OK TOYOTA, Now give us our diesel hybrid.

With BEVs, PHEVs, Fuel cell vehicles, Diesels etc. we are well past the point where MPG is the be-all-end-all of efficiency measurements. Computing a Diesel on MPGe sounds like the thing to do.

If the difference isn't worth considering, why are you bothering to argue about it? To me, all energy use is worth reducing.

Treating your hybrid like an EV and then saying that a diesel hybrid will do better in HYBRID mode with a larger battery is nonsensical. What evidence do you have that a diesel hybrid will do better IN HYBRID MODE with a larger battery?

You will note that Toyota has not been increasing the size of their battery in non-plugin hybrids. Surely, if it was 'well proven', they would do so. One needs to differentiate between having a battery at all, and having a larger battery. When you consider that all that electric power comes from fuel use, this becomes clear.

 

Very relevant when miles per gallon is used as a proxy for carbon emissions.

My sympathies to your abused battery.

Sources? When Toyota increased mpg from Gen I to Gen II, they actually shrank the battery. When they increased mpg again from Gen II to Gen III, they didn't change the battery capacity.

A larger battery would slightly help those of us who frequently descend tall mountains. But it would be useless to the majority of Prius drivers who operate in flatter terrains, in fact the increased weight would hurt their performance. Is there any evidence that a larger battery will help the overall fleet mpg of non-plugins?

Gasoline only has a higher mass energy density. Diesel still has the higher volumetric energy density.

 

It wasn't straight out, but I said that.

Just wanted to point out that diesel having more x% energy per gallon than gasoline, doesn't make the gas equivalent mpg = diesel mpg minus x%. The topic isn't that clean cut.

 

This is an established fact. Argon Labs extensively tested the Gen II Prius and discovered no significant loss of mileage even with half battery capacity. Said another way, the standard Prius battery is twice as big as it needs to be. Presumably, Toyota did this to allow for battery degradation over the life of the vehicle.

Extrapolating from this, doubling the size of the battery in the Prius would actually reduce mileage. This is because the extra battery capacity does not improve mileage, but hauling around extra weight decreases mileage.

The EV argument is specious. Driving in EV mode is inefficient, unless you have plug-in charging. Having a bigger battery to allow for longer EV running only increases the EV losses.

The only exception to the above comes in the special case of very large hills. Mountain drivers may benefit from a larger battery, as they frequently experience long regeneration. This is not a common case.

Tom

 

The hill does not have to be that big. I fill up the battery routinely in the winter, and often in the summer unless I bleed off charge with AC. It happens more than you would guess because there is no easy way to drain the battery before the descent, so I often start at half 'full' or more. I think it was more of a problem in my G2 than our CTh, but that is only an impression.

If I remember numbers correctly, the nominal capacity of the battery is 1.2 kwh, and 40% is used = ~ 0.5 kwh. If I start the descent with a half full battery, and regen is 50% efficient, I can store 0.5 kwh of potential energy.

E = 0.5 kwh = 1.8*10^6 joules = mgh = 1400*9.8*h
So height of hill (h) = 131.2 meters

 

Isn't true that the larger the battery, the lower its internal resistance? If so, wouldn't a larger battery be able to capture more energy during regen?

I'm sure there is point when cost, weight, and space trump any advantages of a larger battery, and the pack in the gen3 is likely at that limit.

 

Are you thinking of the study brought (ironically!) to our attention by the troll tpfun ?

I was under the impression that study did not find reduced max discharge rates, which can be used as a proxy for capacity. At least that was my take away from Jayman's posts -- I myself have no opinion, being an electricity idiot.

 

Winter driving and highway driving often cause the battery to run at a high SOC. This is because the ICE has to run almost continuously, so any extra capacity is used to charge the battery. Having a larger battery doesn't really help this situation, other than to hold it off for a short interval.

With regeneration it is true that a bigger battery has the potential for recovering more energy. However, as stated before, it doesn't pay off for non-mountain driving. The amount lost to hauling around a heavy battery more than offsets the gains from long descents. Of course this isn't true for every driver; this is true for the average driver.

Not necessarily. Internal resistance is determined by a variety of factors, including chemistry and geometry. But certainly a bigger battery has the potential to recapture more regenerated energy. It all comes down to trade-offs, as we have discussed so many times before.

Tom

 

Which would presumably have little affect if they increased the 'size' of the battery by adding more cells, yes?

 

If you add cells in parallel, the resistance goes down. It's simply a matter of surface area.

For a given battery chemistry, the internal resistance is mostly a function of surface area. For example, a lead-acid starting battery has thin plates with lots of surface area. This allows it to deliver a large current for a short interval, such as starting, and also allows it to recharge quickly, since most of the charge is on the surface.

On the down side, a starting battery cannot withstand deep cycles. If heavily discharged, the plates crumble and fall in pieces to the bottom of the battery. Deep cycle batteries have much thicker plates. It takes longer to recharge a deep cycle battery, since the charge must work down into the plate, but they can structurally withstand deep cycling.

Once again it comes down to trade offs. Do you want low resistance or deep cycle capability? No one design does it all.

Tom

 

Best to compare miles per gallon (or equivalents) and carbon emissions separately.

But increased its W/kg.

Don't confuse weight of the battery with power.

 

Directly comparing miles per gallon of different fuel systems, without adjusting for the differences, just leads to confusion and wrong choices.

I'm more interested in overall system carbon emissions that in an 'MPG score'.

Oh, I'm so sorry. When you wanted bigger batteries, I thought you wanted bigger total electrical capacity, not bigger volume or greater weight or energy density. My apologies for confusing your intentions.

But I stand by my statement. Gen I's nominal battery capacity was about 1.78 kWh (273.6 V x 6.5 Ah). Gen II decreased battery capacity to about 1.31kWh (201.6 V x 6.5 Ah), while increasing MPG about 12%. Gen III kept the same battery capacity as Gen II, while still increasing MPG another 9%.

 

Unless of course the buying criteria is miles per gallon. That is the motivator for Prius owners, just one example.

That is a perfectly valid buying criteria also.

Lowering weight while maintaining battery power. You have the same battery power wise, a "bigger" battery measuring W/kg and smaller battery measuring weight.

Back to the specs on the V60 Diesel/Hybrid/EV, one of the reasons it gets such high hybrid mode mpg rating is the more powerful battery pack.

 

Okay fuel capacity is a small problem. . . considering all the other pluses.

It's the same complaint for electric cars, in fact they have less range than a CNG vehicle.
There's more CNG infrastructure available than for electric.
CNG is a proven system.
Every year they are finding new ways to increase fuel volume.
CNG is actually less volatile than gas.
It's certainly cleaner than diesel without all the high tech necessary to clean up gas or diesel.
It's much cheaper. I fill at home for a little over one dollar per gallon.
Methanol, IIRC, has less power per gallon than CNG as does propane and is the main reason those aren't used.
We have butts loads of CNG here in the states and the infrastructure to move it around.
Creates jobs for American's.
Keeps money in American rather than sending it to some country that doesn't like us.

There are more . . . Gimme a hybrid with CNG and I'll be all over it. That's one solution to address your concern of limited fuel capacity.

 

Increasing the density of something does NOT make it bigger. In any sense. The lower weight of the newer Prius battery helps the mileage, no doubt. But you can work out by how much if you like, the relevant term is 1/2 Mc V^3 / distance traveled between stops. However, all the proves is that LIGHTER batteries improve mileage, not that BIGGER (higher capacity) ones do. In fact, it is (weak) evidence that SMALLER (lower capacity) ones provide higher mileage.

After all your arguments that this is true have been shown to be incorrect, you circle back to the original claim, and again expect people to accept it without any evidence (or at this point even any justification).

 

The electric grid goes pretty much everywhere. I am not sure where the nearest CNG facility is to me, but it is surely a substantial drive. Electricity comes right to my house (and everyone else's house as well)

Did you mean something other than 'volatile'? Since CNG is already a gas it is extremely (i.e. completely) volatile.

At what pressure? Gallons probably isn't the best unit for this comparison. (see also below)

Energy per gallon
CNG: 33,000 - 38,000Btu @ 3000 psi; or 38,000 - 44,000 @3600 psi
Gasoline: 114,000 Btu
Propane: 84,000 Btu
Methanol: 56,000 - 66,000 Btu

[by the way that makes your cheaper CNG cost at least $2.60 per gallon (of gasoline equivalent), probably a lot more since it seems unlikely you have 3600 psi NG at your house.]

 

As pointed out, it's three dimensional chess. Which dimension gets bigger? The PHYSICAL size is less but the amount of power stays the same, your power to weight ratio is BIGGER.

Not really concerned about people accepting the published mileage ratings for the Volv0 V60. Some who are skeptical claimed the car didn't even exist and then, having to confront that it is in production and for sale, then claimed it couldn't get the published mileage. We do know the Volvo has a bigger battery pack and does get much higher mileage. We report. You decide.

 

WHO CARES?! You can't run anything on power to weight ratio. You can ONLY run things on POWER (actually energy). You are suffering from unit confusion. Physical size does not equate to mass. Power is not equivalent to Energy.

You claim that a higher energy battery (more kWh) improves mileage in hybrid mode. Prove just that.

 

And here I thought power to weight ratio was a key factor in transportation. Oh well.

 

Of the GAS TANK? What is the power to weight ratio of your gas tank? That is what you are trying to tell us important about the Battery. Make that "Extreme unit confusion"

REPEAT: You claim that a higher energy battery (more kWh) improves mileage in hybrid mode. Prove just that.