IEEE Electrification Magazine - June 2017 - 32

20,000
15,000
10,000
5,000
0
-5,000
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

-10,000
(a)

slightly, diesel generators and energy storage will be adjusted to stabilize the voltage and frequency of the microgrid.
When the output of the PVs decreases significantly, the
security and stability control devices will shed the unimportant load, and the energy storage will be set at discharge
mode immediately to keep the important  load on line.
Then, the other diesel generators will be started to bring all
shedded load back in service. At night, based on the load
level, energy storage will provide appropriate energy support, and some diesel generators will also run to meet the
power requirement (load minus energy storage).

(%)

27
25

PV-Diesel Mode 1 (10-MW PV Units)

23

The operating characteristics are similar to PV-diesel-storage mode 1, except that no energy storage is available.
If the PV output decreases, the deficiency will be supplied
by the diesel generators or by load shedding.

21
19
17
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

15
(b)
PV-Diesel-Storage
Mode 1
PV-Diesel
Mode 1

PV-Diesel-Storage
Mode 2
PV-Diesel
Mode 2

PV-Diesel Mode 2 (7-MW PV Units)
The operating characteristics are similar to PV-diesel-storage mode 2, except that energy storage is not available.
If the PV output decreases, the deficiency will be supplied
by the diesel generators or by load shedding.

economic analysis of the Isolated Microgrid
Figure 5. (a) Net cash flow and (b) investment recovery rate results.

the capacity configuration design, the peak output of PVs is
set at 80% of their installed capacity. Considering the daily
operation characteristics, the following four typical diesel/
PV/energy storage configuration modes are designed.

PV-Diesel-Storage Mode 1 (10-MW PV Units,
1-MW·2-h Energy Storage)
During daytime operation, one diesel generator (2.2 MW) runs
as the main generation resource for the isolated microgrid
and provides frequency and voltage support. The PVs supply
the remaining electricity. When the output of the PV decreases slightly, diesel generation and energy storage will be
adjusted to stabilize the voltage and frequency of the
microgrid. When the output of the PVs decreases significantly, the security and stability control devices in the microgrid
will shed the unimportant load, and the energy storage will
be set at discharge mode immediately to keep the important
load on line. Then, the other diesel generators will be started
to bring all shedded load back into service. At night, based on
the load level, energy storage will provide appropriate energy
support, and some diesel generators will also run to meet the
power requirement (load minus energy storage).

PV-Diesel-Storage Mode 2 (7-MW PV Units,
1-MW·2-h Energy Storage)
During daytime operation, two diesel generators run as the
main generation resources for the isolated microgrid and
provide frequency and voltage support. The PVs supply the
remaining electricity. When the output of the PV decreases

32

I E E E E l e c t r i f i c ati o n M agaz ine / j un e 2017

The initial investment of a large-scale isolated microgrid
includes the construction of the PV system, the construction of the energy storage system, and the construction of
the secondary system. The later-stage investment includes
system overhaul, system operation and maintenance,
energy storage battery replacement, and other investments. The calculation formulas are as follows:
Z investment = Z PV + Z storage + Z secondary + Z maintenance ) Y
+ n storage ) Z storage + n overhaul ) Z overhaul,

(1)
(2)

Z PV = a PV C PV + b PV,

(3)

Z storagy = a storage C storagy + b storage,
Z secondary = a secondary ^C PV + C storageh + b secondary,

(4)

where Z pv = investment of PV; Z storage = investment of energy storage; Z secondary = investment of secondary equipment;
Z ma int enance = cost of maintenance; n storage = replacement
times of energy storage; n ouvehaul = times of overhaul;
Z overhaul = cost of overhaul; a pv = cost factor of PV; C pv =
installed capacity of PV; b pv = additional cost of PV;
a storage   = cost factor of energy storage; C storage = installed
capacity of energy storage; b storage = additional cost of energy storage; a sec ondary = cost factor of secondary equipment;
and b sec ondary = additional cost of secondary equipment.
The benefit of the microgrid comes from the cost saving
through using the PV generation to replace the diesel generation. The formula for the total microgrid benefits calculation is
Z benefits =

T

8Z

i=1

kWh

W i,

(5)



Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2017

IEEE Electrification Magazine - June 2017 - Cover1
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