Monday, June 22, 2009

What is the right PHEV battery range?

GM has picked 40 miles as the battery range for the Chevy Volt. Looking at the chart above, you can see why. Nearly 80% of US drivers would be able to do all their daily driving without ever using gasoline. Then when they want to take the car on a longer trip to the beach or mountains (or Seattle or LA), the first 40 are battery powered and then the electricity for the rest of the trip comes from the on-board gasoline powered generator that makes enough electricity to keep the batteries in a charge sustaining mode. If you pull over for dinner1 and are lucky enough to find a place to plug in, you can put some juice in the batteries and then get another 10 or 15 miles of cheaper/cleaner battery powered travel before going back to the generator.


That sounds like a pretty good use-case. They have the eco & wallet friendliness of an EV for daily driving and the range of a typical car for the weekend get-aways. What is not to love? Given the infrastructure we have right now, this seems like the right car at the right time. Apparently, not everyone thinks this is the great new way to make cars.

Bloomberg reports:
A rechargeable auto with the Volt’s target range of 40 miles on electricity is "not cost effective in any scenario" a study by Carnegie Mellon University in Pittsburgh found. Plug-in cars with smaller batteries may be a better value, according to the study, which doesn’t cite the Volt by name.

The study is an attempt to test how prices and driving habits may shape consumer choices among current hybrids and new [plug-in] models.

With lighter, cheaper batteries, a plug-in with 7 to 10 miles of electric range or a conventional hybrid may provide the best mix of price, faster charge times and efficiency, Michalek said. His study was accepted this week for publication in a future issue of the journal Energy Policy.
A 10 mile electric range vehicle might be cheaper. It would certainly be cheaper to manufacture, but the 10 year cost of ownership depends on your personal driving habits, the future cost of gas, and the government incentives for plug-in cars. Currently, that incentive goes up with the size of the battery pack. A small pack can mean little or no incentive, whereas the 16kWh pack in the Volt qualifies for the full $7500 of federal incentive.

While some think that 40 miles of electric range is too far, others think it is too short. Tesla CEO Elon Musk says that, for reasons he explains here, a 40 mile range battery pack is about half the size (and cost) of a 200 mile pack rather than one fifth as simple ratios would suggest. Regen and acceleration are more stressful on a small battery pack compared to a pure EV's large pack. And in a PHEV once the batteries are drained, they are, for the most part, just dead weight.

This is an emerging area of technology. If the answers to these complex questions were simple, we'd all be driving it by now. That is the nice thing about competition. Different car companies can make different cars; incentives can help bring new technologies to market and the marketplace will decide. Each consumer can ask themselves how much electric range is important to me and how much more, if any, am I willing to pay for that? For the winners, economies of scale bring down the price and the incentives can move to the next area that needs development.



Sidebar 1) Note that the Chevy Volt's generator will not run and charge up the batteries during that roadtrip dinner break. The generator only functions prevent the batteries from being overly discharged, not to fully charge them. Having the generator fully charge the batteries would use more gas, lower the gas mileage and pollute more than plugging in.

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