IEEE Power & Energy Magazine - November/December 2021 - 89

2020, there were about 1,100 5-min real-time market intervals
when system-wide prices were negative.
In Germany, negative-price events increased significantly
in 2020. In the day-ahead market, hourly events
increased by 40% to 298 h compared to 2019. In the quarterly
intraday auction, the events increased by 86% to
2,041 15-min intervals. The overall market value of these
negative-price events (€-149 million) increased from
2019 (€-134 million) but was less than in 2017 (€-152
million), as the negative prices mainly occurred during
times with low market volumes (nights and weekends).
Additionally, the negative prices were not as low in 2020
(an average of €-15.5/MWh) as in 2019 (€-17.3/MWh)
and 2017 (€-26.5/MWh).
In 2019, Denmark West experienced negative prices during
less than 2% of the year, even though VRE exceeded
demand for about 25% of the year. Two thirds of these negative-price
situations were shared with neighboring Germany.
As Denmark is usually a price taker in one of the bigger
adjacent markets, this shows that the cross-border market
functions well and that low-cost energy in most surplus situations
still has value, as it can be sold where it is needed.
In the Japanese energy market, market prices cannot
be lower than ¥0.01/kWh. The percentage of (almost) zero
prices was 3% in fiscal year 2019. In Kyushu, where large
PV capacities are located, this was 4% in 2019 and 5% in
2020. Although the PV capacity has been increasing, system
operation improvements to reduce curtailment while maintaining
stable operation have moderated the percentage of
PVs curtailed. The frequency of zero-price periods has been
increasing in other parts of Japan, too.
VRE Curtailment
System operators may dispatch a VRE plant below its potential
real-time output, curtailing it due to transmission congestion
or system-wide overgeneration. VRE plants may
also downregulate, or curtail, their output as an economic
response to negative prices. Curtailment can be viewed as
flexibility from VRE. However, curtailed energy is lost and,
therefore, should be kept to a low level. Selecting other flexibility
resources can be considered so that most of the clean
energy available is dispatched, and VRE curtailments are
reserved for critical situations.
Over the past few years, China has worked hard to
avoid VRE curtailment. In 2020, the curtailment of VRE
was under 5%. Going forward, planning for flexibility
in the system is a high priority. This includes VRE projects
with storage, retrofit of coal-fired power plants, and
140
120
100
80
60
40
20
Northeastern Area Hourly Production and Monthly Average
Interconnected System Hourly Production and Monthly Average
figure 4. The hourly VRE production in Brazil: 2020 renewable penetration. (Data source: Operador Nacional do
Sistema.)
november/december 2021
ieee power & energy magazine
89
Share of Installed Capacity
Thermal
23%
23%
Interconnected System
Northeast Area
Hydropower
66%
31%
Renewables
10
12%
46%
20 30%
(%)
40
50
60
70
Percentage of Demand
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.

IEEE Power & Energy Magazine - November/December 2021

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