Environmental Engineering Reference
In-Depth Information
In other words, there are not enough winds above 12 m/s for the larger generator to offset the dif-
ferences in generator efficiency at lower wind speeds, and also, there would be increased cost for a
larger generator and gearbox.
8.6 BERGEY XCEL
A Bergey Xcel wind turbine was installed at the AEI Wind Test Center in August 1991 and is
still operating in 2008. The specifications are three-phase, 240 V, permanent magnet alterna-
tor, rated at 10 kW. The variable voltage, variable frequency is converted to DC, which is then
inverted to 60 Hz for connection to the utility line. Power and wind speed were sampled at 1 Hz
and then averaged over 15 min. This time sequence data were then averaged over 1 month for
each 15 min period to give an average day for the month. As expected, the power (Figure 8.10)
varied widely by season and time of day. From these data it is noted that spring 1992 was a
below-average wind period.
Power curves indicate performance, and when compared to the manufacturer's curve, the mea-
sured power curve ( Figure 8.11 ) at the site was lower, even when corrected to standard density [15].
This means that the energy production would be lower than that predicted from the manufacturer's
power curve. Part of that is due to the efficiency of the inverter, especially at high wind speeds (see
information on inverters in Chapter 7 ).
Power curves for shorter time periods will indicate performance of the wind turbine when
compared to baseline experimental power curves at a site. Of course, there is some scatter of the
data, especially at the high wind speeds with few data points. However, low power curves indicate
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Month
FIGURE 8.10 Power for Bergey Xcel, 10 kW, for average day, by month from March 1992 through December 1993.
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