IEEE Power & Energy Magazine - Grid Edge 2023 - 37

The term self-sufficiency describes the share
of total energy consumption that is covered
by PV generation.
In addition to the power system balance, power flows are
also influenced by high feed-in gradients, increasing the risk
of unforeseen congestion.
Another major operational challenge is related to the
quality of short-term PV forecasts. Real-time data must be
available on a large scale to improve forecasts and extrapolation
of the actual feed-in. The situation at the beginning of
April 2013 illustrates the fact that the quality of PV forecasts
in particular needs to be further addressed by R&D activities.
On 3 April 2013, close to 20 GWp of PV feed-in was forecasted
for Germany at the day-ahead stage. These forecast
feed-in values had to be marketed by the German TSOs and
individual direct marketers on the European Power Exchange
day-ahead market (the portfolios of these individual marketers
encompass some 20% of the installed PV capacity in
50Hertz's control area). In contrast to the day-ahead forecast
of 20 GW, the peak of the intraday forecast only reached
values close to 16 GW and, even worse, the actual feed-in
was estimated to be around 11.5 GW. In consequence, the
German TSOs and the direct marketers had to balance out
8,800 MW on the intraday market. This forecast error led to
open positions and exhausted the control and reserve power
over all four of the German control areas. The German power
10
20
30
2008
10
20
30
40
2008
2009
2010
2011
2012
Feed-In of Renewables in the 50Hertz Control Area
Amounted to 36.7 TWh Representing ~37% of Total Energy Consumption
figure 12. Generation capacity and the corresponding feed-in of RES within the 50Hertz service area (sources: 50Hertz
Transmission GmbH and www.netztransparenz.de).
march/april 2015
ieee power & energy magazine
37
2013
22.8
2009
23.7
2010
24.8
2011
28.2
2012
35
2013
36.7
system could no longer be independently balanced and had
to be supported from neighboring countries. This particular
example highlights the importance of accurate PV forecasts
in high-PV-penetration scenarios.
To lower the risk of inaccurate forecasts, 50Hertz has contracted
four independent forecast providers for PV feed-in.
They are offering PV feed-in data for Germany, the 50Hertz
control area, and certain DSO regions. The time horizon of
their individual forecasts is up to 96 hours (day-ahead) and
for short-term forecasts, up to eight hours; both types have
three daily updates. In addition, they also provide nowcasting,
with updates as frequent as every hour. The final forecast
that is used by the TSO is a combined and weighted forecast
from all four forecast providers. The resulting forecast is a
linear combination of the four individual forecasts to ensure
robustness during extreme weather events. The individual
weights are determined by means of statistical analysis.
The final forecasts are used to perform grid calculations and
identify possible grid congestions and voltage violations,
for example. On average, the accuracy of the combined PV
forecast has reached root mean square errors of 5-7%. This
reveals a need for further improvement, especially since the
underlying installed PV capacity is continuously increasing.
Other RES Biomass Wind PV System
18,008
11,304
13,395
15,101
21,915
22,727
Installed
Feed-in (TWh)
Capacity (MW)

http://www.netztransparenz.de

IEEE Power & Energy Magazine - Grid Edge 2023

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