Environmental Engineering Reference
In-Depth Information
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Power fluctuation (±% available capacity)
Figure 5.18
Ireland wind power fluctuations - cumulative distribution
to activate, disabling production across the network. Within Ireland excessive
wind speeds are very rare and likely to be localised, so that such a scenario is
inconceivable. However, as discussed below, various measures are available to
limit short-term wind variability.
The variability benefits in the transition from the N. Ireland region (14,000 km 2 )
to the entire island (84,000 km 2 ) are less dramatic than might be expected, given
the increased land mass. This is mainly due to the concentration of wind farm sites
in the north-west of the island, a region which is partly in N. Ireland and partly in
the Republic of Ireland (Figure 5.8). A contrary factor, however, is that the results
were taken when most wind generation in N. Ireland was of the older fixed-speed
induction machine type, sensitive to changes in wind speed, while in the Republic
of Ireland DFIG (doubly fed induction generator) machines were more common.
Newer wind farms are likely to be clustered near existing ones, so the benefits of
geographical diversity will begin to wane. For Ireland, it was estimated that most
of the benefits of diversity were achieved with an installed wind farm capacity of
850 MW (SEI, 2004). One factor which could help push this threshold higher is a
greater penetration of offshore generation - in general, the correlation in output
between two onshore sites is higher than that between an onshore and offshore
wind farm. Similar benefits could be achieved by siting wind farms in a variety of
terrain and subject to differing weather patterns, e.g. hills, coasts, deserts.
An alternative method of quantifying wind variability is to determine the fre-
quency distribution of partial wind power production. Figure 5.19 shows the load
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