POWER March 2013 - 63

EMISSIONS
The Facts About Wind Energy's Pollution Reductions
Editor: The American Wind Energy Association (AWEA) recently contacted
POWER to request an opportunity to respond to the editorial
" Under Siege " published in the December 2012 issue. The following
is AWEA's response to that editorial.
As wind energy's growth has continued, spurred by improving
technology and declining costs, wind energy's role in reducing
harmful pollution has become even clearer. Empirical data for the
United States and Europe clearly indicates not only that wind
energy results in the expected pollution reductions by directly
offsetting the use of fossil fuels at power plants, but that by
displacing the most expensive and therefore least efficient power
plants first, wind energy results in even larger pollution savings
than expected.
There is no dispute that every MWh of wind energy added to the
power grid displaces a MWh that would have been produced by the
most expensive power plant currently operating, which is typically
the least efficient fossil-fired power plant. However, some have
attempted to claim, without support, that adding wind energy
to the power system can negatively affect the efficiency of other
power plants, reducing the emissions savings produced by wind
energy.
Fortunately, a large body of real-world data is now available
to assess how wind energy affects the efficiency of other power
plants, allowing one to approach the question from multiple angles.
To start with, the U.S. Department of Energy collects detailed
data on the amount of fossil fuels consumed at power plants, as
well as the amount of electricity produced by those power plants.
By comparing how the efficiency of power plants has changed in
states that have added significant amounts of wind energy against
how it has changed in states that have not, one can test the unsupported
hypothesis that wind energy has a negative impact on
the efficiency of fossil-fired power plants.
The data clearly shows that there is no such relationship, and
in fact, states that use more wind energy have seen the efficiency
of their fossil-fired power plants fare slightly better than
states that use less wind energy. Specifically, coal plants in the
20 states that obtain the most electricity from wind saw their average
efficiency decline by only 1.00% between 2005 and 2010,
versus 2.65% in the other 30 states. Increases in the efficiency
at natural gas power plants were virtually identical in the top
20 wind states and the other states, at 1.89% and 2.03% improvement
respectively. The efficiency of fossil-fired power plants
fared comparably well in the top 10 wind states (which obtain
between 5% and 16% of their electricity from wind), with coal
plant efficiency increasing by 0.51% in the top 10 wind-using
states and declining by 2.65% in the other 40 states, while gas
plant efficiency improved by 0.78% in the top 10 wind states and
2.17% in the other 40 states.
Similar results can be found in International Energy Agency
data for Europe, which shows that the top 5 wind countries (which
obtain between 7% and 23% of their electricity from wind) saw
the average efficiency of their natural gas power plants increase
by 11% as they ramped up their use of wind energy from 1999March
2013 | POWER
2010, larger than the 7% increase in efficiency seen across all of
OECD Europe. Over that time period, coal plant efficiency fell by
1% in the top 5 wind countries and remained unchanged across all
OECD Europe countries.
Another method to assess whether wind energy is producing
the expected emissions savings is to calculate whether increases
in the use of wind energy are correlated with decreases in the
amount of carbon dioxide emitted per MWh produced. A correlation
coefficient of 0 would indicate that there is no statistical
relationship between wind energy output and emissions intensity,
a coefficient of -1 would indicate that wind output increases
always coincided with increases in emissions, and the observed
coefficients of nearly +1 indicate that increases in wind output
nearly always coincided with major decreases in emissions. The
correlation between increasing wind energy output and declining
emissions intensity in the leading wind energy countries over
the period 1999 to 2010 was extremely strong, with a correlation
coefficient of .77 for Denmark, .82 for Germany, .86 for Portugal,
.90 for Spain, and a whopping .96 for Ireland.
These correlation coefficients were far higher than for any other
possible explanatory factors for the observed decreases in emissions
intensity, such as increased use of hydroelectric or nuclear
energy, increased use of natural gas instead of coal, changes in
the efficiency of fossil-fired power plants, or changes in electricity
imports or exports. If wind energy were causing large declines in
the efficiency of fossil-fired power plants, zero or negative correlations
would have been found, instead of correlations approaching
1.
These findings are further confirmed by the preliminary results
of a new report from the National Renewable Energy Laboratory
that uses empirical data from another source, EPA's network of
power plant continuous emissions monitors, to evaluate the impact
of wind energy on the efficiency of all fossil-fired power
plants in the Western U.S. The in-depth, multi-year, and peer-reviewed
analysis found that even in a scenario with wind providing
25% of all electricity in the Western U.S., wind's total impact on
the efficiency of fossil-fired power plants would be " negligible, "
accounting for less than 0.2% of the emissions savings produced
by wind energy. As a result, carbon dioxide emissions declined by
29-34% in the 25% renewable energy case. Moreover, the analysis
found that adding wind energy to the grid actually slightly
increases the average efficiency of coal and natural gas combined
cycle power plants by offsetting the least efficient plants.
No matter how one approaches the question, the data is clear
that wind energy greatly reduces fossil fuel use and pollution.
Moreover, the results discussed above are in addition to a large
body of independent grid operator, utility, and government analyses
and data that have already examined how wind energy interacts
with the power system and unanimously found that wind
energy produces pollution savings that are as large or larger than
expected.
-Michael Goggin is the manager of transmission policy at the
American Wind Energy Association.
www.powermag.com
63
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POWER March 2013

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