German Renewable Energies Act
Figure 5: Effects of Unlimited Orders on Market Clearing Price & Trade Volume
by the volume of the unlimited bids ∆V (bid curve 2). Without an adjustment of the demand curve, the trade volume increases by V2 - V1 and the price drops to P2. Since the offer is lower at P2 than at P1 if unlimited bids are not considered, the difference between V2 and V1 is smaller than ∆V. This constitutes the cause for the increase in the trade volume in Figure 4 which is lower as against the WEP forecast.
Day-Ahead Forecast Errors & Intra-Day Trade Volumes According to the provisions of AusglMechAV, the quantity
Source: EEX
of the limited length of the time series. It is apparent that with increasing forecast WEP energy quantities the trade volume does not increase to the same degree as the energy volume forecast. This does not mean that the forecast WEP feed-in volume is not fully marketed through the exchange. This effect is due to the fact that prices, which fall while the forecast WEP quantities for feeding-in increase (Figure 3) displace parts of the offers contained in the bid curve. This connection is shown qualitatively in Figure 5. Without consideration of the unlimited orders for EEG
marketing, the price P1 and the trade volume V1 for a single hour are established in a simplified manner on the basis of the intersection of bid curve 1 and the demand curve. If unlimited offers are considered in addition, the bid curve shifts to the right
of energy marketed or procured by the transmission system operators on the intra-day market corresponds to the difference between the day-ahead forecast and the quantity of wind energy expected on the basis of short-term forecasts until the actual feed-in. In line with this, the quality of the day-ahead forecast is decisive for the intra-day volume traded by the transmission system operators.
... with increasing forecast WEP energy quantities the trade volume does not increase to the same degree
Figure 6 shows the difference between the forecast and actual
WEP feed-in (forecast error) with regard to the forecast feed-in depending on the expected daily feed-in. The values correspond to the total of the data published by the four transmission system operators in Germany for every delivery day in the first quarter of 2010. In evaluating the forecast error, the fact that the
Figure 6: Deviation of the Actual Feed-In by Wind Energy Plants From Forecast (forecast error)
Source: EEX
transmission system operators forecast the entire WEP feed-in for their balancing area and that the hourly forecast values in the analysis considered here are aggregated over 24 hours in each case has to be taken into account. Since the time-lag between the forecast and the actual feed-in, thus, does not amount to 24 hours for all values and since the forecasts in Figure 6 are aggregated both in terms of region and in terms of time, the forecast error considered here is not identical to the forecast error of day-ahead forecasts of the wind speed which are established for a single site and a single point in time 24 hours in advance. The forecast error in Figure 6 decreases, while the forecast WEP feed-in increases. Figure 7 shows the development of weekly trade volumes on the intra-day market of EPEX Spot for
worldPower 2010 87
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