February 24, 2009
Real World Plug-In Hybrids Disapppoint On Efficiency
A Seattle test of hybrids modified to be rechargeable and theoretically to run 30 miles on electric power produced disappointing results so far. 14 specially customized plug-in hybrid Toyota Priuses did not do much better than standard Priuses in fuel efficiency. (thanks "Fat Man")
Try 51 miles per gallon, city and highway combined. Not counting the cost of the electricity.
It's what 14 plug-in Priuses averaged after driving a total of 17,636 miles. The pilot project is one of the few in the nation to subject plug-in hybrid cars to regular motor-pool duty, as opposed to being driven by hypermilers or alt-energy enthusiasts.
Vehicles engineered for production quality will probably do better than these customized cars.
The article also points to Google's own fleet of hybrids and plug-in hybrids. At that web page Google provides data on how these vehicles compare in fuel efficiency. Their Ford Escape hybrids are averaging 28.6 mpg while their pluggable versions of the Escape hybrd get 37.7 mpg for a 32% improvement. Not earth shattering. Their conventional Prius hybrids get 42.8 mpg while their pluggable Priuses get 54.9 mpg for a 28.3% improvement Again, not exactly the end of the oil era. Google breaks out the numbers by car. The best has done 60.5 mpg. But if you look at single day results you can find cars hitting 107 mpg.
Why these disappointing results? A fleet car could get driven a lot in a day and run down its batteries. To maximize the benefit of a pluggable hybrid one really need to drive almost the battery's range each day but no more. Someone who happens to commute a distance that is a little less than the range of a hybrid's battery is the best candidate to get maximal benefit. People who drive too little will pay for higher battery costs that take a long time to pay back. People who drive too much will run much of the time on gasoline.
I also wonder how motivated fleet car users will be to plug in every time they stop somewhere they can plug in. Then there's the need to stop at places where plugging in is even possible. There's no golden bullet for replacing oil.
The improvements of conversion-based PHEVs depend a great deal on driver behavior. Hyper-miling is far more effective in a PHEV, but if the driver doesn't adjust style to make use of the storage the effects will be less (perhaps far less) than optimal.
Users have reported upwards of 90 MPG in Prius PHEV conversions. These are probably from owners, not fleet users who may not drive the same model every day let alone the same vehicle.
"There's no golden bullet for replacing oil."
And no silver bullet either. There is a ~$950/troy oz. difference.;-)
"if the driver doesn't adjust style to make use of the storage the effects will be less (perhaps far less) than optimal."
It is not realistic to expect that any large number of people will change their driving style to fit technology. They won't even put down their cell phones to avoid dying. Technology needs to fit people, not the other way round.
In my '05 Prius, my year-round average is 53-54 mpg (56 summer & fall, declining to 49/50 Jan./Feb.). Assuming a conservative improvement of 20% (based on the above figures: I'm making a conservative assumption, since presumably I've already maximized my efficiency), that yields a mileage of 63-64 mpg. I'll take that.
I suspect the key will be to use electric on stretches where the gas efficiency is low; and use gas where gas efficiency is relatively high (65-75 mpg). One quickly learns inclines, smooth road, etc., which influence mileage. This should allow one to double the useful mileage.
It is not realistic to expect that any large number of people will change their driving style to fit technology.
Then they'll have to wait for cars designed to be PHEVs from the ground up. I, for one, am quite willing to hyper-mile and regularly beat my EPA highway mileage rating.
A car that refuses to accelerate toward a red light would prevent lots of rear-end collisions. It would also do wonders for energy consumption, by controlling behavior. Insurance companies may demand such things, and energy savings would be an inevitable byproduct.
It looks to me like the main problem is that they're starting with a Prius. A Prius (parallel hybrid) will use gas even if you stay within the 30 mile range of the batteries. If you drive with a leadfoot or at highway speeds, the battery doesn't get used that much.
A plug-in like the Chevy Volt (series hybrid), that uses only the battery for the first 40 miles, will use the battery 80% of the time. Combine that with a MPG twice as large as the average US light vehicle for the 20% of driving after the battery runs low, and you get a 90% reduction in fuel consumption (or a 900% improvement in MPG).
Elsewhere (can't recall and can't find with a search) I read that the fuel economy of the converted Prii is changed radically by how aggressive the driver's style is. The drivers ranking 0-1 (on 0-10) got ~100 MPG, 2-3 got ~50 MPG, and 4-6 got ~40 MPG.
Of course, driving style has a similar though less pronounced effect with the unconverted Prius also. The bigger PHEV battery increases the effect of electric propulsion and regenerative braking if the driver allows them to.