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Balancing demand, conventional generation and wind power

Effect of wind power on scheduling of reserves

In this section, we outline the way in which wind affects the operation of the other generators in the system. For further information on power system operating principles, please refer to Annex H.

Primary reserves

Wind power development will have little or no influence on the amount of primary reserves required. On second/minute timescales, rapid variations in the total wind power capacity output occur randomly, such as existing load variations. When aggregated with load and generation variations, the increase in variability due to wind is very small. Furthermore, the amount of primary reserve allocated in the power systems is dominated by potential outages of large thermal generation plants, meaning it can easily cope with these rapid variations.

Secondary and tertiary reserves

The impact of wind power on the need for secondary reserves will only be significant and increase from wind energy penetrations levels of 10% upwards. The main impact of wind power will be on how conventional units are scheduled to follow load (hour to day timescales). If the output from a wind plant could be accurately predicted one to two days in advance, schedulers could more easily determine units that would need to be committed. The lack of an accurate forecast adds further uncertainty to the commitment decision, on top of the uncertainty associated with load forecasting. The result is that a unit might be unnecessarily committed, or that it may not be committed when this is required. In this case, the generation mix of the power system determines scheduling in view of expected wind power production – the greater the flexibility of power units, the later unit commitment decisions can be made.

The estimate for extra reserve requirements due to wind power (ref. EWEA 2005, Holttinen 2007) is in the order of 2 to 4% of the installed wind power capacity at 10% penetration of gross consumption, depending on how far ahead wind power forecast errors are corrected by reserves (this is dependent on the gate-closure times).

Short-term forecasting of wind in system operation

Clearly, short-term forecasting becomes increasingly important for system operation as wind power penetration increases. In regions with high penetration levels, such as certain areas of Spain, Germany, Denmark and Ireland, wind farm operators routinely forecast output from their wind farms. These forecasts are used by system operators to schedule the operation of other plant, and for trading purposes. The benefits of the application of short-term forecasting depend, to a large extent, on national regulatory, technological and site specific issues. The main advantages are cost reductions and improved system security.

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