IEEE Power & Energy Magazine - November/December 2019 - 106

Bilateral trading between VG producers and electricity users
permits buying and selling electricity among VG enterprises and
some industrial and commercial power users and companies.
The target increases the proportion of nonfossil generation
capacity in China from the current 41% to more than 60% by
2035, with most of the growth consisting of VG power. The
large-scale integration of VG power into the power grid will
have a profound effect on the planning and operation of the
power system.

being connected to the grid, the conventional electric users,
who have up to now been largely passive, need to become
prosumers. The distribution network needs to be upgraded to
satisfy the needs of flexible access, plug-and-play capability,
and friendly interaction of these facilities on the users' side
with the power system.

The Concepts of Power-System Planning
Need to Be Updated

Emerging New Market Players

At present, VG is incorporated into power system planning
with approaches only suitable for low amounts of VG penetra-
tion, in which VG is only viewed as a supplementary power
source. To accommodate future power systems with high
VG penetration, the planning concepts need to be updated.
Flexibility, economic viability, and security will be the core
criteria. Power system planners should not only consider the
economics of various types of power sources, such as wind
turbines, PV facilities, coal-fired plants, and nuclear-power
stations, but they also should reevaluate the functional role
of these resources in ensuring the safety, reliability, and flex-
ibility of the power supply. In addition, the rapid development
of distributed power generation and energy-storage technolo-
gies must be considered in transmission and distribution net-
work planning. The planning issue is especially important in
China, where the electricity demand in 2035 is forecast to be
twice that of 2015.
Reviewing Balance and Stability of the Power System

Forecasters say the capacity of VG in China will reach
1.3-1.4 TW by 2035. According to an analysis of VG varia-
tion characteristics, the daily maximum power fluctua-
tion would then reach 600 GW. This is equivalent to twice
the current maximum load of East China, which is the
system load center. This will pose huge challenges to
the power grid's daily balancing. In August 2018, SGCC
encountered a situation with the minimum output of wind
and solar generation of only 10.99 GW, accounting for
only 3.9% of the total wind and solar generation capacity.
Alternatively, the large-scale replacement of conventional
generators by VG power plants would lead to a significant
reduction of the inertia level in the power systems, result-
ing in the deterioration of the power grid's ability to reli-
ably respond to disturbances.
Calling for a Smarter Distribution Network

With a large number of distributed variable generators,
microgrids, electric vehicles, and energy-storage devices
106

ieee power & energy magazine

The large-scale integration of VG poses higher require-
ments for the f lexibility of the power system, but the
ever-decreasing electricity market price poses chal-
lenges to the survivability of thermal power generators
that can provide needed ancillary services. The market
framework and products need to be redesigned to ensure
the operational flexibility and reliability of the power
system to accommodate the rapid development of dis-
tributed VG and energy storage as well as electric pro-
sumers. At present, China is exploring mechanisms for
distributed generation and battery storage to participate
in market trading.

Key Issues of a Growing Power System
With High Penetration of VG
Updating Planning Methodology and Concepts for
VG-Dominated Power Systems

The following measures for system planning and operation
should be adopted:
1) Identify the typical operation modes of the system. In
power systems dominated by VG, typical operation
modes will be more diverse. It is necessary to study
how the power-system operation will be affected and
what typical operation modes should be considered in
power-system planning and in generation scheduling.
2) Introduce new planning guidelines, which should be
oriented around sources of flexibility.
3) Consider the need for new stability behavior of power
systems with high VG penetration, including such
concerns as frequency instability caused by insuffi-
cient inertia and power-system power-angle voltage
instability caused by power electronic devices.
A Need to Establish a 3D Framework
of Policy Market Regulation

For the policy part, a clearly defined long-term vision for
the energy-supply transformation, such as a minimum
VG energy target or maximum carbon emission target, is
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IEEE Power & Energy Magazine - November/December 2019

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