Operation of power systems - Wind Power Integration: Connection and System Operational Aspects - page 207

Just over 12 per cent curtailment is less than might be expected because
curtailment takes place at higher wind speeds, which occur less frequently. In fact,
the curtailment may be less significant for the following reasons:

The wind is likely to be less productive at times of low demand, especially in
northwestern Europe (see Figure 5.9).

●

The economic loss (ignoring subsidies) is less at low demand, due to lower
energy marginal cost.

●

The wind sector could provide emergency reserve at times of low demand,
reducing the need to run extra thermal generators.

●

Excess wind generation could be exported through an interconnector, as
discussed in Section 5.3.3. If we include a 1,000 MW interconnector (I/C) in the
example, with SNSP ¼ 0.7, the allowed wind generation at the various demand
levels is as shown in the third column above. The curtailment, calculated as before,
is 1,072,890 MWh, or 6.9 per cent. The interconnector has rescued 856,320 MWh,
or 98 MW on average. An interconnector built solely to provide an export path to
avoid wind curtailment is unlikely therefore to be viable, confirming the conclusion
in Section 5.3.3. On the other hand, occasional export of wind energy through an
interconnector used mainly for import of thermal energy makes economic sense, as
exemplified by the 500 MW East-West Interconnector between Britain and Ireland.
The effect of demand variation on potential wind penetration may be asses-
sed by assuming a flat load duration characteristic, with a constant demand of
6,000 MW. Wind capacity is again taken as 6,000 MW. Taking SNSP as 0.70,
and with 1,000 MW of interconnection available for export, the allowed wind
generation is 4,900 MW. The curtailment is now 3.1 per cent of potential wind
energy, and the wind energy penetration is 28.6 per cent. It may be concluded
that, short of extensive use of energy storage and demand-side participation, it is
extremely difficult, or expensive, to achieve a wind energy penetration greater
than the wind sector's capacity factor. Storage and load control options that may
help are explored below.

5.5 Energy storage/demand-side participation

For system equilibrium, electrical generation must equal the load demand, as dis-
cussed in Section 5.2, so that the ideal system demand profile would be invariant.
Under such circumstances, the most efficient generation could be scheduled to
operate continuously at the desired level. However, the daily variation in electrical
demand and the variable nature of renewable energy sources requires that thermal
generating units be scheduled to start-up/shutdown in sympathy with load variation,
with most of these units being further required to participate in load following and
cycling behaviour. In Section 5.3, against a background of increasing wind gen-
eration, various measures were examined to lessen the load-following burden
placed on the remaining synchronous plant: prediction of wind farm output; inte-
grating wind forecasting into unit commitment; geographical dispersion; incor-
poration of power electronics control; and reduction in wind farm variability by