Today, a windmill report. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
Every few years in this
series I need to go back and revisit
windmills. They first appeared in
the Arab world, maybe twelve hundred years ago. A
radically different form of windmill turned up in
Northern Europe around AD
1200. And it never left.
The eighteenth century saw windmills with feedback
control systems. They kept the fan facing into the
wind and varied the pitch of the blades to
compensate for changing wind speeds. The American farm windmill was
perfected in the late nineteenth century, and we
still see it, everywhere.
Now, as truly grand windmills promise to provide
significant electric power, even their name has
changed. Now they're "wind turbines." They no
longer directly mill grain. And that word
turbine refers to rotating blades,
systematically designed to collect as much power as
possible from a stream of air or water.
These aren't fundamentally different from windmills
and waterwheels. They're just far larger and more
efficient. Their complex designs better adapt them
to the unsteady and inconstant wind. They operate
in winds from roughly ten to fifty miles an hour,
and they do best in winds of about thirty miles an
The electrical output of a wind turbine has to
match the alternating current that flows in our
power lines. The propeller speed can be held
constant by varying the pitch of its blades and
controlling its speed electrically. Or the speed
can be allowed to vary and the power output
converted to sixty hertz AC.
Either form is complex, but the payoff in renewable
power is huge. Medieval windmills generated maybe
six horsepower; wind turbines can reach a thousand
times that. Here in the United States, wind turbine
towers (some almost five hundred feet high) already
supply five billion watts of our total power usage.
And yet ....
An earnest young man, handing out literature on
wind power, recently stopped me. He did a fine job
until he told me that wind power did no
environmental damage. "Oh," I asked, "what
about manufacturing all that capital equipment?
What about the vast land they occupy -- the birds
they kill?" He said he'd go get the answers and
have them the next day.
Of course the only answer is that any large-scale
power production sullies our environment -- no
matter what kind. We need to quit looking for
panaceas and learn the ancient art of compromise.
Those great blades, whirling in the sky, are ideal
in some places (like the wind-blown plains of La
Mancha), but they're a poor choice in others. Some
wealthy environmentalists have been alarmed to find
them rising near their own country estates.
The wind turbine is a glorious machine. But we need
to mix and stir: photovoltaic cells; nuclear,
direct solar, wind, water, and tidal power; fossil
fuels along with energy conservation measures. What
we really need to remember is that no
one-size-fits-all technology will ever
solve our voracious energy needs.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
For a great deal on wind turbines and other renewable
energy forms, see the January-February 2003 issue of
Renewable Energy World, Vol. 6, No. 1. See
especially pp. 30-40 and 83-89.
K. Q. Seelye, Windmill Farms Sow Environmentalists'
Identity Crisis. New York Times, National
Report, Thursday, June 5, 2003, p. A22.
Much material about wind turbines (including images)
is available on line. See, e.g.,
This page on large wind turbines.
The venerable Aeromotor
farm windmill. The
tail vane roughly controls its speed. (Photo by John Lienhard)
The Engines of Our Ingenuity is
Copyright © 1988-2003 by John H.