Based on the analysis of development data (both dynamometer and road-test) using a draft federal fuel economy methodology for extended-range electric vehicles (EREV) under discussion by the Environmental Protection Agency (EPA), GM expects the Chevrolet Volt will achieve city fuel economy of at least 230 mpg US, given a single charge per day (as the methodology assumes).
Based on the same draft EPA methodology, the Volt would also deliver “triple-digit” combined cycle fuel economy along with combined cycle electricity consumption of 25 kWh/100 miles, according to GM. At the US average cost of electricity (approximately 11 cents per kWh), GM calculates that a typical Volt driver would pay about $2.75 for electricity to travel 100 miles, or less than three cents per mile.
From the data we’ve seen, many Chevy Volt drivers might be able to be in pure electric mode on a daily basis without having to use virtually any gas. EPA labels are a yardstick for customers to compare a vehicles’ fuel efficiency. So, a vehicle like the Volt that achieves a combined triple-digit fuel economy is a game-changer...The key to high-mileage performance is for a Volt driver to plug into the electric grid at least once each day.—GM CEO Fritz Henderson
Both GM and EPA, which is supportive of GM’s exercise, point out that (a) the methodology is not finalized; (b) that the data is preliminary, development-level data; and that (c), the EPA hasn’t yet done the testing itself. Nevertheless, said Frank Weber, Global Vehicle Line Executive and Chief Engineer for the Volt:
The 230 city mpg number is a great indication of the capabilities of the Volt’s electric propulsion system and its ability to displace gasoline. Actual testing with production vehicles will occur next year closer to vehicle launch. However, we are very encouraged by this development, and we also think that it is important to continue to share our findings in real time, as we have with other aspects of the Volt’s development.
While the fuel economy (FE) for combustible fueled vehicles (such as gasoline, diesel, compressed natural gas, or an ethanol blend) can easily be expressed in mpg, and fuel economy for an all-electric vehicle can be expressed in miles per gallon of gasoline equivalent (mpge), the arrival of new technologies that can operate in all-electric mode, a conventional hybrid mode, or some combination of the two complicates the situation.
The EPA is revisiting the FE label provisions as they apply to those types of vehicles, and is working with automakers, the SAE, the State of California, the Department of Energy and others to address these issues. The EPA anticipates issuing guidance and/or a rule this year.
Broadly, the EPA is considering using two additional approaches to FE calculation and labelling: one for extended range electric vehicles, and one for PHEVs.
For the EREV category, EPA would include vehicles that can complete all the EPA required drive traces for the FTP, highway, US06, and SC03 without some assist from a combustion engine (either for propulsion or as a genset). For this type of vehicle (into which category the Volt falls), EPA notes that there are three possible modes of operation to consider for FE labeling: all-electric operation (charge depleting mode), hybrid operation (charge sustaining mode) and a combination of the first two.
- For all-electric mode, FE would be expressed in miles per gallon equivalent (mpge) and/or kWh per 100 miles. Fuel consumption, FCEV, would be measured by SAEJ1634, without the C coefficient adjustment. Fuel consumption is adjusted via the 5-cycle, derived 5-cycle, or other appropriate method.
- City and highway fuel economy when the vehicle is in hybrid operation (charge sustaining mode) would be calculated and displayed as done for hybrids now.
- When the vehicle operates in a combination of modes, some electric-only and some conventional hybrid operation, the value could be displayed in mpg, but only when accompanied by the appropriate amount of kWh/100 miles consumed.
For plug-in vehicles that require some assist from the engine for propulsion or as a generator for the test cycles (i.e., a plug-in hybrid), EPA suggests two types of FE labeling:
- When the vehicle is in an electric assist operation, fuel economy would be expressed in miles per gallon equivalent (mpge) that incorporates both the electrical and gasoline consumption into one city and one highway FE. Gasoline and electricity consumption while in blended mode would be measured as in SAEJ1711 (earlier post). In addition to mpge, FE could be displayed separately for each fuel for the electric assist portion of the label in kWh/100 miles.
- City and highway fuel economy when the vehicle is in hybrid operation would be calculated as for hybrids now.
The Volt, which is scheduled to start production in late 2010 as a 2011 model, is expected to travel up to 40 miles on electricity from a single charge of its 16 kWh Li-ion battery pack and be able to extend its overall range to more than 300 miles with its flex-fuel-capable engine-generator. Tony Posawatz, Vehicle Line Director for the Volt, said that the Volt is delivering 40 miles all electric in both city and highway cycles.
|“In the future, ‘mpg’ ultimately will be moot.”|
According to US Department of Transportation data, nearly eight of 10 Americans commute fewer than 40 miles a day. A Volt driver’s actual gas-free mileage will vary depending on how far he or she travels and other factors, such as how much cargo or how many passengers they carry and how much the air conditioner or other accessories are used.
However, Posawatz notes that since the Volt results are based on a single charge per day—and that given the recharge time of 6-8 hours on a standard 110V outlet or half that on a 240V charger, the Volt has the potential to deliver better than 230 mpg performance if it can charge multiple times per day.
Along those lines, GM used a media event at the Plug-in 2009 conference to show a prototype home 240V charging unit, as well as a second, portable 110V unit that would be stored in a container in the vehicle. Both use the J1772 connector.