Page 338 - Fluid Power Engineering

298 Chapter Thirteen

selections are not necessarily the best. The choices may lead to a large
number of permutations and combinations and a spreadsheet-based
sensitivity analysis combined with wind analysis software can help
to make appropriate decisions.

Wind speed. When making decisions about selecting among

competing sites, small differences (10% or less) in average
annual wind speed should not lead to automatic decision of
selecting site with higher wind speed. An extreme example is
used to illustrate this: Site A has a steady wind speed of 6 m/s.
Site B has an average wind speed of 5.5 m/s with a step profile:
3.0 m/s 50% of the time and 8 m/s 50% of the time. Power
curvesofmostturbineswillyieldmorethandoubletheenergy
at 8 compared to 6 m/s. As this illustrates the same amount of
energy is produced annually, even though the average wind
speed is different; therefore, annual energy production should
be computed and used for comparing sites.
Higher elevation. Sites at higher elevation tend to have higher

wind speed, for example, a mountaintop. Sites with higher el-
evation will have lower air density and, in most cases, higher
turbulence because of mountainous terrain. Both these fac-
tors lead to lower energy production. In addition, the total in-
stalled cost is also likely to be higher because of lack of roads
and infrastructure, which will lead to higher transportation,
turbine installation, and utility interconnection costs. An en-
ergy production model that takes into account air density and
turbulence coupled with a realistic cost estimation model is
required to compare the scenarios.
Tower height. Taller towers experience stronger winds (func-

tion of shear) and, therefore, higher energy production. Taller
towers also result in higher project cost because: Cost of tower
itself, cost of cranes to install, and cost of foundation to sup-
port the heavier tower. Project specific analysis can provide
the appropriate tradeoff. As an example, consider a compari-
son of 80- versus 100-m tower.
From a cost standpoint: (a) Tower cost is approximately

50% higher, (b) other costs like transportation cost, crane
cost, and foundation costs are likely to be 1.5−2 times. From
Table 13-1, the cost of tower is 11.6% of total installed cost;
total transportation cost is 8%, assume 25% is related to
tower transportation; construction cost is about 11%, as-
sume 25% is related to tower. Therefore, the total cost im-
pacted is about 16%. For a 2.5 MW turbine at $2,000/KW
the impacted cost is $800,000. If 80-m tower is replaced with
100-m tower, the cost is likely to increase by $360,000.