Energy Storage in Advanced Vehicle Systems

<div class='quotetop'>QUOTE(Eric Nothman @ Jul 28 2006, 01:17 PM) [snapback]293870[/snapback]</div>

Thank you for the link, that was indeed a good overview.

I've been thinking about this a lot lately, and doing some analysis from the standpoint of an economist. I'm not sure I'd agree entirely with their cost analysis. I certainly agree that moving toward a very large battery pack (toward a full BEV) doesn't appear cost-effective at current battery prices.

But what has astonished me is that even a very small PHEV battery pack can displace a large fraction of gasoline consumption, based on the US average distribution of trip lengths (drawn from the National Household Travel Survey). For example, a 10 mile PHEV pack would reduce gasoline consumption by 25%, based on the assumption that the pack could be recharged at the end of every round-trip (from home, back to home), using national average trip length data.

So, while the linked study shows straight hybrid to be cheapest, I am certain that, for some people, the PHEV 10 mile pack would be a money-saver over the life of the vehicle (as opposed to the four-year period studied here). It would definitely be a winner for those with multiple short round trips to/from home during a day (e.g, "socker moms"). I'm pretty sure of that because that's my (wife's) situation, so I took care to model that. So, whatever their model, if it's an optional PHEV 10 (say) pack, the cost-effectiveness for purchasers will be a function of the purchaser's own travel patterns. I'm betting that, even at current battery costs and lifetime, there's already a pretty big slice of the market for whom a PHEV 10 would be cost-effective on a 100,000 mile ("life-of-the-car") basis. At US average travel patterns and current gas prices, PHEV 10 would only be worth about $1300 in gas cost savings for the Prius (mainly because you don't burn all that much gas in the first place), but the average is not relevant if it's an option.

Toyota has announced they will offer PHEV, rumored to be a 9 mile PHEV. That suggests they've figured it out too -- a small pack offers a substantial gas consumption reduction for the average US driver, and truly large reductions for the "soccer mom" travel pattern. In my own case, I've (roughly) estimated that it would reduce our gas consumption by about 50%, based on the way the Prius runs (80% electric use up to 125% of pack size, due to the need to run the ICE somewhat even when there is battery capacity available), and the distribution of our trips. So, rationlly, all other things equal, I'd be willing to pay about $2600 for a PHEV 10 option, based on a 100,000 mile planning horizon, merely in terms of gas cost savings at $3/gallon.

There are several threads here discussing the fact that Toyota will offer PHEV in a few years. Several people have remarked that even a small PHEV option essentially turns the Prius into an electric-gas hybrid, instead of a gas-electric hybrid. In my own case, driving 10K miles a year, an itty-bitty 10 mile battery pack would mean I'd put only 5K miles per year on the ICE. At that rate, the Pruis ICE is likely to outlast me. Kind of changes your thinking a bit.

Anyway, thank you again for the interesting link.