Prius Plug-In Proves More Fuel Efficient Than Hybrid Version in Road Trial

Actual fuel savings depends on how far people drive their PHEVs, a Toyota engineer says. Nineteen miles a day saves 71% of fuel, compared with a hybrid Prius, and at 31 miles a day, the savings is 41%.

William Diem, Correspondent

May 3, 2011

5 Min Read
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PARIS – Toyota’s Prius plug-in hybrid electric vehicle saves 41% more fuel than the basic Prius on trips of 31 miles (50 km) a day, according to results from the first year of on-road testing in Japan.

The outcome of another field trial that includes 80 PHEVs in Strasbourg, France, will be available in several months, says Rody El Chammas, an engineer at Toyota Motors Europe working on the project.

El Chammas explains Toyota’s strategy and first experimental results to 200 engineers attending the recent Automotive Power Electronics symposium here sponsored by the SIA French automotive engineering society.

“We think the electric vehicle will be limited to short-range commuters,” he says. “The plug-in hybrid EV has potential as the most promising solution to replace conventional vehicles.”

Toyota sought a plug-in that would save the most fuel in general and opted for a less-expensive, shorter electric-only range of 13 miles (23 km), compared with the Chevrolet Volt’s 35-50 miles (56-80 km) or Nissan Leaf’s 100 miles (160 km).

“A smaller battery is more affordable to more consumers,” says El Chammas, “so the impact on fuel savings will be high.”

Some 45% of users in the Japan test drove less than 20 miles (32 km) a day, so their daily fuel use was zero, he says. And because they had a 1.8L gasoline engine on board, they didn’t worry about driving further.

Most drivers of the 200 plug-in hybrids in the Japanese fleet trial used the car for business, and Toyota was able to track results of the daily drives on the same route.

Prius plug-in currently being tested in France, Norway and Austria.

It was no surprise the extremes of cold and hot weather reduced the range of the PHEVs. At 32° F (0º C), range is cut in half; above 77° F (25º C), when the air conditioning kicks in, the range sinks again. But in addition to the effects of weather on the draw of electricity, Toyota also found a “traffic jam” effect.

In good weather on the same route, when the drives averaged 19.4 mph (31.2 km/h), the EV range was about 4 miles (2.5 km) more than when speeds were averaging 13.7 mph (22 km/h).

The loss of EV range is not critical to driving, of course, because the engine starts when required. The engine also is designed to be sensible about the battery charge.

“In some conditions, if you have very poor weather like -20º C (-4° F), the electrical efficiency will be very low,” El Chammas says. “But we can start the engine to heat the cabin and heat the battery, and then start using electricity. Thus, you can also optimize the thermal management system.”

About 76% of the Japanese users said the electric motor power was sufficient, and 88% said the effect on fuel consumption was good or very good.

Characteristcs of the Prius Hybrid and Prius Plug-In

Base Prius

Plug-In Prius

Battery Chemistry




1.3 kWh

5.2 kWh





92.5 lbs. (42 kg)

353 lbs. (160 kg)

EV Range

1.25 miles (2 km)

14 miles (23 km)

Trunk Space

15.7 cu.-ft. (446 L)

14 cu.-ft. (403 L)

Fuel Efficiency Ratings


89 g/km CO2

59 g/km CO2


78 mpg (3 L/100km)

134 mpg (1.75 L/100 km)


51 mpg (4.6 L/100 km)


The biggest problem to show up so far, he says, is the need to make charging more convenient. A user in Strasbourg, for example, says the charging cord gets dirty, so he uses a rag to wipe it down and wraps up the cord to keep the trunk clean.

The Strasbourg experiment began in late April 2010, sponsored by the French electric-utility EDF and the town, located on the border with Germany.

EDF developed charging posts that know which car is being charged, so it can bill the right person. Home versions charged at night, when the only electricity being produced in France is from nuclear and hydraulic sources that do not emit carbon dioxide.

The plug-in Prius recharges in 100 minutes with European 240V systems and in 180 minutes on 110V grids. “There is no need for fast charging,” El Chammas say, “because we have the engine.”

The city of Strasbourg is learning how many public charging spots might be needed as electric cars become more common, and how they are used and misused. At least one charger has been vandalized. Sensors in the charging areas keep track of how often regular cars are squatters in the parking places reserved for the Prius experiment.

In Europe, the plug-in Prius also is being tested in Norway and Austria, and last month the EDF and Toyota leased three plug-in Prius units to the Paris City Hall.

Sales of the car begin in 2012, El Chammas says. When the program was announced in December 2009, Toyota said it planned to begin selling plug-ins this year.

The plug-in version is designed to be as little changed as possible from the base Prius. The cars use the same 1.8L 98-hp engine and 60kW (80-hp) synchronous AC electric motor.

The big change is the addition of the onboard charger that changes 110V and 240V AC into DC current to charge the battery and the replacement of the 1.3-kWh nickel-metal-hydride battery with a 5.2-kWh lithium-ion battery.

The air-cooled Li-ion battery is larger than the battery it replaces, so trunk space is reduced by 10%.

Actual fuel savings depends on how far people actually drive their PHEVs. El Chammas says 19 miles (30 km) a day saves 71% of fuel, compared with a hybrid Prius, and at 31 miles (50 km) a day, the savings is 41%.

In Europe, 75% of daily trips are less than 50 km, he says, while in the U.S. 66% are below that and in Japan it’s 90%.

Europe and Japan have agreed on ways to create an “official” fuel-efficiency standard, with Japan rating PHEVs at 134 mpg (1.75 L/100 km) and Europe at 59 g/km of CO2, the equivalent of 94 mpg (2.5 L/100 km).

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