PLUG-IN HYBRIDS….This new report suggesting that widespread use of plug-in hybrid vehicles would reduce greenhouse gas emissions no matter what kind of electricity generation you use is pretty interesting. Based on a “well-to-wheels” model for CO2 emissions, it concludes that even if you assume that your electricity comes entirely from the dirtiest of old-tech coal plants, a plug-in hybrid generates about 325 grams per mile of CO2 compared to 450 g/mile for a conventional car.

Sounds great. However, it’s worth noting that under this scenario a conventional hybrid is about equally efficient: it generates around 300 g/mile of CO2. It turns out that most of the benefit of the plug-in hybrid comes not from the fact that electricity generation from plants is more efficient than electricity generation from an internal combustion engine, but from the mundane fact that the battery cuts down on engine use around town no matter where it gets its power from. The plug-in hybrid is superior only if it gets its electricity either from coal plants that use carbon sequestration or from sources like nuclear or biomass, and since carbon capture isn’t likely to be in widespread use for a long time (if ever), and renewable sources are likely to grow slowly, it means that plug-in hybrids aren’t likely to be a substantial improvement over conventional hybrids for a long time.

It’s still a technology well worth pursuing, though. Not only does it have more room for improvement than conventional hybrids, but it’s also a bridge technology that can help drive demand for electrical infrastructure while still providing a car that ordinary people are likely to buy. Once that infrastructure is in place, it makes all-electric vehicles far more marketable, and it’s likely that advances in battery technology will make electric vehicles both more efficient and more consumer friendly over the next decade or two. So bring on the plug-in hybrids.