IEEE Electrification Magazine - September 2015 - 6

TECHNOLOGY LEADERS

Figure 3. An energy storage building of redox-flow battery system (6 MWh).

battery, a planned transmission from
the mega solar plant was achieved.
Another issue is voltage control on
a grid system with a high penetration
of PVs. For example, the voltage near
the connecting point may fluctuate
from output changes from a largescale PV station and it may become
difficult to keep voltages within operational standards. In the Hokuto
demonstration, an inverter capable of
controlling reactive power was introduced and demonstrated to show
such control is effective for voltage
management.
In a demonstration of projects
related to PV systems on grid-interconnection of clustered photovoltaic
power generation (FY 2002-2007),
voltage management by a distributed

Ventilation Fan

house-level battery system was
tested. In this case, battery storage
systems take on an important duty to
keep voltage within the standard and
at a lower voltage access line to home.
In this project, more than 550 rooftop PV generation systems are
installed in houses in Ohta city,
Gunma Prefecture, Japan. This project
demonstrates technologies related to
voltage control and protection
technology as islanding detection on
the distribution network.
To avoid PV system output restrictions, an external storage box is
installed along with the PV system at
each house. Each box contains an
inverter, storage battery, and monitoring equipment (Figure 5). The voltage
on the distribution line sometimes

Inverter4 kVA

Lead-Acid Battery
(4,704 Ah Cell)

Control Terminal

Figure 5. The clustered PV project and its battery box.

6

Figure 4. The Wakkanai site for mega solar power (5 MW).

I E E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2015

becomes higher than the maximum
nominal voltage because of too much
power flow reversed from the PV system. In this case, the storage battery
provides charging energy and keeps
the line voltage within nominal operational range (101 ± 6 V, 202 ± 20 V).
NEDO also studies balancing
demand, and some renewable energy
resources are tested in small power
systems connected to the utility
power system. In those projects, the
battery system is one of the key
technologies that establishes balanced
microgrid operation.
The demonstrative project of
regional power grids with various new
energies (FY 2003-2007) was one of the
most notable projects in the history of
NEDO and was done in collaboration
with the 2005 World Exposition in
Aichi, Japan.
In the Aichi subproject, power supply resources such as fuel cells, PV cells,
and a battery storage system were
installed. All of the equipment was
made up of inverter-based resources.
The main resources of this microgrid
system were fuel cells and PV systems.
There were three types of fuel cells
introduced: two molten carbonate fuel
cells (MCFCs) of 270 and 300 kW, one
25-kW solid oxide fuel cell, and four
200-kW phosphoric acid fuel cells. Fuel
for the fuel cells is mainly supplied by
city gas. Some percentage of the fuel for
each MCFC was produced by a methane fermentation system and a gasification system. The total capacity of the



Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2015

IEEE Electrification Magazine - September 2015 - Cover1
IEEE Electrification Magazine - September 2015 - Cover2
IEEE Electrification Magazine - September 2015 - 1
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IEEE Electrification Magazine - September 2015 - Cover3
IEEE Electrification Magazine - September 2015 - Cover4
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http://www.nxtbook.com/nxtbooks/pes/electrification_september2015
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http://www.nxtbook.com/nxtbooks/pes/electrification_september2014
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