Testing Plug-In Hybrids: What the Results Mean

By Ucilia Wang

When it comes to plug-in hybrids, your mileage will vary. All over the place. Look at Google's highly touted, seven-week test of converted plug-in hybrid electric Priuses. The results showed that the cars were able to achieve an average of 93.5 miles per gallon. "The plug-ins did great, getting as much as 93 MPG average across all trips, and 115 MPG for city trips!" boasts Google.org on its website.

That's good and fits in with the 100-mile-per-gallon standard often associated with the cars. But a close look at how Google did the tests, and it became apparent the tests don't reflect real-life.

Google hired five professional fleet drivers from a local shuttle service and had them drive on designated city and highway routes mostly located in flat Silicon Valley and under mild weather. Each trip was designed to allow the tester to complete it with power from a fully charged battery pack. (Google said some trips used up the entire battery before they ended).

Google also instructed drivers to accelerate moderately, though it claimed it didn't otherwise teach the drivers tricks for getting the best mileage.

The Department of Energy conducted its own tests in a more hoi polloi fashion and got about half that.

As major carmakers get ready to launch mass-produced plug-in hybrids over the next few years, everyone from government agencies, private car fleet owners, utilities and researchers are carrying out more road tests to gauge just how good of a fuel economy you could expect from a plug-in hybrid. The plug-in hybrid passenger cars that can be seen on the road today are regular hybrids – mostly the Prius or Ford (F) Escape – that have been outfitted with an extra battery pack and a cord for charging via a standard electrical outlet.

There are no national testing rules for determining a plug-in hybrid's fuel economy. The U.S. Environmental Protection Agency is still working on that. In the mean time, the U.S. Department of Energy's Advanced Vehicle Testing Activities program has been conducting a series of field tests in controlled and real-life settings with 12 models – mostly Prius and Escape – in 20 states and Canada.

The DOE started testing of plug-in hybrid cars in partnership with private and public fleet owners in 2006, and some of the recent results (.pdf) showed that drivers in real-world conditions were achieving an average of 51 miles per gallon when the same cars could yield more than 100 miles per gallon in controlled or lab settings (see baseline testing results (.pdf) and accelerated testing results (.pdf) of a Prius converted by Hymotion).

What happened? For one thing, those drivers were just going about their own business instead of traveling only on designated routes in more ideal weather conditions. The tests were done in different types of terrains, and the results included mileage data from when the cars' battery packs were in use and after they were depleted. And those battery packs were not necessary fully charged before each trip.

The tests involved not only fleet drivers but also consumers. The program partnered with UC Davis a year ago to launch a test involving about 70 members of the American Automobile Association in California, said James Francfort, a staff engineer for the DOE program at the Idaho National Laboratory. Most of the drivers didn't start taking their Hymotion Priuses on the road until last fall.

The DOE also has carried out controlled tests (.pdf) that use selected drivers who travel on designated roads. The Hymotion Prius has shown to achieve an average of 79.5 miles per gallon (.pdf).

Interestingly, Google – before it hired chauffeurs – was getting similar results in its plug-ins. Some got 66 miles per gallon.

Driving behavior, climate and road conditions all influenced the outcome, Francfort said. Electric cars are far more efficient at using its fuel than gasoline-powered cars. That means poor driving habits could have a greater impact on the fuel economy of an electric car, Francfort said (see page 18 of Francfort's presentation (.pdf)).

An electric motor can make use about 75 percent of the energy while an internal combustion engine can achieve about 20 percent efficiency, according to a DOE Website, Fueleconomy.gov.

Accelerating quickly is a major no-no for getting better fuel economy. When you speed up quickly, it requires a burst of energy that takes more battery juice. Cranking up the air conditioning also will lower the fuel economy. So will conquering steep hills. (Dave Hermance, the deceased Toyota (TM) exec who helped develop the second generation Prius, came up with some of the feathering techniques for increasing mileage.)

"But probably the single issue is: Have batteries been charged?" Francfort said. It isn't just about charging the battery in full before each day's use. "It may also be a lack of access to a place to charge, or of time due to job requirements."

Battery technologies matter, of course. The cars used in the program are converted plug-in hybrids, and the lithium-ion batteries are more experimental, said Tim Murphy, manager of the DOE program.

"You can educate people about how to get the best performance out of the car," Murphy said. "As batteries become better over time, they are going to handle more harsh driving, and we are going to start seeing better average performances."

A regular Prius can achieve a combined city/highway mileage of 46 miles per gallon, Toyota said. Companies that offer covert kits, such as Hymotion (owned by battery maker A123 Systems) and Hybrid Plus, often tout their plug-in hybrids as being able to achieve more than 100 miles per gallon.

Those companies, as with automakers, also are quick to note that the actual mileage could vary based on the driving style, the weather and other factors.

That said, it doesn't hurt to create a tip sheet to train consumers to get the most of fuel savings from their plug-in hybrids, especially when companies such as General Motors (GM) plan to start selling them within two years.

That's what the folks at the DOE program are doing as part of its public outreach effort, Francfort said. He expects to complete the tip sheet in about two months.

Comments

[a. palmer jr.:]

General Motors may not be around in 2 years to compete unless they get massive bailouts.

Apr 12 08:41 AM

[whisperonth...:]

My general assumption is that no one will be able to take the haphazard driving methods out of all the drivers. We also can't change the weather and it would be too expensive to make hills and mountains go away. Therefore, since we can't change the variables, we must accept that expecting 100 mpg is a bit much unless we live in California and drive exactly those routes. Since there are 49 states filled with people who have clearly chosen not to live in California (smart people!), the 100 mpg is out.

Additionally, with the expected prices of electric cars so high, this would place them out of range for most of us, even if the economy were not stretched exceedingly thin.

Last of all, with the price of electricity competing with the price for gasoline, will this direction help with financial ability? If the cost for a "fix" (for global warming, or whatever the problem) is too high, it won't succeed.

Let's be realistic. Electric cars are not really where we should be going, until we can get a financially viable product which solves all the other problems. My excitement level is way too low on this.

Apr 12 09:35 AM

[John Petersen:]

It's almost enough to make you wonder whether we wouldn't all be better off spending $2,500 to buy a Tata. They'll reportedly deliver 59 mpg and leave $37,500 in savings that could be spent weatherizing your home and investing in other alternatives that offer reasonable paybacks.

Apr 12 09:37 AM

[whisperonth...:]

$37,500 is a nice chunk to put down on a more efficient new home, and with the interest rates lower, it might just be more responsible and could help get the economy moving faster. Assuming, of course, that one can get a bank to loan you the money...

The Tata would save us money, be more fuel efficient (raspberries to the oil shieks), and we'd all look silly together. I might have to check into getting one! It would keep the kids from wanting to go everywhere with me.

Apr 12 09:56 AM

[Butch:]

Can anyone tell me how the mileage quoted for these tests is calculated? Is it only the gasoline used during the test period or is it the gasoline equivalent for all of the the energy used? That is, the total BTUs of energy used from all sources, gasoline and the charging of the batteries from the grid.

Apr 12 10:20 AM

[dan-d:]

It true, most people cannot afford a prius or other energy efficient vehicle. Someday a car will be developed, like the VW was in the 30's , that the average income earner can afford. Probably that day it not to far away but, until then, smog producing gas engines are their only choice.

Apr 12 11:55 AM

[AndyInGA:]

Now any improvement in mileage good. If one can get 70 miles a gallon from plug-in hybrid Prius versus 45 miles for regular hybrid, it is still a significant improvement. Now the improvements in mileage has to be balanced against incremental costs. There will be lot more takers of plug-in if it comes with around $5k premium over the gasoline only models without including government subsidies. Any thing above it will make it less appealing for the mass market.

One may not get Tata Nano in US for $2,500. With US safety regulation and market needs, it will be more like $6-7k range.

Apr 12 12:08 PM

[fran:]

after our economic disaster and associated employment problems plus debt levels, a TATA may be the only choice that many can make. any money left will go toward debt and increased taxes and cost of living-- for those fortunate to have "extra $$".


On Apr 12 09:37 AM John Petersen wrote:

> It's almost enough to make you wonder whether we wouldn't all be
> better off spending $2,500 to buy a Tata. They'll reportedly deliver
> 59 mpg and leave $37,500 in savings that could be spent weatherizing
> your home and investing in other alternatives that offer reasonable
> paybacks.

Apr 12 01:19 PM

[carbonates:]

Tata's Nano isn't street legal in the U.S., especially not California! The Nano is nowhere near meeting U.S. safety standards, and won't even meet U.S. emissions requirements. Perhaps people don't realize how restricted the US auto manufacturers are by regulations. By the time the Nano is made to conform to U.S. regulations it will likely cost 10 times more and get half as much mileage.

The real problem with these battery powered cars is that the natural resources to build large numbers of lithium ion batteries do not exist (at least not until the price of lithium starts approaching the value of gold or platinum). The entire battery grade output of one of the major lithium producers (there are only a few) will be needed to build only a few hundred thousand cars per year. The electronics industry already consumes most of the supply. Until a realistic battery solution that relies on materials that are actually available exists, this has only a small-scale potential and will be limited to the high-end market.

Of course, for about $1,000 conversion, and another $2,000 to $3,000 for a home fueling station I can convert a street legal vehicle to natural gas and fuel it up at home from my natural gas line, improving my mileage, reducing my emissions, and saving money. Actually, I can buy CNG vehicles fairly cheaply already on the used car market.

Apr 12 05:31 PM

[Cobra 1:]

I suggest someone go out to the NERC website or DOE and see what the demand to capacity ration is before we go out and start producing a million EC's. At the rate we are going there is a negative 2% demand to capacity, that's only from decommissioning, the new demand on the electrical grid per year is increasing by 6%. That's a negative 8%, you thought you hated expensive gas, wait till the price per kW is at 30 cents or $3!

Until we are able to increase the presence of nuclear power plants, the true cost of using EC's will not be known. Many will speculate, but, until they are plugged in, SWAG!

Apr 12 08:48 PM

[Doug Korthof:]

There's a VAST difference in type of battery.
Hymotion is using Lithium, which so far has not been economical in plug-in cars.

The best and most economical battery for plug-ins is NiMH, which can be improved to last for more than 100,000 miles (perhaps more than 200,000 miles) and can be ENTIRELY recycled.

Not a fantasy: the Toyota RAV4-EV, as well as the 1999 EV1, RangerEV and HondaEV, all use NiMH, as well as the Prius, Insight, etc., no one expects Lithium to actually work in plug-in cars.

Ask youirself, why aren't auto makers using more economical, longer-lasting, proven technology, NiMH??

The answer may surprise you, it has nothing to do with weight (Lithium batteries weighing 400 lbs. in the so-called VOLT only yield 8 kWh; whereas lead or NiMH of the same weight would yield up to 12 kWh, enough to go up to 72 miles on a charge).

WHY NOT USE NIMH?? Even lead-acid would be fine for the VOLT, or other "extended range EVs", the 1997 and 1999 EV1 wtih PSB lead acid had over 100 miles range, the bateries are fully recyclable, and the cost is almost as low as NiMH for the life of the batteries.

Apr 13 12:49 AM

[happycajun:]

Not too sure about the methology used by Google here. First, the "cost" is understated when taxes are taken into account. The cost per gallon of gasoline includes certain taxes that are not levied on residential electric power, hence cannot be compared in determining the longer term economic impact of the "plug-in" cars. Secondly, while the write-up of Google's "rechargeIT" test is extremely vague on this point - the mpg calculation is based solely on gallons of gasoline consumed in the test. Hence, the fully charged battery pack is running the vehicle more and less gasoline is burned. No attempt was made to log charging times, indeed the report shows that users were discouraged from taking a vehicle that was not fully charged. The "energy cost" sections do take into account the cost of electricity used to charge the vehicles - based on residential electrical rates from the EIA. No attempt is made to calculate the emissions resulting from increased power generation at the powerplant. There is no indication as to how electric energy consumption was measured in the study. I would need to see a stronger analysis of the data before I drew any solid conclusions from this test.

Apr 13 09:36 AM

[Larrysyr:]

The hybrid/EV technology remains in its infancy. Google is showing what is possible. Others are showing what is more reasonable to expect. All are analyzing the current. situation.

As the technology develops, the full consequences of increased electrical demand will be better understood. The range and uses of electric cars will increase, giving them an increasing role in the transportation picture.

Hybrid/EV cars currently occupy a market niche, but that isn't where I expect them to be in the future.

Apr 13 10:08 AM

[User 394266:]

Plug-in cars of the future are getting all the positive press, BUT no-one has projected the average cost in increased home electrical bills for one of these babies that is driven, say, 12,000 miles a year.
Nor has there been a serious article about whether the local electrical grids will accommodate big power draws if whole sub-divisions are "plugged in" every night. How about a comprehensive article?


On Apr 12 08:41 AM a. palmer jr. wrote:

> General Motors may not be around in 2 years to compete unless they
> get massive bailouts.

Apr 13 04:13 PM