Last week I wrote about the benefits of hybrid electric vehicles, or HEVs. Driving in past generations of electric vehicles was like “driving with the gas light always on,” but plug-in hybrids (PHEVs) finally make personal electric transportation practical: you use electric power when you’re making small trips around town, but you have the full flexibility of a gasoline engine for longer trips. So now that we have this option, is running on electricity really cleaner than gasoline?

First, let’s talk energy efficiency.

A former thermodynamics professor once told me that electric cars were actually dirtier because, if you compared at the points of power generation, internal combustion engines (ICEs) are more efficient than power plants. Coal plants, the most common, are indeed around 33% energy efficient, compared to 37% in an internal combustion engine at optimal operation.

But at low speeds and with frequent stops — in other words, city driving — ICEs drop to 20% efficiency. And that’s not even the whole picture; consider all the energy that’s wasted on refining, trucking, and pumping the gasoline. Capturing petroleum energy consumes 1.23 Btu to produce 1 Btu of gasoline (45% efficient), which means that the overall system efficiency for ICEs drops to 17% highway and a shameful 9% city. When the efficiencies from the generation (33% efficient) and transmission and delivery (93% efficient) of electricity are stacked onto the 90% efficiency of an electric motor, the overall electricity-powered car system is 27% energy efficient.

So an electric motor has a higher energy efficiency than a gasoline-powered internal combustion engine. A reduced energy footprint is one big aspect of a successful Cleantech product, but there are more things that we must consider, like toxicity and, ultimately, economic viability. In part two next week I’ll address these aspects of PHEVs.

Disclosure: At the time of the writing of this post, I have no financial relationships with any of the organizations mentioned, except as explicitly indicated.

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About the Author

Asheen Phansey has filled both R&D and operations roles in various biotech firms and startups, and currently consults on biomimetic technologies for Aurora Flight Sciences, a maker of autonomous aircraft systems; he is now leveraging his experience in technology entrepreneurship into a career in Cleantech and sustainable business. He is excited to teach (and learn) about sustainable-business practices, such as cradle-to-cradle manufacturing and biomimicry, to the PosiPeople community. Asheen holds a BS in Chemical Engineering from Cornell University and is currently pursuing his MBA at Babson College; he is a huge New England Patriots fan, gets easily lost in books, and loves talking ideas with everyone he meets.