Environmental Engineering Reference
In-Depth Information
As the result of many engineering improvements, the weighted-average 2007 capacity
factor increased from 22 percent for projects installed prior to 998, to 32 to 35 percent for
machines installed from 2004 to 2006. Regional wind resources, siting, and turbine age are
important considerations, but it is clear that machine performance is continuing to improve.
Of the projects built before 2004 only 3.6 percent had capacity factors higher than 40 percent,
compared to 25.9 percent for projects constructed in 2004 to 2006 timeframe.
Specific Energy Output
Another performance parameter that is directly related to the purpose of wind power
stations is
specific energy output
, expressed in terms of kilowatt-hours per unit of rotor swept
area during a specified time period. Table 4-2 is an example of the use of this parameter
by the California Energy Commission to determine the effect of turbine size on wind energy
production in 99 [CEC 992]. Capacity factors are also included for comparison.
Table 4-2.
Specific Energy Output of Early Wind Turbines in California during 99,
According to Size
[CEC 992 & manufacturers literature]
Power rating
(kW)
Specific energy output
(kWh/m
2
/y)
Capacity factor
to 50
438
6%
5 to 00
670
9%
0 to 50
785
22%
5 to 200
833
22%
20 to 600
856
23%
,500
2
947
34%
Plus one 750-kW turbine
2
For comparison; not in 99 data set: 2007 commercial .5-MW turbine with 77 m
rotor diameter, 80-m hub height, assuming 7 percent losses due to nonavailability,
array wind losses, blade soiling, and electrical outages
Operation and Maintenance Costs
Operations and maintenance costs have decreased as operational environments are better
understood and machine designs are improved. In 987, the
Electric Power Research Institute
(EPRI) estimated O&M costs to be 0.8 to .2 cents per kWh (in 987 dollars, not levelized).
Assuming a capacity factor of 0.25, the annual O&M costs for a 50-kW system would range
from $900 to $,300, and from $3,200 to $4,800 for a 200-kW system. O&M costs for small-
scale machines are higher per kilowatt-hour than for large-scale turbines, because many of
the same activities have to be performed on each of many of the smaller units. Thus, there
are economies of scale that can be realized in O&M costs.
The actual project O&M costs today are consistent with the early estimates. A survey
done in 2007 showed that O&M costs averaged from $40/MWh for projects built in the early
980s, to $9/MWh for projects installed in 2006. Data for projects built in the last 6 years
are shown in Figure 4-37.
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