3.8 Wind power stations impose additional frequency keeping costs on the power system that are greater than, for instance, from hydropower stations. From the point of view of system operation, the major problems with wind power are that it is unpredictable and that it can fluctuate very rapidly. These rapid fluctuations means that with wind power connected to the system, frequency keeping becomes more difficult and more expensive. At the moment, frequency keeping plant operates to manage fluctuations in the range of +/- 50 MW. Experience with integrating the output of the Manawatu wind farm shows that wind generation has increased the need for – and hence the cost of – system frequency keeping.
3.9 The unpredictability of wind generation means that the system operator cannot be confident of the output of wind farms more than an hour so into the future. Because it takes longer than one hour to bring one of the large steam turbines at Huntly coal-fired power station from “hot standby” (that is stopped but warmed up and ready to start) to full load, then very often, the system operator will be forced to keep thermal and hydro plant connected to the system and running at less than full load because of the need to have generating capacity available in case the wind drops or the expected wind does not eventuate. This is inefficient and expensive. The costs fall on the consumers. …
4.0 Meeting the Demand for electrical energy
4.1 When determining the need for new generation, sufficient electrical energy must be available to meet the forecast power demand for electricity over the critical autumn-winter period in a dry hydro year when hydro-inflows are 15-20% lower than average and the power demand is at its maximum. The autumn and winters of 1998, 2001, 2006 and 2008 are typical examples. If insufficient energy is available, the lake levels will fall, prices will rise dramatically and an electricity savings campaign may be needed to minimise or avoid the risk of power cuts.
4.2 Wind farms generate electrical energy whenever the wind is blowing. If the energy is not needed at the time that it is generated, it can often be stored in hydro storage lakes. But there are important caveats to this because, as I show below, on average, the output from the wind farms in New Zealand is about 9% below annual average output during the March to August period when lake levels are most likely to be low and there is a risk of a serious shortage. The output of the wind farms is at its highest level during the spring time. This is when the snow melts and supplies additional water into the hydro lakes. As a result of the snow melt and spring rains, the prices are often very low in the late spring and early summer thus demonstrating that any extra electricity generated during this period is of less value to our power system. …
5.12 The above and Exhibit 2 demonstrate that the System Operator’s policy of assuming that there will be no output from wind farms when scheduling generation for the day, is realistic and prudent.
5.13 I am confident that, even with widely distributed windpower, it would be risky to assume that as much as 20% of the capacity would be available during system peak demand times. Assuming that 10% would be available would be less risky because it would happen less often and, if the system operator was wrong, the chances are that there would be sufficient capacity available on the system to substitute for the missing 10%. …
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