored in the battery - and that's what the electric motor taps into.

    And, the second law of thermodynamics says no system is 100% efficient, so you’d have to use more energy to charge the battery than the battery could put out to run the car. Of course, efficiency is a tricky thing – it might be that running a car is not a terribly efficient use of gasoline. But it seems completely implausible that using a gasoline engine to generate electricity to charge a battery to run an electric motor to turn the wheels of your car is more efficient than just using the gasoline engine to turn the wheels directly.

    I can see that you might save energy if the generator only runs when the car is idling – when you’re stopped at a traffic light, for instance. But then again, you’d still need more gasoline to idle as well as run the generator than if you were just sitting there idling. Seems like you could simply tune the engine to idle at a very low rate and use less gas. And anyway, wouldn’t those be the exact times you’d want to shut down the gasoline engine and let the battery take over?

    I did hear of one system where the generator is tied in to the braking system, and the momentum you lose while braking is used to crank the generator and charge the battery. But this doesn’t sound like it could possibly produce enough energy on its own to run the car – unless you’re a horribly inefficient driver, and spend all your time gunning the engine and then slamming on the brakes.

    I know hybrids do have great gas mileage, but they also have pretty small engines. I have to wonder what the gas mileage of that same engine would be without the generator and the added weight of the battery (it’s super heavy).

    Am I missing something? Or is this the scam of the century?
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    Oct 08, 2011 7:49 PM GMT
    Yes you are...

    Hybrids capture energy otherwise lost to heat and friction when braking, decellerating, or that generated when going downhill etc which can be used to power additional momentum at a later time

    The electric engine doesn't need to generate the full momentum...just enough to keep the car in motion when gas has been used to reach cruising speed
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    Oct 08, 2011 8:35 PM GMT
    Eventually solar cells will be small enough, powerful enough, and economical enough to use for charging the battery. In the meantime, having hybrids will help work out the kinks they run into with battery power in general.
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    Oct 08, 2011 8:51 PM GMT
    MsclDrew saidYes you are...

    Hybrids capture energy otherwise lost to heat and friction when braking, decelerating, or that generated when going downhill etc which can be used to power additional momentum at a later time

    The electric engine doesn't need to generate the full momentum...just enough to keep the car in motion when gas has been used to reach cruising speed.

    True. Also the internal combustion engine can be made with a smaller displacement in a hybrid, consuming less fuel. Plus the hybrid engine tends to operate at a more constant speed (rpm), as it drives the electric generator at revolutions close to its ideal volumetric efficiency, at which the least fuel produces the most energy.

    In contrast, an engine that drives the wheels directly must constantly change its rpms to match road speed and load, not able to stay within its optimal rpm range, becoming least efficient in stop & go traffic, and it continues to consume fuel at idle. Whereas many hybrids will turn their gasoline engine off completely at stops of more than a minute, the electric motor and battery ready to instantly drive the car forward when traffic permits.
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    Oct 08, 2011 9:03 PM GMT
    Way too much thought into this. The desirable end result is higher MPG. Hybrid buyers don't give a shit about saving energy or the law of thermodynamics.

    Also, consider that different auto manufactures have different hybrid systems. Toyota's system tries to use the electric motor as much as possible. The gas motor kicks in under heavy load/acceleration. Honda's system is somewhat opposite. It runs the gas motor pretty much all the time. The electric motor kicks in under heavy load/acceleration. Not a bad thing. The gas motor has a small displacement and tuned for efficiency. Great for highway driving, but not so great when entering the freeway or climbing hills. So this is where the electric motor comes handy.

    So when buying a hybrid car, one really has to examine the type of driving they do and get the right type of hybrid. Otherwise, they may be disappointed.
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    Oct 08, 2011 11:46 PM GMT
    The easiest splaining is that an electric generator and motor is more efficient at providing power to the wheels than an internal combustion enging/transmission. . Much like a diesel locomotive.. the diesel engine doesn't power the train, it powers generators which in turn provide electricity to the traction motors on the wheels. Just thought I say that because most people don't realize it and think the diesel engine is turning the wheels.
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    Oct 09, 2011 12:04 AM GMT
    They are fine as a local solution to smog, perhaps - such as in L.A.

    But the whole thing is smoke and mirrors (pun intended).

    The energy that goes into making the things is never accounted for when environmentalists tout the awesomeness of these cars.

    FORD F-150 or nothing.
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    Oct 09, 2011 12:17 AM GMT
    JackNWNJ saidThey are fine as a local solution to smog, perhaps - such as in L.A.

    But the whole thing is smoke and mirrors (pun intended).

    The energy that goes into making the things is never accounted for when environmentalists tout the awesomeness of these cars.

    FORD F-150 or nothing.


    Or Chevrolet 1500 Silverado 5.3ltr V-8 icon_biggrin.gif
  • FredMG

    Posts: 988

    Oct 09, 2011 12:31 AM GMT
    Hybrid cars don't "save energy"- pound for pound a hybrid uses as much energy as a hummer (presuming you could find a 4000 lb hummer or a 10,000 lb prius). If you want to "save" energy, or use less gas or electricity ride a bike or walk.

    Oh, yeah, and where do you put all those toxic batteries when you're done with them? At least the lard I burn off my fat ass by cycling comes back in the form of beer.
  • JP85257

    Posts: 3284

    Oct 09, 2011 12:50 AM GMT
    LVmotoJock said
    JackNWNJ saidThey are fine as a local solution to smog, perhaps - such as in L.A.

    But the whole thing is smoke and mirrors (pun intended).

    The energy that goes into making the things is never accounted for when environmentalists tout the awesomeness of these cars.

    FORD F-150 or nothing.


    Or Chevrolet 1500 Silverado 5.3ltr V-8 icon_biggrin.gif

    F250 Lariat PowerStroke.

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    Oct 09, 2011 12:51 AM GMT
    FredPDX saidHybrid cars don't "save energy"- pound for pound a hybrid uses as much energy as a hummer (presuming you could find a 4000 lb hummer or a 10,000 lb prius). If you want to "save" energy, or use less gas or electricity ride a bike or walk.

    Oh, yeah, and where do you put all those toxic batteries when you're done with them? At least the lard I burn off my fat ass by cycling comes back in the form of beer.


    Poppycock
  • FRE0

    Posts: 4863

    Oct 09, 2011 12:55 AM GMT
    paulflexes saidEventually solar cells will be small enough, powerful enough, and economical enough to use for charging the battery. In the meantime, having hybrids will help work out the kinks they run into with battery power in general.


    I'm not sure what you have in mind here. If you expect solar cells on the car to do the work, that won't happen. Even if the solar cells were 100% efficient, the area available on the car would be insufficient to collect enough energy.
  • Posted by a hidden member.
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    Oct 09, 2011 1:27 AM GMT
    Different manufacturers use different techniques, but they all use clever tricks to recover energy to recharge the battery, rather than just using the gas engine. For example, they can recover energy during braking or when coasting.

    Whether or not they really save energy over the lifetime of the vehicle, including manufacturing and disposal/recycling is debatable. I bought a hybrid because I believed it was important to invest in the technology, even though it is probably just a stepping stone to some other non-gasoline engine type.
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    Oct 09, 2011 1:39 AM GMT
    FredPDX saidOh, yeah, and where do you put all those toxic batteries when you're done with them? At least the lard I burn off my fat ass by cycling comes back in the form of beer.


    Lead acid, nickel metal hydride, and lithium ion batteries used in hybrid and electric cars have long been recycled. All the manufacturers do this, and most put stickers on the battery packs (that aren't accessible to consumers, BTW) with information and dollar amounts, in the multiple thousands, that they will pay for the packs.

    Unlike consumer electronics, where the batteries are more likely to end up in landfills due to consumer indifference, even tho they can be efficiently recycled as well (at your local Best Buy), end-of-lifing a car is actually a regulated process, with licenses, permits, etc., and battery recycling has LONG been part of it (like for decades and decades). Hybrids and electrics don't change that process, they just leverage it.

    Talking about "toxic batteries" and "what to do with them" just shows a lack of awareness of not only the most basic information about hybrids or electrics, but about normal car batteries as well. If you've ever bought a new lead-acid battery for your car, you surely know the place that sells you a battery will take your old one. They don't do that out of kindness. They get money for em. Don't trust me, just spend 10 minutes on the web with Google and you'll easily be able to separate fact and fiction on this topic.

    As to the weird "energy" arguments here, I don't think it's worth engaging other than to encourage anyone to do a little reading away from RJ on the net about the difference between "energy" and "energy from gasoline" and what MPG figures mean when comparing normal and hybrid cars. All the answers are there, without the bizarre theories of physics and economics we're seeing on this thread. The net will be obvious that hybrids save gasoline (versus the average normal car of the same size), because the gasoline engine is smaller and the combination of electric and gasoline "engines" raise the aggregate efficiency because the electric part of the "engine" is more efficient. This is one of the reasons they've been making train engines as hybrid electric/diesel for decades now (in addition to the power and torque characteristics of electric motors vs combustion engines) -- a combination that is even more efficient (in MPG) that electric/gasoline is.

    All that said, a smaller car, powered with a small, highly efficient diesel engine, will trump any hybrid if you want to change your metric from "volume of oil required to move the equivalent weight at the equivalent speed over the equivalent route" to "what is the most oil-efficient way to move 4 people and 5 bags of groceries." But if you want to buy a big 4 door sedan, or SUV, or truck, the hybrid engine will save gas versus the regular one for that same sedan/SUV/truck. Will it do it in an economic way for the average driver? No, not at current world-wide recession prices (taxi cabs, for example are a completely different matter, which is why you notice the fleets are all going hybrid). If gas goes back up to $5/gallon, then yes, the economics start to look OK again for the average driver, depending on the lifetime of the investment.

  • Thirdbeach

    Posts: 1364

    Oct 12, 2011 4:09 AM GMT
    A few years ago Car and Driver Magazine did a test on the Hybrid technology.
    The average drive would need to keep their hybrid for an extra 100,000 to 150,000 miles in order to save back the higher purchase price of the hybrid compared to a gas only subcompact car.


    this is an article from two years ago comparing some hybrids:
    http://www.caranddriver.com/reviews/comparisons/09q3/2010_honda_insight_vs._2010_toyota_prius_1998_chevy_metro-comparison_tests
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    Oct 12, 2011 4:11 AM GMT
    FredPDX saidHybrid cars don't "save energy"- pound for pound a hybrid uses as much energy as a hummer (presuming you could find a 4000 lb hummer or a 10,000 lb prius). If you want to "save" energy, or use less gas or electricity ride a bike or walk.



    That's a load of bullshit. Plus, you won't catch anyone tossing one of these batteries. They're very expensive and can be reused indefinitely.
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    Oct 12, 2011 4:11 AM GMT
    Most hybrids on sale in the US are full hybrids which can run in limited electric mode, most around town or low speed local roads. When using the energy captured while braking these hybrids eliminate the very inefficient moment when your gasoline engine is trying to move thousands of lbs from a stop. This is why a 1.8L Prius engine is returns 50 MPG city and a 1.8L Elantra engine only 29 MPG.

    In practical use for the consumer a hybrid is generally more efficient than a non hybrid car. If we factor in the energy spent during production most hybrids still come out ahead after several years.

    My hybrid is one that really isn't any more efficient than other gasoline powered compact cars but I can still manage 40 MPG or so driving it as hard as I please. I personally don't care a bit about the environmental impact, I drive it because I like the instant power and style.



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    Oct 12, 2011 4:14 AM GMT
    iguanaSF said
    FredPDX saidOh, yeah, and where do you put all those toxic batteries when you're done with them? At least the lard I burn off my fat ass by cycling comes back in the form of beer.


    Lead acid, nickel metal hydride, and lithium ion batteries used in hybrid and electric cars have long been recycled. All the manufacturers do this, and most put stickers on the battery packs (that aren't accessible to consumers, BTW) with information and dollar amounts, in the multiple thousands, that they will pay for the packs.

    Unlike consumer electronics, where the batteries are more likely to end up in landfills due to consumer indifference, even tho they can be efficiently recycled as well (at your local Best Buy), end-of-lifing a car is actually a regulated process, with licenses, permits, etc., and battery recycling has LONG been part of it (like for decades and decades). Hybrids and electrics don't change that process, they just leverage it.

    Talking about "toxic batteries" and "what to do with them" just shows a lack of awareness of not only the most basic information about hybrids or electrics, but about normal car batteries as well. If you've ever bought a new lead-acid battery for your car, you surely know the place that sells you a battery will take your old one. They don't do that out of kindness. They get money for em. Don't trust me, just spend 10 minutes on the web with Google and you'll easily be able to separate fact and fiction on this topic.

    As to the weird "energy" arguments here, I don't think it's worth engaging other than to encourage anyone to do a little reading away from RJ on the net about the difference between "energy" and "energy from gasoline" and what MPG figures mean when comparing normal and hybrid cars. All the answers are there, without the bizarre theories of physics and economics we're seeing on this thread. The net will be obvious that hybrids save gasoline (versus the average normal car of the same size), because the gasoline engine is smaller and the combination of electric and gasoline "engines" raise the aggregate efficiency because the electric part of the "engine" is more efficient. This is one of the reasons they've been making train engines as hybrid electric/diesel for decades now (in addition to the power and torque characteristics of electric motors vs combustion engines) -- a combination that is even more efficient (in MPG) that electric/gasoline is.

    All that said, a smaller car, powered with a small, highly efficient diesel engine, will trump any hybrid if you want to change your metric from "volume of oil required to move the equivalent weight at the equivalent speed over the equivalent route" to "what is the most oil-efficient way to move 4 people and 5 bags of groceries." But if you want to buy a big 4 door sedan, or SUV, or truck, the hybrid engine will save gas versus the regular one for that same sedan/SUV/truck. Will it do it in an economic way for the average driver? No, not at current world-wide recession prices (taxi cabs, for example are a completely different matter, which is why you notice the fleets are all going hybrid). If gas goes back up to $5/gallon, then yes, the economics start to look OK again for the average driver, depending on the lifetime of the investment.



    "bizarre theories of physics"?! a piece of me just died
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    Oct 12, 2011 4:20 AM GMT

    312538_189811704428295_100001984010666_4
  • Posted by a hidden member.
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    Oct 12, 2011 4:29 AM GMT
    Hybrid cars make it easy to spot other gay men on the highway.
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    Oct 12, 2011 5:08 AM GMT
    if you insist on saving the planet, one ugly car at a time... you'd be better off just having a small fuel efficient car like the Mazda 2, or the new Fiat. what kills me is hybrid vehicles such as the (now defunct) Lexus 600LS Hybrid.. ( sold for approx $115.000) or the 6.0l Cadillac Esclade Hybrid... Really... Are we that stupid.... The new Volt, is (and dont quote me) in the high $30's to $40ies, you csn buy a Chevy Alero for $10k, and hav tons of money for fuel, maintenance, Hawaii...
    A personal fave was the Chrysler Aspen Hybrid...(actually i'd own one in a sec..) nice size, lots of options, and V8 power. (The Durrango had the ugly interior) Love to talk cars... icon_cool.gif
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    Oct 12, 2011 5:11 AM GMT
    oh, 2008 Saab 9-7 Alero.... has the LS1.... yikes, killer power.
    2005 PT GT Drop Head Coupe,
    98 GMC Sierra, 4x...
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    Oct 12, 2011 5:17 AM GMT
    Iceblink saidHybrid cars make it easy to spot other gay men on the highway.


    I'm glad I didn't purchase the Escalade Hybrid then.
  • MSUBioNerd

    Posts: 1813

    Oct 12, 2011 5:30 AM GMT
    It is likely true that first, and probably even second generation hybrids will not save consumers money over the car's full lifecycle. That doesn't mean that they don't provide energy savings -- money and energy are two different things.

    As for the environmental impact of the cars, the major studies do explicitly take the manufacturing process into account. It's simply incorrect to say that they don't.

    And why would a pound for pound measurement of environmental impact be meaningful in a vehicle in the first place? One of the most common routes to energy efficiency is to make the vehicle lighter while maintain safety.

    As for the Volt, it's important to consider where your area's electric power is coming from. If you're getting power primarily from coal, the Volt's environmental savings are way lower than if you're getting substantial amounts of your local energy from nuclear or hydroelectric sources. This is a link to an EPA tool that uses 2007 data to show what your local power sources are, and compares it to the national average. Mine, for example, is heavier on coal than the national average, and lower on essentially everything else, so plug in electrics are less of a good choice in my region.

    Also, in addition to the energy recovery from braking and thermal capture, some hybrids are capable of electrical conversion of small amounts of fuel in a method far more efficient than the process of running an internal combustion engine. Though there are obvious thermodynamic limits, the mere fact that you're going through potentially more energetic transfers doesn't mean you're coming out less efficient, if each step is individually more efficient, the sum total may be as well.
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    Oct 12, 2011 5:38 AM GMT
    I can only speak for the General Motors Hybrid technology.

    For their Full-size SUV and Pick Ups you can drive up to 40-MPH on electric power alone. Once you pass 41, the gas engine kicks in shutting the electric one off. If you driving speed drops under 41, the electric engine kicks in and so on. Their electric system is charging as you move.

    What I don't like (or get) about the GM hybrid system is they're under powered versus the gas engines. They're great if all you do is drive in the city under 41 MPH. But seriously, who would be driving under 45?! Doesn't make any sense.

    Last week the dealer asked me if I wanted to trade in one of my Escalades for a Hybrid one and I said no. Why would I be giving up a 6.2L with 403 HP 0-to-60 in 6.2 secs. for a 6.0L 332HP and 8.2 secs. to reach 60 miles real-life-size Power Wheels??? Gas price is NOT an issue for me.

    Another thing to think about is the battery pack has a limited lifetime and they eventually will need to be replace at a cost of no less than $6K which will do more harm to the environment (and your pocket) than 100 H2s.

    In the end you're not really saving a lot of gas with a hybrid.