WMOD00380

• Title: One Viewpoint Concerning Unit Sizes in the Development of Wind Turbines
• Date: 11/1/1981
• Weather Modification - Doc Type: Report

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Fig. 1 Relationship between energy cost of wind power and capacity
ratings of individual machines

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RAT E D POW E R, M W

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turbulence rather than from the windstream entering the
upwind border in the layer of air between the ground and the
topmost reach of the wind machines.
None of these studies analyzed the average cost of energy
when a specific nontrivial capacity goal such as 25 GW has
been attained, nor has any other study of which the authors
are aware. Such an analysis must consider the effect of the
experience curve of unit cost reduction with increasing
numbers of machines produced above the entry level of
commercialization and certain other important engineering
and marketing aspects related to the size and number of
machines. These size and number-related aspects include the
size of the forward leap in technology, the spectrum of in-
ventive, innovative manufacturing, and managerial talents
that would become involved, and the size of collateral
markets (other than the primary mission) that would con-
tribute to decreases in unit cost through additional produc-
tion.

2 Assumptions, Data, and Methods

The optimum size of windpowered generator will be af-
fected by the average windspeed at the windfarm site and to a
lesser extent by choices of design parameters. Two examples
of calculations exhibiting these effects of shown in Figs. 2 and
3. The optimum is also affected, as will be shown, by the size
of the wind power target for the total mission analyzed and by
the experience rate (that is, the rate at which unit cost
decreases as the number of machines increases and
technological advances are made).
For the present study, the results of the Kaman mission
analysis, as shown in Fig. 2, were adopted as preferred
guidance. A curve was drawn representing the envelope of
minimum costs, equivalent to assuming that, at each rated
power, the ratio of rated-power windspeed to median wind-
speed was selected to yield the lowest cost of energy. The
resulting energy cost was taken to represent the cost from the
1000th machine, the ending point of the Kaman calculations.
The NASA solicitation had specified the winds peed frequency
distribution for each mean windspeed, and the variation of
windspeed with height above the ground. The Kaman
calculations took these factors into account, as well as the cost
of connecting the electrical output to a utility distribution
circuit at up to 34.5 kV. At each rated power, the rated-power
windspeed also determined the corresponding power density
in the windstream and hence the swept area of the rotor and
the cost-of-energy minimization likewise determined the plant
factor. The only variable not taken into account through the
minimum-cost envelope from Fig. 2 is the possibility of in-

Journal of Solar Energy Engineering

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RATED POWER,MW
Fig. 2 Relationship between energy cost of windpower and capacity
ratings of individual machines, for various mean and rated windspeeds,
after Kaman [3]

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POWER RATING ,MW

Fig. 3 Relationship between energy cost of windpower and capacity
ratings of individual machines, for various rotor diameters and mean
windspeeds, after Lockheed [4]

creasing the ground clearance and thus raising the rotor into a
regime of stronger wind.
Although this study was made originally early in 1978 when
the mission studies were fresh, the few additional machine-
size-related estimates of cost based on design studies and
prototypes have not been methodical enough in their ap-
proach to energy costs as a function of machine size to
supersede the earlier mission studies, and production ex-
perience has not passed beyond the prototype phase.

Estimation of National Windpower Goal. At present, no
national windpower goal has been set for the year 2000 and
beyond, and estimates of what output wind power might
achieve in the next 20-30 years vary widely in their magnitude
and in the assumptions upon which they are based. One of the
most methodical estimates so far presented is by Merriam [7],
who has explicitly considered such factors as the present and
future cost of wind machines, cost of wind energy relative to
coal, capacity credit, total wind-energy resource, physical
constraints, and alternative self-renewing energy sources. He
specified a series of steps for review and evaluation leading to
a projection of windpower utilization. However, even he
stopped short of an algorithm capable of transforming these
considerations into an estimate of windpower penetration into
the electric utility power market. In the last analysis, his
estimate, like every other so far put forward, seems to rely
most heavily on the estimator's opinion of what is reasonable
or unreasonable.

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NOVEMBER 1981, Vol. 1031307