Parallel vs. Series Hybrid

This is not exactly a Leaf question, but it seems there are alot of knowledgeable folks on this forum.

When we bought our Leaf we also test-drove a Chevy Volt (that's "V"). I thought the series hybrid architecture of the Volt was "the best architecture" but we did not like the feel of being in the Volt, so we ended up buying our Leaf (and like it very much!). But, i have always wondered why the series plug-in hybrid architecture has not taken off more than it has. it seems like all the plug-in hybrids now have a very low all-electric mile range, like ~15-25 miles (the Volt had, if i recall correctly, ~55 miles as the electric range).

I have a few questions, if anybody would know about these to compare parallel vs. series plug-in hybrids.

1. Given that a hybrid burns 1 gallon of gasoline, which introduces more pollutants and CO2 into the air, the generator burning the gallon of gasoline (series) or the ICE engine burning the gallon of gasoline (parallel)?

2. Given that a hybrid burns 1 gallon of gasoline, which provides more range, if it is a generator burning the gallon (series) or an ICE burning the gallon (parallel)?

3. Which is more costly to manufacture, a plug in hybrid with an on-board generator (series) or with an on-board ICE (parallel)?

Thanks!

Don't have time to elaborate now, but Volt isn't really a pure series hybrid system. It's a long story. It relates to their complex transaxle.

e-Power is an example of a series hybrid arrangement:
https://global.nissannews.com/en/releases/release-0032ff05aa6577577d36a0990c001c71-161102-02-e.

You an see more at https://global.nissannews.com/en/channels/e-power and https://www.nissan-global.com/EN/INNOVATION/TECHNOLOGY/ARCHIVE/E_POWER/.

However, AFAIK, at least with gen 1 Volt (not sure about 2), gen 1 Volt does behave like a series hybrid when there's sufficient charge in the big battery. https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=30980&id=36863&id=40924 lists the "AER" ratings for '11, '16 and '19 Volts.

I can't speak to gen 4 and 5 Prius, but non-plugin gen 1 to 3 Prius were series/parallel systems.

tomcon said:

This is not exactly a Leaf question, but it seems there are alot of knowledgeable folks on this forum.

When we bought our Leaf we also test-drove a Chevy Volt (that's "V"). I thought the series hybrid architecture of the Volt was "the best architecture" but we did not like the feel of being in the Volt, so we ended up buying our Leaf (and like it very much!). But, i have always wondered why the series plug-in hybrid architecture has not taken off more than it has. it seems like all the plug-in hybrids now have a very low all-electric mile range, like ~15-25 miles (the Volt had, if i recall correctly, ~55 miles as the electric range).

I have a few questions, if anybody would know about these to compare parallel vs. series plug-in hybrids.

1. Given that a hybrid burns 1 gallon of gasoline, which introduces more pollutants and CO2 into the air, the generator burning the gallon of gasoline (series) or the ICE engine burning the gallon of gasoline (parallel)?

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I think you meant to ask which is more efficient? A gasoline generator will burn 1 gallon of gas to produce roughly 7 kWh of energy. The same gallon of gas in a vehicle varies with the vehicle. Taking a very efficient and small gas car that gets 40 mpg, compared to the generator is going to be hard to think it out, but you need numbers to compare. If you put this in a Leaf and used it to measure distance driving at non-highway speeds of around 50 mph, perfect weather, flat course, etc to get 5 miles/kilowatt hour, then the generator with 1 gallon of gas would get you about (5 x 7) 35 miles of range. The small car that gets 40 miles on one gallon achieved a slightly better range. That's a "napkin" math way to visualize the difference between the two and that is ideal settings. Since the two are so close, optimizing the generator or the hybrid could lead one over the other in many ways back and forth.

2. Given that a hybrid burns 1 gallon of gasoline, which provides more range, if it is a generator burning the gallon (series) or an ICE burning the gallon (parallel)?

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Depends on the vehicle and how it is setup.

3. Which is more costly to manufacture, a plug in hybrid with an on-board generator (series) or with an on-board ICE (parallel)?
Thanks!

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Hard to say, depends on the manufacture I suppose.

tomcon said:

it seems like all the plug-in hybrids now have a very low all-electric mile range, like ~15-25 miles

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No. You can skim https://www.fueleconomy.gov/feg/PowerSearch.do?action=noform&path=1&year1=2011&year2=2023&vtype=Plug-in+Hybrid&pageno=1&rowLimit=50&sortBy=Comb&tabView=0. You can ignore the BMW i3 REx as it's a special case (long story) but it's also a series plug-in hybrid.

Googling for longest range phev by all electric range also turns up some.

Outlander phev is in series 95%+ of the time . Only in high stress fast velocity situations does it go parallel.

So, I will get a better feel for gas and ev efficiency in a couple weeks once I drive my mother's a few times, but based on epa rating, it suggests that an efficient high compression small gas engine can do better.

The turbo 3 in our Rogue can get 34+ mpg at 70mph in good weather, and I have seen north of 42 mpg in slow highway situations (55-60mph).

Which weighs more, a pound of feathers or a pound of gold ?

A more useful way to pose this question is pollution/CO2 per mile. For CO2 the answer is per MPG. For other pollutants it can be a rabbit hole but a not bad approach is to compare either the federal or CARB pollution ratings for each vehicle.

Bottom line: Toyota are the king of hybrids. By far.

^^^ I'll buy that for $1!
I have a different perspective: hybrids are the worst of both worlds...so I don't think there's any "best scenario" for them. That's why I didn't even consider the Volt when I bought my Leaf, but history (and sales) did not treat the Volt kindly.
In general, EVs have less parts/lower cost of assembly than ICE cars.

Stanton said:

I have a different perspective: hybrids are the worst of both worlds

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I'm not a fan either. They had their place when battery costs were $500 - $1,000 a kWh, but they carry a rather long list of trade-offs. I drove hybrids for nearly 15 years, but I swapped to EV when the price came down. I've thought on and off about buying a plug-in hybrid truck when (if) they come out, but I'll be happier if I can just buy a small, 150 EPA mile range EV truck.

tomcon said:

it seems like all the plug-in hybrids now have a very low all-electric mile range, like ~15-25 miles (the Volt had, if i recall correctly, ~55 miles as the electric range).

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Electric cars are expensive and heavy because of the battery. The advantage of the plug in hybrid is that you can use a much smaller battery without range anxiety. Most of my trips are short. They combine the advantages of electric and ICE, but you could say they combine the disadvantages.

RNeil said:

They combine the advantages of electric and ICE, but you could say they combine the disadvantages.

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The biggest being the complexity and maintenance that goes along with it.

knightmb said:

RNeil said:

They combine the advantages of electric and ICE, but you could say they combine the disadvantages.

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The biggest being the complexity and maintenance that goes along with it.

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That is too broad a brush.
Toyota's 'Prime' hybrid plug-in has the same exceptional reliability as the Toyota hybrid. I cannot say regarding, and do not have the confidence in, other manufacturers.

As for maintenance, it ain't much if the plug-in capability is being used as intended. And *that* is one of the trade-offs of these cars: they have to be plugged in after most every trip, and it turns out that few households have that kind of habit.

I'm going to interject another use case for which PHEVs aren't well suited: people who use the EV drive the great majority of the time, and who don't take long trips. Our PIP suffered seriously from the ICE not getting enough run time. Toyota didn't make a real effort to plan for that, either.

LeftieBiker said:

I'm going to interject another use case for which PHEVs aren't well suited: people who use the EV drive the great majority of the time, and who don't take long trips. Our PIP suffered seriously from the ICE not getting enough run time. Toyota didn't make a real effort to plan for that, either.

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I have heard the same complaint from Volt drivers. The highest EV only mode driving hybrid, at the EV shows I attended, one owner had +50k miles of EV only range and like 100 miles (no typo) of gas driving had to buy fuel stabilizer and have chevy do warranty maintenance on the gas engine portion due to non-use.

The best solution for that particular dilemma (other than NOT buying a PHEV) would probably to make them dual fuel, gas and propane/CNG, and tell buyers like us to run the ICE on CNG.

I have a different take on the OP's questions:

For the same size car, a serial hybrid should be slightly more efficient (drive a little farther on 1 gallon of fuel) because the engine could run at its most efficient speed and load. Also, the generator portion of the powerplant should weigh less than the increased weight of the complex transaxle/planetary gear unit for a parallel hybrid compared to a conventional reduction gear unit for an EV or serial hybrid.

Emissions should be slightly lower for a serial hybrid because the engine could run at its most efficient and cleanest speed and load.

I might be interested in a serial hybrid truck or SUV for a tow vehicle on long trips if one with suitable size and ratings becomes available. The increase in complexity is not as bad as for a parallel hybrid. It would also be nice if the engine and generator could be used for backup power when grid power was not available.

I think it's all pretty complicated and much depends on the use case. There are some good details here: https://www.ucsusa.org/resources/all-about-drivetrains#:~:text=Hybrids%20that%20use%20a%20series,can%20provide%20mechanical%20power%20simultaneously.

I do love my Rav4 Prime and I use it nearly 100% EV when around town and 100% Hybrid (ie ICE running) when doing road trips of over 100 miles. It has about a 40 mile EV range which covers nearly all my errand type trips, but to be honest, I usually take the Leaf for commuting and errands since it is smaller and more efficient.

I do try to run the ICE on the Rav4P at least once every 2 weeks or so but 20 miles or so seems sufficient for that. On long trips I average about 36-38 mpg going at normal highway speeds (70+). It's also a good 4WD vehicle since in EV mode it can crawl at any speed over very rough roads. It's also nice to be able to charge the battery on long downhills without using the brakes.

If I had only one car, I could make this work pretty well but as mentioned, a 40 mile EV range is quite limiting for most people.

Seems like it was a lively discussion -- Thanks (from TomCon, original poster)

I got some great ideas reading thru the responses.

The Nissan Arizon (now a concept car) sounds exciting. I wonder how far away production might be.

I learned that the RAV4 PHEV might be close to what i am looking for to replace our other car (not the Leaf, a Mazda CX5). I need an AWD for mountain driving in the snow. A PHEV with an electric range "sufficient for most days in town" is what i'd like. That way i'm not using gas much at all except on road trips. For long trips, i do not see a full EV as al that practical, even with a very large battery. In my mind an electric range "sufficient for most days in-town" is around 60-70 miles. Many PHEVs seem to have too low of an electric range, around 15-30 miles, which i view as "too little". This RAV has 42 mile range. I'd like a little more than that, but probably would settle for that if that's all there is available in an AWD.

I did not get a clear answer on CO2 if anybody knows this. Lets say you have a PHEV that is now past its electric range. So, you are burning gas. Say you drive 50 miles. How does the series PHEV (gas running the generator) compare to the parallel PHEV (gas running an ICE) in terms of pollutants or CO2?

I would pitch a PHEV (one or the other architecture) as having one amazing advantage over an EV....small battery. Why use all those resources to build so many 300+ mile batteries, when the vast amount of days most people could still be all-electric with a battery in the 60-70 mile range? The world would use ~75% less lithium and other rare earth metals to build those batteries. its a pretty big savings. And we'd still probably get ~90% of all miles driven as electric. Seems like a great tradeoff to me. Not to mention "reduction of range anxiety".

Thanks for the discussion!

Tomorrow, I tend to agree with your line of thought, with the drawback really being the complexity and hence additional maintenance of 2 power trains.

Sandy Monroe had an episode talking about a fuel cell patent where the hydrogen was held in a stable solid form. If you could use a small form fuel cell with a cartridge form for the "gas", that might be really interesting at this moment in time.

With some of the new battery tech jumping from 250 w/kg to over 700 w/kg my gut says 1000 evs may not be that far away. At even a 500 mile winter range charging times become much less important.

Just my 2 cents

I did not get a clear answer on CO2 if anybody knows this. Lets say you have a PHEV that is now past its electric range. So, you are burning gas. Say you drive 50 miles. How does the series PHEV (gas running the generator) compare to the parallel PHEV (gas running an ICE) in terms of pollutants or CO2?

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If you accept fuel economy as an indicator of combustion efficiency, then the Toyota PHEVs get very good economy even with the battery depleted, because they use the additional capacity in Hybrid mode to store more energy from braking and from low load situations. Our old PIP was, IIRC, rated for 5 more MPG than the regular hybrids in that situation. It would be interesting to know which if any of the current PHEVs do similar things to use the EV battery even when it's depleted for driving.

tomcon said:

I would pitch a PHEV (one or the other architecture) as having one amazing advantage over an EV....small battery. Why use all those resources to build so many 300+ mile batteries, when the vast amount of days most people could still be all-electric with a battery in the 60-70 mile range? The world would use ~75% less lithium and other rare earth metals to build those batteries. its a pretty big savings. And we'd still probably get ~90% of all miles driven as electric. Seems like a great tradeoff to me. Not to mention "reduction of range anxiety".

Thanks for the discussion!

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It would have been a very persuasive argument many decades ago with low capacity batteries, but gasoline on it's own is a chemical formula and will always be the same power density. You can make better use of it (burn it to make electricity to drive a vehicle instead of a complicated combustion engine to the drive the vehicle) but it still has it's limits which aren't going to change. The stuff coming out of the ground isn't going to one day break the laws of physics and come out twice as efficient to burn.

Knowing that, battery tech is constantly evolving and getting better. Look at the 2011 Nissan Leaf as an example. The battery size was 24 kWh and the chemistry was poor by today's standards. Even people that baby the battery had to deal with rapid degradation and range loss. Fast forward to 2018 and the Nissan Leaf had an upgraded battery chemistry and capacity of 40 kWh. The same physical size battery has evolved from 24 kWh to 40 kWh. Now the Leaf has double the range of the Gen 1, more powerful inverter for quicker acceleration, and the battery chemistry is better able to handle hot climates to last longer. Then in 2019, the Leaf got another upgrade to the 62 kWh battery. Now the Leaf has more speed, more range, even better chemistry for longer life. All of that happened in under a span of 10 years.

This is Nissan battery tech, the other EV manufactures are accelerating battery tech much faster than Nissan. What will battery tech be in another 10 years? If you keep up with the research on it, battery tech will surpass "gas" energy density within that time. So a battery that weight less than a gallon of gas will have more energy that out right burning the gas. The oil and gas still have many uses, the industry will never disappear just because everyone starts driving an EV and gas stations become less and less useful.

Looking future forward, trying to maximize small batteries in a hybrid is useful now, but not part of any near future road map that I would see for a company to be successful in the future. EVs are in demand because the more people use them, the more they appreciate not making a trip to the gas pump or auto store for oil changes, filters, belts, etc. I don't demonize gas vehicles because some people need them right now and can't wait years for a used, cheap EV to come on the market for them. But the future for personal vehicles is EVs and it won't fix the world climate issue on its own, but it's just one of the many pieces to the puzzle of solving the climate crisis for this planet.