shopping for a wind turbine: Power vs. energy
by MICK SAGRILLO
All too often, when people interested in a wind tur- bine go shopping, they compare turbine models based on power rating of the generator and cost of
the turbine. Doing so is foolish. By comparison, when you
shop for a car you look for the features you need, the warranty, the fuel efficiency and proximity of the dealer. You
would not choose a car based only on the upper number on
the speedometer and the cost.
Most speedometers top out at 120 mph, although
some range up to 130 mph or so. Does a higher speedometer range mean the
car is better? If the
speedometer only
reads to 100 mph,
does that mean the
car is inferior? How
often do you drive at
120 mph, or even 80
mph?
To prevent damage to the speedometer, its top reading
is a number higher
than the car might
do with the throttle
wide open, going
downhill with a tailwind. Will it ever
reach that top number? Probably not. But to someone
who doesn’t know about the engineering rationale, the top
number looks impressive.
mick sagrillo (msagrillo@
wizunwired.net) of
sagrillo Power & Light is
a small-wind consultant
and educator.
Turbine
model
#1
#2
#3
Rated power Rated
of the wind speed
generator
10 k W
10 k W
11 k W
40 mph
27 mph
21. 25 mph
Rated power
at 25 mph per
AWEA standard
2. 4 k W
8.0 k W
13. 9 k W
Swept area
of the rotor
49 square feet
415 square feet
1425 square feet
Electricity generated
annually at 11 mph
average wind speed
3,335 k Wh
12,700 k Wh
29,127 k Wh
I once saw a lawn tractor with a speedometer that went
up to 60 mph. Of course it was a joke: Lawn tractors don’t
actually do 60 mph. But the salesperson confided that it was
their best-selling model. As consumers, we’re impressed
with what we perceive as power, regardless of what
is actually delivered. Sales and marketing people
know how to capitalize on this infatuation. But is
the top speedometer number what you’re actually buying? Of course not.
So, why do potential wind turbine customers
look at the generator power rating of the wind turbines they’re interested in? It’s easy to use for compari-
22 July/August 2011 SOLAR TODAY solartoday.org
Copyright © 2011 by the American Solar Energy Society Inc. All rights reserved.
son purposes, and we think we understand it. While most
wind turbines are marketed this way, unfortunately, few
people understand the power ratings of wind turbines. And
fewer people realize that their wind turbine will reach its
rated power only at a relatively high, and very infrequent,
wind speed.
