Operation of power systems - Wind Power Integration: Connection and System Operational Aspects - page 172

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Figure 5.25 Wind variability versus power system time scales

to 4-8 per cent of the wind capacity, assuming a 20 per cent wind penetration.
Similarly, for the Ireland system the secondary reserve target should increase by
9-10 per cent for the current wind capacity of around 2,000 MW (SEI, 2004). The
wide variation in reserve requirements is dependent on the inherent flexibility of the
plant mix, and the interaction between wind forecasting time horizons and elec-
tricity market operation (see Section 5.3.4 and Chapter 7). Clearly, the regulating
impact and cost will be less for a hydro-based power system than for a (part-loaded)
fossil-fuelled/nuclear-based power system. Market arrangements may also range
from hourly predictions to day ahead forecasting, greatly affecting the errors asso-
ciated with the forecast, and hence the need for both secondary and tertiary/repla-
cement reserve. At low wind penetration levels hourly wind variability can often be
handled by the existing plant commitment (no extra costs). Increased part-loaded
plant and dedicated reserves may be required at higher penetration levels, leading to
extra costs, but this should be obtainable from the existing generation. For example,
the DENA study in Germany, projecting forward to 2020, envisaged no need for
additional balancing plant to regulate wind variability (DENA, 2005). Assuming
day-ahead wind forecasting, the required day-ahead reserves, available in the form
of intra-hourly primary and secondary reserve, were estimated for a 2015 scenario
with 14 per cent wind penetration. The required positive regulation was on average
9 per cent of the installed wind farm capacity, with a maximum value of 19 per cent.
The corresponding negative regulation was 8 per cent on average, with a maximum
requirement of 15 per cent. This compares with 2003 average requirements of
þ 9 per cent/-5 per cent of installed wind farm capacity, and maximum requirements
of 14 per cent, when wind penetration was 5.5 per cent. For the Nordic power
system, the hourly reserve requirements were estimated conservatively to increase