Monday, January 25, 2010

910 Miles Per Gallon*

Yesterday provided one of those occasional treats that makes blogging about energy so enjoyable. In conjunction with the Washington Auto Show, I had the opportunity to drive a demonstration version of the eagerly-awaited Chevrolet Volt around an impromptu test track, accompanied by the Volt's Vehicle Line Director, Tony Posawatz, who answered every question that occurred to me and many that didn't. The experience was exhilarating. For a bona fide car of the future the Volt--even in "pre-production" form--looked and handled like a real car that I could imagine myself driving around town or on a long trip, aside from its impressive technology and efficiency. That's an important distinction, since to be truly successful the Volt and its eventual siblings must be able to compete beyond a niche market of green-oriented consumers.

My test-drive of the Volt was the latest in a series of advanced vehicle experiences that includes driving a Fuel Cell Equinox a couple of years ago and goes back to a spin around Phoenix behind the wheel of an EV-1, GM's first electric vehicle, in the late 1990s. I asked Tony to what extent the Volt incorporated EV-1 technology, and his answer confirmed that while no actual parts were shared, its design philosophy and engineering DNA owe much to that earlier effort.

At first, when I drove the Volt onto the big, empty parking lot where GM had set up its test track for the DC Auto Show, I was disappointed that I didn't sense that immediate high-torque response I recalled from the EV-1--the kick that my GM contacts at the time called the "EV-1 grin." Then Tony pressed the "sport" button, and the grin was back. While my Acura might be able to beat the Volt's 0-60 miles-per-hour acceleration by several seconds, most drivers should be quite satisfied with the Volt's responsiveness and handling, even when compared to the entry-level luxury cars with which the Volt's expected price puts it into contention--and which its energy efficiency beats hands down.

The technical aspects of the Volt are fascinating, starting with the battery pack, which consists of 400 lb. of Lithium-ion batteries configured as "prismatic cells" that facilitate easier heat management than some other designs. That's a critical factor for battery life, since the battery must dissipate a fair amount of heat during its charge/discharge cycles, and its performance and efficiency are affected by ambient temperature. When plugged in, some of the energy the Volt draws from the grid is used to "condition" the battery, not just recharge it. That should help GM deliver on its expectation that the car's battery pack should last for 10 years and 150,000 miles of normal driving, over which its capacity would gradually decline, while still ultimately retaining at least 70% for later use in other, non-automotive applications. The potential after-life value of the battery could be a critical element of the lifecycle economics of a plug-in hybrid or Range-Extended Electric Vehicle like the Volt.

I was particularly interested in the battery's recharging requirements, in relation to the energy density concerns I discussed in last Tuesday's posting. The Volt recharges in two modes: At 240 V and drawing between 15-30 amps, it takes up to 3 hours to restore the roughly 50% of the battery pack's 16 kWh maximum charge used in "charge-depleting" operation--that first 40 miles or so of battery-only driving that provides the car's main selling point. Recharging on 120 V household current takes more like 8 hours. I was somewhat surprised that Tony seemed to share my view that Volt drivers are unlikely to wait until the middle of the night to recharge their cars, unless their highest priority is minimizing their electricity costs (and possibly emissions.) He has apparently been using a Volt on weekends and cited the benefits of daytime recharging at home or office to keep the battery ready for use, consistent with the main purpose of owning such a car.

The switchover from battery-only operation to driving with the onboard generator running was one of the key features I was anticipating, based on my concern that the Volt would ultimately be handicapped in low-battery, "charge-sustaining" operation by its reliance on a fairly small 4-cylinder engine. After all, the performance expectations in the category the Volt aspires to are set by powerful engines similar to the V-6 in my Acura TL, which delivers 270 peak horsepower. Well, you could have fooled me. The Volt I drove yesterday was intentionally given just enough battery charge to last about 3 miles, and when I passed that point and the little engine fired up, there was no discernible change in performance. That's apparently because the car is never really driven by the engine alone, since the battery is never completely drained. The accelerator controls only the flow of current from the battery to the electric motor; meanwhile the car's software runs the engine as needed to keep the battery charged to acceptable levels, but not to recharge it fully. That's a subtle distinction, because when I pushed the car hard in this mode, I heard the engine rev up noticeably with that characteristic 4-banger tone that provided the one discordant note in an otherwise near-luxury experience. But the trade-off was evident when I pulled the car into its tent shelter and switched it off. The cumulative fuel economy display on the dash read a whopping 910 mpg.

That result prompted an interesting discussion about what fuel economy really means in a car like this, which dutifully calculated mpg based on the tiny amount of gasoline consumed in the last lap of several miles of mostly battery-powered driving. I got a sense that GM recognizes the shortcomings of mpg in measuring such a vehicle's energy usage, though they are clearly quite focused on it as the primary metric of both consumers and the existing and proposed federal fuel economy standards. But even knowing intellectually that the car's electric efficiency, which Tony confirmed is in the range of 200-250 Watt-hours per mile, or 4-5 miles per kWh, equates to roughly 58-72 miles per gasoline-gallon-equivalent of natural gas going into a gas turbine power plant somewhere, that 910 mpg still got my attention with its implication of very rare visits to the gas station.

Recently, I indicated that while plug-in hybrids and full EVs might not yet be ready for the mass market, they do look ready for "innovators and early adopters", the folks who routinely queue up for the latest iPhone and long ago swapped out their cable set-top boxes for streaming video. If the pre-production car I drove yesterday, with the further refinements Tony Posawatz hinted would be incorporated between now and then, was any indication, the production cars that reach showrooms late this year should have early adopters salivating in anticipation, particularly with help from a federal tax credit that maxes out at $7,500 per car and for which the Volt should qualify in full. Based on his comments and my own experience with the car, there's every indication that the Volt is on track to meet its late-2010 launch target. I will be eagerly awaiting the first comment reporting that one of my readers has bought one.

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