A test fleet of plug-in hybrids cruising around Seattle averaged 57 mpg in June. Although that's well short of the 100 mpg often touted for such cars, officials monitoring the fleet say it's a "real world" figure they're pleased with.
Seattle outfitted 14 Toyota Prius hybrids with plug-in conversion kits more than a year ago to see what the technology could do. The trial is one of several that Idaho National Laboratory is monitoring nationwide. When we wrote about the program earlier this year, the cars had racked up about 17,000 miles and averaged 51 mpg. That prompted some people to wonder if plug-ins offer more hype than hope.
But the cars are showing steady improvement, said Scott Thomsen of Seattle City Light, one of the agencies testing the cars. The fleet averaged 57 mpg in June, the latest month for which data were available. The fuel economy during charge-depleting mode -- when the electric motor is doing most of the work, with the gasoline engine occasionally coming in for a little extra oomph -- climbed to an average of 69 mpg.
"That was a 10 mpg increase, and that's where you're maximizing the plug-in operation of the vehicle," Thomsen said. "That's a significant increase."
Those figures are averages. Individual drivers have eked out some impressive numbers, with one guy getting 211 mpg on a trip from downtown Seattle to West Seattle, Thomsen said.
What does he attribute the improved performance to?
Warmer weather and more vigilant driving.
The 51 mpg average we saw earlier this year was recorded through the fall and winter. When it's cold, the Prius will run its gasoline engine until the catalytic converter warms up. This reduces CO2 emissions but prevents a plug-in hybrid from running on electric power. As the weather changed and the temperatures climbed, so too did the fuel economy because the engine was cutting out sooner, Thomsen said.
Driver behavior plays a huge role in maximizing fuel economy in a plug-in hybrid. You've got to use a light touch on the accelerator, mind your speed and plug in at every opportunity to keep the battery charged. The plug-ins are divvied up among the city, King County, Seattle City Light, the Port of Seattle and Puget Sound Air Quality (a 14th car in Tacoma wasn't included in the current data set). Fleet managers have been telling drivers how their driving style impacts fuel economy.
"You hope the message is getting through. It's an educational effort," Thomsen said.
Thomsen conceded the cars haven't been getting charged as often as he'd like -- further impacting overall fuel economy -- because the fleet also is testing smart grid software developed by GridPoint. The software controls when a car is charged, a handy tool that could allow consumers to plug in their cars when it's most convenient but not have them draw electricity until the software tell them too.
"The working theory here is, as we move forward, consumers who agree to participate could plug in the car, enter the time they need to have it charged by and allow the utility to determine when and how fast the car is charged based upon how big the load demand is," Thomsen said. That potentially could save consumers money because they could plug in the car whenever they want but not draw power until off-peak times.
Now 57 mpg might not sound like much, especially when the 2010 Prius gets 50 mpg (EPA combined). But the test fleet is running 2005 Prius hybrids with Hymotion conversion kits. The '05 Prius gets 46 mpg (EPA combined); Thomsen says those in Seattle's fleet are getting 36 to 42.
"So you're going from about 40 mpg to 57 mpg," he said. "That's a pretty sizable jump. It's 42.5 percent. If there were a product on the market that offered a 42.5 percent increase in your fuel economy, would you be interested? If you took this technology and applied it to the current model Prius to add 42.5 percent to the fuel economy, wouldn't that be great?"
Thomsen notes that increase in fuel economy is accompanied by a corresponding decrease in CO2 emissions from the tailpipe.
It's worth noting that the Prius wasn't designed to be a plug-in hybrid. The biggest problem is the electric motor is too small, so the car relies more heavily on the gasoline engine. Software also limits the top speed in all-electric mode to 34 mpg. Anything more than that and the engine takes over. Cars designed from the ground up to be plug-in hybrids, like the plug-in Prius that Toyota is working on will almost certainly offer far better fuel efficiency than a converted car.
"We believe this is pioneering a technology to see what it is capable of, with the full expectation that as it goes forward you'll see further improvement," Thomsen said. "We look at this as an opportunity to look at a significant number of cars in real-world conditions and see if it has some promise. Ultimately the public will decide if this is something that will take off."
Photos: Seattle City Light
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