Sunday, June 7, 2009

Plug-In Hybrids

In Toyota: Plug-in Hybrids Will Have Limited Appeal, Jim Motavalli makes the world of the Toyota much more complicated, at least until we look at things a little further. I wondered what the Toyota people had in mind during their presentation. As a Prius driver myself, it seems to me that adding a large battery does not produce a difference in kind that would force a new brake design for example. More like having an extra passenger in the car, and that does not require redesign. Further, the extra weight only means that a driver adjusts his driving style once again. One of the wonderful features of the Prius and the Honda hybrid is that they offer enough instrumented feedback so that one can adapt one's driving patterns to get better mileage. One possibility is that they are trying to dampen some of the exaggerations about mileage. At an MIT symposium on the Smart Grid, I heard one speaker say that plug-in vehicles would get 150 miles per gallon equivalent. I did not believe that, and sought to clarify whether that number includes the inefficiencies inherent in production and distribution of electricity. The consensus in my area of the room was that it does not. Proper treatment of these inefficiencies would yield roughly 50 mpg equivalent, interestingly in alignment with the Toyota numbers. In other words, once again, it is very difficult or impossible to get something for nothing, but it is possible to create the illusion of getting something for nothing. Toyota is to be honored if it is bucking this opportunity.

On a more skeptical note, one may consider that the Prius "crossed the gap" to adoption around 2003. At least, this is how Toyota and the auto industry saw things at the time...although I thought that judgment was a little premature. Recognizing this, one can also hypothesize that Toyota has a vested interest in protecting its offering. Some of the things Toyota people say may therefore be biased by this effort.

More broadly and technically, I see opportunity for better gas mileage with my Prius, but am a little skeptical of simple notions of plugging into the Grid as the source for those increased miles per gallon. Illusory miles per gallon, yes. Real miles per gallon, no. What I recognize is that, as I drive, there are some opportunities for better mileage as a result of a larger battery. At most this would be a 10% improvement, consistent with Toyota's projections. However, if one spends a lot of time in heavy urban driving, then the extra battery capability could be very valuable. Such driving is very draining on the batteries, and they can then be recharged when one gets out of the inner city. I have found the Prius to be better at battery life during such driving than is the Honda, so optimization can be done differently by different manufacturers, and Honda may have more opportunity in this area than does Toyota. Again, this is consistent with what Toyota has stated.

Where this all becomes very interesting is in interaction with the eventual Smart Grid. The vision for the Smart Grid is that car batteries interact with the Grid, calling for electricity when they are recharged during low-demand periods, and providing on-peak electricity when in the parking garage during peak hours during the day. Optimizing this system is not simple, because it is large and fundamentally statistical. We certainly want to avoid demanding more electricity if the amounts and timing will increase the production of greenhouse gases. Nevertheless, the vision has a chance of being accurate and is worthy of exploration.


Bob S said...


I am not sure how you are considering the miles obtained from plugging in as "illusionary".
This energy taken from the grid means direct miles traveled without fossil fuel involed. In the pacific NW, we have very little coal used, none in off-peak times, meaning no carbon involved with the miles used under electric drive when charged at that time.

Maybe you are referring to the current Prius design, in which plugging in is basically worthless considering the small on-board storage capacity. WIth a larger pack capacity, one could go forever without needing gas if the daily commute is less than the capacity of the battery.

Even if charged by coal produced electricy, the electric drive comes out with less CO2 emitted than an equivalent ICE vehicle burning gasoline because of the significantly higher efficiencies of electric drive systems.
Also, the miles driven from burning the feedstock that goes into creating Ethanol will result in 80% more miles traveled than to burn that ethanol in a vehicle.

For an electric vehicle, with a grid-tied solar array on your own home's roof, you can be net-zero in energy use for driving, no illusion involved.


oliver kuttner said...

Dear Sir,
I have done a fair amount of work on the real mpg subject and you are correct (actually erring on favor with the plug in. if you email me direct I will send you a few papers we wrote internally which I may post on the web in the near future. It is our opinion that in the context of the USA grid the electric car with its very efficient motor only has an efficiency of 22%. My email is It seems that policy today is driven by wishfull thinking with incomplete information. This is unfortunate. You are right. the Chevy volt will be a 40 mpg heavy car at best if the accounting is done properly.
Regards- I wish we were wrong.

oliver kuttner said...

send me your direct email and i will send you an internal paper we prepared which will show you that the electric car is at best 22-25% efficient in the context of todays grid.
I wish it were not so but reality is the Chevy Volt is at best a 40 mpg car and Toyota knows why they are staying away from the plug in. After several years of pursuit of this electric option it will become clear that it left a lot to be desired. Smart people (especially if they contributed setting off the avalanche by building a very efficient car first and a good hybrid second) want to distance themselves from this coming awakening to reality You are right there is no 150 mpg plug in Toyota. The people at Toyota are smart enough to know their own very good child. The problem is that now in the USA some otherwise very smart people are making important policy decisions which are based on incomplete math.
To the man from the NW. the grid is essentially national. while there are many hydro plants where you life it does not matter. We have no business to add cars to the grid until we get rid of (or if you believe the clean coal lobby) clean up coalpower plants first. That job is very big. If we fill the requirements for power with nuclear and do the upgrades neccessary for a fleet change to all chevy volts then it is about 8 trillion dollars. About 1.2 to 1.8 trillion is for buying oil to do the construction alone.
That action in itself will raise the price of oil and our deficit. The only true answer is efficiency. Low weight low drag. Further as you managed there is some fruit to be had from driving style. - that may be directly linked to mindfulness and education.
On the smart grid I have one comment. The batteries for a real plug in cost some $10,000.-- to $15000.-- (see recent NY times article on batteries and DOE energy density goals revised downward by 333%) These batteries have a life that is determined by Number of charge cycles. Howlong do you think people will allow power companies to use their batteries for pennies a day to store their excess power? The math will not add up and people will opt out. Battery energy storrage is very expensive. In the long run it has great legacies in production and disposal pollution Regards oliver

oliver kuttner said...

Sorry for leaving two comments i did not realize the comment went in before i registered.