IRV'S SHEET: Hybrid Tech: You Comment, We Respond

Back on September 8th, I published a quick piece I called "Hybrid Tech: Parallel vs. Series." One of the great things about the blogosphere is that it’s a two-way street, a format that invites, if you will, call and response, point and counterpoint.

So it wasn’t long until our friends at CalCars.org (or, more formally, California Cars Initiative for Plug-in Hybrids), to respond to my post with some interesting points. If you haven’t already done so, you can read them by scrolling down to the comments section of my September 8 post.

While we’re pleased that the folks there are willing to engage in this important discussion, our general reaction to those comments is that unlike the Blue Ray-vs-HD/DVD metaphor that some have suggested, we don't see the series-vs-parallel discussion as an either/or sort of thing. We do not believe that only one solution will be adopted, and all others will be abandoned.

Instead, what we expect is a diversity of solutions. That makes this a very exciting time for anyone who is interested in advancing automobile technology. Just as is the case with conventional internal-combustion engines, we expect to see many different approaches and nuances.

In any case, it seems appropriate for me to clarify a few things, so here goes. .  .

First of all, it is asserted that existing Nickel Metal Hydride (NiMH) batteries similar to those used so successfully by Toyota’s Hybrid Synergy Drive (HSD) system could drive the Chevrolet Volt (a hybrid prototype that was shown at the Detroit Show in January) 20 miles electrically without any change in the Volt's weight or other parameters – if they were designed for what’s called deep discharge. Currently, with most NiMH batteries, deep discharge is problematic because the deeper the discharge, the shorter the battery life. And obviously longer life is preferable to shorter life.

Anyway, the CalCars comments point out that that 20-mile figure is double the 10-mile EV range that Volt prototypes reportedly will have – and importantly, they attribute that range claim to Toyota.

First and foremost, that 10-mile range is not our claim. That was published in a story written by Jeff Green and Alan Ohnsman in Bloomberg.com on August 3, and published again on GM-Volt.com. That story cited unattributed information from inside General Motors saying that the Volt prototype will have a range of 10 miles. So that range figure appears to be right from the General’s mouth.

Just for the record, here, we have no idea what’s going on inside General Motors, and further, have nothing to gain by downplaying their successes, and their advances, with hybrid technology. In point of fact, we wish them the best, because we believe that everybody benefits from hybrids, and from hybrid research and technology.

With that being said, let us be sure that we all are talking with reference to the same set of definitions. Honda’s hybrid, for instance, isn't a series hybrid system. It’s a parallel hybrid system. Our Hybrid Synergy Drive system isn't a parallel hybrid system. It's a series/parallel hybrid system. The difference is the Honda system doesn't have an EV mode (series), but ours does. Likewise, the Volt doesn't have a traditional powertrain mode (parallel), but ours does.

Now, here’s the deal:

Do we favor NiMH technology? Of course we do. Toyota is heavily invested in NiMH battery technology. In fact, we think we’ve probably produced more hybrids using NiMH batteries than all other manufactures combined.

But because of our deep experience with NiMH technology, we also recognize the limits of these batteries with respect to cost, size, weight, recycling and life under wide state-of-charge swings. That is why we're developing new Lithium Ion technology.

In theory, of course a series hybrid could be developed that pulled a 20- mile range from NiMH batteries. But it would have to be a purpose-built car that depended upon technology that's not applicable to other products. Meanwhile, Toyota's HSD can be applied, and is being applied, across our entire product range.

But there’s more that needs to be said about this business of battery-only driving range – and forgive me, here, but this will require some engineering talk.

When range is discussed, it's important to also consider more than just the traction load. We also need to consider non-traction electric loads, AKA "hotel loads."

In many, if not most cases, at low speeds, the "hotel load" (and for you non-technoids, "hotel load" basically means the power demand from devices that are necessary or that are demanded by consumers, but that are not part of the powertrain that propels the vehicle), can be higher than the traction load. And as the automobile becomes increasingly electrified (steer by wire, brake by wire, heat pumps, active suspension, etc.), the "hotel load" will require considerably more battery energy.

Toyota thinks that it's important to let our customers know what they can realistically expect to experience in the future. Sure, it's possible for Car A to get a 20-mile electric range when driven at low speed with the air conditioning, lights and stereo turned off. But that obviously is not how the average person drives. When we factor in high-speed driving, use of the air-conditioning system, the audio system and so forth, Car A's actual all-electric range will be quite a bit less than that 20-mile grail.

But what’s more important here is that this discussion about the efficiency of one approach over another is, we believe, misplaced. What’s important is not the specific efficiency of a battery vs. a transmission. What’s important is the overall package, its acceptance by customers and the product's contribution to sustainable mobility.

The market for vehicles in the U.S. is around 17 million cars and trucks a year. In order to make a substantial reduction on our environmental footprint, the automobile industry needs products that can go to market today, be affordable, sell in large volumes, be easily serviceable and be capable of operating within the parameters of standard vehicle warranties. At Toyota, with Hybrid Synergy Drive, that's exactly what we're doing.

~ Contributed by Irv Miller, Group Vice President, Corporate Communications

Comments

[Andy]

Irv, wow, this post sure has a different tone than your last "go-buy-a-locomotive" post.

I wish you guys the best as you develop Lithium Ion technology along with the rest of the automotive industry. I agree the argument isn't so much parallel vs series vs parallel/series, but more on developing the right battery pack.

[AES]

Irv said "Just for the record, here, we have no idea what’s going on inside General Motors, and further, have nothing to gain by downplaying their successes, and their advances, with hybrid technology. In point of fact, we wish them the best, because we believe that everybody benefits from hybrids, and from hybrid research and technology."

It's crucial that GM succeed for a number of reasons. First, it's made a sincere effort to correct its image and role in the green car scene, and it has some superior technology to contribute.

Secondly, if foreign automakers achieve even greater success than they already have - mostly due to outdated reputations about reliability and economy, as well as trouble with unions - there are going to be disasterous long term results for the American economy. Toyota may have many jobs in America - Irv's being one of them - but ultimately the flow of most of the cash is going OUT of the country and into banks on foreign soil.

Don't get me wrong, you shouldn't buy a lemon to save America, but if it were down to a plug-in Prius vs. a GM Volt, there's more to consider than just MPG numbers.

[AES]

As for the whole technology debate: conveniently redefining the Prius as "series/hybrid" doesn't really help much. If the plug-in HSD engine has to cope with driving the wheels as well as recharging a larger generator, it's become a jack of all trades, and a master of none. It'll have to deal with a lot of dynamic load changes no matter what the situation.

re:deep cycling -> Irv, you're blowing smoke. Deep cycling is a familiar problem to anyone with EV experience, and upgrading a car's battery pack in size doesn't alter the problem - or its solutions - one iota. If anything, making the pack larger actually makes the solution somewhat easier, since there are fewer constant cycles that risk depleting the battery. The Prius doesn't let its tiny pack even get below 80% SOC, because it gets cycled for constant small loads that are proportionally large to the pack size.

re:"hotel loads" - as with houses and hotels themselves, this is a problem that is far better addressed with intelligent insulation and design, rather than the appliance itself. ALL cars' mpg ratings are made under ideal conditions without unnecessary loads - Prius included! Taking aim at any car's all-electric range with "hotel loads" is really a bit of a cheap shot, and a hypocritical one at that.

[Duane]

Irv,
Great comments and very informative. I recently came across your blog when doing research on the Prius and really enjoy it. I'll be checking it every day.

[Peter]

I see so much technology driven by trends and I hope that manufacturers, in the rush to PHEV, don't lose sight of the fact that some of us live in apartments and don't have places to recharge.

I want an efficient vehicle, but I am not (at this time) interested in a plug in hybrid even if it has a mode to deal with this. It doesn't make sense for me to pay more for bigger batteries and plug in charging circuits that I can't use.

If any manufacturer goes PHEV route, I think they should include and entry model of the same with smaller battery and normal HEV operation.

[AES]

Clarification real quick:

Increasing pack size helps protect against deep cycling because you can deliver more range on a partial discharge. (duh)

I think Mr.Kramer's original comment about deep cycling was intended to demonstrate the obvious limitations of NiMH chemistry, and the impetus for the PHEV industry to embrace the currently available advanced lithion ion technology. It was almost definitely NOT an urge for automakers to start making models that deep cycle.

[pdbw]

Well, thanks for clearing that up. Or making it muddier. For example...
1. To begin with, I can't backtrack to the original post (Hybrid Tech: Series v Parallel); when I click on the link in this post, I get 'page not found'. Now, of course, it could be a coincidence, but a pessimist might think you're trying to conceal your problems...
2. "We don't see the series-vs-parallel discussion as an either/or sort of thing". Really? That's not what this quote from the previous post sounds like: "You can buy a vehicle powered by the system right now, today. But if you want a series hybrid, well – you can cross your fingers and wait for a few years until some difficult engineering and production problems are solved." In other words, buy our proven technology or cross your fingers for something that doesn't exist.
3. "We have...have nothing to gain by downplaying [General Motors'] successes, and their advances, with hybrid technology." Uh, yeah, you do. You can sell more hybrids by sowing the seeds of fear, uncertainty, and doubt about competing technologies. See previous point--which says, "Buy Toyota's proven technology or wait to see if the General can address some difficult engineering and production problems."
4. "Okamoto’s expression of our belief in the superiority of parallel hybrids apparently raised some eyebrows." Uh, yeah, it did. Especially since you are apparently not building parallel hybrids, but series/parallel hybrids. Get your story straight...
5. "Toyota thinks that it's important to let our customers know what they can realistically expect to experience in the future." A bit holier-than-thou, isn't it? Especially coming from a company whose flagship hybrid has been criticized for getting close to EPA estimates (as noted here, among other places: http://blogs.cars.com/kickingtires/2006/10/prius_mileage_1.html). ALL companies feel this way, Irv.

(RoadMaster Edit Note - Refernced link has been corrected. Thanks.)

[Felix Kramer]

We at CalCars.org are encouraged and energized by the continuing dialogue. We agree that everyone benefits by discussions of hybrid research and technology.

We've asked Ron Gremban, our Technology Lead, to respond to some of the technical issues you just raised. (To keep it short, we don't address everything!)

Ron wanted to be sure to start by saying that "since its introduction, I have been in awe of the engineering that went into the '04+ Prius and Toyota's Hybrid Synergy Drive." (And in his Sept 13 response, he attributed the 10-mile Volt prototype range information to Toyota only because we hadn't seen the previous news reports on which the comment was based.) Ron continues:

I agree wholeheartedly that series, parallel, and series/parallel hybrids and PHEVs will co-exist for some time in the marketplace, if not from now on. No single configuration has all the advantages.

Part of Toyota's strong experience with NiMH batteries comes from the deep-discharge 1990s-technology NiMH packs used in Toyota's RAV4 EVs, some of which by now have well over 100,000 miles on them without significant battery degradation. In fact, the Electric Power Research Institute (EPRI)'s prediction that NiMH and Li-ion batteries can both last the life of a PHEV is based on that field data as well as its PHEV-specific laboratory testing. Yes, cycle life of any battery is reduced with deeper discharge. This merely means that the engineering tradeoffs between pack size, depth of discharge, cycle life, power handling capabilities, etc. must be chosen carefully, using both engineering and economic expertise.

"Hotel loads" must be supplied, if not from a battery, from gasoline at the internal combustion engine (ICE)'s same 15-35% efficiency as available to propel the vehicle. Therefore, all the advantages of using grid electricity to propel the vehicle apply equally to using grid electricity to supply hotel loads. Even when this energy provides less EV range in cold or hot weather use, it is still displacing the same amount of gasoline (or more, since electric A/C compressors are far more efficient than engine-driven ones). The one exception is cabin heating, which is normally supplied from ICE waste heat. When it is too cold for an air conditioning heat pump to efficiently heat the cabin, EV purity can be sacrificed (independent of hybrid type) by running the ICE occasionally to build up sufficient waste heat for cabin heating. ICEs produce so much waste heat that mere occasional operation will be quite sufficient.

Plus a final note from Felix Kramer, returning to a less technical perspective: We agree with Irv Miller's description of the attributes of cars that can sell in the millions. But we suggest a way to get there most rapidly, reflecting the urgency of climate crisis and fossil fuel dependency, is by producing (and selling in surprisingly substantial numbers) "good enough to start Version 1.0" PHEVs from which automakers will all learn. Remember the first cellphones: brick-sized and costing in the thousands? We're glad the manufacturers started producing them to continue improving them while scaling up production.

-- Felix Kramer, Founder, The California Cars Initiative

[Kenneth Dove]

The only thing that I cannot, and will not, tolerate is the following statement:

"But because of our deep experience with NiMH
technology, we also recognize the limits of these
batteries with respect to cost, size, weight,
recycling and life under wide state-of-charge
swings. That is why we're developing new Lithium Ion technology."

SURELY, Toyota realizes the ABUSE that all of the NiMH packs in each and every Toyota RAV4 EV has endured, and yet they make these claims?

How costly can NiMH be? ($400 per kWH?)
How much can a 40 mile pack weigh? (300 pounds is the answer)
It will recycle for hundreds of thousands of miles.
Its longevity is proven EVERY DAY in the hundreds of RAV 4 EV's on the roads.

SIGH.

In a nutshell, here is the problem as I see it:

IF the automakers agree that NiMH is a viable, ready for prime time option, then they all would HAVE to acknowledge its readiness for CURRENT COMMERCIAL PHEV APPLICATIONS.

By disrespecting NiMH so utterly and completely, they leave themselves an out, namely uncertain Li ion battery technology and therefore do NOT feel compelled to offer the consumer a plug in alternative.

If I had and extra 50 thousand bucks, I would just buy myself a RAV 4 EV, which seems to be what today's market will bear for this wonderful vehicle. Then fabricate a home made genset to haul behind it....sheesh. It has already been done, BTW..........

[AES]

Kenneth Dove-

NiMH can withstand lots of cycles, and it IS cheap(er), but it also has very low energy density.

As for your 300 pound estimate for a 40 mile NiMH pack, if you calculate 8kWh using the specific energy of Toy's prismatic cells, the battery would actually weigh 400 pounds. Add on a lot more if you want partial discharge.

NiMH has no future for plug-ins.

[kert]

Lets consider the realistic battery options for a second.
LiFePO vs NiMh.

The first important variables for are specific power, and specific energy.

Specific energy is easier, its inherent to chemistry:
Current LiFEPos on mass market have roughly ~100wh/KG. Current NiMh has ~80wh/Kg.

Specific power is trickier, as its more dependent on cell construction, specific power can commonly be expressed in C rate, ie a safe discharge rate relative to cell capacity, but for better overview lets talk W/Kg numbers.
Nanotech-enhanced LiFEPos have advertised 10C rates, which equates to ~1000w/Kg. Realistically,they are used more in 5C ranges, ie 500w/Kg.
NimHs can take and are taking roughly 3C ranges, which would equate to around ~250w/Kg.
Note that peak charge rates for packs can be smoothened out using capacitor banks.

Now, lets talk longevity. The most important variable affecting longevity, when operating at the edge of performance, is peak charge and discharge rates, for both chemistry types. For NiMH, maintaining proper average SOC is also important. Lithiums have calendar life issues as well, i.e. they lose capacity in time, regardless of their use. There is no real data as of yet for LiFEPo on that, as the tech hasnt been on market for any significant time.

RAV4EVs have shown, that NiMH can last a long number of cycles, in several thousands, with well conditioned packs, and properly maintained discharge rates. Laboratory tests have also proven that LiFEPos can do that. Calendar life remains a question.

So now if you put these numbers in perspective, the differences are not all that big. It is certainly possible to construct a BEV using both of them. BEV is a bit easier, because you have to put in enough Wh in the first place to get any decent range, which will mean that your peak available power from the pack, at its maximum C rate, will far exceed anything that you can pump into motor or get down to the road. Examples are on the roads as well.

Now PHEV is trickier. Start scaling down from say, 100 mile range pack, and at some point you will get into zone where your designed power, will get into "uncomfortable" C zone for cells. Where exactly this point is, depends on given chemistry, particular cell construction and so on. Because NiMH has lower C rates, i.e. less Watts available per kilogram of batteries, NiMH would actually require your pack be bigger to not hurt the cells with too high discharge rates.
As mentioned before, the issue can be smoothened a bit with large enough capacitor banks, but it has only marginal effects, considering real-life usage scenarios.
Because the NiMH pack would be bigger for given available power, by about twice as much compared to LiFEPos, its contained energy will be about twice as big as well, which means that you can avoid deep cycling as well and maintain the most favorable SOC.

So lets bounce some more numbers for 40PHEV. Considering that average EVs on roads consume about 300Wh/mile ( thats on the high side ), you need roughly 12KwHs, lets err on the caution side and say 15KwHs of batteries. 15KwH pack is going to weigh, at 100Wh/Kg 150Kg.
At 5C discharge rate for LiFEPOs, 15KwH is going to give you 75Kilowatts peak power, or just above 100Hp , with 3C for NiMH thats only 45KW.

So it comes down to: what peak power do you want from the car ? How much power do you draw constantly at highway speeds ? What is the comfortable C rate for the given battery cells, to maintain acceptable longevity ?
If you have calculated all that, you need to consider how much all that is going to cost.

Designing a 40PHEV around both NiMH and around LiFEPo is certainly possible, but there are lots of variables to consider, and NiMH definitely has a disadvantage due to lower C rates. It does not mean, though, that NiMH would be impossible.

But its not clear win scenario for either one. Even though NiMH is cheaper, on retail anyway, for the same other design variables ( power, range ) you need more of them. I have no idea on bulk pricing with direct deals for auto manufacturers.

Now there are other variables, like environmental friendliness to consider as well. Certainly, with the all important time to market NiMH wins, but its not a clear cut case of win-win for everyone.

[AES]

Kert - overall, a very good post, but your estimates of specific energy are a bit off.

"Current LiFEPos on mass market have roughly ~100wh/KG. Current NiMh has ~80wh/Kg."

On the cell level, mass market LiFePO4's can actually get slightly higher than that - up to 120Wh/kg for 18650's, and around 108Wh/kg for the kind currently used in automotive use.

NiMH isn't nearly as fortunate - the prismatic cells that the current Prius uses top out around 45 Wh/kg. The high energy, large format cells from Cobasys (who inherited the EV1/Ovonics technology) do slightly better than this at around 55Wh/kg. The 80Wh/kg number you provide is probably the theoretical maximum, and small format consumer cells probably get the closest to this. It's not as close of a playing field as you portray it as, and specific energy is a HUGE factor for PHEV viability.

[pdbw]

Well, I suppose I should correct myself. I meant to say, "Especially coming from a company whose flagship hybrid has been criticized for NOT getting close to EPA estimates." (Note change in caps). And thanks for fixing my, er, "refernced" link...

[AES]

This is the sort of stuff that Toyota should be addressing:

http://www.autobloggreen.com/2007/10/02/matsushita-suspends-liion-battery-production-after-fire-at-plant/

Matsushita is part of the group that Toy goes to for batteries, including li-ion cells. Apparently, their cobalt cathode cells have gotten a bad rep lately over overheating, explosions, etc etc, and now they've shut their plant down.

Did Toyota use these cells in their plug-in experiments? Did they simply choose the wrong battery supplier/chemistry for their cells? A simple admission of this fact might go a lot further in the public eye than simply saying the batteries don't exist.

[Frank a Prius owner x 2]

As a 2 x Prius owner, I am outraged to find out that Toyota is lobbying against the Senate Bill with higher mileage requirements.

If Toyota does not cease and decist I will have to buy a car from a more responsible company. See NYTimes piece at: http://www.nytimes.com/2007/10/03/opinion/03friedman.html?_r=1&th&emc=th&oref=slogin

[Jeff]

Toyota - why are you joining the Detroit Big 3 in lobbying Congress against the increase in mileage standards for American cars and trucks? Toyota can already achieve the mileage proposal for 2020 today in Europe and Japan. For a self styled green company, that is reprehensible. I'm buying Honda for my next car. Reprehensible.

[pharmacy]

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[jorge]

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