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Nov. 6, 2004. 01:00 AM
Wind farms can change weather
Preliminary study sheds light on impact
Researcher calls for better rotor design
NEW YORK-Wind turbines have been hailed as an environmentally friendly
way to reduce the world's dependence on fossil fuels. But a wind farm with
hundreds or even thousands of large turbines removes an enormous amount of
energy from the air. So, is wind power really benign?
In one of the first studies to get at that question, scientists
modelled the impact of a hypothetical large-scale wind farm in the Great
Plains. Their conclusion, reported in The Journal Of Geophysical Research,
is that thousands of turbines concentrated in one area can affect local
weather.
The impact, said the study's lead author, Somnath Baidya Roy, comes
not so much from the turbines' rotor blades slowing down the air but from
atmospheric mixing that occurs in the blades' wake. This creates warmer,
drier conditions at the surface.
"We found that it's the turbulence generated by the rotor that is
crucial when you talk about the impact on local meteorology," said Baidya
Roy, who did the research at Princeton but is now at Duke.
The simulated wind farm in the study consisted of 10,000 turbines,
with rotor blades 50 metres long, in a 96-by-96 kilometre grid in
north-central Oklahoma.
In the Great Plains, there is a nighttime stream of fast-moving air
that separates cool, moist air near the ground from drier, warmer air above.
The simulation found that the turbines catch this nocturnal jet, and the
ensuing turbulence causes vertical mixing.
The warming and drying that occur when the upper air mass reaches the
surface is a significant change, Baidya Roy said, and is similar to the
kinds of local atmospheric changes that occur with large-scale
deforestation.
"You might see some kind of convective clouds or scattered rainfall
here and there," Baidya Roy said.
Even though the study was only preliminary, he said, it pointed to the
need to improve rotor design to reduce turbulence. A wind farm of the size
used in the simulation is much larger than those that have been built so
far, but it is not out of line with what is being considered as more power
from renewable resources is sought.
"When you think of wind energy, people have a quaint idea of a lone
windmill by the river," he said. "We are quite a ways from that, actually."
NEW YORK TIMES
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