Operation of power systems - Wind Power Integration: Connection and System Operational Aspects - page 168

20

(over 12 h)
(over 4 h)
(over 15 min)

15

10

5

0

-5

-10

-15

01 Jan 01 Mar 01 May 01 Jul 01 Sep 01 Nov 31 Dec

Time (day)

Figure 5.22 Northern Ireland/Republic of Ireland net wind power transfers

only 4 MW. Figure 5.22 shows the necessary power transfers to minimise variability
across the island, for time horizons of 15 minutes, 4 hours and 12 hours. Over
15 minutes, power transfers of only 2-3 MW in either direction are necessary, which
further increases to 7-10 MW up to 12 hours ahead.
The cumulative distribution of these variations is shown in Figure 5.23.
Looking 15 minutes ahead, interconnection provides a 50 per cent reduction in
variability for approximately 20 per cent of the time and a 90 per cent reduction for
only 4 per cent of the time. Similarly, over a 12 hour period, a 50 per cent reduction
in variability is achievable 8 per cent of the time, and a 90 per cent reduction for
2 per cent of the time. Although, in this case, there is limited potential for inter-
connection to reduce island variability, an alternative perspective is that reserving,
say, 1 per cent of interconnector capacity would provide much of the available
benefit. HVDC interconnection already exists between N. Ireland and Scotland and
between the Republic of Ireland and Wales, also rated at 500 MW. However, even
though, conceivably, a larger geographical area could be defined uniting Ireland
and Great Britain, initial analysis suggests that the benefits in terms of reduced
wind variability are limited - when wind production in Ireland was less than
10 per cent of available capacity, wind production in Great Britain was also less
than 10 per cent of capacity for 94 per cent of the time (Gardner et al. , 2003).

5.3.3 System operation and wind variability
As distinct from wind forecasting, and the desire to predict wind profiles accurately
over a desired time period, wind output will also exhibit variability. Even if the