It takes power to make power—even with a
solar grand plan. From the mining of quartz sand to the coating
with ethylene-vinyl acetate, manufacturing a photovoltaic (PV) solar
cell requires energy—most often derived from the burning of fossil
fuels. But a new analysis finds that even accounting for all the
energy and waste involved, PV power would cut air
pollution—including the
greenhouse gases that cause climate change—by nearly 90 percent
if it replaced fossil fuels.
Environmental engineer Vasilis Fthenakis, a senior scientist at
Brookhaven National Laboratory in Upton, N.Y., and his colleagues
examined the four most common types of PV cells: multicrystalline
silicon, monocrystalline silicon, ribbon silicon and thin-film.
(Other contenders, such as amorphous silicon or
superefficient multijunction cells were excluded for lack of
data or lack of widespread application to date.) Even taking into
account the low efficiency of thin-film solar cells or the energy
needed to purify silicon for the other types of PV, all proved to
entail significantly fewer emissions in their entire life cycle than
the fossil fuels needed to produce an equivalent amount of
electricity.
In fact, most of their dirty side derived from the indirect
emissions of the
coal-burning power plants or other fossil fuels used to generate
the electricity for PV manufacturing facilities.
These four types of solar cells pay back the energy involved in
their manufacture in one to three years, according to an earlier
analysis by the same team. And even the most energy-intensive to
produce—monocrystalline silicate cells with the highest energy
conversion efficiency of 14 percent—emit just 55 grams (1.9 ounces)
of globe warming pollution per kilowatt-hour—a fraction of the near
one kilogram (2.2 pounds) of greenhouse gases emitted by a
coal-fired power plant per kilowatt-hour.
Even though thin-film solar PVs employ heavy metals such as cadmium
recovered from mining slimes, the overall toxic emissions are "90 to
300 times lower than those from coal power plants," the researchers
write in Environmental Science & Technology.
The energy benefits of solar photovoltaics will only improve as the
technology continues to
boost its efficiency at converting sunlight to electricity or
proves to last longer than the 30 years anticipated by
manufacturers. "There is no reason for this not to last a lot more
than 30 years," Fthenakis says.
If
solar energy begins to power its own production—a so-called PV
breeder cycle, in which PV-generated electricity goes to produce
more PV cells—the outlook is even sunnier. "I think 30 percent of
the energy consumption in the [manufacturing] facilities is easily
met from the land they have available [on] the roof and in the
parking lot," Fthenakis says.
And, as Fthenakis and colleagues argued in a
recent article in Scientific American, if storage technologies
such as compressed air improve, then PV could provide the majority
of electricity needs in the U.S. "With storage," Fthenakis says, "it
is feasible to go to 100 percent."
© 2015 Scientific American, a Division of Nature America, Inc.
http://www.scientificamerican.com/article/solar-cells-prove-cleaner-way-to-produce-power/