IEEE Power & Energy Magazine - November/December 2020 - 50

2 GW of thermal generation, 1.8 GW of energy storage by
PSH plants, and 1.9 GW of power export via an interconnection line to a nearby balancing area. Table 2 describes the
results of the renewable generation curtailment operation.
From the first renewable generation curtailment in Kyushu
through June 2019, there were 56 renewable generation
restriction operations. From March to May, when demand
is low because of the minimum air-conditioning loads and
maximum irradiation, there were more frequent renewable
generation curtailments, with a maximum of 2.57 GW.

System Operation

20 ber
19

PV-Wind
September 2017

Electricity Demand
Fiscal Year 2016

Population
October 2016

Land
October 2016

Capacity (GW)

Generation forecasting of PV and wind generation is beginning to be used to enhance system operations. A PV generation forecast uses irradiance data from eight sites to
predict the PV output. Since January 2018, however, the
number of sites collecting irradiance data has increased to
47, greatly improving the accuracy of the PV output predictions
(Figure 6). PV output predictions are carried out using three
models, each with its strengths and weaknesses, depending on the weather pattern. Predictions of their performance
have been continuously evaluated.
During real operations, when
satellite data are matched with
10
8.86
historical insolation patterns,
8.53
three predictions are weighted
7.85
8
to yield an average forecast for a
6.97
3-h horizon, as in Figure 7. The
6.16
6
satellite data are fit with historical
4.71
patterns to yield weights for each
forecast model. The 3-h predic4
Launch of FIT
tion is given by the weighted aver2.71
age of the three forecast models.
2
Figure 8 gives an example of
1.11
0.74
0.56
a
flexible
thermal plant operation
0.41
to
meet
the
ramp-up of residual
0
demand during the evening. In
addition to the flexible operation
of pumped-storage units (300 MW
× 6; 250 MW × 2), four combinedcycle gas turbine (CCGT) axes,
figure 3. PV deployment in Kyushu. (Source: Kyushu EPCO; used with permission.)
which are composed of one combustion turbine and one steam turbine that have shorter start-up times, are synchronized in a
short interval of roughly 15 min. Each axis, receiving a dis18% Wind (1%)
patch order 2 h before the target time, is paralleled in every
15 min.
To accommodate more PV and wind generation, an effective
11%
option
was to increase the operational capacity of the ac inter10%
10%
PV (17%)
connection with Honshu via the Kanmon line, with a thermal
capacity of 2.5 GW. A grid stabilization system was installed
to immediately and selectively trip multiple major generation
plants in case of a failure of the line (Figure 9). Recently, in
Kyushu and some other balancing areas, utility-scale battery
energy storage systems (BESSs) are also being deployed. They
provide a small but fast system frequency regulation service.
Figure 10 depicts a 50-MW, 6-h NaS BESS in Kyushu. The system consists of two battery banks with 63 800-kW subunits.
With a capacity of 300 MWh installed at one site, the system is one of the world's largest energy storage facilities.
figure 4. A comparison of Kyushu's PV deployment and
related factors as percentages of Japan's total. Note the significant difference between Kyushu's share of the total electricity demand (10%) and the total PV and wind generation
(18%). (Source: Kyushu EPCO; used with permission.)
50

ieee power & energy magazine

Renewable Energy Generation
Curtailment Procedures
Online curtailment is key for the efficiency and security of
renewable generation restriction procedures, the reduction of
the required amount of renewable generation limitation, and
november/december 2020

IEEE Power & Energy Magazine - November/December 2020

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