The first item on a Google search for "wind power limits 10% usa energy " deals with
carbon emission problems scaling wind power
Existing estimates of the life-cycle emissions from wind turbines range from 5 to 100
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this study concludes that a more practical upper limit for wind penetration is 10%.
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sible wind energy industry in the U.S.”
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"Each wind turbine creates behind it a "wind shadow" in which the air has been slowed down
by drag on the turbine's blades. The ideal wind farm strikes a balance, packing as many
turbines onto the land as possible, while also spacing them enough to reduce the impact of
these wind shadows.
But as wind farms grow larger, they start to interact, and the
regional-scale wind patterns matter more.
Keith's research has shown that the generating capacity of very large wind power
installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per
square meter. Previous estimates, which ignored the turbines' slowing effect on the wind,
had put that figure at between 2 and 7 watts per square meter.
In short, we may not have access to as much wind power as scientists thought.
An internationally renowned expert on climate science and technology policy, Keith holds
appointments as Gordon McKay Professor of Applied Physics at the Harvard School of
Engineering and Applied Sciences (SEAS) and as Professor of Public Policy at Harvard
Kennedy School. Coauthor Amanda S. Adams was formerly a postdoctoral fellow with Keith and
is now assistant professor of geography and Earth sciences at the University of North
Carolina at Charlotte.
"One of the inherent challenges of wind energy is that as soon as you start to develop
wind farms and harvest the resource, you change the resource, making it difficult to
assess what's really available," says Adams.
But having a truly accurate estimate matters, of course, in the pursuit of carbon-neutral
energy sources. Solar, wind, and hydro power, for example, could all play roles in
fulfilling energy needs that are currently met by coal or oil.
"If wind power's going to make a contribution to global energy requirements that's
serious, 10 or 20 percent or more, then it really has to contribute on the scale of
terawatts in the next half-century or less," says Keith.
If we were to cover the entire Earth with wind farms, he notes, "the system could
potentially generate enormous amounts of power, well in excess of 100 terawatts, but at
that point my guess, based on our climate modeling, is that the effect of that on global
winds, and therefore on climate, would be severe -- perhaps bigger than the impact of
doubling CO2."
"The real punch line," he adds, "is that if you can't get much more than half a watt out,
and you accept that you can't put them everywhere, then you may start to reach a limit
that matters."
In order to stabilize Earth's climate, Keith estimates, the world will need to identify
sources for several tens of terawatts of carbon-free power within a human lifetime. In the
meantime, policymakers must also decide how to allocate resources to develop new
technologies to harness that energy.
In doing so, Keith says, "It's worth asking about the scalability of each potential energy
source -- whether it can supply, say, 3 terawatts, which would be 10 percent of our global
energy need, or whether it's more like 0.3 terawatts and 1 percent."
"Wind power is in a middle ground," he says. "It is still one of the most scalable
renewables, but our research suggests that we will need to pay attention to its limits and
climatic impacts if we try to scale it beyond a few terawatts."
The research was funded by the Natural Sciences and Engineering Research Council of
Canada.
