Volt User Experience, No Hype, Just the Facts

By Dave Tuttle

The hype has died down since the delivery of the first Chevrolet Volts in late 2010.  Now, with over 30,000 miles on my 2011 Volt, I have learned a great deal about the way this vehicle functions; the most favorable usage environments, actual efficiencies, and ongoing maintenance requirements.

 

In conversations with other drivers, it is clear that there is considerable confusion about the different types of plug-in electric vehicles (PEVs).  There are substantial differences in the powertrain architectures, driving characteristics and modes, and the “electric range” of each type.  It is reasonable to assume that most drivers are not, will never want to become, nor should be required to become experts in vehicle powertrain architectures.  Most drivers simply want to reliably, economically, and conveniently drive and refuel their cars.  The many new variations of PEVs, hybrids, advanced Diesels, and newest generation of advanced gasoline engines add to the confusion of which vehicle type is most appropriate for their needs. 

To try to better explain PEVs, it is best to separate PEVs into two types: 1) pure battery electric vehicles (BEVs or “EVs”) which have only a battery and traction motor/ or motors for propulsion (1), and 2) plug-in hybrid electric vehicles (PHEVs) which have a combination of an electrically driven motor/ or motors combined with a petroleum (or fossil fuel) based engine (2).  Both of these types can be “plugged” in and charged from the grid, if designed so. BEVs are easier to conceptualize and have a number of compelling attributes.  One charges the BEV battery from the electric grid (or power source), the battery powers the electric motor or motors, and once the vehicle battery is depleted the vehicle must be recharged or parked.  There are no tailpipe emissions, maintenance is likely to be much lower than a conventional vehicle, and the electric motor powertrain typically emits lower levels of vibration and noise inside and outside the cabin than a vehicle with an internal-combustion engine.

The Chevrolet Volt is a more complex “extended range electric vehicle” (eREV) which is a specific type of PHEV. The Volt is not a traditional Hybrid nor is it a purely electric car.  It has a unique powertrain which drives the first 25 to 50 miles entirely on electricity alone (across all speed and load conditions from 0 to 101 miles per hour) like a pure battery electric vehicle (e.g. Nissan Leaf or Tesla Model S).  Once the battery is depleted the Volt automatically shifts to an efficient Hybrid-like mode for another 300-340+ miles using its 1.4L, 4-cylinder gasoline engine.  This powertrain architecture solves the century old “range anxiety” issue experienced in pure BEVs at the cost and complexity of a combined electric + internal combustion engine.  Travel survey data indicates that over 70% of Americans daily commuting is less than 35 miles per day, so most drivers can electrify all of their daily commute with this type of vehicle Powertrain architecture (3).  If a driver needs to travel on a long trip, then an extended-range “PHEV-eREV” such as a Volt can be driven any distance simply by refueling at gas stations every 300 miles as one would drive any conventional gasoline/diesel vehicle.

While each driver’s own electric range & efficiency will be determined by the “3 T’s“: Temperature, Terrain, and driver Temperament, the author has typically achieved 31 to 38 miles of initial electric range (over the course of 2.5 years).  An “all electric range” (AER) of 35+ miles is achieved the vast majority of days with the range declining only during substantially colder or hotter weather.  When using only the battery’s energy to power the vehicle during cold days, there is no gasoline engine waste heat to warm the passenger cabin and hence energy must be diverted to cabin heating which reduces the electric driving range.  In warmer weather patterns, the air conditioning load increases (similar to a conventional vehicle) but does not reduce the electric range as substantially as the winter passenger heating loads.  My particular daily commute is regularly less than 25 miles so the vast number of days are driven using only electricity.  The gasoline engine backup is typically only used on long out of town trips or during an atypical day of driving with many cross-town trips. Once the battery is depleted and the gasoline engine is automatically deployed, a measured 35-42mpg is the norm (technically called “Charge Sustaining mode”) at Interstate highway speeds at or above 70mph.

With an average daily commuting distance of less than the all electric range, many months typically pass without refueling at a gasoline station.  The occasional long out-of-town trip is usually the cause for a stop at the gas station.  As an example, over the past 13 months, over 13,000 miles have been traveled on 51 gallons of gasoline (or about 6 gas refills).  For those who dislike the chore of refilling at a gas station, having your own “personal electric refueling station” at home every night is a very attractive advantage for owning a plug-in electric vehicle.  The Volt has a specially designed fuel storage system combined with automatic engine software to avoid aged gasoline from getting stale and causing problems.

Measurements of electric drive efficiency over 2 years indicate an average of 3.08 miles per kWh.  This is slightly better than the EPA certified tests of 2.78 miles per kWh (4).  Assuming a 35 mile daily commute, comparing the cost to drive a Volt to an equivalently sized conventional vehicle (~30 mpg) yields $1.25 of electricity ($0.036/ mile) compared to $4.08 using gasoline (~$0.12/ mile), a 69% savings in cost (assuming the US average electricity price of $0.11/ kWh and $3.50/gallon*).  A driver’s individual savings will be determined by their local gasoline and electricity prices and particular driving patterns.  Generally, the greater the percentage of miles that can be driven on electricity, the greater the fuel cost savings.  Presently, electric vehicles such as the Volt carry a higher purchase price compared to a similarly sized conventional vehicle.  This additional cost is mainly driven by the large expensive battery, power electronics, and lower production volumes.  While the technology is expected to further improve and decline in cost over time decreasing this price premium, the rate of improvement will likely be slower than the rapid rate of cost improvements that consumers have come to expect with computers, for example.

Charging the battery has been designed to be safe and simple with the advent of the common “J1772″ charging interface.  This J1772 interface is common across all major vehicle manufacturers and includes safety control electronics which do not energize the vehicle-side of the connector unless it is plugged into the vehicle and a safety check is successfully completed.  Unlike an extension cord from a common wall receptacle, a  J1772 compliant EVSE (electric vehicle supply equipment) cordset is automotive-grade durable for long life and weather proof for all season use.

A driver can charge using the J1772 “Level-1″ cord to safely plug into one of the ubiquitous standard grounded 120V home electrical wall outlet receptacles to charge even a fully depleted Volt battery overnight.  This Level-1 cord set is included free with the vehicle as standard equipment and incorporates ground fault interrupt and other safety circuitry.  For convenience, drivers can avoid winding and stowing this cord in their trunk every day by simply leaving this charge cord in their garage always plugged into the 120V wall outlet.  The driver can choose to depend on the gasoline engine backup to assure that they are never stranded or stop at a public EVSE to opportunity charge the battery.  The vast majority of public charging stations have their own common J1772 cord attached which plugs directly in the vehicle.

A “Level-2″ 240V EVSE fast charger can be useful to increase the number of miles driven by electricity by reducing the time to charge the vehicle.  A Level-2 EVSE does not need to be replaced with every new electric vehicle. A Level-2 EVSE can cost between $700-$2500 for hardware and installation but is a permanent upgrade to the home which can be used over many years and successive generations of vehicles from different manufacturers.  A faster charge time is typically advantageous on days with multiple sets of errands to drive which cumulatively are greater than the all-electric-range of 35 miles, as experienced on weekends.  The cost of a Level-2 EVSE typically includes a licensed electrician installing a dedicated electrical circuit for vehicle charging and ensuring the home service entrance is sufficiently sized for the faster charging.

Analysis of emissions shows that even with coal in the grid generation mix, electric vehicles create lower emissions under the majority of circumstances (5). The emissions advantages of PEVs over conventional vehicles will vary based on the regional electricity grid mix, the season, the time of day as well as the source of the gasoline/diesel fuel (e.g oil from tar sands or deep water off-shore rigs -vs- productive conventional oil wells).

Maintenance costs to date at 30,000 miles have been lower than any conventional vehicle the author has owned previously.  Since most of the miles have been driven electrically, the engine oil was required to be replaced once at 2 years/25,000 miles compared to 3 or 4 times with a 5,000 to 7,500 service interval on a conventional vehicle.  The regenerative braking feature on the Volt has led to minimal brake pad wear.  From the wear rate experienced to date, the author expects to achieve beyond 100,000 miles service life on the brakes compared to a typical 30k to 40k mile interval experienced on past conventional vehicles with his own driving demands.  Beyond a single oil change, the only other maintenance has been tire rotations every 7,500 miles (similar to a conventional vehicle).

In summary, in this author’s experience, a PHEV-eREV like the Volt has proven to be reliable, enjoyable to drive, lower emissions, lower fuel and maintenance cost vehicle without any range limitations or need to change driving behavior.  While there is a considerable initial price premium at this time, the Volt demonstrates that electrified vehicles can be no-compromise replacements for conventional vehicles with advantages in operation and maintenance costs, emissions, and home refueling convenience.

*  Volt:  35 miles x 1kWh/3.08 miles x $0.11/kWh =  $1.25 on electricity
Conventional 30mpg vehicle: 35 miles x 1gallon/30 miles x $3.50/gallon = $4.08 using gasoline

References
(1) Electric Vehicles definition, US DOE,  http://www.fueleconomy.gov/feg/evtech.shtml, accessed 7/24/12
(2) Plug-in Hybrids definition, US DOE,  http://www.fueleconomy.gov/feg/phevtech.shtml, accessed 7/24/12
(3) Vehicle Electrification-Driving to a Sustainable Future, Plug-In 2011 Conference Presentation, Pamela Fletcher, General Motors
(4) US DOE/EPA fuel economy projections, http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=30980, accessed 7/24/12
(5) Union of Concerned Scientists: State of Charge: Electric Vehicles’ Global Warming Emissions and Fuel-Cost Savings Across the United States, http://www.ucsusa.org/clean_vehicles/smart-transportation-solutions/advanced-vehicle-technologies/electric-cars/emissions-and-charging-costs-electric-cars.html, accessed 7/24/13

 

 

David Tuttle received the B.S. and M.Eng. degrees in Electrical Engineering with Highest Honors from the Speed Scientific School, University of Louisville, Louisville, KY. and the M.B.A. degree with the Dean’s Award from the University of Texas at Austin. He is currently a Research Fellow and Ph.D student in the Department of Electrical and Computer Engineering at the University of Texas at Austin.  His current research interests are PEVs, Smartgrid, PEV interactions and synergies with the electric grid, and renewable energy

Dave was one of the original designers and technical team leaders of the POWER1 microprocessor which launched IBM's UNIX/RISC systems.   He then led the joint Apple/IBM/Motorola team which designed the first PowerPC microprocessor that launched the Apple PowerMac and IBM PowerPC based systems.  He went on to lead multiple R&D teams responsible for high speed fiber optic based adapters & switches, the POWER2-SC microprocessor (used in the 1997 IBM Deep Blue chess playing Supercomputer which beat World Chess Champion Garry Kasparov), and other advanced processors and systems.  He later formed a design team for Sun Microsystems focused on power efficient multi-core/multi-thread microprocessor development.     From 2006 to 2007 he was the team manager of the University of Texas DARPA Urban Challenge autonomous vehicle team and an adviser to the UT-Austin Mechanical Engineering Department of Energy/ChallengeX hybrid vehicle development team.   Today, he is one of the researchers in Austin’s Pecan Street Consortium/University of Texas Plug-In Vehicle and Smartgrid research project.