Unlimited mpg? The great Volt debate

[Hurricane]

Unlimited mpg? The great Volt debate
At some point, the EPA will have to give GM's new electric car a fuel-economy rating. It won't be easy.

By Peter Valdes-Dapena, CNNMoney.com staff writer
September 15, 2008: 10:44 AM EDT

NEW YORK (CNNMoney.com) -- How do you measure the fuel economy of an electric car? Is it the equivalent of 80 miles per gallon? 8,000?

Turns out it's a thorny issue - and General Motors is currently in long-term discussions with the Environmental Protection Agency to develop a standard.



The decision could make a big difference for GM, which is expected to unveil the Volt this week. The automaker's first long-range electric car could hit showrooms by 2010. The compromise between GM and the EPA could have a major impact on how effectively the Volt is marketed.

Discussions are still a long way from resolution, but progress is being made, said GM spokesman Kyle Johnson. "This is a very analytical and a very thoughtful process," Johnson said.

The EPA will say only that it is "still developing its policy for testing, measuring, and reporting fuel economy for plug-in electric hybrid vehicles."

The Volt's lithium-ion batteries will hold enough juice to drive the car for about 40 miles, GM has said. Once the car goes beyond that, a small gasoline engine will turn on, generating electricity to power the wheels.

When gasoline is providing the power, the Volt might get as much as 50 mpg. Since the gas engine is only generating electricity and because the battery will still have enough charge leftover to provide additional power for passing and merging, the Volt will still be very efficient even when running on gas power.

But that mpg figure does not take into account that the car has already gone 40 miles with no gas at all.

So let's say the car is driven 50 miles in a day. For the first 40 miles, no gas is used and during the last 10 miles, 0.2 gallons are used. That's the equivalent of 250 miles per gallon. But, if the driver continues on to 80 miles, total fuel economy would drop to about 100 mpg. And if the driver goes 300 miles, the fuel economy would be a just 62.5 mpg.

One way to perform a these tests has been suggested by the California Air Resources Board, which will have to test these cars to ensure compliance with that state's strict emissions standards. The CARB tests are based on a set of standards created by the Society of Automotive Engineers in 1999, anticipating just this sort of challenge.

GM's solution: Embrace the complexity. A fuel economy window sticker proposed by GM in an April 2008, presentation to federal regulators shows fuel economy measured three ways: City and highway miles per gallon, city and highway miles per kilowatt hour and city and highway range (electric-only and total range.)

Assuming car shoppers know their local electrical rates, that information should allow them to judge how much the Volt would cost them to drive compared to other cars.

More here: http://money.cnn.com/2008/09/15/auto...ings/index.htm

[eurohazard]

GM's solution: Embrace the complexity. A fuel economy window sticker proposed by GM in an April 2008, presentation to federal regulators shows fuel economy measured three ways: City and highway miles per gallon, city and highway miles per kilowatt hour and city and highway range (electric-only and total range.)

This works for me!

[Bornfromparents]

I thought the engine would turn on and recharge the batteries for another run of 40 miles, cycling back and forth. So say it goes 40 miles on electric and say 60 miles before it charges the batteries back up again. Maybe that is too much to wish for.

[PhishPhood]

Originally Posted by Bornfromparents

I thought the engine would turn on and recharge the batteries for another run of 40 miles, cycling back and forth. So say it goes 40 miles on electric and say 60 miles before it charges the batteries back up again. Maybe that is too much to wish for.

Just speculation.. but from my own experience I think that we'll find that the gas-free segment, however long it is in theory, is predicated on driving the vehicle in perfect conditions in the most optimal manner. Rain, snow, sleet, wind, ultra cold temps, heavy AC usage, very fast highway driving and extra weight in the vehicle from cargo or passengers are all going to deteriorate the 'charge life' thus shorten the gas-free segment. As they say there is no free lunch.

The laws of physics will prevail. In the way most people drive and in the varied conditions we have on this continent from Arizona in summer to Alberta in winter I wouldn't be surprised to find that the 'real world' gas-free driving is somewhat less than 30 miles as an annual daily average.

[ohmywrd8]

It makes sense. The EPA is probably biased anyways.

[PhishPhood]

Originally Posted by ohmywrd8

It makes sense. The EPA is probably biased anyways.

LOL... it can't be biased, that's victim-speak. The EPA tests were designed 30+ years ago well before the Volt or any other advanced vehicle was even a gleam in a designer's eye. There isn't a different test for EREVs and one for hybrids and one for diesels and one for gassers. There is just one set of tests for all vehicles.

Every vehicle maker knows exactly what the EPA test protocols are and how the tests are done. Every vehicle maker performs these exact tests in their own labs on their own equipment. Recently the EPA has been delegating the testing to the vehicle makers themselves, the EPA just surveys and validates that the tests were done accurately. The vehicle makers know as they complete the tests and submit the results what the EPA will have them report.

[ronald mcretard]

Originally Posted by Bornfromparents

I thought the engine would turn on and recharge the batteries for another run of 40 miles, cycling back and forth. So say it goes 40 miles on electric and say 60 miles before it charges the batteries back up again. Maybe that is too much to wish for.

No, the gas engine will only keep the batteries at a lower charge state. After the first 40 miles you won't get significant EV-only mode until after you plug-in again to charge the batteries.

This way, you use the same amount of gas, but you put less stress on the batteries.

[ohmywrd8]

Originally Posted by PhishPhood

LOL... it can't be biased, that's victim-speak. The EPA tests were designed 30+ years ago well before the Volt or any other advanced vehicle was even a gleam in a designer's eye. There isn't a different test for EREVs and one for hybrids and one for diesels and one for gassers. There is just one set of tests for all vehicles.

Every vehicle maker knows exactly what the EPA test protocols are and how the tests are done. Every vehicle maker performs these exact tests in their own labs on their own equipment. Recently the EPA has been delegating the testing to the vehicle makers themselves, the EPA just surveys and validates that the tests were done accurately. The vehicle makers know as they complete the tests and submit the results what the EPA will have them report.

Was a joke lol.

[jbernie]

Good to see GM & the EPA working together, certainly they will need to address this issue now as I doub't the volt will be the only vehicle of this type that will come to the market. Certainly a 48mpg number will do a lot to hurt both GM & the Volt but also the ability to get more vehicles of this type to market.

Will be waiting to see what the compromise is.

[Sinner]

Originally Posted by PhishPhood

Just speculation.. but from my own experience I think that we'll find that the gas-free segment, however long it is in theory, is predicated on driving the vehicle in perfect conditions in the most optimal manner. Rain, snow, sleet, wind, ultra cold temps, heavy AC usage, very fast highway driving and extra weight in the vehicle from cargo or passengers are all going to deteriorate the 'charge life' thus shorten the gas-free segment. As they say there is no free lunch.

The laws of physics will prevail. In the way most people drive and in the varied conditions we have on this continent from Arizona in summer to Alberta in winter I wouldn't be surprised to find that the 'real world' gas-free driving is somewhat less than 30 miles as an annual daily average.

I agree that "your mileage may vary" day to day but the 40 miles GM is shooting for is how far it will go in 10 years after thousands of charge/discharge cycles. Like any cell phone, flash light or laptop the charge will be far greater when new. My guess is that the Volt will go significantly further than 40 miles when new.

I used to work in a warehouse and all our equipment was electric. When we got new batteries they'd last 10-15 hours before needing a charge but after they aged or weren't depleted completely before charging that time shrunk to 2-8hrs.

[roteague]

Originally Posted by Sinner

I agree that "your mileage may vary" day to day but the 40 miles GM is shooting for is how far it will go in 10 years after thousands of charge/discharge cycles.

The 40 mile rating is end of life - in other words, how far you can drive on the batteries after 10 years.

[pinyon]

Originally Posted by ronald mcretard

No, the gas engine will only keep the batteries at a lower charge state. After the first 40 miles you won't get significant EV-only mode until after you plug-in again to charge the batteries.

This way, you use the same amount of gas, but you put less stress on the batteries.

Is it known how regenerative braking will factor into this? In heavy city driving will the batteries get enough recharge to cycle back to EV mode for a while?

[prototype66]

WHAT A LOADED QUESTION! LOL
Very tricky to figure this one with so many variables!

[slowinthefastlane]

They should probably just change the rating to be a formula based on energy used. For instance, if they did the following:

1. Fix the gasoline cost at $4/gallon.
2. Fix the electricity cost at $0.09/kilowatt hour.
3. Fill up the tank and fully top off the battery.
4. Run the vehicle through the standard test loop.
5. Calculate the amount of energy used by looking at how much gas is left in the tank and how much power is left in the batteries.

The posted amount would be in cost per mile for city and highway rather than miles per gallon. This is similar to the way that appliances are rated with the EnergyGuide label:

http://www.ftc.gov/bcp/edu/pubs/cons...mes/rea14.shtm

This will take into account all kinds of power trains and will also take into account energy saving techniques like regenerative braking.

[Black Rabbit]

The importance of this cannot be understated. The most important number is the one that averages with the rest of the GM fleet to determine overall fleet mpg. This is the number that allows GM to sell profitable Silverados.