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International Comparison of Wind and Solar Curtailment Ratio

Authors:
International Comparison of
Wind and Solar Curtailment Ratio
Yo h Ya su da
Kansai University, Japan
yasuda@mem.iee.or.jp
Lori Bird
NREL, USA
Enrico Maria Carlini
Ter na, Ita ly
Ana Estanqueiro
LENG, Portugal
Damian Flynn
University College Dublin, Ireland
Alain Forcione
IREQ, Canada
Emilio Gómez Lázaro
Uni. de Castilla-La Mancha, Spain
Paraic Higgins
Queens University Belfast, UK
Hannele Holttinen
VTT, Finland
Debra Lew
GE Energy Management, USA
Sergio Martin-Martinez
Uni. de Castilla-La Mancha, Spain
John McCam
SEAI, Ireland
Nickie Menemenlis
IREQ, Canada
J. Charles Smith
UVIG, USA
AbstractAs the penetration of VRE (variable renewable
energy), mainly wind and photovoltaic energy, has developed
widely and rapidly, curtailment of VRE has taken on
increased interest. This paper introduces a new evaluation tool,
named the “C-P map”, that shows the correlation between
VRE curtailment ratios and energy penetration ratios of VRE
in selected countries/areas. The C-P map can illustrate
historical trends for VRE curtailment ratios in a given
country/area at a glance, and help any comparison between
historical curves. Using the C-P map, this paper classifies the
selected countries/areas into several categories, depending
upon the level and trends of VRE curtailment. The
classification helps to understand how curtailment occurred in
the past and how it may change in the future in the selected
grids.
Keywords- wind power; photovoltaic; VRE (Variable
Renewable Energy); curtailment ratio; penetration ratio
I. INTRODUCTION
The incorporation of increasing amounts of renewable
energy in electricity systems primarily from variable
renewable sources, such as wind energy and solar
photovoltaic generation, has become an energy policy
priority in a majority of countries. Ever since the possibility
of large penetrations of variable renewable generation was
first proposed, the ultimate limits on VRE (variable
renewable energy) penetration have been the subject of
research. One early wind energy study suggested that, if all
of the variable renewable output must be utilized, only
modest levels of penetration might be possible. Other
research showed that, if relatively small amounts of the
variable renewable output were foregone or “curtailed”,
significantly higher penetrations would be feasible. One
study that explored the nature of curtailment proposed that it
would increase exponentially with increasing wind energy
penetration [1]-[3].
Curtailment of VRE is now becoming an increasingly
important issue with the increasing penetrations of VRE
worldwide. Previous investigations [4]-[5] have explored
some trends in the curtailment of VRE: Italy, China and
Tex as in t he U.S . have reduced their curtailment ratios from
values in excess of 10%, experienced in the early stages of
development, while Spain and Ireland show slight increases
with increasing VRE penetration ratios, despite efforts to
keep the curtailment ratio less than 1%. After the previous
investigations, it is becoming clear that there are some
countries that have common features in curtailment trends.
It is important to monitor curtailment, as declining
curtailment trends may give evidence for the success of
measures to efficiently integrate VRE. Direct comparison of
curtailment levels in different systems is not necessarily
appropriate, as there are a range of system specific factors
that contribute to curtailment. Prior work has provided some
high level evaluation tools that may be applied to assess the
severity of the challenge for incorporating VRE within
particular power systems and allow objective comparison of
curtailment levels [6]. Söder et al. [7] proposed a “maximal
share of wind power” criterion
Share of wind power =
Max. wind power [MW]
Min. consumption [MW] + possible export [MW]
and applied this to compare wind power penetrations in
Gotland, West Denmark, Schleswig Holstein, Ireland and
New Mexico. Ackermann [8] applied this criterion to
compare wind energy penetration in Denmark, Spain,
Ireland and Texas in 2013 and 2020. Yasuda et al. [9]
proposed the flexibility radar plot as a qualitative indicator
of the flexible system resources that might allow curtailment
to be minimised in systems with high VRE penetrations.
To in vest iga te suc h curtailment trends more
quantitatively, this paper introduces a new evaluation tool,
named the “C-P map”, that shows the correlation between
VRE curtailment ratios (curtailed energy per estimated VRE
energy generated) and energy penetration ratios of VRE
(VRE energy per annual gross generation) in the selected
countries/areas.
The paper also proposes new metrics, namely the C-P
ratio” and “C-P gradient”. The former is defined as the
quotient of the given curtailment ratio by the given
penetration ratio for the selected grid in the selected year,
whereas the latter is the gradient of the C-P curve at the
given point on the C-P map. Using the C-P map and metrics,
this paper classifies the selected countries/areas into several
categories depending upon the level and trends of VRE
curtailment. The classification helps to understand how
curtailment has occurred in the past and how it may change
in the future for the selected grids.
II. STATI ST IC S F OR VRE CURTAILMENT
In general, there are no mandated rules regarding the
publishing of unified statistical data on VRE curtailment
from TSOs (transmission system operators). The previous
papers investigated various documents created by TSOs,
regulators and national/international organisations to gather
the statistical data on curtailment of VRE in several
countries/areas.
Tab les I - IV show available statistical data for VRE
curtailment in available European countries, several RTOs
(regional transmission operators) in North America, China
and Japan, respectively. It is noted that most cases of
curtailment, excluding Japan, were associated with wind
energy. So far, there is limited information available on
curtailed PV energy across the world. In contrast, several
TABLE I. STATIS TIC AL DATA F OR VRE CURTAILMENT IN EUROPEAN COUNTRIES
Country
Year
Total Generation
(GWh)
Wind
(GWh)
PV
(GWh)
Curtailed Energy
(GWh)
Curtailment
Ratio
A
B
C
D
F = D/(B+C)
Denmark
2014
31,905
13,079
596
almost zero
0.00%
Germany
2011
613,068
48,883
19,599
0.421
0.61%
2012
629,812
50,670
26,380
0.385
0.50%
2013
635,267
53,400
30,000
0.127
0.15%
Ireland
2011
27,472
4,380
–––
0.106
2.42%
2012
27,592
4,010
–––
0.103
2.57%
2013
26,041
4,541
–––
0.171
3.77%
Italy
2009
292,641
6,543
676
0.700
9.70%
2010
302,064
9,126
1,874
0.527
4.79%
2011
302,584
9,856
10,688
0.264
1.29%
2012
299,277
13,407
18,637
0.166
0.52%
2013
289,807
14,811
21,228
0.152
0.42%
2014
277,897
14,966
23,299
0.121
0.32%
Portugal
2014
52,886
12,103
630
0
0.00%
Spain
2008
313,758
31,777
2,562
0.108
0.31%
2009
294,620
36,991
5,961
0.070
0.16%
2010
301,527
43,692
6,425
0.315
0.63%
2011
293,848
42,160
14,882
0.073
0.13%
2012
297,559
48,126
16,386
0.121
0.19%
2013
285,260
54,338
17,950
1.166
1.61%
(note) Only wind, no PV, is curtailed in European countries.
(data source) Tota l g en era ti on, wi nd an d P V e ne rgy : R ef. [10], curtailed Energy: Ref.[5].
TABLE II. STATI STI CA L DATA F OR VRE CURTAILMENT IN NORTH AMERICA
RTO
Year
Total Generation
(GWh)
Wind
(GWh)
PV
(GWh)
Curtailed
Energy (GWh)
Penetration
Ratio
Curtailment
Ratio
A
B
C
D
E = (B+C)/A
F = D/(B+C)
ERCOT
2009
N/A
N/A
N/A
N/A
6.2%
17.1%
2010
N/A
N/A
N/A
N/A
7.8%
7.7%
2011
N/A
N/A
N/A
N/A
8.5%
8.5%
2012
N/A
N/A
N/A
N/A
9.2%
3.7%
2013
N/A
N/A
N/A
N/A
9.9%
1.2%
2014
N/A
N/A
N/A
N/A
10.6%
0.5%
MISO
2010
N/A
N/A
N/A
N/A
3.6%
4.2%
2011
N/A
N/A
N/A
N/A
5.0%
3.4%
2012
N/A
N/A
N/A
N/A
7.1%
2.5%
2013
N/A
N/A
N/A
N/A
9.0%
4.6%
2014
N/A
N/A
N/A
N/A
6.1%
5.5%
Hydro-Québec
2014
216,703
6,670
–––
0
3.1%
0%
(note) Only wind, no PV, is curtailed in the U.S. and Canada.
(data source) Penetration ratio in ERCOT: Ref.[11], Penetration ratio in MISO: Ref.[12],
Curtailment ratio in ERCOT and MISO: Ref.[13]. All data in Hydro-Québec: Ref.[14].
Figure 1. C-P m ap of selected count ries (Group I)
Japanese utilities have estimated possible curtailment for
PV, due to its anticipated rapid growth in the near future.!
III. ANALYSIS USING C-P MAPS
To analy se the statistical VRE curtailment data from
various countries/areas quantitatively, the paper proposes a
new evaluation tool, named the “C-P map”, as a correlation
map between VRE curtailment ratios and VRE penetration
ratios. Figures 1, 2 and 3 show C-P maps for the selected
countries/areas grouped by their historical tendencies.
A. C-P Map of Group I: Well-operated
Figure 1 shows a group of (European) countries, i.e.
Denmark, Portugal, Spain, Ireland and Germany, where
VRE curtailment has been minimised in a “well-operated”
system management paradigm. For every country in this
group, VRE curtailment (only wind, in fact) has been
restrained to less than 4%, despite high VRE penetration
ratios. The fact that all of these countries are ranked in the
top-five countries with the highest VRE penetration ratios in
the world is not a coincidence. It can be understood that the
TSOs in these countries have suitably planned and operated
their grids to accept large volumes of VRE, with available
legislative and regulatory schemes in the last decade.
According to Spain's TSO, Red Eléctrica de España
(REE), deviations from imposed (wind) setpoints are
occurring, during curtailment periods and the recovery of
production once the limitations are released. REE has
proposed a new mechanism to minimise undesired
production losses, by performing dynamic curtailment
management, allowing control centres to modify the
setpoints according to prevailing weather conditions and
maintain production as constant as possible. In this way it
can help maintain power system operations, maximising the
integration of wind energy. REE expects to curtail 1.6 TWh
(2.2% of variable RES) in 2016, and for 2020, it is estimated
that 3.6% of wind and solar generation may be curtailed
[17].!
B. C-P Map of Group II: To b e im pr ov ed and imp ro vi ng
In contrast, Fig.2 shows a second grouping where VRE
curtailment ratios are significantly higher than those in
group I. Although the selected countries/areas, i.e. China,
Italy and two RTOs in the U.S. have relatively low
penetration ratios, the curtailment ratios are plotted in a wide
range, but less than 20%. It is interesting to note, in general,
the countries/areas show decreasing trends in their historical
C-P map curve.
These trends indicate that efforts to improve the
undesirable (curtailment) situation by the given TSOs/RTOs
has gradually borne fruit in the form of negative gradients
for their historical curve. While the fact that China and
TABLE III. STATI ST ICA L DAT A FOR VRE CURTAILMENT IN CHINA
Country
Year
Total Generation
(GWh)
Wind
(GWh)
PV
(GWh)
Curtailed
Energy (GWh)
Curtailment
Ratio
A
B
C
D
F = D/(B+C)
China
2012
4,994,038
95,978
6,366
20,820
17.12%
2013
5,432,843
134,900
8,700
16,230
10.74%
(note) Only wind, no PV, is curtailed in China.
(data source) Tota l g en era ti on, wi nd an d P V e ne rgy in 2 012 : R ef .[1 5], others: Ref.[5].
TABLE IV. STATI STI CA L DAT A F OR VRE CURTAILMENT IN JAPAN (FUTURE ESTIMATES)
Utility
Case
Total Generation
(GWh)
Wind
(GWh)
PV
(GWh)
Curtailed
Energy (GWh)
Penetration
Ratio
Curtailment
Ratio
A
B
C
D
E = (B+C)/A
F = D/(B+C)
Hokkaido
Current situation
(2014)
33,134 663 217 0 2.7% 0.00%
Case I: acceptable
VRE capacity
32,723 1,704 49 5.2% 2.90%
Case II: higher
penetration
32,723 3,001 394 9.2% 13.14%
Tohoku
Current (2014)
83,829
1,631
312
0
2.3%
0.00%
Case I
80,366
11,535
692
14.4%
6.00%
Case II
80,366
15,205
1,728
18.9%
11.37%
Kyushu
Current (2014)
87,783
607
992
0
1.8%
0.00%
Case I
88,736
11,773
494
13.3%
4.20%
Case II
88,736
17,473
1,919
19.7%
10.99%
(note) Only PV, no wind, will be curtailed in estimates from Japanese utilities.
(data source) Ref.[16].
Figure 4. Conceptual illustration of the C-P ratio in a C -P map
Figure 2. C-P m ap of selected countries/area s (Group II)
Figure 3. C-P m ap of selected are as (Group III)
Tex as (ER CO T) display similar trends may be coincidental,
a common cause can be surely considered. China has a
strong national movement to install wind turbines, despite a
delay in the construction of long-distance transmission lines
between the inner continental area and the high population
coastal areas. Also, Texas established a CREZ (Competitive
Renewable Energy Zone) scheme, which promotes
investment for wind power plants in inner desert areas
before the completion of transmission lines to the coastal
metropolitan area. In recent times, wind curtailment and
associated negative electricity prices in Texas have been
dramatically improved, following the gradual completion of
transmission lines in the CREZ scheme [18]. Italy also
overcame an uncomfortable situation with a high
curtailment ratio of nearly 10% in former years, to finally
achieve a low ratio less than 1%.!
C. C-P Map of Group III: Possiblly deteriorating
The final group for the C-P map relates to estimated PV
curtailment in the near future, completed by several utilities
in Japan. The country is now facing strong PV growth after
enforcement of a FIT (Feed-in Tariff) Law in 2012, while
other renewables, including wind, biomass, micro hydro and
geothermal, have not yet developed in a similar fashion, due
to a mismatch of renewable policies, including strict
environmental assessment schemes.
Several Japanese utilities announced their “acceptable
VRE capacity”, i.e. the maximum installed capacity
whereby they can curtail PV and wind energy without
compensation according to the FIT Law and the relevant
Ministerial Order. At a working group of the METI
(Ministory of Economy, Trade and Industory, Japan), held in
December 2014, the utilities published their estimated
results for the case of high PV penetration in the near future.
Figure 3 shows selected results, summarised in Ref. [8],
from the published data, and indicate the possibility of
significantly high curtailment ratios associated with future
PV development.
The results may well be overestimates, and remain a
matter of debate, given that the selected data in Table IV and
Fig. 3 represents the worst case for each utility. However,
the anouncement by the utilities and the METI resulted in
considerable negative impact on the Japanese renewables
market.
IV. C-P RAT I O A ND C-P GRADIENT
The previous section showed C-P maps for selected
countries/areas, divided into several groups according to
historical trends. Here, more quantitative analysis is
performed using new evaluation indicators, named the “C-P
ratio” and the “C-P gradient”.
A. Definition of C-P Ratio
The C-P ratio is a simple metric to show the VRE
curtailment level in a given country/area. A C-P ratio, R, is
simple defined as the quotient of the curtailment ratio C and
the energy penetration ratio P, as following:
. (1)
The C-P ratio, therefore, indicates the location of the
individual plot for a given year of the selected
countries/areas in the C-P map.
Figure 4 illustrates a conceptual map where the C-P
plane was divided into three zones, “green”, “yellow” and
“red” according to the critical C-P ratio, R. In this paper,
each zone is experimentally defined as the area where R is
less than 0.1, greater than 0.1 and less than 0.5, and greater
than 0.5, respectively. The green zone reflects the “well-
operated” countries, such as Denmark, Germany, Ireland,
Portugal, and Spain with high penetration ratios but low
curtailment ratios. The red zone indicates the “to be
improved” situation, with a high curtailment ratio despite a
RC
P
Figure 5. Conceptual illustration of the C-P grad ient in a C-P map
(a) closing-up correlation map (b) correlation map in wider area
Figure 6. Correlation maps between the C-P r atios and C-P gra dien ts of sele cted coun tries /areas
low penetration ratio, which includes part of the historical
plots of Group II.
B. Definition of C-P gradient
In contrast, the C-P gradient shows the historical
curtailment trends. The definition of the C-P gradient, G, is
given by the following equation:
GΔC
ΔP
, (2)
where
Δ
C and
Δ
P are the backward difference of C and P,
respectively.!
The C-P gradient G indicates the trend of the historical
curve for the selected countries/areas: a negative G implies
an improving effort to reduce the curtailment ratio, a
positive G greater than 0.5 expresses a warning of a possible
deterioration in the curtailment ratio for the future. Figure 5
illustrates a sample concept with various cases of the C- P
gradient.
C. Quantitative analysis using C-P ratio and C-P gradient
Given that the groupings employed in the previous
section were qualitatively and tentatively proposed, a
quantitative analysis is now performed using the above-
proposed indicators, the C-P ratio and the C-P gradient.
Figure 6 presents the resulting analysis, as the
correlation map between the C-P ratios and C-P gradients
for the selected countries/areas. Figure 7 also illustrates an
evaluation of the correlation map linking the two indicators.
The previous sections introduce three status levels, with
“green”, “yellow” and “red” identified by the C-P ratios, and
three trends including “deteriorating”, “stable”, and
“improving”, according to the C-P gradients. Therefore,
classifications with nine categories can be defined in the
correlation map of the two indicators as follows:
(1a) red but improving,
(1b) red and stable,
(1c) red and even deteriorating,
(2a) yellow and improving,
(2b) yellow and stable,
(2c) yellow and deteriorating,
(3a) green and still improving,
(3b) green and stable,
(3c) green but deteriorating.
By matching the plots and history of the corresponding
map in Fig. 6 to the conceptual map in Fig. 7, trends for
selected countries become clear; e.g. Italy and ERCOT have
both significantly improved and finally achieved a “good”
condition, while China requires more effort for the future.
Ireland is gradually heading towards the yellow zone, as
system stability limits become increasingly active, while
Spain, similar to several utilities in Japan, will reach the red
zone in the near future without reform to their grid planning
and operations. Until now, Hydro-Québec has not conducted
any curtailment, but this could become a real possibility in
the future.
The reasons for curtailment vary among countries/areas
and have changed over time. In Ireland, curtailment is for
reliability/stability reasons. ERCOT and China were in the
process of building transmission that was not yet ready
when the wind plants were installed. MISO has network
congestion in windy regions.
Summarising the results from Fig. 6, a classification into
nine categories is given in Table V, which provides an
overview on worldwide curtailment trends by objective and
quantitative indicators, with information expressed visually
and qualitatively by the C-P maps of Figs. 1, 2 and 3.
For example, Italy and ERCOT have moved from
position (1a) to (3a) in the last five years, which indicates
that an undesirable situation has been successfully
Figure 7. Classification of Curtailment Trend
by the C-P ratio and the C-P gradien t
improved, while China remains in position (1a), and
requires further improvement. Spain has gradually fallen
into (3b) from (3a), and may reach (3c) or (2c) in the near
future. Also, Ireland is at risk of sliding into (2c) without
appropriate countermeasures (which are indeed in hand),
which follows from its synchronously isolated grid. The
latest trend for MISO was slightly surprising and needs
further investigation of what happened and how to resolve
the situation. The Japanese utilities also require effort to
reduce curtailment towards (1b) or (2b) in the near future.
V. CONCLUSIONS
This paper proposed a novel tool, C-P map, and new
indicators, C-P ratio and C-P gradient, for a quantitative
and objective evaluation of curtailment trends from VRE
(variable renewable energy; i.e. wind and solar) in an
international comparison. Using these objective and
quantitative indicators, the historical trends for VRE
curtailment were classified and compared across several
countries/areas.
Also, it would be useful to move the discussion from
curtailment being a badthing, to how advantage can be
taken of curtailment to obtain more services from curtailed
VRE. For example, ERCOT achieves upward primary
frequency reserves from curtailed wind. These ancillary
services are valuable and show that curtailment does not
need to be seen as a waste of energy. Further discussions are
needed to create appropriate market structures with the
optimal VRE curtailment and to provide ancillary services
from VRE plants.
As grid conditions, energy mix and management of
power systems vary, these comparisons should take into
account the operating practices and available flexibility of
each region. Still, experience and knowledge in one
country/area can be informative to others. An international
comparison with objective measures can help gather best
practices. It is hoped that the newly proposed concepts in
this paper, C-P map, C-P ratio and C-P gradient, will enable
improved evaluation of VRE curtailment, and provide help
in planning and operating power systems in order to further
optimise curtailment of wind and solar generation in the
future.
ACKNOWLEDEMENT
This paper is part of R&D collaboration in the
International Energy Agency Wind Implementation (IEA
Wind) Task25 “Operation and Planning of Power Systems
with large amount of wind energy”.
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TABLE V. CLASSIFICATION OF CURLTAILMENT TRENDS IN SELECTED COUNTRIES/AREAS
class
trend
(a)
(b)
(c)
C-P Gradie nt
G < 0
0 G < 0.5
0.5 G
status
C-P Ratio
improving
stable
deteriorating
(1)
0.5 R red
China, Italy(2010),
ERCOT(2010)
MISO Japan (in future)
(2)
0.1 R < 0.5
yellow –––– Ireland ––––
(3)
R < 0.1 green
Germany, Spain(2009),
Italy(2014), ERCOT(2004)
Hydro-Québec, Denmark,
Portugal, Spain(2013)
–––
!
... Ireland [5], Spain [9][10][11], UK [12], the U.S. [4], and China [13][14][15][16]. Only a few studies investigate international comparisons on curtailment [17][18][19][20][21][22]. Estimated future curtailments can also be used as one important outcome from integration studies [7, 23,24]. ...
... Several of the authors of this work have previously introduced an evaluation tool, named the "C-P map", in order to quantitatively visualize curtailment trends. This C-P map shows the correlation between VRE curtailment ratios (curtailed VRE energy per generated VRE energy) on the y-axis, and energy shares from VRE per annual consumption on the x-axis, for given countries/areas [18]. This article enhances the preliminary concept of the C-P map, and renames it to "C-E Map" since the neutral terminology "energy share" of VRE is preferred over the term "penetration ratio". ...
... This article enhances the preliminary concept of the C-P map, and renames it to "C-E Map" since the neutral terminology "energy share" of VRE is preferred over the term "penetration ratio". The novelty of the current study is a direct result of time passing since Ref. [18] was published. Individual systems now incorporate much higher shares of renewables than even a few years ago, the reasons for, and consequences of, curtailment have grown, and various measures have been introduced to moderate, or even reduce, curtailment levels. ...
Article
Full-text available
As the share of VRE (variable renewable energy) has grown rapidly, curtailment issues have arisen worldwide. This paper evaluates and compares curtailment situations in selected countries using an objective and quantitative evaluation tool named the “C-E map” (curtailment-energy share map). The C-E map is a correlation map between curtailment ratios that mean curtailed wind (or solar) energy per available energy and energy shares of wind (or solar). The C-E map can draw a historical trend curve in a given country/area, as an at-a-glance tool to enable historical and/or international comparison. The C-E map also can classify the given countries/areas into several categories, according to the current levels of curtailment ratio and historical trends. The C-E map helps institutional and objective understanding of curtailment for non-experts including policy makers.
... Calculating curtailment requires that all the supplies and Based on the CP ratio, each country can be classified on its current (latest) situation using three colours, namely, red, yellow and green. In addition, the CP gradient shows the current (latest) trend of the curtailment using three classifiers: deteriorating, stable and improving [10]. From this, the following summaries can be drawn. ...
... A large increase in curtailment from 2018 to 2019 from 0.22% to 3.01% led to a classification of yellow and deteriorating. This indicates that the curtailment in Kyushu is worsening, which is in line with the analysis performed in 2015 [10]. ...
Article
Full-text available
High variable renewable energy (VRE) penetration led to the first-ever VRE curtailment in Japan, occurring in Kyushu in October 2018. Since then, there has been an average of 3% solar curtailment, with a peak of 13.7% in April 2019, resulting in approximately ¥9.6 billion of wasted energy. The VRE curtailment is expected to worsen as VRE penetration continues to increase along with nuclear energy increment in line with Japan’s 2030 energy goals. To prevent this curtailment and increase energy stability, a novel, logic-based forecasting method using hourly supply/demand data was developed. Initially, inaccurate results were returned; however, after several rounds of calibration that adjusted the quartile value of the max/min operating windows, the overall accuracy of this method was increased to 97% of real curtailment. This calibrated model was then used to test several curtailment mitigation scenarios. Some scenarios increased curtailment, while the two most successful scenarios, which reduced the installed nuclear capacity either seasonally or totally, limited curtailment by 95% and 97%, respectively. Another scenario with increased grid interconnection between regions reduced curtailment by 79%. Moreover, it would provide other benefits by unifying the national grid thereby increasing disaster resistance, reducing curtailment, improving grid flexibility and allowing for higher VRE penetrations. Currently, the situation is worsening, and some actions are required to reduce the curtailment and to achieve its 2030 energy goals in Japan. The mitigation measures studied by the logic method could be recommended to be referred to.
... However, the rapid expansion of utility-scale PV across Australia in 2018 and 2019 (about 3000 MW of increased capacity) has led to increased curtailment in 2019, due to both PV-specific system reliability issues and negative daytime market prices (AEMO, 2020). Outside of Germany, PV curtailment in Europe has been limited (Bird et al., 2016;Yasuda et al., 2015), though increasing PV penetration may drive future PV curtailment, particularly in Portugal and Spain (Bossman et al., 2018). In Japan, PV curtailment was reported for the first time on the Japanese mainland in 2018, though some PV curtailment may have occurred previously on remote islands (Tsukimori, 2018). ...
... In Japan, PV curtailment was reported for the first time on the Japanese mainland in 2018, though some PV curtailment may have occurred previously on remote islands (Tsukimori, 2018). Future PV curtailment levels are projected to reach as high as 10% of available output in Japan at higher PV penetration levels (Yasuda et al., 2015). ...
Article
Solar photovoltaic (PV) systems generate electricity with no marginal costs or emissions. As a result, PV output is almost always prioritized over other fuel sources and delivered to the electric grid. However, PV curtailment is increasing as PV composes greater shares of grid capacity. In this paper, we present a novel synthesis of curtailment in four key countries: Chile, China, Germany, and the United States. We find that about 6.5 million MWh of PV output was curtailed in these countries in 2018. We find that: Policy and grid planning practices influence where, when, and how much PV is curtailed; Some PV curtailment is attributable to limited transmission capacity connecting remote solar resources to load centers; PV curtailment peaks in the spring and fall, when PV output is relatively high but electricity demand is relatively low. We discuss available measures to reduce PV curtailment as well as increasing PV curtailment in the contexts of evolving grids and energy technologies.
... However, it is a rough estimation and still greatly depends on transmission line capacity and infrastructure, demand, and transmission capacity to neighbouring countries. The authors of [40] identified the curtailment ratio of a few countries, that is, the ratio of curtailed energy and summation of wind and PV generation. In a six-year period, it is shown that at the penetration ratio (the ratio of summation of wind and PV generation and total generation) of 2.5-13.8%, the curtailment ratio varied from 9.7-0.3% in Italy. ...
Article
Full-text available
Renewable Energy Sources (RES) have drawn significant attention in the past years to make the transition towards low carbon emissions. On the one hand, the intermittent nature of RES, resulting in variable power generation, hinders their high-level penetration in the power system. On the other hand, RES can aid not only to supply much more eco-friendly energy but also it allows the power system to enhance its stability by ancillary service provision. This article reviews the challenges related to the most intermittent RES utilised in Belgium, that is, wind energy and solar energy. Additionally, wind speed and solar irradiance variations, which are the cause of wind and solar intermittency, are studied. Then, recent techniques to forecast their changes, and approaches to accommodate or mitigate their impacts on the power system, are discussed. Finally, the latest statistics and future situation of RES in the Belgian power system are evaluated.
... For example, in 2016 the national average wind and solar PV curtailment rates reached 17.0% and 10.3% respectively (Fig. 1). This is in great contrast with many other renewable energy leaders such as Denmark, Germany and the State of Texas in the USA, where the penetration rate of renewable energy is higher than in China, yet the curtailment rate is kept below 5% (Yasuda et al., 2015;Bird et al., 2016;International Energy Agency, 2016). ...
Article
China's power system has faced major challenges to integrate the rapidly growing capacity of wind and solar power. In the context of a highly regulated power system, different localities have sought to use market-based approaches to mitigate this integration problem. In this paper, we use three cases to illustrate why and how these approaches have been implemented. The three cases involve the generation rights trading between hydropower and thermal power in Sichuan province since the late 1990s, the generation rights trading between wind power and thermal power, and the trading of peak regulating ancillary service in northeast China since 2012, and the generation rights trading between renewable units and captive power units in northwest Gansu province in recent years. Our analysis shows that these approaches have enhanced power system flexibility and improved renewable energy integration by circumventing the regulated wholesale power tariff, overcoming the constraints to economic dispatch arising from planned generation and long-term power purchase agreements, incentivizing relevant players to enhance power system flexibility, and providing appropriate price signals for renewable energy investment. Policy recommendations are to improve the mechanism for generation rights trading, increase trading items of ancillary services, and regulate the operation of captive power plants. China's experiences can provide helpful insights for other economies with regulated power systems.
... Wind curtailment soared from around 100-200 GWh/year before 2013 to values as high as 1200 GWh/year in 2013 accounting for 1.6% of the total RES electricity generation. Ever since the curtailment from wind has remained relevant ( Fig. 1) [10,11], in terms of volume and resolution cost, which makes the application of PtG favourable in such instances. ...
... In most regions, curtailment is implemented as a last resort and is viewed as a negative externality that should be avoided if possible. That is why curtailment in most regions has been declining even though the amount of wind and PV is increasing [14]. RE curtailment can form part of normal system operation during long-term capacity expansion modelling as a method to reduce the number of future units required for generation flexibility (especially from a ramping rate perspective). ...
Conference Paper
Full-text available
Wind and solar photovoltaic (PV) systems are expected to contribute significantly to the future electricity generation of South Africa. However, the output power from wind and PV is variable and uncertain in all time scales. Therefore, as the share of wind and PV generation increases, so does the need to invest in generation flexibility. However, if the grid is over-invested in generation flexibility, some capacity will only be needed for a few hours annually, which is not cost efficient. This paper presents a preliminary investigation into the feasibility of implementing renewable energy curtailment as a method to reduce the need for generation flexibility in the future South African grid. It concludes that implementing renewable energy curtailment during infrequent extreme ramping rate events can potentially be a least cost option as compared to investment in low capacity factor generation flexibility. Accurate short-term weather forecasting and curtailment automation are however required for effective implementation of this option.
Chapter
This chapter examines the post 3-11 politics in Japan about promoting renewable energy versus restarting nuclear power plants. The Abe administration’s support for the restart of some nuclear power plants, based on the safety authorizations given by the Nuclear Regulatory Authority, and Abe’s personal pronuclear position, are often assumed to mean that the Abe administration was hostile toward renewables and wanted to return to the pre-3-11 goal of nuclear expansion. This chapter asks whether this is an accurate assessment of the Abe administration’s energy policy. It finds that the answer is no. Rather, the Abe administration merely slowed down the phase out of nuclear power, while continuing its immediate predecessors’ policies of promoting renewable energy through electricity market liberalization, unbundling of grid ownership from generation, promotion of storage capacity for renewables, including the promotion of the hydrogen economy, which all facilitate the further adoption of renewable energy.
Conference Paper
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High penetrations of wind and solar generation on power systems are resulting in increasing curtailment. Wind and solar integration studies also predict increased curtailment as penetration levels grow. This paper examines experiences with curtailment on the bulk power system in countries around the world. It discusses how much curtailment is occurring, how it is occurring, why it is occurring and what is being done to reduce curtailment. This summary is produced as part of the International Energy Agency Wind Task 25 on Design and Operation of Power Systems with Large Amounts of Wind Power.
Book
Full-text available
There are already several power systems coping with large amounts of wind power. High penetration of wind power has impacts that have to be managed through proper plant interconnection, integration, transmission planning, and system and market operations. This report is a summary of case studies addressing concerns about the impact of wind power s variability and uncertainty on power system reliability and costs. The case studies summarized in this report are not easy to compare due to different methodology and data used, as well as different assumptions on the interconnection capacity available. Integration costs of wind power need to be compared to something, like the production costs or market value of wind power, or integration cost of other production forms. There is also benefit when adding wind power to power systems: it reduces the total operating costs and emissions as wind replaces fossil fuels. Several issues that impact on the amount of wind power that can be integrated have been identified. Large balancing areas and aggregation benefits of large areas help in reducing the variability and forecast errors of wind power as well as help in pooling more cost effective balancing resources. System operation and working electricity markets at less than day-ahead time scales help reduce forecast errors of wind power. Transmission is the key to aggregation benefits,electricity markets and larger balancing areas. From the investigated studies it follows that at wind penetrations of up to 20 % of gross demand (energy), system operating cost increases arising from wind variability and uncertainty amounted to about 1 4 /MWh. This is 10 % or less of the wholesale value of the wind energy.
Article
Full-text available
The amount of wind power in the world is increasing quickly. The background for this development is improved technology, decreased costs for the units, and increased concern regarding environmental problems of competing technologies such as fossil fuels. The amount of wind power is not spread equally over the world, so in some areas, there is comparatively a high concentration. The aims of this paper are to overview some of these areas, and briefly describe consequences of the increase in wind power. The aim is also to try to draw some generic conclusions, in order to get some estimation about what will happen when the amount of wind power increases for other regions where wind power penetration is expected to reach high values in future
Book
The second edition of the highly acclaimed Wind Power in Power Systems has been thoroughly revised and expanded to reflect the latest challenges associated with increasing wind power penetration levels. Since its first release, practical experiences with high wind power penetration levels have significantly increased. This book presents an overview of the lessons learned in integrating wind power into power systems and provides an outlook of the relevant issues and solutions to allow even higher wind power penetration levels. This includes the development of standard wind turbine simulation models. This extensive update has 23 brand new chapters in cutting-edge areas including offshore wind farms and storage options, performance validation and certification for grid codes, and the provision of reactive power and voltage control from wind power plants. Key features: Offers an international perspective on integrating a high penetration of wind power into the power system, from basic network interconnection to industry deregulation; Outlines the methodology and results of European and North American large-scale grid integration studies; Extensive practical experience from wind power and power system experts and transmission systems operators in Germany, Denmark, Spain, UK, Ireland, USA, China and New Zealand; Presents various wind turbine designs from the electrical perspective and models for their simulation, and discusses industry standards and world-wide grid codes, along with power quality issues; Considers concepts to increase penetration of wind power in power systems, from wind turbine, power plant and power system redesign to smart grid and storage solutions. Carefully edited for a highly coherent structure, this work remains an essential reference for power system engineers, transmission and distribution network operator and planner, wind turbine designers, wind project developers and wind energy consultants dealing with the integration of wind power into the distribution or transmission network. Up-to-date and comprehensive, it is also useful for graduate students, researchers, regulation authorities, and policy makers who work in the area of wind power and need to understand the relevant power system integration issues.
Article
Greater penetrations of variable renewable generation on some electric grids have resulted in increased levels of curtailment in recent years. Studies of renewable energy grid integration have found that curtailment levels may grow as the penetration of wind and solar energy generation increases. This paper reviews international experience with curtailment of wind and solar energy on bulk power systems in recent years, with a focus on eleven countries in Europe, North America, and Asia. It examines levels of curtailment, the causes of curtailment, curtailment methods and use of market-based dispatch, as well as operational, institutional, and other changes that are being made to reduce renewable energy curtailment.
Conference Paper
This paper evaluates various aspects of flexibility in power systems worldwide within the multi-country study framework of IEA Wind Task 25: which grid components/ actions have been favoured for enhancing suitable flexibility in different areas/countries/regions, and how have TSOs/ISOs/ utilities intended, and will intend, to manage variable generation in their operating strategies? One methodology to evaluate the diversity of flexibility is a “flexibility chart”, which can illustrate several flexibility parameters (e.g. interconnection, hydro, CCGT, CHP) in a polygonal radar (spider) chart.
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