http://www.designnews.com/author.asp?section_id=1386&doc_id=278386&cid=nl.dn14.20150818&dfpPParams=industry_auto,industry_alt,aid_278386&dfpLayout=blog
So, Just How "Green" Are Electric Vehicles Really?
Al Bredenberg, Contributing Writer
These days you can practically generate electricity writing about
electric vehicles. The topic has become a lightning rod for partisan
rhetoric. For some, the EV personifies everything evil about government
influence and free markets. From the other side, you might get the
impression that the EV is the salvation of humankind and planet Earth.
Recent research into the environmental and energy impacts of EVs has
revealed that the picture is (surprise) more nuanced than the extremists
might like to admit.
Just considering “pure” battery electric vehicles (BEVs) — i.e.,
completely grid-dependent EVs — the International Energy Agency (IEA)
estimates the global stock rose from about 180,000 vehicles in late 2012
to 665,000 units at the end of 2014, with the US leading the way at 39%
of the market. The movement of BEVs is increasing rapidly, shooting up
from 45,000 sold worldwide in 2011 to more than 300,000 in 2014.
EVs now account for more than 1% of new car sales in the US, Norway,
Sweden, and the Netherlands. The automobile isn't the only
transportation mode that's going electric. IEA says that at the end of
2014, the global stock of electric buses stood at 46,000; electric
two-wheeled bikes were at an astonishing 235 million units.
Debates over the greenness of vehicle technologies tend to center around
tailpipe emissions. To evaluate lifecycle emissions of a vehicle, you
have to go beyond driving emissions (the air pollutants resulting from
operating the vehicle).
EVs offer an important environmental benefit via their zero tailpipe
emissions (kind of a paradoxical term, as an EV has no tailpipe.) Zero
emissions are clearly valuable in an urban setting.
However, critics point out that the electricity an EV needs has to be
generated somewhere, so the zero-emissions descriptor ignores the air
pollutants emitted during power generation.
Both observations have merit. A MIT study found that air pollution
causes 200,000 premature deaths per year in the US. Out of those deaths,
53,000 can be attributed to road transportation and 52,000 to power
generation. The study found that the danger tends to be localized, i.e.,
those living or working close to the emissions are more likely to be
killed by them.
The National Academy of Sciences recently released a study by a team at
the University of Minnesota that considerably updates our understanding
of the air-quality impacts of light-duty vehicles in the US. The group,
led by biosystems engineering researcher Christopher W. Tessum, compared
10 alternatives to conventional gasoline vehicles, including gasoline
hybrids, diesel vehicles, compressed natural gas (CNG) vehicles, and
corn and cellulosic ethanol vehicles. The researchers also studied the
environmental impacts of BEVs powered by electricity generated by
various sources, including coal, natural gas, an average US
power-generation mix, and a mix of renewable sources (wind, hydro, and
solar).
Tessum calculated the lifecycle health impacts of emissions from the 11
types of passenger cars (conventional gasoline plus the ten
alternatives). Because this was a lifecycle analysis, the study took
into account emissions during both production (manufacturing) and
consumption (tailpipe), examining health effects of ground-level ozone
(O3) and fine particulate matter (PM2.5).
The researchers confirmed that the air-quality impacts of EVs really do
depend on how their power is generated. Their study showed that vehicles
powered by coal-generated electricity, corn ethanol, or grid-average
electricity increased health impacts by 80% or more relative to
conventional gasoline. Employing natural gas or renewables decreased
health impacts by 50% or more over conventional gasoline.
These results point to health and environmental benefits from the use of
EVs in areas where low-emission power generation is employed. They also
suggest the potential health benefits of a long-term shift away from
coal-fired generation to natural gas generation and renewables.
However, the batteries used in electric vehicles have environmental
effects that distinguish them in important ways from internal-combustion
engine counterparts. In a future article we'll examine those impacts and
how they will likely be affected by the rapid innovation taking place
around battery technologies.
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