I thought I read somewhere that using the HV battery only to propel a hybrid for too long will cause higher CO2 emissions. Is this true and are there designs for future hybrids to use other batteries that do not have this as a side effect?

 

That is indeed true. It is more efficient to use the mechanical energy produced by the ICE than to generate electricity, store it in a battery, and then use the electrical power to move the vehicle. You loose 10 to 20% in this indirect use of the energy (some in the motor-generator, some in electrical losses due to resistance, and the rest in battery charge/discharge losses). The same losses occur when you are regenerating (slowing) the car and storing the energy, but that is better than throwing 100% away as heat as is done in non-hybrid cars.

JeffD

 

That sounds like it came from a naysayer. Viewed in an isolated light and ignoring that these circumstances would occur by themselves pretty rarely, there could be higher emissions:

- re-starting an engine always takes slightly more fuel in that 1 or 2 seconds (more like .25 second for a hybrid) than it would running 1 or 2 seconds at steady state. (rebut: But it was off for many more seconds...net balance in favor of shutting it off. 7-10 seconds is the tradeoff time)

- if the recharging occurs while the engine is idling, proportionally more emissions will be released than if the car is being driven- an unloaded engine has higher emissions than a loaded one. (rebut: 1) the battery has to be pretty low for this to happen; the vast majority of recharge occurs while driving and/or braking. 2) the engine would've been idling in a normal car anyway, so where's the difference?)

- if the engine has been off for a long time, it will have cooled down, possibly shutting down the catalytic converter and spewing far more emissions. This is why the engine always runs for a few minutes when cold- to get the converter up to operating temp to be able to meet emissions standards. (rebut: Again- pretty rare occurrence, given that the battery can only propel a car for a few miles. Not likey the engine will cool down much)

Momentarily higher emissions have nothing to do with the type of battery; they are a consequence of stopping and restarting the gas engine. On balance, by not running an engine for awhile and by having a smaller engine, a hybrid has fewer emissions to pump out- overwhelmingly offsetting the tiny uptick that occurs at startup.

 

Yes; but it needs to be kept in context. Most regen will occur during braking or as a small parasitic while loaded, warm, and driving anyway. Add to that emissions from idling engines at lights and practically idling engines prowling through parking lots, and the hybrid wins out

 

Not a naysayer by any means - I just bought a FEH and love it. Given that I bought the thing for fuel efficency and reduced emissions, I wanted to understand if my attempts to get extreme efficency (run on HV as long as possible) had the side effect of spewing more CO2.

Sorry for being obtuse here, but I am still curious given the responses: is the HV battery a source of CO2 or not? If the reason for an increase in CO2 is only that driving soley on the HV battery requires a long ICE burn to regen, then it does seem like a negilible argument.

 

Sorry for the confusion- I wasn't calling you one; I meant the original author of that statement.

No, batteries do not create CO2. They are sealed. In actuality, they are standard "D" cells that have been matched to each other for optimum life and performance (no you cannot just replace one or 2 yourself, or even the whole pack with a bunch of shelf D cells)

Your 2nd part is correct- any 'increase' in emissions is purely because the engine has to run a little longer or harder or when it would not normally be running, to recharge the battery. But in comparison to ANY non-hybrid who's engine would be constantly running anyway, the hybrid still wins the emissions contest.

Now the confusing flip side- the most fuel-efficient way to run is avoid recharging the battery from the engine at all costs. Any and all recharge should come from slowing down intentionally- which you also want to minimize because braking means you are not coasting as long as possible for free. The bottom line is to avoid using the electric motor too much, except when it 100% makes sense- crawling through a parking lot, etc. The other poster is correct in that relying on the battery as a power source incurs inefficiencies that are not present using the gas engine.

Think of it this way:
"If I absolutely cannot avoid burning gas, would I rather have it give its life to push me forward directly, or indirectly in a way that is more lossy? Given all the options my wonderful vehicle has to move forward, what is the best use of my precious gas at this particular moment?"
Apply that thought to all aspects of driving and you'll be an instant hypermiler.

Read through the many threads in the FEH forum (Prius and HH too, since your systems are similar) on how to maximize efficiency. COASTING (not driving with the elctric on) as long and as far as possible with the engine off is the #1 fuel (and emissions!) saver.

 

Great summary - thanks! Do you think future design trends might mitigate this and allow for longer periods of battery operation, or are batteries always going to be relegated to being only a supplementary form of power?

 

The latter; for the forseeable future, using the existing vehicle and economic models. The whole point of the original hybrids (and only valid one, to some) is to use the electric as a supplement that permits use of a much smaller gas engine than could otherwise be used. Ford's own marketing for the FEH captures this: "V6 performance with 4 cylinder economy." You only need that extra kick infrequently and for short periods- why should you have to carry around a big engine all the time for that?

There are technologies being developed that enable more energy storage, quicker recharge, weigh less, etc etc. "Being developed" is the operative phrase...a long way from "easily mass produced with the reliability and pricing required for consumer acceptance." For a not-entirely-fair comparison, the microchip was "being developed" in 1958; you probably didn't get a hand calculator until about 1978 or even touch a PC until the early 80s.

We'll be drinking primarily liquid fuel for a long, long, long, time. Very few substances pack the same energy into the same volume and are as easy to transport and handle as liquid hydrocarbons. Fortunately that fuel doesn't need to be exclusively fossil-based gasoline or diesel.

 

Hi Hardifeh:

___Are you talking about the sealed Ni-MH pack off-gassing on a charge cycle or the FEH as a system emitting more CO2? CO2 emissions from the pack are for all intents and proposes nonexistent. CO2 from your FEH is 100% correlated to the FE you receive in the FEH. It is ~ 19.6 #’s CO2 that is emitted from consuming a std. gallon of gasoline and another ~ 8.5#’s from the well the tank to create that gallon. Running in EV for as long as the FEH will allow is about the fastest way to take your FE through the roof in one and thus lessen your GHG emission footprint on the earth.

___The basics of stretching your FEH’s FE and thus limiting her CO2 output can be found in the following excellent thread by GaryG entitled The Low Gear Advantage. I can tell you from personal experience that the FEH is easily worth 60.0 + mpg around town when driving in that slower speed suburban/city environment after you have set her up properly and learned the L Gear techniques as described. Out on the highway with a hell bent for FE at all costs mindset; she is good for ~ 45 - 46 mpg in my experience when all the stars are aligned and in decently warm ambient temperatures. I am not talking about 65 + mph w/ A/C on MAX out on the flats in the middle of Oklahoma or Montana but a nice 55 mph cruise with enough traffic congestion to give you some EV/Glide into the tangles and all 4 types of drafts just from driving amongst everybody else. Your FEH when pushed is an absolutely remarkable machine in the FE and emissions arena when considering its rather large size and excellent utility.

___Good Luck

___Wayne R. Gerdes

 

Like Wayne said, CO2 is directly proportional to the amount of fuel you get. The more miles per gallon your vehicle does, the less CO2 you're emitting. A vehicle that gets 25mpg puts out twice as much CO2 per mile as a vehicle that gets 50mpg. It doesn't matter if you ran on batteries 10% or 90% of the time, if you get 50mpg then you get 50mpg.