Page 305 - Alternative Energy Systems in Building Design

WIND TURBINE ENERGY ECONOMICS 279

One megawatt of wind energy can generate between 2.4 and 3 million kWh annually.
The towers are mostly tubular and made of steel. The blades are made of fiberglass-
reinforced polyester or wood-epoxy.

Wind Turbine Energy Economics

The energy payback time is the term used to measure the net energy value of a
wind turbine. In other words, it determines how long the plant has to operate to
generate the amount of electricity that was required for its manufacture and
construction.
Several studies have looked at this question over the years and have concluded that
wind energy has one of the shortest energy payback times of any energy technology.
A wind turbine typically takes only a few years (3–8 depending on the average wind
speed at its site) to pay back the energy needed for its fabrication, installation, opera-
tion, and retirement.
Since you cannot count on the wind blowing, what does a utility gain by adding
100 MW of wind to its portfolio of generating plants? Does it gain anything? Or
should it also add 100 MW of fueled generation capacity to allow for the times when
the wind is calm?
First, it needs to be understood that the bulk of the value of any supply resource is
in the energy that the resource produces, not the capacity it adds to a utility system.
In general, utilities use fairly complicated computer models to determine the value in
added capacity that each new generating plant adds to the system.
According to some models, the capacity value of a new wind plant is approximately
equal to its capacity factor. Thus, adding a 100-MW wind plant with an average
capacity factor of 35 percent to the system is approximately the same as adding 35 MW
of conventional fueled generating capacity.
The exact answer depends on, among other factors, the correlation between the time
that the wind blows and the time that the utility sees peak demand. Thus wind farms
whose output is highest in the spring months or early morning hours generally will
have a lower capacity value than wind farms whose output is high on hot summer
evenings.
Since wind is a variable energy source, its growing use presents problems for utility
system managers. At current levels of use, this issue is still some distance from being
a problem for most utility systems.
A conventional utility power plant uses fuel, so it normally will run much of the
time unless it is idled by equipment problems or for maintenance. A capacity factor of
40–80 percent is typical for conventional plants.
A wind plant is “fueled” by the wind, which blows steadily at times and not at all
at other times. Although modern utility-scale wind turbines typically operate 65–80
percent of the time, they often run at less than full capacity. Therefore, a capacity factor
of 25–40 percent is common, although they may achieve higher capacity factors during
windy weeks or months.