Parallel vs. Series Hybrid

[cwerdna]

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?

How much CO2 that's emitted is directly related to the type of and how much fuel is burned.

Per http://web.archive.org/web/20110427044311/http://www.epa.gov/oms/climate/420f05001.htm, burning a gallon of gasoline produces 19.4 pounds of CO2. Want to produce less? Burn less of it and/or burn something w/less carbon content.

For pollutants (e.g. https://www.epa.gov/greenvehicles/light-duty-vehicle-emissions lists NOx + NMOG, CO, PM, HCHO), that has no relationship to fuel consumption. You can have really inefficient (by fuel economy and thus CO2 output) ICEVs that do well on that and very efficient ones that do poorly.

 

[SageBrush]

One of the trade-offs that happen in plug-in hybrids (PHEV) occurs with pollution. Even in the (for an ICE) clean Toyota, most of the pollution occurs in the first few minutes of ICE operation while the catalytic converter is warming up. So a RAV prime driven for 40 miles in EV and 5 miles in ICE will pollute about the same as a regular RAV. If the PHEV is used in a day with multiple stops, it can pollute MORE than a regular ICE because the engine retains less heat and the catalytic converter goes through multiple full re-warming cycles.

I use pollution to mean the toxins spitting out of tailpipe other than CO2

Another trade-off to be aware of is that some owners (I was one of them) found the transition from EV to ICE to be something to avoid. On a long trip the car is a hybrid and the driver typically does not think about the operation mode. But in daily driving the EV only driving mode range becomes a target to not exceed, and every day becomes a fight to keep the ICE off.

Too cold ? ARGGH
5 miles past the EV range ? ARGGH
4 miles past the EV range ? ARGGHHH
3 miles past the EV range ? ARGHHHGHH
2 miles past the EV range ? ARRRGGHHHHH
1 mile past the EV range ? ARRRGGGHHHGHGHHGHGH

The more a person knows and cares about pollution, the less attractive a PHEV becomes unless the EV range fits within a predictable and consistent usage profile.

 

[SageBrush]

burning a gallon of gasoline produces 19.4 pounds of CO2.

That is correct for the CO2 coming out of the tailpipe, but it ignores all the CO2 emissions generated to mine the oil, transport the oil, turn the oil into gasoline, and transport the gasoline to a refueling station. 24 - 30 pounds of CO2 per gallon gasoline is a fairer accounting, depending where the oil came from. Oil from shale is by far the worst.

 

[WetEV]

burning a gallon of gasoline produces 19.4 pounds of CO2.

That is correct for the CO2 coming out of the tailpipe, but it ignores all the CO2 emissions generated to mine the oil, transport the oil, turn the oil into gasoline, and transport the gasoline to a refueling station. 24 - 30 pounds of CO2 per gallon gasoline is a fairer accounting, depending where the oil came from. Oil from shale is by far the worst.

Looking at RMI's "Oil Climate Index plus Gas", there is no standard oil. More than a 10:1 ratio between the worst and the best. Fracked (oil from shale) isn't the worst, neither is tar sands or heavy oil. There is quite a variation even in conventional oil. The worst oil of all seems to be from Iran's Salman field, which seems to flare a large amount of natural gas.

https://ociplus.rmi.org/oil/salman

 

[SageBrush]

Looking at RMI's "Oil Climate Index plus Gas", there is no standard oil. More than a 10:1 ratio between the worst and the best. Fracked (oil from shale) isn't the worst, neither is tar sands or heavy oil. There is quite a variation even in conventional oil. The worst oil of all seems to be from Iran's Salman field, which seems to flare a large amount of natural gas.

https://ociplus.rmi.org/oil/salman

That is a very interesting website. Kudos to RMI
Still, I think it is evident that non-combusted methane release is poorly accounted for, and that represents a huge additional unknown.

 

[LeftieBiker]

Flaring generally refers to burning plumes of methane. I don't doubt, however, that a lot of methane escapes without being burned, but ends up accounted for in that category.

 

[SageBrush]

Flaring generally refers to burning plumes of methane. I don't doubt, however, that a lot of methane escapes without being burned, but ends up accounted for in that category.

Yeah, and since methane has some 20x - 30x the GWp of CO2, the actual carbon (equivalent) emissions can easily be double. I hate to say it, but while we were all focused on dirty coal, arguably even worse methane has been choking the earth.

 

[tomcon]

Wow...is there actually thought that battery density will reach to or above gasoline density? Thats amazing! If you said only 25mpg and a 500 mi range thats 20 gallons ~200 lbs weight. It seems to me the battery industry is always promising "the next battery tech breakthrough way ahead of when they occur"...having followed electric car lit since the 1980s (when i bought plans in Popular Science for $20 on how to convert a car...which i never actually did). SO would be exciting to see that density soon. True that it would kind of make moot my idea of reducing battery size by using a hybrid design.

Still i must admit some concern on battery size. From what i read about all the mining that will be needed for all the anticipated electric car battery production that will be needed. Since gas tanks are so "low tech" it seems like it might be something to really consider...small batteries enough for "98%+ of usual days for usual people's needs" and then supplement with on-board gasoline.

Fortunately for me i think my Mazda CX5 has another 3-5 years, so i hope by then my options are much more interesting than i am seeing at this moment!

 

[knightmb]

Wow...is there actually thought that battery density will reach to or above gasoline density? Thats amazing! If you said only 25mpg and a 500 mi range thats 20 gallons ~200 lbs weight. It seems to me the battery industry is always promising "the next battery tech breakthrough way ahead of when they occur"...

The battery tech already exist, but it's usually too expensive or not safe for consumer use. The thinking is that 10 more years of progress might make it possible to mass produce and be safe enough for consumer use. It all depends on what drives the market. Hopefully EV adoption will accelerate that technology progress. It is not sure bet, might be delayed by unknown variables. No one can fully predict the future.

 

[WetEV]

Yeah, and since methane has some 20x - 30x the GWp of CO2, the actual carbon (equivalent) emissions can easily be double. I hate to say it, but while we were all focused on dirty coal, arguably even worse methane has been choking the earth.

Depends on time period, of course. Methane is a fairly short lived gas in the atmosphere, about a decade.

Mining coal releases a lot of methane as well.

 

[SageBrush]

Yeah, and since methane has some 20x - 30x the GWp of CO2, the actual carbon (equivalent) emissions can easily be double. I hate to say it, but while we were all focused on dirty coal, arguably even worse methane has been choking the earth.

Depends on time period, of course. Methane is a fairly short lived gas in the atmosphere, about a decade.

The half life of methane is 8.6 years. Its GWp100 is 28x that of CO2, ,while its GWp20 is about 86x that of CO2. These GWp numbers come from the fact that on a weight basis, methane is 120x more potent a GHG than CO2

People argue whether to use the 20 or 100 year timeframe. Either way methane is BAD, but I'm inclined to use the 20 year timeframe due to the amplification effects of tipping points. When the 20 year time frame is used, fugitive emissions of about 1.2% equal the CO2 emitted by coal combustion. I've read that average fugitive emissions are around 3%, although this may be an underestimate and some mining is much higher.

It is hard to escape the conclusion that methane has been a hidden AGW villain for far too long.

 

[LeftieBiker]

Methane also has the downside (to put it mildly) of becoming self-releasing as the planet warms. It's already starting to boil out of Arctic lakes and, IIRC, the Northern seas...

 

[WetEV]

Methane is a fairly short lived gas in the atmosphere, about a decade.

The half life of methane is 8.6 years.

Was, not is.

The half life of methane depends on the methane concentration. Closer to 12 years now.

https://en.wikipedia.org/wiki/Atmospheric_methane

Its GWp100 is 28x that of CO2, ,while its GWp20 is about 86x that of CO2. These GWp numbers come from the fact that on a weight basis, methane is 120x more potent a GHG than CO2

Again, GWp is a function lifetime and thus of concentration. And if methane increases in concentration, IR bands of methane become more saturated and methane becomes less potent, but still much higher than CO2.

People argue whether to use the 20 or 100 year timeframe. Either way methane is BAD, but I'm inclined to use the 20 year timeframe due to the amplification effects of tipping points. When the 20 year time frame is used, fugitive emissions of about 1.2% equal the CO2 emitted by coal combustion. I've read that average fugitive emissions are around 3%, although this may be an underestimate and some mining is much higher.

It is hard to escape the conclusion that methane has been a hidden AGW villain for far too long.

Twenty years ago I would have agreed. But methane has gotten a lot of attention over the past 20 years.

We can avoid the worst of it. Will we?

 

[DougWantsALeaf]

Can the RV4 prime drive in 4wd in ev mode?

 

[goldbrick]

Can the RV4 prime drive in 4wd in ev mode?

I believe so. The rear wheels are EV only and AFAICT the EV/HV mode is completely independent of any other driving modes (Trail, ECO, etc).

In fact, I love EV mode for harsh 4WD roads since it is possible to crawl at an extremely slow speed up the rough stuff since the EV system has full power at lower speeds unlike an ICE.

What I'm not sure of is when the rear wheels are engaged. Eg, it's completely possible that the car only provides energy to the front wheels when driving down the highway. There is a display on the info screen that shows the power distribution but I don't know if that reflects reality. It's sort of a cartoon. I'd assume that the rear wheels are only powered when needed but I don't know how the car determines when to do that.

 

[DougWantsALeaf]

Cool, so the Rav4 Prime can run in both series and parallel modes.

 

[goldbrick]

I guess it depends on what series and parallel hybrid modes mean. The ICE never simply acts as a generator to power the electric motors although there is a 'charge mode' that makes the ICE 'over-drive' the transmission to allow the excess power to charge the battery. In this mode the ICE will charge the battery when stopped so I guess that would be a series mode setup. Normally though, the ICE and the traction battery operate in tandem to supply power to the wheels. Without battery power the car couldn't move, so the controls will start the ICE when the battery reaches about 20% charge if using only EV power.


This video really made it all clear for me. Take a look if you have time. https://www.youtube.com/watch?v=MsvVD0FaF28

 

[martinwinlow]

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!

I would like to think that most people are sufficiently intelligent than to fall for the hybrid marketing nonsense/fraud that the makers of hybrids peddle constantly. In reality, it is probably simply either that having both an engine *and* electric drive is too much for most motorists to get their heads around or people just follow the money; if an incentive exists to buy a hybrid then people will take advantage of it. This was a big thing here in the UK until the government removed both purchase subsidies and tax incentives. Hybrids were dropped like hot potatoes. Interestingly, I read a piece from one of the big UK leasing companies (who deal with hundreds of thousands or cars each year) saying that 99% of the plug-in hybrids returned at lease-end still had their charging cables in their sealed bags, ie in 3 years (the typical UK car lease period) they were never used.

I don't think there is usually much difference in the actual physical layout of series or parallel hybrid drive trains. So, I would doubt there is much in it in efficiency terms. Maybe one is better (or even capable) of doing regen...?

But it's all a bit academic. Hybrids are a complete waste of time if your end game is reducing our reliance/addiction to burning fossil fuel (which it should be for everyone where reasonably practical); more so for those who can afford to 'early adopt' EV technology.

Why? Because car companies only make hybrids so they can continue to rip off their customers through ridiculously over-priced and often completely unnecessary servicing costs of hugely complex engines and associated mechanical and electrical gubbins (much of which is related to emissions controls). For example, the typical modern ICEV has an engine with some 250 highly engineered moving parts (the gearbox, often one with multiple clutches, isn't far behind). By contrast, an equivalent EV (equivalent in terms of size and drivetrain capability) might have a dozen moving parts... You do the maths.

With a *good* rapid charging infrastructure, even relatively low range EVs are a perfectly reasonable alternative to ICEVs as Tesla has already proven and will, I'm sure, continue to do so until the point where seeing an ICEV on the roads is a comparative rarity. Of course in the meantime, you can bet Big Oil and Auto is going to fight tooth and nail (and often using highly questionable - if not downright unlawful (eg Dieselgate)) tactics to maintain market share.

Don't fall for it. Don't believe what you see/hear/read in the media as they are pretty much all being funded by Big Oil/Auto's *massively* deep pockets.

 

[LeftieBiker]

That was overly simplistic. If there was no good use case for a hybrid, then they wouldn't have done so well, for so long. The fact is that US charging infrastructure does not, even now, support everyone driving an EV. Marketing pitches aren't magic: there has to be something good there to sell. And what there is there is the ability to increase the fuel efficiency of a family-sized car by ~50% even if that family has no way to charge the car. Hybrids also eliminate the range anxiety that, rationally or not, plagues Americans in particular.

(I'm having trouble here with page formatting that won't change...)

 

[RPaulThomas]

Why? Because car companies only make hybrids so they can continue to rip off their customers through ridiculously over-priced and often completely unnecessary servicing costs of hugely complex engines and associated mechanical and electrical gubbins (much of which is related to emissions controls)

Not sure I can completely agree with this, it has merit but as Leftie says it is boiling an extremely complex 100+ year old industry(ies) into one statement. In the 8 years I owned and drove an SUV (last car before EV) I did not require any over-priced maintenance (at all) of the drive train. So, for me, I paid standard cost for a used SUV and drove it to 120,000 kms for zero added cost to run. This by the way is also true of my 40+ years of owning and driving ICE.

However, all the talk about cold catalytic and hidden gasoline emissions do suggest that hybrids are not the panacea for carbon. They are good for a narrow use case, and that ones personal driving habits need to be carefully considered. Having moved from a rural setting from an urban I am leaning back to hybrid, but only if my 40-50 km shopping round trips can be covered by battery, meaning a PHEV likely. Then longer trips would make the use of gas somewhat more justified.

In the end I am still commited to reducing my carbon footprint. Even installed a heat pump in my house to use cleaner (Ontario) electricity as opposed to natural gas for heating. Small steps in reduction will eventually help our planet, long after I'm gone.