4 The Transition of China’s Power System
153
respectively in 2019, ranking the first in the world, serious curtailment of wind and
solar have also occured. According to the data from the National Energy Administration, wind curtailment from 2012 to 2017 averaged at 12.6%; and that in most of
the wind farms in the Three Northern regions even exceeded 20%. The reasons for
load-shedding vary from region to region, but in essence, the uptake of renewable
energy is hampered by the lack of flexibility in the power system. For power grid in
north Hebei and Gansu, the main reason is the lack of power consumption and flexibility incentives; for western Inner Mongolia and three northeastern provinces, it’s
mainly due to the long heating period with insufficient peak regulation of conventional units. In 2018 and 2019, the government and the industry worked hard to
address wind and solar curtailment, and the wind curtailment was brought down to
7 and 4%. Figure 4.23 shows the active power balance of the system in low and high
uptake of renewable energy scenarios.
Currently, with the low percentage of renewable energy and lower level of
volatility and uncertainty, flexibility could take a back-seat in the planning until
the system is scheduled for operation. Wind and solar curtailment resulted from
inflexibility in isolated areas and timeslot of the system is acceptable from an engineering standpoint. If inflexibility occurs in the future scenario with a high uptake
of renewable energy in the power system, the problem will be even worse, with
widespread wind and solar curtailment and a subsequent system failure, thus putting
Table 4.13 Characteristics of power system flexibility
Characteristics
Connotations
Examples
Directionality
Upward power adjustment
Downward power adjustment
Load increase (reduction in
renewable energy)
Load decrease (increase in
renewable energy)
Multi-spatial-temporal
characteristics
Flexible supply and demand are
related to the time scale and are
subject to space constraints
Frequency modulation (≤15 min),
ramping (15 min–4 h), peak
regulation (24 h)
On the spatial scale, flexible
resources cannot move freely
State dependency
Both flexible supply and
demand are strongly correlated
with system state
Regulation of conventional units
and energy storage is related to
their output level and historical
state. Flexibility requirements are
related to load levels, renewable
energy output and other
conditions
Bi-direction convertibility Under certain conditions,
flexible supply and demand can
be converted to each other
Demand response, wind/solar
power curtailment, etc.
Probabilistic
characteristics
Necessary to build a framework
for uncertainty analysis using
probabilistic methods
Use random variables to describe
flexibility
153
respectively in 2019, ranking the first in the world, serious curtailment of wind and
solar have also occured. According to the data from the National Energy Administration, wind curtailment from 2012 to 2017 averaged at 12.6%; and that in most of
the wind farms in the Three Northern regions even exceeded 20%. The reasons for
load-shedding vary from region to region, but in essence, the uptake of renewable
energy is hampered by the lack of flexibility in the power system. For power grid in
north Hebei and Gansu, the main reason is the lack of power consumption and flexibility incentives; for western Inner Mongolia and three northeastern provinces, it’s
mainly due to the long heating period with insufficient peak regulation of conventional units. In 2018 and 2019, the government and the industry worked hard to
address wind and solar curtailment, and the wind curtailment was brought down to
7 and 4%. Figure 4.23 shows the active power balance of the system in low and high
uptake of renewable energy scenarios.
Currently, with the low percentage of renewable energy and lower level of
volatility and uncertainty, flexibility could take a back-seat in the planning until
the system is scheduled for operation. Wind and solar curtailment resulted from
inflexibility in isolated areas and timeslot of the system is acceptable from an engineering standpoint. If inflexibility occurs in the future scenario with a high uptake
of renewable energy in the power system, the problem will be even worse, with
widespread wind and solar curtailment and a subsequent system failure, thus putting
Table 4.13 Characteristics of power system flexibility
Characteristics
Connotations
Examples
Directionality
Upward power adjustment
Downward power adjustment
Load increase (reduction in
renewable energy)
Load decrease (increase in
renewable energy)
Multi-spatial-temporal
characteristics
Flexible supply and demand are
related to the time scale and are
subject to space constraints
Frequency modulation (≤15 min),
ramping (15 min–4 h), peak
regulation (24 h)
On the spatial scale, flexible
resources cannot move freely
State dependency
Both flexible supply and
demand are strongly correlated
with system state
Regulation of conventional units
and energy storage is related to
their output level and historical
state. Flexibility requirements are
related to load levels, renewable
energy output and other
conditions
Bi-direction convertibility Under certain conditions,
flexible supply and demand can
be converted to each other
Demand response, wind/solar
power curtailment, etc.
Probabilistic
characteristics
Necessary to build a framework
for uncertainty analysis using
probabilistic methods
Use random variables to describe
flexibility