Wind farms will cause more environmental impact than
previously thought
BY Leah Burrows
The down side to wind power
When it comes to energy production, there’s no such
thing as a free lunch, unfortunately.
As the world begins its large-scale transition toward
low-carbon energy sources, it is vital that the pros
and cons of each type are well understood and the
environmental impacts of renewable energy, small as
they may be in comparison to coal and gas, are
considered.
In two papers — published today in the journals
Environmental Research Letters and Joule — Harvard
University researchers find that the transition to
wind or solar power in the U.S. would require five to
20 times more land than previously thought, and, if
such large-scale wind farms were built, would warm
average surface temperatures over the continental
U.S. by 0.24 degrees Celsius.
“Wind beats coal by any environmental measure, but
that doesn’t mean that its impacts are negligible,”
said David Keith, the Gordon McKay Professor of
Applied Physics at the Harvard John A. Paulson School
of Engineering and Applied Sciences (SEAS) and senior
author of the papers. “We must quickly transition
away from fossil fuels to stop carbon emissions. In
doing so, we must make choices between various low-
carbon technologies, all of which have some social
and environmental impacts.”
Keith is also professor of public policy at the
Harvard Kennedy School.
One of the first steps to understanding the
environmental impact of renewable technologies is to
understand how much land would be required to meet
future U.S. energy demands. Even starting with
today’s energy demands, the land area and associated
power densities required have long been debated by
energy experts.
In previous research, Keith and co-authors modeled
the generating capacity of large-scale wind farms and
concluded that real-world wind power generation had
been overestimated because they neglected to
accurately account for the interactions between
turbines and the atmosphere.
“The direct climate impacts of wind power are
instant, while the benefits of reduced emissions
accumulate slowly.”
— David Keith
In 2013 research, Keith described how each wind
turbine creates a “wind shadow” behind it where air
has been slowed down by the turbine’s blades. Today’s
commercial-scale wind farms carefully space turbines
to reduce the impact of these wind shadows, but given
the expectation that wind farms will continue to
expand as demand for wind-derived electricity
increases, interactions and associated climatic
impacts cannot be avoided.
What was missing from this previous research,
however, were observations to support the modeling.
Then, a few months ago, the U.S. Geological Survey
released the locations of 57,636 wind turbines around
the U.S. Using this data set, in combination with
several other U.S. government databases, Keith and
postdoctoral fellow Lee Miller were able to quantify
the power density of 411 wind farms and 1,150 solar
photovoltaic plants operating in the U.S. during
2016.
“For wind, we found that the average power density —
meaning the rate of energy generation divided by the
encompassing area of the wind plant — was up to 100
times lower than estimates by some leading energy
experts,” said Miller, who is the first author of
both papers. “Most of these estimates failed to
consider the turbine-atmosphere interaction. For an
isolated wind turbine, interactions are not important
at all, but once the wind farms are more than five to
10 kilometers deep, these interactions have a major
impact on the power density.”
The observation-based wind power densities are also
much lower than important estimates from the U.S.
Department of Energy and the Intergovernmental Panel
on Climate Change.
For solar energy, the average power density (measured
in watts per meter squared) is 10 times higher than
wind power, but also much lower than estimates by
leading energy experts.
This research suggests that not only will wind farms
require more land to hit the proposed renewable
energy targets but also, at such a large scale, would
become an active player in the climate system.
The next question, as explored in the journal Joule,
was how such large-scale wind farms would impact the
climate system.
“If your perspective is the next 10 years, wind power
actually has — in some respects — more climate impact
than coal or gas. If your perspective is the next
thousand years, then wind power has enormously less
climatic impact than coal or gas.”
— David Keith
To estimate the impacts of wind power, Keith and
Miller established a baseline for the 2012‒2014 U.S.
climate using a standard weather-forecasting model.
Then, they covered one-third of the continental U.S.
with enough wind turbines to meet present-day U.S.
electricity demand. The researchers found this
scenario would warm the surface temperature of the
continental U.S. by 0.24 degrees Celsius, with the
largest changes occurring at night when surface
temperatures increased by up to 1.5 degrees. This
warming is the result of wind turbines actively
mixing the atmosphere near the ground and aloft while
simultaneously extracting from the atmosphere’s
motion.
This research supports more than 10 other studies
that observed warming near operational U.S. wind
farms. Miller and Keith compared their simulations to
satellite-based observational studies in North Texas
and found roughly consistent temperature increases.
Miller and Keith are quick to point out the
unlikeliness of the U.S. generating as much wind
power as they simulate in their scenario, but
localized warming occurs in even smaller projections.
The follow-on question is then to understand when the
growing benefits of reducing emissions are roughly
equal to the near-instantaneous impacts of wind
power.
The Harvard researchers found that the warming effect
of wind turbines in the continental U.S. was actually
larger than the effect of reduced emissions for the
first century of its operation. This is because the
warming effect is predominantly local to the wind
farm, while greenhouse gas concentrations must be
reduced globally before the benefits are realized.
Miller and Keith repeated the calculation for solar
power and found that its climate impacts were about
10 times smaller than wind’s.
“The direct climate impacts of wind power are
instant, while the benefits of reduced emissions
accumulate slowly,” said Keith. “If your perspective
is the next 10 years, wind power actually has — in
some respects — more climate impact than coal or gas.
If your perspective is the next thousand years, then
wind power has enormously less climatic impact than
coal or gas.
“The work should not be seen as a fundamental
critique of wind power,” he said. “Some of wind’s
climate impacts will be beneficial — several global
studies show that wind power cools polar regions.
Rather, the work should be seen as a first step in
getting more serious about assessing these impacts
for all renewables. Our hope is that our study,
combined with the recent direct observations, marks a
turning point where wind power’s climatic impacts
begin to receive serious consideration in strategic
decisions about decarbonizing the energy system.”
|
|