631
HYBRID POWER-SUPPLY SYSTEM COMPOSED OF PHOTOVOI.TAIC AND FUEL-CELL SYSTEMS
N. Kato, K. Kurozumi, N. Susuki and S. Muroyama
NTT Facilities Inc., Japan
and one stand-alone hybrid power-supply
ABSTRACT
system
composed of photovoItaic and fuel-cell systems.
This paper describes a hybrid power-supply system
that combines a photovoitaic system with a fuel-cell
2.
system for use as an auxiliary gene.rator for long-term
SUPPLY SYSTEMS
backup. The hybrid system exhausts no harmful gases
such as NOx and SOx, and noise and vibration levels
are much lower than those of conventional systems
that combine a photovoltaic system with an engine
generator.
The
hybrid system
environmentally
is
friendly and requires little maintenance. We have
developed two grid-connected hybrid power-supply
systems
and
system.
The
stand-alone
former
hybrid
has
power-supply
been
introduced
experimentally into on-line computer systems for data
communications, and the latter has been introduced
into a repeater station for wireless communications.
GRID-CONNECTED
HYBRID
2.1 Configuration
The configurations of the two grid-connected hybrid
power-supply systems -are shown in Figs. 1 and 2.
Both systems use 5-kW photovoltaic modules, an
interactive inverter, 17 pieces of 38-Ah, 12-V valve
regulated
lead-acid
(VRLA)
Clean-energy
systems
telecommunications
battery
cell (PEFC) systems, and a power controller. The
system shown in Fig. 1 additionally uses two l-kW
uninterruptible power supplies (UPSs).
are
in
high
demand
and
for
data
powered system is connected to the UPSs on the
output side of the interactive inverter (Fig. 1). The
communications systems. Photovoltaic systems are
DC-powered
now widely used for telecommunications systems,
inverter on the. input side (Fig. 2).
such as for repeater stations and remotc tcrminal (RT)
optical
way the fuel-cell systems are connected. The AC
powering
in
batteries,
charger, two 1-kW portable polymer electrolyte fuel
The main difference between these two systems is the
1. INTRODUCTION
boxes
POWER
networks.
photovoltaic systems are
these
In
used
either
networks,
as
grid
connected or a stand-alone system. Both systems
require an auxiliary generator in case of a lengthy
power failure or a period without sunshine.
one
is
connected to the
interactive
We developed and commercialized the l-kW portable
fuel-cell system (2).
Its external appearance and
specifications are shown in Fig. 3 and Table 1. The
system takes about one minute to warm up, and it can
output 1 kW for three hours using two 10-1 hydrogen
gas cylinders. The gas cylinders can be replaced while
fuel-cell system is operating,
which enables
Conventionally, an engine generator is used as an
the
auxiliary generator for long-term backu p. However, an
significantly longer continuous operation. To apply the
engine generator has several disadvantages: it is noisy,
fuel cell system to the hybrid system, we added two
vibrates strongly, emits harmful gases such as NOx
new functions; the fud-cell system can be started and
and SOx, and requires high maintenance. To eliminate
stopped remotely by sending it a signal, and it can
these problems,
alternative
generators
have
been
output warning signals when problems occur.
studied. Fraunhofer Institute for Solar Energy Systems
ISE (Germany) developed a hybrid power-supply
The powe.r controller includes these functions:
system that combines a photovoltaic system with a
thermoelectric generator for use in a telecommuni
cations repeater station (1).
. control battery charge
We tried to apply a fuel-cell system as an auxiliary
generator for a
generates
photovoltaic system. 1be system
electric
power
by
an
electrochemical
reaction between hy drogen and oxygen; therefore, it
exhausts no harmful gases, and its noise and vibration
levels
are much
lower
compared
to
an
engine
generator. In this paper, we present two grid-connected
INTELEC 2001, 14-1 B October 2001
Conference Publication No. 484, lEE,
detect power failures
monitor battery voltage
start and stop the interactive inverter
start and stop the fuel-cell systems
'display trouble messages of the interactive inverter
and the fuel-cell syste m s
'control the fuel-cell system output power
(only for the hybrid system shown in Fig. 2)
632
Grid
5kW photovoltaic
modules
100VAC
lkW fuelcell
system (x2)
Figure 1: Configuration of grid-connected hybrid power-supply system using
AC-power fuel-cell systems.
Grid
5kW photovoltaic
modules
100VAC
38Ah,12V
batteries
(X17)
Fuel
cells
DC/DC
<
_____ _
Signal
lkW fuelcell
system (x 2)
I
I
I
I
I
I
--------
Datacommunications
equipment
Figure 2: Configuration of grid-connected hybrid powersupply system using
DC-power fuel-cell systems.
633
2.2 Operation
The configurations of the two hybrid grid connec ted
systems differ, but the following operations are the
same. An opetation program installed in the power
controller controls all operations automatically. When
the elect ri c power generated by the photovoltaic
system
exceeds
the
required
load
power,
the
pbotovoltaic system supplies the surplus power to the
power grid by reversing the power flow. On the other
hand, when .the load requires more power than the
photovoltaic system can generate, the grid power is
used to make up for the shortfall. These operations are
the same as in conventional photovoltaic systems.
When a power failure occurs, the photovoltaic system
stops for
Figure 3:
few seconds to avoid affecti ng the grid
External appearance of
portable PEFC system.
power. Then, the photovoltaic system changes to an
isolated operation mode; the power controller operates
the switches so batte ry power is supplied to important
loads for the data-communications equipment on ly
and the interactive inverter is disconnected from the
grid. If the power failure continues for a long time and
TABl E l-Specifications of portable PEEC system
Rated po wer (kVlJ)
Size (mmJ
550(W) x 500(0) x 1000 (H)
Volume (I)
275
Weight (kg)
With two 10-1
120 H. cylinders
battery voltage falls lower than the pre- determined
value, the power controller sends signals that operates
the fuel-cell systems. The fuel-cell systems begin to
warm up after they receive the signals; when they are
ready
to output power, they supply it to the important
loads.
After recovering from a power failure, the power
Noise (dB)
the switches to reconnect the
interactive inverter to the grid and sends signals that
Permissible operation
temperature range tel
Warm up time (min)
Operation time (hr)
controller operates
( Hz
at 1 kW, with two 10-1)
cylinders
40 (1
m from system)
0-40
stop the fuel-cell systems. When the fuel-cell systems
stop, the grid resumes supplying power to the loads,
and the battery charger starts charging the batteries
3.1 Conliguration
The advantage of the hybrid system shown in Fig. 1 is
hybrid power-supply system. This system addition al ly
with grid power.
Figure
shows the configurations of our stand-alone
that a power failure does not interrupt power supply to
uses a wind generator as a power generator. It is
stops running for a few seconds, because the UPSs
wind generator, a lO-kW DC interactive converter, a
the hybrid system shown in Fig. 2 interrupts the power
Ah, 2-V VRLA batteries, and a l-kW DC-power
system stops; however, the capacity of the line used to
DC interactive converter supplies -48-VDC power to
increasing the number of parallel connecting fuel-cell
supplies 100-VAC power to the ventilation fan, lights,
the important loads when the
photovoItaic system
supply power to the loads during this time. In contrast,
supply for a few
seconds when the photovoltaic
supply power to important loads can be enhanced by
systems.
These
systems
composed of 7.7-kW photovoltaic modules, a l-kW
l-kW converter, a 750-VA inverter, 23 pieces of 2000-
portable phosphoric acid fuel-cell (PAFC) system. The
the telecommunications equipment, and the inverter
and outlets. We set the number and capacity of the
two
grid-connected
were
introd ced
hybrid
into
power-supply
on-line
computer
systems for data communications in an experiment in
March 2000 and are now being field-tested.
VRLA batteries so they can supply power to the loads
over seven continuous days without sunshine or wind.
The external appearance of the photovoltaic modules
and the wind generator is shown in Fig. 5. The
photovoltaic modules are mounted onto a pole to
3. STAND-ALONE HYBRID POWER-SUPPLY
SYSTEM
reduce the installation area and to avoid being covered
with snow in winter. The temperature of this region
falls to around -30C in winter, so to prevent the low
634
7.7-kW
photovollaic
modules
8 VDC
-4
t-r-__
_.,._-,--_______---i
l-kWwind
generator
Telecommunications equipment
Ventilation
\--+--I
l-kWfuel
cell system
fan
Ughts
Outiets
Heater
Dehumidifier
Drain
pump
Figure 4: Configuration of stand-alone hybrid power-supply system.
temperatures
from
affecting
performances
of
the
converter, batteries, or fuel-celI system, these parts are
installed in the basement of the holding box (Fig. 5).
The installation of the converter and batteries
are
shown in Fig. 6. The lO-kW DC interactive converter
is composed of two 5-kW converter units. These units,
the l-kW converter unit for the wind generator, and
the 750-VA inverter unit are all mounted onto the
same rack.
Figure 7 shows the in!>1allation of the portable PAFC
system.
This
system
was
developed
before
the
development of portable PEFC systems and is not
being produced anymore. The PAFC system operates
for
three
hours
using
cylinders; in addition,
three
6.7-1
hydrogen
gas
replacing the hydrogen-gas
cylinders while the PAFC system is operating, like in
the PEFC system, enables much longer continuous
operation. The PAFC system takes about ten minutes
to warm up, which is significantly longer than the
PEFC system. However, we chose the PAFC system
because it performs better at low temperatures. To
apply it to the stand-alone hybrid system, we added
the same new functions as to the PEFC one.
Figure 5: External appearance of photovoltaic
modules and wind generator.
3.2 Operation
When the total output power of the photovoltaic and
wind generation is s ufficient to power the loads, it is
supplied to the loads, and surplus power is used to
charge the VRLA batteries. On the other hand, when
the total output power is insufficient to power the
loads during periods of no sunshine or wind, the
batteries back-up the required power of the load. If the
non-sunshine or non-wind period continues for
long
time and the VRLA-battery voltage falls to the pre-
determined
value,
the
DC
interactive
convc.rtc..r
automatically sends a warning signal to an off-site
maintenance person and an operation signal to the
fueJ-celI system. The fuel-ceIJ system begins to warm
up after it receives the signal, and when it is ready to
output power, it supplies power to charge the batteries.
Here, the state of the VRLA-battery voltage falling to
the pre-determined value corresponds to a continuous
non-sunshine or non-wind period over six days.
635
If the non-sunshine or non -wind condition continues
much longer and the batteries cannot supply power
any longer, we can use a portable e ngine generator and
a portable rectifier to manually supply power to the
loads and to charge the batteries (Fi g.
4). The
portable
engine generator also powers a heater, a dehumidifier,
and a drain pump to create comfortable working
conditions for the maintenance person.
This stand-alone hybrid power-supply system was
introduced
into
repeater
station
for
wireless
communications in December 1998. Since then, the
system
operated
automatically
for
long t ime
providing backup power, demonstrating that the hybrid
system works well.
Figure 6; Installation of converter, inverter,
and batteries.
4. CONCLUSION
We have developed two grid-connected hybrid power
supply systems and a stand-alone hybrid power-supply
system tbat combine a pbotovoltaic with a fuel-cell
system for use as auxiliary generators for long-term
backup.
They are controlled automatically by
operation program. They are
en
an
vironmentally f ri end ly
and require little maintenance, and we expect it to be
in demand for application in telecommuni-cations and
for general use .
REFERENCES
1. A. Steinhuser, W. Schultz, H. Schmidt,
"Pbotovoltaic Power Supply for Telecommunication
Network Computers in Remote Areas", TELESCON
2000, 221-225.
2. N. Kato , T. Murao, K. Fujii, T. Aoki, S. Muroyama,
"l-kW Portable Fuel Cell Syste m Based on PEFCs"
TELESCON 2000, 209-213.
Figure 7: Installation of portable
PAFC system.
