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Plug-in hybrids: even old coal is better than gasoline (but renewables are best of all)


All the cool kids have been linking to a new report that concludes plug-in hybrids are a potentially significant source of greenhouse gas reductions if adopted on a wide scale in the United States. This conclusion is not surprising — conventional wisdom has favored plug-ins for a while — but the study’s use of sophisticated models and scenario analysis puts some hard figures around the possible benefits.

Plug-in hybrids, as you probably know, are a form of hybrid-electric vehicle that you can charge by plugging into a wall socket. Although not yet commercially available, the technology is not exotic. You can buy a conversion kit for your Prius for about $10,000.

Update: The cost of a conversion kit does not indicate the cost to an average car buyer. The study projects trends out to 2050. When plug-ins are mass produced, assume that the vehicles will cost roughly the same as gasoline-powered cars do today.

The report mapped out nine different scenarios by varying both the market penetration of plug-ins and the carbon intensity of the U.S. electrical grid. In even the most pessimistic scenario, plug-ins result in significant emissions reductions. In the median (and presumably most likely) scenario, plug-ins shave about half a gigaton of carbon from annual U.S. emissions. To put this in perspective, this is about 10% of the reductions we need to stabilize the climate. Not bad.

The study’s authors also modeled changes to air quality under each scenario. One criticism of plug-ins is that, by shifting fuel consumption from cars to electric utilities, they potentially concentrate particulates and other nasty emissions in certain geographical areas. The study mostly allays these concerns. A small number of areas do see an increase in pollutants, but the large majority of the U.S. will experience a meaningful improvement in air quality.

Because plug-ins run mostly on electricity, their environmental benefit depends heavily on the carbon intensity of the grid. If your local grid is powered by old coal plants, plug-ins actually emit slightly more emissions than regular hybrids (but still far less than conventional cars). In aggregate, though, plug-ins are somewhat better than hybrids using even today’s grid, and the benefits quickly grow larger if we assume future legislation further tilts energy production towards cleaner technologies.

This is a story we like a lot for two reasons that don’t get emphasized often enough: the first is that plug-ins are commercially realizable in the very near term. We can’t wait for exotic technologies to save us from climate change. The second is that plug-in hybrids don’t require significant changes to consumer behavior. Somewhat perversely, some environmentalists see this as a negative. We don’t. The more comparatively easy reductions in greenhouse gas emissions we can find, the better.

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