I've mentioned plug-in hybrid cars in several previous postings. This idea has been one of the main energy transformational technologies cited by the Geo-green movement, which aligns environmentalists with those concerned about national security, the War on Terror and the US trade balance. Now there's a grassroots campaign working to stimulate demand for this technology. They call themselves Plug-In Partners and aim to coordinate "local and state governments, utilities, and environmental, consumer and business organizations." Intriguingly, they suggest that these vehicles will be able to recharge their batteries overnight at the cost equivalent of gasoline at about $0.75/gallon. Overall, this is a pretty good idea, but it has a few problems that will need to be addressed before it is ready for the mass market.
The concept is fairly simple. Take a hybrid car, which supplements its internal combustion engine with a battery and electric motor, and give it two additional components: a bigger battery, to allow it to drive for 20-60 miles without consuming any gasoline, and a plug to recharge it from an outlet, rather than waiting to store up braking energy as present hybrids must do. What could be wrong with that, beyond the cost of the additional hardware inflating the purchase price?
I see two pitfalls at this point. First, you have the complex question of the relative efficiency and cleanliness of the source of electricity used. Typically, recharging overnight would mean using "baseload" power. Depending where you live, that could come from nuclear plants, coal powerplants or hydroelectric dams. You might get a bit of wind power in there, too, but clearly no solar in the dark. So in most cases, plug-in hybrids won't use "alternative energy"--unless you count nukes as such--but rather exchange one conventional fuel for another. The environmental consequences of that switch are not as straightforward as you might think. In any case, though substituting electricity for gasoline seems entirely reasonable, I'm not sure I want to subsidize it by taxing gasoline but not taxing the coal that ends up powering plug-in hybrids.
That leads to my second concern. If these vehicles are really successful, as they would have to be to make a dent in our energy problems, pretty soon the agencies responsible for keeping the roads repaired will go broke, because they rely on motor fuel taxes for their funding. Initially, we can choose to subsidize the situation I described above and let plug-in hybrids pay no more for their power than you pay to run your toaster, but then pretty soon we must come up with a different way to collect the money for maintaining our highways. We will either have to get very clever about this, or pay for roads out of income or property taxes. That won't be popular.
The picture gets even more interesting when you add the possibility of making the plug-in hybrid into a flexible fuel vehicle, able to run on ethanol. That raises the usual concerns about the efficiency of ethanol production and its associated subsidies, and ought to be the subject for another day.
On balance, I think this is a very promising technology that could change the energy equation in the US, as well as globally. If it works here, consider its impact in China. But before it goes "pro", its supporters will have to work out the issues described above, and they won't be doing this in a vacuum. Plug-ins must compete with other choices, including European-style diesel cars, which cost much less and deliver impressive fuel economy. Don't forget that the first 20 mpg improvement in gas mileage is worth much more to the average consumer than the next 60 mpg increment. That stacks the deck in favor of diesels and regular hybrids, and against more complex and costly solutions, such plug-in hybrids or fuel cells.