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