Field of the Invention
The present invention relates to a DC power
distribution system.
Background of the Invention
Conventionally, there is known a DC power distribution
system which distributes a DC power to a DC load by
associating an AC/DC converter converting AC power supplied
from a power system into DC power with a distributed power
source such as a solar cell and fuel cell. Generally, the
DC power distribution system includes a storage battery as
an emergency power source to supply the DC power to the DC
load in an emergency such as a power failure at night.
Further, at ordinary times, the storage battery is charged
by the DC power supplied from the AC/DC converter or the
distributed power source such as a solar cell and fuel cell,
and the storage battery is discharged in an emergency to
supply the DC power to the DC load.
In the DC distribution system disclosed in Patent
Document 1, for example, if a power failure has not occurred
in the power system and the remaining capacity of the
storage battery is greater than a predetermined percentage
(e.g., 20%) of the full charge capacity, the storage
battery is discharged. Then, the storage battery is charged

when the remaining capacity of the storage battery has
dropped to the predetermined percentage.
That is, at ordinary times, the DC power stored in the
storage battery is supplied to the DC load as long as the
remaining capacity of the storage battery is not less than
the remaining capacity required in the power failure. In
this case, the storage battery is always maintained in a
state where the power capacity of the predetermined
percentage is stored as the DC power required in an
emergency such as a power failure. Thus, in case of
emergency, the required DC power can be supplied to the DC
load.
[Patent Document 1] Japanese Patent Application
Publication No. 2009-159730
Meanwhile, in the conventional DC distribution system,
the charging and discharging of the storage battery are
controlled such that the remaining capacity does not fall
below the predetermined percentage, but it is concerned that
it may be impossible to ensure the power required in the
power failure. Since a terminal voltage of the storage
battery is proportionate to the remaining capacity (charged
state) of the storage battery, the remaining capacity of the
storage battery can be estimated based on the terminal
voltage of the storage battery. For example, if the
terminal voltage of the storage battery is changed from 30 V
when fully charged to 15 V which is half of that when fully

charged, the remaining capacity of the storage battery is
estimated to be 50%.
However, the storage battery deteriorates with time
due to a temperature change in the installation environment,
repetitive charging and discharging or the like. Further,
the total capacity of the storage battery, i.e., the amount
of power when fully charged changes due to the aging of the
storage battery. For example, if the amount of power when
fully charged is 100 Wh when the storage battery is a new
product, the amount of power when fully charged is 80 Wh
when the storage battery has degraded.
Further, in the system of Patent Document 1, if the
amount of power corresponding to 20% of the capacity (100%)
when fully charged is reserved for the emergency, the amount
of power reserved for the emergency is 20 Wh in the new
product and 16 Wh in the degraded product. In this case,
the terminal voltage when fully charged will be the same
value regardless of changes in the total capacity of the
storage battery. As in the above-mentioned example, if the
terminal voltage of the new product when fully charged is 30
V, the terminal voltage of the degraded product when fully
charged is also 30 V.
Accordingly, although the charged state (%) of the
storage battery required based on the terminal voltage of
the storage battery is the same, the amount of power
actually stored in the storage battery is different between

the new product and the degraded product. Thus, even if the
system determines that the constant remaining capacity has
been ensured, it is concerned that the actual remaining
capacity may be less than a predetermined percentage of the
total capacity of the new storage battery. In this case,
the power required during the power failure may not be
provided sufficiently.
Summary of the Invention
In view of the above, the present invention provides a
DC power distribution system capable of more reliably
ensuring the power required in the power failure.
In accordance with an aspect of the present invention,
there is provided a DC power distribution system including:
a storage device, wherein the storage device includes a
first storage battery which is discharged to supply a power
to an electric device only in a power failure, and a second
storage battery which is discharged to supply a power to the
electric device in a normal mode. The storage device and
the electric device are supplied with a DC power from a
power generation device which generates power using natural
energy and a DC power which has been converted from an AC
power supplied from a commercial power source, and the first
storage battery is discharged to supply a power to the
electric device when the power supply from the power

generation device and the commercial power source is
interrupted.
With the present invention, the power of the first
storage battery is not used when it is not in the power
failure. That is, the power stored in the first storage
battery is reserved for the power failure and supplied to
the DC devices during the power failure and the like. As
described earlier, the power stored in the single storage
battery is used for the power failure as well as normal
times in the conventional example. In this case, it may be
impossible to sufficiently ensure the power for the power
failure due to the degradation of the storage battery and
the like.
In this regard, with the present invention, by
separately providing the first storage battery for exclusive
use, which is discharged only in the power failure of the
commercial power source and the second storage battery for
normal use, which is discharged when it is not in the power
failure, e.g., at night, the power required in the power
failure is reliably ensured by the first storage battery for
exclusive use. Further, during the non-power failure or
when the power generation device cannot perform power
generation, it is possible to use the power stored in the
second storage battery. Thus, it is convenient to use.
The DC power distribution system may further include a
controller for controlling charging and discharging of the

first and second storage batteries, wherein the controller
may switch roles of the first and second storage batteries
at a predetermined timing.
If the first and second storage batteries are
independently used for the power failure and when it is not
in the power failure, respectively, the number of times of
charging and discharging of the second storage battery when
not in the power failure is significantly larger than that
of the first storage battery which is discharged only in the
power failure. Accordingly, the second storage battery is
easier to deteriorate than the first storage battery.
In this regard, according to the present invention, by
switching the roles of the first and second storage
batteries at a predetermined timing, it is possible to
equalize the number of times of charging and discharging of
the first and second storage batteries. Thus, it is
possible to equalize the lives of the first and second
storage batteries. Further, the control unit controls the
storage battery for the ordinary times to discharge and the
storage battery for the power failure not to discharge at
normal times. That is, the control unit discharges the
storage battery for the power failure only in an emergency
such as a power failure.
In the DC power distribution system, at least one of
the first and second storage batteries may be accommodated
under a floor of a building.

It is usually low in temperature under the floor of
the building, which is stably maintained. And the self-
discharge amount of the storage battery depends on the
temperature and increases as the temperature increases. For
that reason, it is preferable to install the storage battery
under the floor of the building. With the present invention,
the temperature rise of the storage battery is suppressed,
thereby achieving the long life of the storage battery.
Further, the DC power distribution system may include
a setting unit which sets roles of the first and second
storage batteries to a role for the power failure or a role
for the normal mode through manual operation.
With the present invention, the roles of the first and
second storage batteries can be set to either of the role
for the power failure and the role for the ordinary times
through the operation of the setting unit. Thus, it is
convenient to use.
Preferably, each of the first and second storage
batteries is provided as a battery set including a plurality
of single batteries, and wherein the setting unit sets
respective roles of the single batteries included in the
first and second storage batteries to a role for the power
failure or a role for the . normal mode through manual
operation.
With the present invention, the power capacity
allocated for the power failure and the power capacity

allocated for the ordinary times can be delicately adjusted
through the operation of the setting unit. For example, the
power capacity allocated for the power failure can be
appropriately changed depending on the power failure
protection time desired by the user. In this case, it is
possible to ensure the proper backup capacity to the user's
environment.
Further, it is preferred that the power generation
device is a solar cell which generates power using sun light
as the natural energy.
Effects of the Invention
With the present invention, since the storage battery
for discharging only in the power failure and the storage
battery for discharging at the ordinary times, are
separately provided, the backup power required in the power
failure can be more reliably ensured.
Brief Description of the Drawings
The objects and features of the present invention will
become apparent from the following description of
embodiments, given in conjunction with the accompanying
drawings, in which:
FIG. 1 is a block diagram schematically showing a DC

power distribution system;
FIG. 2 is a block diagram showing a configuration of a
control unit in accordance with first and second embodiments
of the present invention;
FIGs. 3A and 3B are graphs which illustrate voltage
variations of storage batteries for the power failure and
the ordinary times in the system in accordance with the
second embodiment of the present invention;
FIGs. 4A and 4B are a perspective view and a cross-
sectional view showing an installation state of the storage
battery for the power failure in accordance with a third
embodiment of the present invention, respectively;
FIG. 5 is a block diagram illustrating a configuration
of the control unit in accordance with a fourth embodiment
of the present invention;
FIGs. 6A to 6C are a front view of a setting switch in
the initial state, a circuit diagram showing (series)
connection of the storage batteries in the initial state,
and a circuit diagram showing (parallel) connection of the
storage batteries in the initial state, respectively;
FIGs. 7A to 7C are a front view of the setting switch,
a circuit diagram showing (series) connection of the storage
batteries, and a circuit diagram showing (parallel)
connection of the storage batteries, respectively; and
FIGs. 8A to 8C are a front view of the setting switch,
a circuit diagram showing (series) connection of the storage

batteries, and a circuit diagram showing (parallel)
connection of the storage batteries, respectively.
Detailed Description of the Embodiments
Hereinafter, embodiments of the present invention will
be described in detail with reference to the accompanying
drawings which form a part hereof. Throughout the
specification and drawings, like reference numerals will be
given to like parts having substantially the same function
and configuration, and a redundant description thereof will
be omitted.

A power distribution system of a house in accordance
with a first embodiment of the present invention will be
described with reference to FIGS. 1 to 3. First, an
overview of the system will be given.

As shown in FIG. 1, the house is provided with a power
supply system 1 to supply power to various devices
(illumination device, air conditioner, home appliance, audio
and visual device, etc.) installed in the home. The power
supply system 1 supplies power to various devices not only
from a home commercial power source (AC power source) 2 such
that the various devices operate, but also from solar cells
3 producing electricity from sun light. The power supply

system 1 supplies power to an AC device 6 being operated by
an alternating current power source (AC power source) as
well as DC devices 5 being operated by a direct current
power source (DC power source).
The power supply system 1 includes a controller 7 and
a DC panel board (having a DC breaker therein) 8 as a
distribution board of the system. Further, the power supply
system 1 includes a control unit 9 and a relay unit 10 to
control the operation of the DC devices 5 in the house.
Connected to the controller 7 is an AC panel board 11
via an AC power line 12 in which an AC power branches. The
controller 7 is connected to the commercial power source 2
via the AC panel board 11 and also connected to the solar
cell 3 via a DC power line 13. The controller 7 receives an
AC power from the AC panel board 11 and a DC power from the
solar cell 3, and converts these power into a specific DC
power to be supplied to the devices.
Further, the controller 7 outputs the converted DC
power to the DC panel board 8 via a DC power line 14, or
outputs the converted DC power to a storage battery 16 via a
DC power line 15 to store the power. The controller 7 not
only receives the AC power from the AC panel board 11, but
also converts the power of the solar cell 3 or the storage
battery 16 into an AC power to be supplied to the AC panel
board 11. The controller 7 exchanges data with the DC panel
board 8 via a signal line 17.

The DC panel board 8 is a kind of breaker for DC power.
The DC panel board 8 distributes the DC power inputted from
the controller 7, and outputs the distributed DC power to
the control unit 9 via a DC power line 18, or outputs the
distributed DC power to the relay unit 10 via a DC power
line 19. Further, the DC panel board 8 exchanges data with
the control unit 9 via a signal line 20, or exchanges data
with the relay unit 10 via a signal line 21.
The control unit 9 is connected to a plurality of the
DC devices 5. The DC devices 5 are connected to the control
unit 9 via DC supply lines 22, each capable of carrying both
DC power and data through a pair of wires. Each of the DC
supply lines 22 transports both power and data to each of
the DC devices 5 via a pair of wires by so-called power line
carrier communications in which a communications signal
transferring data using high-frequency carrier is
superimposed on a DC voltage for operating the DC device.
The control unit 9 obtains the DC power for the DC
devices 5 via the DC power line 18, and understands how to
control which of the DC devices 5 based on an operation
command obtained from the DC panel board 8 via the signal
line 20. Then, the control unit 9 outputs the DC voltage
and the operation command to the instructed DC device 5 via
the DC supply lines 22 to control the operation of the DC
device 5.
The control unit 9 is connected via the DC supply line

22 to switches 23 used when switching the operations of the
DC devices 5 in the house. In addition, the control unit 9
is connected via the DC supply line 22 to a sensor 24 for
detecting a radio wave originating from, e.g., an infrared
remote controller. Thus, the DC devices 5 are controlled by
the communications signal inputted through the DC supply
lines 22 by the operation of the switches 23 or the
detection of the sensor 24 in addition to the operation
instructions from the DC panel board 8.
Connected to the relay unit 10 is a plurality of the
DC devices 5 via individual DC power lines 25. The relay
unit 10 obtains the DC power for the DC devices 5 via the DC
power line 19, and understands which of the DC devices 5
will be operated based on an operation command obtained from
the DC panel board 8 via the signal line 21. Then, the
relay unit 10 turns on or off the power supply to the
instructed DC devices 5 via the DC power lines 25 by an
internal relay to control the operation of the DC devices 5.
Further, the relay unit 10 is connected to a plurality of
switches 26 for manually operating the DC devices 5. By
turning on and off the power supply through the DC power
lines 25 by relay using the switches 26, the DC devices 5
are controlled.
The DC panel board 8 is connected via a DC power line
28 to a DC outlet 27 installed in the house in the form of,
e.g., a wall outlet or floor outlet. If a plug (not shown)

of the DC device is inserted into the DC outlet 27, DC power
can be directly supplied to the device.
Further, a power meter 29 is provided between the
commercial power source 2 and the AC panel board 11 and the
usage of the commercial power source 2 is remotely read from
the power meter 29. The power meter 2 9 has, e.g., a power
line carrier communications or wireless communications
function in addition to the function of remotely reading the
usage of the commercial power source. The power meter 29
transmits the reading results to a power company or the like
through the power line carrier communications or wireless
communications.
The power supply system 1 is provided with a network
system 30 to allow various devices in the house to be
controlled through the network communications. The network
system 30 includes a home server 31 serving as a controller
of the network system 30. The home server 31 is connected
to a management server 32 on the outside of the house
through a network N such as the Internet, and also connected
to a household device 34 via a signal line 33. Further, the
home server 31 is operated by the DC power obtained from the
DC panel board 8 via a DC power line 35.
The home server 31 is connected to a control box 36
via a signal line 37, the control box 36 managing the
operation control of various devices in the house through
the network communications. The control box 36 is connected

to the controller 7 and the DC panel board 8 via the signal
line 17, and also directly controls the DC device 5 via a DC
supply line 38. The control box 36 is connected to, e.g., a
gas/water meter 39 which allows remotely reading of the
amount of gas or water used, and an operation panel 40 of
the network system 30. The operation panel 40 is connected
to a monitoring device 41 including, e.g., a slave device of
an intercommunications system, sensor or camera.
If operation commands of various devices in the house
are inputted through the network N, the home server 31
notifies instructions to the control box 36, and operates
the control box 36 such that various devices are operated in
accordance with the operation commands. Further, the home
server 31 provides various pieces of information obtained
from the gas/water meter 39 to the management server 32
through the network N. Furthermore, when an error detected
by the monitoring device 41 is received from the operation
panel 40, the home server 31 provides the received
information to the management server 32 through the network
N.

Next, the storage battery 16 will be described. In
this embodiment, as shown in FIG. 2, the storage battery 16
includes a first storage battery 51 and a second storage
battery 52. The first and second storage batteries 51 and
52 are connected to the controller 7 via DC power lines 15a

and 15b constituting the DC power line 15. The first
storage battery 51 is set as a backup storage battery whose
power is used only when the power supply from the commercial
power source 2 and the solar cell 3 is interrupted. The
second storage battery 52 is set as a storage battery for
night use, whose power is used at night.
Further, the power capacity of the first storage
battery 51 is set to sufficiently supply the power required
when the power supply from the commercial power source 2 and
the solar cell 3 is interrupted. Here, interrupting the
power supply from the commercial power source 2 and the
solar cell 3 corresponds to a case where the power supply of
the commercial power source 2 is interrupted at night when
the solar cell 3 cannot perform power generation, for
example. Hereinafter, for convenience of explanation, this
case is simply referred to as "power failure."
Further, although the first and second storage
batteries 51 and 52 are provided outside the controller 7 in
this embodiment, these may be provided inside the controller
7. Alternatively, only the first storage battery 51 for
backup may be provided inside the controller 7. This is due
to the following reason. In other words, unlike a normal
mode in which the operating power can be supplied to all of
the DC devices 5, it is assumed that in a power failure mode,
the operating power can be supplied to only a minimum
required portion of the DC devices 5 in many cases.

In this case, the power capacity of the first storage
battery 51 for backup may be set to supply the operating
power to only the minimum required portion of the DC devices
5 whose operation should be ensured during the power failure.
In contrast, it is assumed that the second storage battery
52 being used in the normal mode (ordinary times) is
required to supply the operating power to all of the DC
devices 5. Considering a difference in the power capacity
needed, the size of the second storage battery 52 is likely
to be larger than the size of the first storage battery 51.
Accordingly, it is preferable that the first storage battery
51 having a smaller size is provided inside the controller 7
and the second storage battery 52 having a larger size is
provided outside the controller 7 .

Next, a configuration of the control unit will be
described in detail. As shown in FIG. 2, the controller 7
includes a bi-directional AC/DC converter 61, a DC/DC
converter 62 for the solar cell, a first charge/discharging
circuit 63 corresponding to the first storage battery 51, a
second charge/discharging circuit 64 corresponding to the
second storage battery 52, and a control circuit 65.
The AC/DC converter 61 is connected to the AC panel
board 11 via the AC power line 12, and also connected to a
connection terminal P1 for the DC panel board 8 via a DC
power line L1, the connection terminal P1 being provided in

the controller 7 . The connection terminal P1 is connected
to the DC panel board 8 via the DC power line 14. The AC
power line 12 connecting between the AC/DC converter 61 and
the AC panel board 11 is provided with a voltage sensor 66
for detecting AC power (i.e., voltage) supplied from the AC
panel board 11.
The DC/DC converter 62 is provided in a DC power line
L2 connecting between a connection terminal P2 for the solar
cell 3 and the connection terminal P1 for the DC panel board
8, the connection terminal P2 being provided in the
controller 7. The DC power line 13 connecting between the
controller 7 and the solar cell 3 is provided with a voltage
sensor (not shown) for detecting DC power (i.e., voltage)
supplied from the solar cell 3.
The first charge/discharging circuit 63 is provided in
a DC power line L3 connecting between a connection terminal
P3 for the first storage battery 51 and the connection
terminal P1 for the DC panel board 8, the connection
terminal P3 being provided in the controller 7. Between the
first storage battery 51 (precisely, the connection terminal
P3) and the first charge/discharging circuit 63, the DC
power line L3 is provided with a first voltage sensor 67 for
detecting a voltage (terminal voltage) of the first storage
battery 51.
The second charge/discharging circuit 64 is provided
in a DC power line L4 connecting between a connection

terminal P4 for the second storage battery 52 and the
connection terminal P1 for the DC panel board 8, the
connection terminal P4 being provided in the controller 7.
Between the second storage battery 52 (precisely, the
connection terminal P4) and the second charge/discharging
circuit 64, the DC power line L4 is provided with a second
voltage sensor 68 for detecting a voltage (terminal voltage)
of the second storage battery 52.
In addition, the first and second charge/discharging
circuits 63 and 64 may be internally provided in the first
and second storage batteries 51 and 52.
The AC/DC converter 61 has a function of converting an
AC power into a DC power and a function of converting a DC
power into an AC power. That is, the AC/DC converter 61
coverts the AC power supplied from the AC panel board 11
into a DC power, and supplies the converted DC power to the
DC panel board 8 or the first and second storage batteries
51 and 52. Further, the AC/DC converter 61 may convert the
DC power supplied from the solar cell 3 and the first and
second storage batteries 51 and 52 into an AC power, and may
supply the converted AC power to the AC panel board 11. The
AC/DC converter 61 switches both of the aforementioned
functions based on the switching instructions from the
control circuit 65.
The DC/DC converter 62 for the solar cell converts the
DC power produced by the solar cell 3 into a predetermined

DC power, and supplies the converted DC power to the DC
panel board 8 or the storage battery 16.
The first charge/discharging circuit 63 includes a
DC/DC converter and the like, and controls the charging and
discharging of the first storage battery 51 based on the
instructions from the control circuit 65.
The second charge/discharging circuit 64 includes a
DC/DC converter and the like, and controls the charging and
discharging of the second storage battery 52 based on the
instructions from the control circuit 65.
The control circuit 65 controls such that the function
(operation mode) of the AC/DC converter 61 is switched
between the function of converting an AC power into a DC
power and the function of converting a DC power into an AC
power. Also, the control circuit 65 controls charging and
discharging operations of the first and second storage
batteries 51 and 52 through the first and second
charge/discharging circuits 63 and 64.
Further, the control circuit 65 detects the remaining
capacity (charging state) of the first and second storage
batteries 51 and 52 based on the detection results of the
first and second voltage sensors 67 and 68 using the fact
that the remaining capacities of the first and second
storage batteries 51 and 52 are proportionate to the
terminal voltages of the first and second storage batteries
51 and 52. For example, the control circuit 65 determines

that the remaining capacities of the first and second
storage batteries 51 and 52 decrease when the voltage of the
first and second storage batteries 51 and 52 is reduced.
Specifically, assuming that the terminal voltage and
the capacity of each of the first and second storage
batteries 51 and 52 are 30 V and 100 % when being fully
charged, the control circuit 65 estimates that the remaining
capacity of each of the first and second storage batteries
51 and 52 is 50% when the terminal voltage thereof is 15 V,
which is half of that when fully charged. Based on the
estimated remaining capacities (charging state) of the first
and second storage batteries 51 and 52, the control circuit
65 can control the charging and discharging of the first and
second storage batteries 51 and 52.
Further, the control circuit 65 includes, e.g., a
clock IC or illuminance sensor (not shown) and acquires,
e.g., the time or illuminance outside the house by using the
clock IC or the illuminance sensor. If it is determined
that the amount of power generated in the solar cell 3 is
insufficient, e.g., at night, the control circuit 65
controls the second storage battery 52 to discharge through
the second charge/discharging circuit 64. The DC power
stored in the second storage battery 52 is supplied to each
of the DC devices 5 through the DC panel board 8. Further,
if it is determined that the amount of power generated in
the solar cell 3 is sufficient, e.g., in the daytime, the

control circuit 65 controls the second storage battery 52 to
charge through the second charge/discharging circuit 64.
Further, the control circuit 65 determines whether or
not a power is supplied from the commercial power source 2,
based on the detection results of the voltage sensor 66 if
the solar cell 3 cannot perform power generation. If it is
determined that the power supply from the commercial power
source 2 is interrupted, the control circuit 65 controls the
first storage battery 51 to perform a discharging operation
through the first charge/discharging circuit 63. The DC
power stored in the first storage battery 51 is supplied to
each of the DC devices 5 through the DC panel board 8.
The control circuit 65 charges the first storage
battery 51 through the first charge/discharging circuit 63
in the normal mode, not in the power failure mode. The
control circuit 65 supplies, to the first storage battery 51,
the DC power generated by the solar cell 3, e.g., in the
daytime, and the DC power supplied through the AC/DC
converter 61, e.g., at night. In this way, the control
circuit 65 controls the charging operation of the first
storage battery 51 such that the charging state (charging
level) of the first storage battery 51 is maintained to
supply the power required in the power failure to the DC
panel board 8.

Next, the operation of the power supply system

configured as described above will be described.

First, in the daytime, the DC power generated by the
solar cell 3 is basically supplied to each of the DC devices
5 through the DC panel board 8. Herein, a surplus power is
supplied to the first and second storage batteries 51 and 52.
If the DC power generated by the solar cell 3 is
insufficient to meet the power required in the DC devices 5,
the power stored in the second storage battery 52 is used.
Further, the DC power generated by the solar cell 3
and the DC power of the second storage battery 52 can also
be supplied to the AC device 6. Since the first storage
battery 51 is set as a backup storage battery to be used in
the power failure, the power of the first storage battery 51
is not used for any purpose other than a backup purpose.

Since the solar cell 3 cannot generate power at night,
basically, the DC power stored in the second storage battery
52 is supplied to each of the DC devices 5. In the daytime
or the like, the same is true if the sunshine condition is
insufficient.

In a situation where the power generation of the solar
cell 3 is impossible, the DC power stored in the first
storage battery 51 for backup is basically supplied to each
of the DC devices 5 when the power supply of the commercial

power source 2 is interrupted, e.g., at night. Accordingly,
even in the power failure, for example, the required DC
devices 5 can be continuously used. The power stored in the
first storage battery 51 is never used in the normal mode
(when it is not in the power failure) , and the charging
state of the first storage battery 51 is always maintained
to meet the power capacity required by the DC devices 5 in
the power failure. Thus, the power required in the power
failure can be surely supplied to the DC devices 5 by the
first storage battery 51 for backup.
Further, in the power failure, the power stored in the
second storage battery 52 as well as the first storage
battery 51 may be supplied to each of the DC devices 5.
That is, the control circuit 65 controls the second storage
battery 52 set to be used in the normal mode to discharge
not only at the ordinary times but also in the power failure.
Accordingly, it is possible to more reliably ensure the
backup power source in the power failure. Further, it is
also possible to increase the backup time during which the
power can be supplied to the required DC devices 5, for
example.

With the embodiment of the present invention, the
following effects can be obtained.
(1) The first and second storage batteries 51 and 52
have been prepared. Further, the first storage battery 51

serves as a power source for backup, which performs
discharging only in the power failure, and the second
storage battery 52 serves as a power source for the non-
power failure (normal mode) , which performs discharging at
night or the like when it is difficult for the solar cell 3
to perform power generation. With this configuration, the
power required in the power failure is stored independently
by using the first storage battery 51. Further, the power
stored in the first storage battery 51 is not used in the
normal mode. Thus, it is possible to more reliably ensure
the power required in the power failure.
(2) Further, since the storage battery for use in the
normal mode and the storage battery for use in the power
failure are separately provided, it is possible to control
the charging and discharging operation of each storage
battery. Accordingly, in particular, it is possible to
extend the life of the first storage battery 51 for backup.
That is, since the first storage battery 51 is discharged
only in the power failure, the charging and discharging are
not frequently repeated unlike a conventional case where the
power required for the power failure and the normal mode is
provided by a single storage battery as described earlier.
Therefore, it is possible to suppress the degradation of the
first storage battery 51, and to ensure the reliable power
supply of the backup power source in the power failure.
(3) Further, for example, as compared to the

conventional case where the power stored in a single storage
battery is shared for the power failure and for the normal
mode failure as disclosed above, it is unnecessary to
strictly control the remaining capacity of the storage
battery. Therefore, it is possible to promote
simplification of the charging and discharging control of
the storage battery using the control circuit 65.
In the conventional system described earlier, when the
power is supplied to the load from the storage battery, it
is necessary to control the discharging of the storage
battery in a range not less than the remaining capacity
required in the power failure of the power system. This is
why the power required in the power failure should be
ensured. However, in this case, since it is necessary to
monitor the remaining capacity of the storage battery, the
control associated with the charging and discharging of the
storage battery may be complicated. According to the system
of this embodiment, since the charging and discharging of
the first and second storage batteries 51 and 52 are
individually controlled, such a problem does not arise.
(4) With the system of this embodiment, at night when
the power generation of the solar cell 3 is impossible, the
power generated in the daytime (power stored in the second
storage battery 52) can be used. Further, the power
required during che power failure can be appropriately
supplied by the first storage battery 51 provided separately

from the second storage battery 52. Thus, it is convenient
to use.

Next, a second embodiment of the present invention
will be described. The power supply system of this
embodiment basically includes the same configuration as
shown in FIGS. 1 and 2. Thus, the same components as those
of the first embodiment are denoted by the same reference
numerals, and a detailed description thereof will be omitted.
The power supply system 1 of this embodiment is
different from the first embodiment in that the roles of the
first and second storage batteries 51 and 52 can be switched
at a predetermined timing. As shown in graphs of FIGs. 3A
and 3B, initially, if the first storage battery 51 is set
for the power failure and the second storage battery 52 is
set for the normal mode, the first storage battery 51 is
maintained in a charged state of a predetermined level (e.g.,
fully charged state) in the daytime. Further, the second
storage battery 52 for the normal mode is charged by the
power generated by the solar cell 3 (time t0).
At night, when it is detected that the second storage
battery 52 is sufficiently charged (time tl) , the control
circuit 65 assigns the second storage battery 52 as a power
source for the power failure and assigns the first storage
battery 51 as a power source for the normal mode. The
control circuit 65 controls the first storage battery 51 set

for the normal mode to discharge at night. Accordingly, as
shown in FIG. 3A, the voltage of the first storage battery
51 is reduced gradually due to the discharge. Further, the
second storage battery 52 set for the power failure is not
discharged, and the voltage of the second storage battery 52
is maintained.
When the daytime comes again, as shown in FIG. 3A, the
control circuit 65 performs the charging of the first
storage battery 51 set for the normal mode (time t2) .
Accordingly, the voltage of the first storage battery 51
increases gradually. At this time, as shown in FIG. 3B, the
control circuit 65 performs neither charging nor discharging
of the second storage battery 52 set for the power failure.
Thus, the voltage of the second storage battery 52 is
maintained in a fully charged state.
Then, as shown in FIG. 3A, when the night comes, and
it is detected that the first storage battery 51 is
sufficiently charged (time t3) , the control circuit 65
switches the roles of the first and second storage batteries
51 and 52 again. That is, the control circuit 65 assigns
the first storage battery 51 as a power source for the power
failure and assigns the second storage battery 52 as a power
source for the normal mode. And the control circuit 65
discharges the second storage battery 52 set for the normal
mode. As shown in FIG. 3B, the voltage of the second
storage battery 52 is reduced gradually due to the

discharging.
In the meantime, as shown in FIG. 3A, if it is
detected that the power supply of the commercial power
source 2 is interrupted (time t4) , the control circuit 65
starts the discharging of the first storage battery 51 set
for the power failure. Since the first storage battery 51
has been sufficiently charged, the power required can be
supplied sufficiently. As the first storage battery 51 is
discharged, the voltage of the first storage battery 51 is
reduced gradually. Further, as shown in FIG. 3B, the
control circuit 65 controls the second storage battery 52
set for the normal mode to continuously discharge even
during the power failure.
Further, when the daytime comes (time t5), the control
circuit 65 performs the charging of both the first and
second storage batteries 51 and 52. After that, when it is
detected that the first and second storage batteries 51 and
52 is sufficiently charged, in the same manner as described
above, the roles of the first and second storage batteries
51 and 52 can be switched between the role for the power
failure and the role for the normal mode.
Further, regardless of whether it is in the daytime or
at night, the roles of the first and second storage
batteries 51 and 52 may be switched between the role for the
power failure and the role for the normal mode based on
detecting that the storage battery set for the normal mode

has been sufficiently charged. Switching the roles of the
first and second storage batteries 51 and 52 is performed
through the control of the first and second
charge/discharging circuits 63 and 64 using the control
circuit 65.
Further, instead of switching the roles of the first
and second storage batteries 51 and 52 whenever any one of
the first and second storage batteries 51 and 52 is
discharged, the roles may be switched between the role for
the power failure and the role for the normal mode at a
predetermined timing. The switch timing may be regular or
irregular. In either case, it is preferable to switch the
roles in a state where the storage battery set for the power
failure is sufficiently charged.
According to the present embodiment, the following
effects can be obtained.
(1) By switching the roles of the first and second
storage batteries 51 and 52 at a predetermined timing, it is
possible to equalize the number of times of charging and
discharging of the first and second storage batteries 51 and
52 and the lives of the batteries.
(2) The voltages of the first and second storage
batteries 51 and 52 are monitored, and it is determined
whether the storage battery for the normal mode is
sufficiently charged. If it is determined that the storage
battery for the normal mode is sufficiently charged, the

roles are switched between the role for the power failure
and the role for the normal mode. Since the storage battery
is sufficiently charged and, after that, is switched to the
role for the power failure, it is possible to more reliably
ensure the power required in the power failure.
(3) When the power failure occurs at night, not only
the storage battery set for the power failure is discharged,
but also the storage battery set for the normal mode
continues to be discharged. Accordingly, it is possible to
more reliably ensure the power required in the power failure.
Further, even in case of using only the storage battery set
for the power failure, it is possible to sufficiently
provide the power required by the DC devices during the
power failure.

Next, a third embodiment of the present invention will
be described. The power supply system of this embodiment
also basically has the same configuration as shown in FIGs.
1 and 2.
As shown in FIG. 4A and 4B, the second storage battery
52 is placed under the floor in the house. A configuration
under the floor is as follows. That is, as shown in FIG. 4B,
a floor 71 of the house includes an opening 72 and a step
portion 73 formed at an inner periphery of the opening 72.
In the opening 72, a storage box 74 is inserted from the top.
The storage box 74 is formed to have an opening at the top,

and a brim-shaped flange 75 is formed at a peripheral
portion of the opening. The flange 75 is engaged with the
step portion 73 of the opening 72 to restrict the downward
displacement of the storage box 74. That is, the
positioning of the storage box 74 in a vertical direction is
made. Further, the storage box 74 is formed of an
incombustible material or fire retardant material. In
addition, the storage box 74 has a water resistance.
The second storage battery 52 is accommodated in the
storage box 74 installed under the floor. An outer surface
of the second storage battery 52 is spaced from an inner
surface of the storage box 74. That is, an air layer is
formed between the outer surface of the second storage
battery 52 and the inner surface of the storage box 74. The
opening at the top of the storage box 74 accommodating the
second storage battery 52 is closed by a lid 76 having an
outer shape corresponding to an inner shape of the opening
72 of the floor 71. An upper surface of the lid 76 attached
to the opening 72 and an upper surface of the floor 71 form
one surface without a step.
Therefore, according to the present embodiment, the
following effects can be obtained.
(1) The second storage battery 52 is installed under
the floor. Since a low temperature and stable environment
is formed under the floor, it is possible to extend the life
of the second storage battery 52. This is because the

degradation of the storage battery is promoted and the life
of the storage battery is shortened as an ambient
temperature of the storage battery is higher. In addition,
it is possible to effectively utilize the space under the
floor.
(2) The second storage battery 52 is accommodated in
the storage box 74 provided under the floor. Thus, unlike a
case where the second storage battery 52 is directly
installed under the floor, it is possible to suppress the
occurrence of poor insulation between the terminals of the
second storage battery 52 or between the second storage
battery 52 and the ground due to moisture, dew condensation
or the like. In addition, it is possible to suppress the
submergence in a flood or the like. In case of flooding
under the floor, it is possible to sufficiently protect the
second storage battery 52 from the submergence by the
configuration shown in FIG. 4B.
(3) The storage box 74 accommodating the second
storage battery 52 is formed of an incombustible material or
fire retardant material. Since the second storage battery
52 may generate heat for some reasons, it is preferable to
accommodate the storage battery in the storage box 74 formed
of an incombustible material or fire retardant material.
(4) The second storage battery 52 for the normal mode
is accommodated under the floor. That is, it is preferable
that the second storage battery 52 whose size is likely to

be larger than that of the first storage battery 51 for the
power failure is installed under the floor where it is easy
to ensure a space.
In addition, the third embodiment may be modified as
follows.
If there is no problem with waterproofing, the
storage box 74 may be omitted, and the second storage
battery 52 may be installed directly under the floor.
A heat dissipation structure may be provided in the
storage box 74 or the storage battery accommodated in the
storage box 74. For example, the storage box 74 is formed
of a metal material having thermal conductivity, and an
outer surface of the storage battery is brought into contact
with an inner wall of the storage box 74. By doing so, if
the storage battery generates heat, the heat is transferred
to the storage box 74 to be dissipated to the outside (in
the atmosphere under the floor).
In this case, wings for heat dissipation or the like
may be formed in the storage box 74. Since a surface area
of the storage box 74 is ensured, a heat dissipation effect
is increased. Thus, by increasing the cooling efficiency of
the second storage battery 52, it is possible to extend the
life of the storage battery.
• A sealing device such as packing may be provided
between the flange 75 of the storage box 74 and the lid 76.
Accordingly, it is possible to prevent water or the like

from entering the storage box 7 4 from a gap between the
flange 75 and the lid 76. Thus, even in case of, e.g.,
flooding above the floor, it is possible to suppress the
submergence of the storage battery in the storage box 74.
• Instead of the second storage battery 52, the first
storage battery 51 may be accommodated in the storage box 74.
Also, both of them may be accommodated in the storage box 74.
• The present embodiment may be applied to the second
embodiment. That is, also in the second embodiment in which
the roles of the first and second storage batteries 51 and
52 can be switched between the role for the power failure
and the role for the normal mode, either or both of the
first and second storage batteries 51 and 52 may be
accommodated under the floor.

Next, a fourth embodiment of the present invention
will be described. The power supply system of this
embodiment also basically includes the same configuration as
shown in FIGS. 1 and 2.
As shown in FIG. 5, the storage battery 16 includes,
e.g., eight storage batteries 81a to 81h. Among the storage
batteries 81a to 81h, four storage batteries 81a to 81d are
set as storage batteries for backup whose power is used only
in the power failure, and the remaining four storage
batteries 81e to 81h are set as storage batteries for the
normal mode whose power is used at night. In the initial

state, the first storage battery 51 mentioned in the first
embodiment may be a battery set consisting of four single
batteries, i.e., the storage batteries 81a to 81d, and the
second storage battery 52 mentioned in the first embodiment
may be a battery set consisting of four single batteries,
i.e., the storage batteries 81e to 81h.
Each of the storage batteries 81a to 81h is connected
to a switching matrix 83 provided in the controller 7 via a
plurality of DC power lines 82a to 82h constituting the DC
power line 15. The switching matrix 83 is connected to the
connection terminal P1 for the DC panel board 8 via two DC
power lines 84a and 84b. A charging circuit 85 is provided
on the DC power line 84a, and a discharging circuit 86 is
provided on the DC power line 84b.
The switching matrix 83 is configured such that a
connection state between the storage batteries 81a to 81h
and between the storage batteries 81a to 81h and the
charging circuit 85 or the discharging circuit 86 can be
switched in various ways based on a switching signal from
the control circuit 65.
For example, the switching matrix 83 connects each of
the storage batteries 81a to 81h to the charging circuit 85
or the discharging circuit 86. Accordingly, the charging
and discharging of each of the storage batteries 81a to 81h
can be individually controlled.
Further, the switching matrix 83 switches the

connection state between the storage batteries 81a to 81h.
For example, the storage batteries 81a to 81d for the power
failure and the storage batteries 81e to 81h for the normal
mode are connected in series or in parallel through the
switching matrix 83. As the number of the storage batteries
connected in series increases, the larger power can be
provided. Further, as the number of the storage batteries
connected in series or in parallel increases, the storage
capacity increases.
Furthermore, the number of the storage batteries
connected in series or in parallel may be appropriately
changed based on a command signal from the control circuit
65. Specifically, among the eight storage batteries 81a to
81h, five storage batteries 81a to 81e may be connected in
series or in parallel and, at the same time, the remaining
three storage batteries 81f to 81h may be connected in
series or in parallel.
In addition, the switching matrix 83 can individually
connect a series circuit or parallel circuit of the storage
batteries to the charging circuit 85 or the discharging
circuit 86. In this case, it is possible to charge each
circuit, i.e., the series circuit or parallel circuit, of
the storage batteries, or supply the power from each circuit,
i.e., the series circuit or parallel circuit, of the storage
batteries .

As described above, in the initial state, the four
storage batteries 81a to 81d among the eight storage
batteries 81a to 81h are set for the power failure, and the
remaining four storage batteries 81e to 81h are set for the
normal mode. In this case, some users may desire to
increase or decrease the backup capacity during the power
failure. In order to respond to these demands, the system
of the present embodiment has adopted the following
configuration.
In other words, the control circuit 65 is connected to
a setting switch 87 for setting the operating environment of
the storage batteries 81a to 81h. As shown in FIG. 6A, the
setting switch 87 includes the same number of operation
knobs 88a to 88h as that of the storage batteries 81a to 81h.
In this example, the operation knobs 88a to 88h are
configured as slide type knobs. The operation knobs 88a to
88h slide and change their position between a first
operation position at which the role of the storage battery
is set for the power failure and a second operation position
at which the role of the storage battery is set for the
normal mode. The control circuit 65 sets the role of each
of the storage batteries 81a to 81h based on the operation
position of each of the operation knobs 88a to 88h.
As shown in FIG. 6A, in the initial state, the
operation knobs 88a to 88d corresponding to the four storage
batteries 81a to 81d set for the power failure are

maintained in the first position, and the operation knobs
88e to 88h corresponding to the remaining four storage
batteries 81e to 81h set for the normal mode.are maintained
in the second position. In this case, based on the
operation position of each of the operation knobs 88a to 88h,
the control circuit 65 connects the storage batteries 81a to
81h through the switching matrix 83 as follows. That is, as
shown in FIG. 6B, the four storage batteries 81a to 81d are
connected in series, and the four storage batteries 81e to
81h are connected in series.
In addition, the setting switch 87 may be provided in
a housing (not shown) of the controller 7, or may be
provided in the above-mentioned operation panel 40. Besides,
the setting switch 87 may be provided as an independent
operation panel.

Next, a case where the backup capacity during the
power failure is changed and set by a user will be described.
First, in case of increasing the backup capacity
during the power failure compared to the initial state, any
one of the storage batteries 81e to 81h set for the normal
mode in the initial state is set for the power failure. For
example, in case of setting the storage battery 81e for the
power failure, as shown in FIG. 7A, the operation knob 88e
corresponding to the storage battery 81e is moved from the
second operation position to the first operation position.

As shown in FIG. 7B, when this is detected, the control
circuit 65 connects the storage battery 81e in series to the
storage batteries 81a to 81d originally set for the power
failure through the switching matrix 83. Thus, the backup
capacity in the power failure is increased by the power
capacity of the storage battery 81e which is connected
additionally.
Further, instead of the storage battery 81e, another
one of the remaining three storage batteries 81f to 81h set
for the normal mode may be connected to the storage
batteries for the power failure. Further, in addition to
the storage battery 81e, one or two of the remaining three
storage batteries 81f to 81h set for the normal mode may be
connected additionally. Further, for example, if the
storage battery for the normal mode is not required, all
storage batteries 81a to 81h can be set for the power
failure.
On the contrary, in case of decreasing the backup
capacity during the power failure compared to the initial
state, any one of the storage batteries 81a to 81d set for
the power failure in the initial state is set for the non-
power failure. As shown in FIG. 8A, for example, in case of
setting the storage battery 81d for the normal mode, the
operation knob 88d corresponding to the storage battery 81d
is moved from the first operation position to the second
operation position.

As shown in FIG. 8B, when it is detected that the
operation knob 88d has been changed to the second operation
position, the control circuit 65 disconnects the storage
battery 81d from the remaining three storage batteries 81a
to 81c and also connects the storage battery 81d in series
to the storage batteries 81e to 81h originally set for the
normal mode through the switching matrix 83. Thus, the
backup capacity in the power failure is decreased by the
power capacity of the storage battery 81d which has been
disconnected from the three storage batteries 81a to 81c.
Further, instead of the storage battery 81d, another
one of the remaining three storage batteries 81a to 81c set
for the power failure may be set for the normal mode.
Alternatively, in addition to the storage battery 81d, one
or two of the remaining three storage batteries 81a to 81c
set for the power failure may be set for the normal mode.
Furthermore, for example, if the backup during the power
failure is not required, all storage batteries 81a to 81h
can be set for the normal mode.
In addition, as in the initial state shown in FIG. 6C,
the four storage batteries 81a to 81d may be connected in
parallel and the four storage batteries 81e to 81h may be
connected in parallel. In either case, the backup capacity
during the power failure can be increased or decreased
compared to the initial state in the same manner as the case
where the storage batteries are connected in series as

described above.
That is, in case of increasing the backup capacity
during the power failure compared to the initial state, as
shown in FIG. 7C, the storage battery 81e is connected in
parallel to the storage batteries 81a to 81d originally set
for the power failure. Also in this case, the backup
capacity during the power failure is increased by the power
capacity of the storage battery 81e.
In case of decreasing the backup capacity during the
power failure compared to the initial state, as shown in FIG.
8C, the storage battery 81d is connected in parallel to the
storage batteries 81e to 81h originally set for the normal
mode. Also in this case, the backup capacity during the
power failure is decreased by the power capacity of the
storage battery 81d.
According to the present embodiment, the following
effects can be obtained.
(1) The user can optionally set the role of each of
the storage batteries 81a to 81h to the role for the power
failure or the role for the non-power failure through the
operation of the setting switch 87. Accordingly, the backup
capacity during the power failure can be optionally changed
and set by the user through the operation of the setting
switch 87. Thus, the backup capacity during the power
failure can be ensured suitably depending on the user's
environment. Further, in the power failure or normal mode,

the appropriate power can be supplied to the DC devices 5
and the like according to the user's environment. Therefore,
it is convenient to use.
(2) In case of changing the role of each of the
storage batteries 81a to 81h, it can be achieved only by
sliding each of the operation knobs 88a to 88h of the
setting switch 87. Accordingly, it is possible to easily
change, e.g., the backup power capacity for the power
failure.
In addition, the fourth embodiment may be modified as
follows.
•In the power failure, the power of the storage
batteries set for the normal mode (storage batteries 81e to
81h in the initial state) as well as the storage batteries
set for the power failure (storage batteries 81a to 81d in
the initial state) may be supplied to each of the DC devices
5. That is, the control circuit 65 discharges the storage
battery set for the normal mode during the power failure as
well as the normal mode. Thus, it is possible to more
reliably ensure the backup power during the power failure.
Further, it is also possible to increase the backup time
during which the power can be supplied to the DC devices 5
and the like.
• The number of storage batteries may be appropriately
changed. For example, the number of storage batteries may
be more than or less than eight. For example, it is also

possible to provide sixteen storage batteries. As the
number of storage batteries increases, the backup capacity
can be more finely adjusted.
• The present embodiment may be applied to the first
embodiment. That is, it is possible to optionally switch
the roles of the first and second storage batteries 51 and
52 between the role for the power failure and the role for
the normal mode through the setting operation of the user.
• The present embodiment may be applied to the second
embodiment. In this case, as shown in the graph of FIG. 3,
the roles of the storage batteries 81a to 81d for the power
failure and the storage batteries 81e to 81h for the normal
mode are switched at a predetermined timing. Thus, it is
possible to equalize the number of times of charging and
discharging of each of the storage batteries 81a to 81h and
also possible to extend the life of each storage battery.
Further, in this case, it is preferable to set the number of
the storage batteries for the power failure to be equal to
the number of the storage batteries for the normal mode.

Further, each of the embodiments may be modified as
follows.
• In the first to fourth embodiments, in lieu of the
solar cell 3 generating power using sun light that is
natural energy, a power generation device using natural
energy other than sun light may be employed. Further, it is

also possible to use the power generation device in
combination with the solar cell 3. As a natural energy
power generation device other than the solar cell 3, for
example, there is a wind power generation apparatus
generating power using wind energy, a geothermal power
generation apparatus generating power using geothermal
energy or the like. Further, a fuel cell may be provided
instead of the solar cell 3 or in conjunction with the solar
cell 3.
• In the first to fourth embodiments, a case where the
power supply system 1 is applied to a detached house has
been described, but it is not limited to the detached house.
For example, the power supply system 1 may be applied to a
multiple dwelling house, an apartment, an office building or
the like.
While the invention has been shown and described with
respect to the embodiments, it will be understood by those
skilled in the art that various changes and modification may
be made without departing from the scope of the invention as
defined in the following claims.

We claim:
1. A DC power distribution system comprising:
a storage device,
wherein the storage device includes a first storage
battery which is discharged to supply a power to an electric
device only in a power failure, and a second storage battery
which is discharged to supply a power to the electric device
in a normal mode.
2. The DC power distribution system of claim 1, wherein
the storage device and the electric device are supplied with
a DC power from a power generation device which generates
power using natural energy and a DC power which has been
converted from an AC power supplied from a commercial power
source, and
wherein the first storage battery is discharged to
supply a power to the electric device when the power supply
from the power generation device and the commercial power
source is interrupted.
3. The DC power distribution system of claim 2, further
comprising a controller for controlling charging and
discharging of the first and second storage batteries,
wherein the controller switches roles of the first and
second storage batteries at a predetermined timing.

4. The DC power distribution system of claim 2 or 3,
wherein at least one of the first and second storage
batteries is accommodated under a floor of a building.
5 The DC power distribution system of any one of claims
2.to 4, further comprising a setting unit which sets roles
of the first and second storage batteries to a role for the
power failure or a role for the normal mode through manual
operation.
6.The DC power distribution system of claim 5, wherein
each of the first and second storage batteries is provided
as a battery set including a plurality of single batteries,and
wherein the setting unit sets respective roles of the
single batteries included in the first and second storage
batteries to a role for the power failure or a role for the
normal mode through manual operation.
7. The DC power distribution system of any one of
claims 2 to 6, wherein the power generation device
is a solar cell which generates power using sun
light as the natural energy.

ABSTRACT

A DC power distribution system is equipped with a
storage device having a first storage battery, which
discharges to electrical apparatuses only during power
failure, and a second storage battery, which discharges to
electrical apparatuses when service is not interrupted. The
electricity storage device and electrical apparatuses are
supplied with DC power from a power generation device which
generates electricity using natural energy, and DC power
which has been converted from AC power supplied from a
commercial power source. When the power supply from the
electricity generation device and the commercial power
source is interrupted, the first storage battery discharges
power to the electrical apparatuses.