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low-Cost Wind Isn’t Cost-Effective
SOLAR TODAY columnist Mick Sagrillo responds (in italics) to a
I wanted to comment on your interesting and helpful article (“Back to
the Basics: Ground Drag,” Jan./Feb. issue).
I particularly noted the graph from the Danish Wind Energy Association.
The interpretation of the graph in the text is incorrect, due to the peculiar
AZIS2010_solar today 102x178:Layout 1 24.02.10 10: 26 Seite 1
orientation of the Danish graph: “Note that ground drag starts ‘breaking’ in
the graph at about 20 meters above the ground, or 66 feet. This is the point
where wind speeds begin increasing more quickly as the effect of ground
drag diminishes and the laminar flow of air over air increases.”
Actually, the wind speed increases very quickly up to 10 or 60 meters
above the ground, and then increases only very slowly thereafter. For
cheapie-me, this means that if I could get up to 50 or 80 feet, I’d be getting
the most for my money.
This is actually the worst place to put a turbine. Here’s why: The
change in wind speed with increasing height above ground is known
as “shear.” A large shear indicates a large change in wind speed over a
short vertical distance. Now put your rotor in those winds. The bottom
of your rotor might see 10 mph, but the top of the rotor might see 12
mph — this would not be unusual at these low heights.
Such situations literally tear up wind turbines in very short order,
months to a few years. They simply cannot deal with the cyclic chang-ing forces on the rotor. This results in an extremely high failure rate of
turbines installed on short towers. Turbines that are not functioning
are not generating electricity.
One has to consider how cost-effective additional height
beyond some baseline height would be. The number of dollars
for installation accelerates, possibly exponentially, as the size and
height of the turbine increase.
Not correct, at least for height of a given turbine, and not increasing turbine sizes.
The reason is that when we are discussing taller towers, we are not
talking about the cost of the taller tower, but the incremental increase
in the cost of the entire installation. A typical 10-kilowatt (k W) wind
system might cost $60,000. An 80-foot tower for that 10-k W system
might cost $12,000, for example. But a 120-foot tower for that same
turbine might cost $13,000. In addition, the additional wiring for the
additional 40 feet might be $400. For a variety of engineering reasons,
the foundations for both towers will likely be the same. Most all of the
rest of the equipment and installation will likely be very close.
So, you could easily see an increase of 50 percent or more in
power available to the turbine, at a cost increase of maybe $58,000
to $60,000. Not much. Paralleling this is a considerable reduction in
wear and tear on the turbine, increasing reliability and life expectancy.
This is why I do these pieces, so that folks understand that there is more
to a wind turbine than just writing a lower check.
Thank you very much, Mick, for your past help, the interesting
article, and for listening.
June 9–11, 2010
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8 April 2010 SOLAR TODA Y solartoday.org
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