IEEE Power & Energy Magazine - November/December 2020 - 61

by comparing cases of uncontrolled charging and smart
charging/discharging. The figure shows nationwide
charging and discharging patterns in CL1-CL5 and the
change in the net demand for each case on 1 April. It is
apparent that the net demand is substantially bottomed
up by the optimized charging and discharging of EVs.
As shown by the demand and supply operation on 2 March
2019 in Figure 14, an extreme over/under PV generation forecast error is a genuine threat to the Kyushu power system. It is
not economical to use thermal plants to maintain upward and
downward flexibility against the rare forecast error. PVs and
wind can supply downward generation flexibility without losing significant production opportunities, and they can supply
upward generation flexibility if the production is reduced in
advance. In the future, there will be substantial possibilities
for demand-side distributed resources. To evaluate the different flexibility requirements and provisions during optimum
system operation, we need to enhance our production cost
model to granularize the total operational flexibility into two
directions-up and down-and different time domains.
Among the different kinds of flexibility, an upward tertiary-
slow flexibility, which can be activated within 30 min, is assumed
to treat extreme forecast errors for residual demand. Figure 25
offers an example of a demand and supply balance of tertiary-
slow flexibility: the requirements for the upward and downward
flexibility (request up and request down) are 6 and 2 GW, respectively. They are met through a combination of traditional power plants
and distributed resources, such as
Nuclear
Power
PV and wind generation, EVs, and
electric HPWHs. The reduced flexibility requirement for thermal plants
means a substantial reduction of
operational cost during standby.
In the distribution area, it is
necessary to manage the power
flow and voltage. Figure 26 demonstrates a possible future arrangement in which a new voltage management server centrally controls
Thermal
step voltage regulators (SVRs),
Power
static synchronous compensators,
Factories
smart inverters of utility-scale PVs,
SVCs, and batteries to manage the
voltage profile of a distribution system. By managing and controlling
resources on both the system side
and the customer side, investment
and operation costs are expected to
be deferred and reduced.

wholesale and retail markets and regulatory frameworks
are to be adapted to the penetration of renewable generation, especially PVs and wind power. Using generators as
flexibility sources is an appropriate technical requirement
not only for conventional but also renewable generators,
especially PV and wind sources. In Japan, the grid connection code has not yet matured compared to the requirement for generators in the network codes developed by
the European Network of Transmission System Operators. The connection code under revision is to prescribe
frequency services for thermal units that are greater than
or equal to 100 MW, whereas the existing grid connection
codes specify limited functions for wind power plants,
such as output deviation limit control, storm control, and
generation droop control, under the existing institutional
structure. For PVs, the Japan PV Energy Association and
Japan Electrical Manufacturers' Association have begun
to work together to develop new requirements for the grid
connection code.

Conclusion
In Japan, the geographically imbalanced and heavy
deployment of renewable energy, especially PVs in
Kyushu, has posed various challenges for power system
operations. System operators have rapidly been developing
and implementing new procedures to secure a stable power

EV and Power Storage

Institutional Issues
Through the process of deregu lation, various institutional
arrangements for the design of
november/december 2020

Hydropower

Wind
Farm

Electricity
System

Virtual Power Plant

Utility-Scale
Solar PVs

Microcogeneration

Shops

Stationary
Battery System

Heat Pump

figure 23. The additional supply flexibility provided by virtual power plants. (Source:
METI; used with permission.)
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IEEE Power & Energy Magazine - November/December 2020

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