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Why Forrest Gump's electric car really is better for the environment


I’ve had a couple of questions on my last post asking: don’t electric cars just shift the pollution away from a car’s tailpipe and to a power plant’s smokestack? This is true, BUT the more important point is that that’s a good thing. Battery-powered vehicles charged up from today’s grid are sooooo much more efficient that, even when charged up from a coal plant, they emit less total green house gases (GHGs) than a similar vehicle burning gasoline. This is for one key reason: electric systems are dramatically more energy efficient than combustion engines, so much so that even accounting for the GHGs emitted from the the nation’s dirtiest power sources (such as pulverized coal) fewer tones of CO2 are lofted into the atmosphere to move a car electrically than to burn gasoline in an engine. And if carbon capture and sequestration ever becomes a reality, of course, it will be easier to capture and stash the CO2 from a single power plant smokestack than from millions of tailpipes. The most recent detailed work in this area that I’m familiar with was published earlier this year by the NRDC in cooperation with EPRI, the power industry’s research arm. The report, “Environmental Assessment of Plug-In Hybrid Electric Vehicles” examines plug-in hybrids rather than pure battery powered cars. PHEVs will run on batteries until they’re depleted, then switch over to a small backup gas engine for propulsion and/or to recharge the battery. The graph below is drawn from the report and shows how a plug in hybrid with a battery range of 20 miles (a PHEV20) compares to today’s gas powered cars. In a gas powered car, the vast majority of GHGs are produced during the combustion of gas in the engine (the red portion of the left most bar). The more gas you replace with with electricity — even from “old” pulverized coal powered plants — the lower GHG emissions fall. Using cleaner sources of electricity such as renewables or nuclear, further cuts down emissions from driving (the columns to the right). Though not depicted here, a pure battery-powered vehicle powered exclusively by renewable energy (from solar, wind or hyrdro) would have virtually no GHG emissions. Though the right battery technology remains a long way off, this is the holy grail for green car zealots, but is already being worked on by DIY garage mechanics. Plug in “electric cars solar energy” into Youtube and dozens of demos pop up. For more on this issue, check out CalCars’ discussion of electric vehicles.

Acronymns above:

Adv SCPC = Advanced Super Critical Pulverized Coal

CC = Carbon capture

CCS = Carbon capture and sequestration

GHGs = Green house gases

IGCC = Integrated Gasification Combined Cycle

GT = Gas (natural) turbine

PHEV = Plug-in hybrid vehicle.

Gasoline well to tank = GHGs produced in the drilling and refining of oil into gas, and delivery of gas to a gas station.

Gasoline tank to wheels = GHGs emitted from combustion of gas in a car engine.

Electricity well to wheels = GHGs emitted along the entire path of creating and using electricity to move a car, from excavation at the coal mine (or creation at the wind mill), over the wires and into your car’s batteries.


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