U.S. patent application number 09/950825 was filed with the patent office on 2002-03-21 for water electrolytic system.
Invention is credited to Handa, Kiyoshi.
Application Number | 20020033332 09/950825 |
Document ID | / |
Family ID | 18769327 |
Filed Date | 2002-03-21 |
United States Patent
Application |
20020033332 |
Kind Code |
A1 |
Handa, Kiyoshi |
March 21, 2002 |
Water Electrolytic system
Abstract
A water electrolytic system includes a water electrolyzer, a
photovoltaic generator which is a power source for the water
electrolyzer, and a DC/DC converter adapted to convert the maximum
output from the photovoltaic generator into a current and a voltage
corresponding to an IV characteristic of the water electrolyzer by
converting current and voltage for a portion of such maximum
output, and to input the converted current and voltage to the water
electrolyzer. With the water electrolytic system, even when an
optimal point of operation of the photovoltaic generator, i.e., the
maximum output from the photovoltaic generator has been varied, the
efficient operation of the water electrolytic system can be carried
out utilizing such maximum output.
Inventors: |
Handa, Kiyoshi; (Saitama,
JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
Suite 400
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Family ID: |
18769327 |
Appl. No.: |
09/950825 |
Filed: |
September 13, 2001 |
Current U.S.
Class: |
204/230.2 |
Current CPC
Class: |
C25B 1/04 20130101; C25B
15/00 20130101; Y02E 60/36 20130101; Y02E 60/366 20130101; Y02E
70/10 20130101 |
Class at
Publication: |
204/230.2 |
International
Class: |
C25B 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2000 |
JP |
2000-285222 |
Claims
What is claimed is:
1. A water electrolytic system comprising a water electrolyzer, a
photovoltaic generator which is a power source for said water
electrolyzer, and a DC/DC converter adapted to convert the maximum
output from said photovoltaic generator into a current and a
voltage corresponding to an IV characteristic of said water
electrolyzer by converting current and voltage for a portion of
said maximum output, and to input the converted current and voltage
to said water electrolyzer.
2. A water electrolytic system comprising a water electrolyzer, a
photovoltaic generator which is a power source for said water
electrolyzer, and a DC power source adapted to add an external
output to the maximum output from said photovoltaic generator in
order to provide a current and a voltage corresponding to an IV
characteristic of said water electrolyzer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a water electrolytic system
designed so that a water electrolyzer is operated by an output from
a photovoltaic generator.
[0003] 2. Description of the Related Art
[0004] A photovoltaic generator has an optimal point of operation,
namely, an operating current and an operating voltage at the time
when the output from the photovoltaic generator assumes a maximum
value. If the optimal point of operation is matched with an IV
characteristic (I: current, V: voltage) of a water electrolyzer,
the water electrolyzer can be operated with a good efficiency.
However, the optimal point of operation is varied depending on the
temperature of the photovoltaic generator, an insolation amount to
the photovoltaic generator and the like and as a result, the
optimal point of operation is not matched with the IV
characteristic of the water electrolyzer. When the photovoltaic
generator and the water electrolyzer have been connected in series
to each other, namely, connected directly to each other, it is
difficult to operate the water electrolytic system with a good
efficiency at all times.
[0005] Therefore, in order to ensure that even when the optimal
point of operation of the photovoltaic generator, i.e., the maximum
output from the photovoltaic generator, has been varied, the water
electrolyzer is operated efficiently by utilizing such maximum
output, a water electrolytic system has been developed (for
example, see Japanese Patent Application Laid-open No. 7-233493),
which includes a water electrolyzer, a photovoltaic generator, and
a high-output type DC/DC converter adapted to convert all of the
maximum output from the photovoltaic generator into a current and a
voltage corresponding to an IV characteristic of the water
electrolyzer to input them to the water electrolyzer.
[0006] However, the high-output type DC/DC converter is large in
size with a weight of about 60 kg and moreover, is of a high cost
and has an efficiency of 80 to 90% and hence, a loss of 10 to 20%
is produced. For this reason, the conventional system has a problem
that it lacks in economy.
SUMMARY OF THE INVENTION
[0007] Accordingly, it is an object of the present invention to
provide an economical water electrolytic system designed so that
even when the optimal point of operation of the photovoltaic
generator, i.e., the maximum output from the photovoltaic generator
has been varied, the water electrolyzer can be operated with a good
efficiency by utilizing such maximum output.
[0008] To achieve the above object, according to the present
invention, there is provided a water electrolytic system comprising
a water electrolyzer, a photovoltaic generator which is a power
source for the water electrolyzer, and a DC/DC converter adapted to
convert the maximum output from the photovoltaic generator into a
current and a voltage corresponding to an IV characteristic of the
water electrolyzer by carrying out the conversion of current and
voltage for a portion of the maximum output and to input the
current and the voltage to the water electrolyzer.
[0009] With such arrangement, when the maximum output from the
photovoltaic generator has been varied, the water electrolyzer can
be operated with a good efficiency by utilizing the varied maximum
output. Moreover, the conversion of current and voltage is carried
out for a portion of the maximum output from the photovoltaic
generator by the DC/DC converter and hence, a loss in the entire
system can be suppressed to a small level, and a low-output type of
a DC/DC converter made in a small size and at a low cost can be
employed, leading to an increase in economy.
[0010] According to the present invention, there is provided a
water electrolytic system comprising a water electrolyzer, a
photovoltaic generator which is a power source for the water
electrolyzer, and a DC power source adapted to add an external
output to the maximum output from the photovoltaic generator in
order to provide a current and a voltage corresponding to an IV
characteristic of the water electrolyzer.
[0011] With such arrangement, when the maximum output from the
photovoltaic generator has been varied, a new optimal point of
operation corresponding to such variation can be allowed to appear
by adding an external output corresponding to the variation to the
varied maximum output, and can be matched with the IV
characteristic of the water electrolyzer and determined as a point
of operation for the water electrolyzer. Thus, the water
electrolytic system can be operated with a good efficiency.
[0012] The above and other objects, features and advantages of the
invention will become apparent from the following description of
the preferred embodiment taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a graph showing a first example of an IV
characteristic for a photovoltaic generator and a water
electrolyzer;
[0014] FIG. 2A is a diagram of an electric circuit of example 1 of
a first embodiment of the present invention;
[0015] FIG. 2B is an equivalent circuit of the electric circuit
shown in FIG. 2A;
[0016] FIG. 3 is a graph showing a second example of the IV
characteristic for a photovoltaic generator and a water
electrolyzer;
[0017] FIG. 4A is a diagram of an electric circuit of example 2 of
the first embodiment of the present invention;
[0018] FIG. 4B is an equivalent circuit of the electric circuit
shown in FIG. 4A;
[0019] FIG. 5 is a diagram of an electric circuit of example 1 of a
second embodiment of the present invention;
[0020] FIG. 6 is a graph showing a third example of the IV
characteristic for a photovoltaic generator and a water
electrolyzer; and
[0021] FIG. 7 is a diagram of an electric circuit of example 2 of
the second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] FIGS. 1 to 4B show a first embodiment of a water
electrolytic system 1. The first embodiment includes example 1 and
example 2. FIGS. 1, 2A and 2B show example 1, and FIGS. 3, 4A and
4B show example 2.
[0023] In example 1, FIG. 1 shows a mode when the maximum output
from a photovoltaic generator 2 has been varied. A line L1
indicates an IV characteristic of the photovoltaic generator 2 at
28.degree. C. (an insolation amount: 1040 W/m.sup.2), and a line L2
indicates an output characteristic of the photovoltaic generator 2.
In this case, an optimal point P1 of operation of the photovoltaic
generator 2 is a point at which the output is a maximum value. Such
maximum output Emax is 1506 W. On the other hand, a line L3
indicates an IV characteristic of a water electrolyzer (number of
water electrolytic cells: 8) 4. When the photovoltaic generator 2
and the water electrolyzer 4 has been connected in series, a point
of intersection between the line L1 indicating the IV
characteristic of the photovoltaic generator 2 and the line L3
indicating the IV characteristic of the water electrolyzer 4 is a
point P2 of operation of the water electrolyzer 4. This point P2 of
operation is at a location displaced from the optimal point P1 of
operation of the photovoltaic generator 2 toward a lower current
and higher voltage side and hence, the highly efficient operation
of the water electrolytic system 1 cannot be desired.
[0024] To deal with this, in example 1, a peak power tracking is
carried out, which comprises controlling a low-output type DC/DC
converter 5, so that the operating current Imax at the optimal
point P1 of operation of the photovoltaic generator 2 is decreased,
and the operating voltage Vmax is increased, measuring a current
Imax-dI and a voltage Vmax+dV lying on the line L3 indicating the
IV characteristic of the water electrolyzer 4, and determining
these current and voltage as an operating current and an operating
voltage for the water electrolyzer 4.
[0025] As in FIG. 2A, in example 1, the low-output type DC/DC
converter 5 is connected in series between the photovoltaic
generator 2 and the water electrolyzer 4. The low-output type DC/DC
converter 5 has a function to conduct the conversion of current and
voltage for a portion of the maximum output from the photovoltaic
generator 2, thereby converting the maximum output into a current
and a voltage corresponding to the IV characteristic of the water
electrolyzer 4 and inputting the current and the voltage to the
water electrolyzer 4, in order to carry out the peak power
tracking. FIG. 2B shows an equivalent circuit shown in FIG. 2A.
[0026] To operate the water electrolyzer 4 under a situation shown
in FIG. 1, the operating current Imax (92.4 A) and the operating
voltage Vmax (16.3 V) at the optimal point P1 of operation of the
photovoltaic generator 2 are first determined. When the
photovoltaic generator 2 and the water electrolyzer 4 have been
connected in series to each other, the point P2 of operation of the
water electrolyzer 4 is a point at which the operating current is
80 A and the operating voltage is 17.8 V.
[0027] When the low-output type DC/DC converter 5 is then operated
to decrease the resistance value of a variable resistor R, as shown
in FIG. 2B, a current dI flows. Therefore, the current to the water
electrolyzer 4 is decreased into Imax-dI, while the voltage is
increased into Vmax+dV. This is continued to measure a current
Imax-dI (73.5 A) and a voltage Vmax+dV (17.7 V) lying on the line
L3 indicating the IV characteristic of the water electrolyzer 4. A
point P3 having these current and voltage is determined as a point
of operation of the water electrolyzer 4.
[0028] Namely, an output of (Vmax+dV).(Imax-dI) is supplied from
the photovoltaic generator 2 to the water electrolyzer 4. In this
case, a portion Vmax.dI of the maximum output Imax.Vmax from the
photovoltaic generator 2 has been converted into (Imax-dI).dV at
the supplied output (Vmax+dV).(Imax-dI), wherein (Imax-dI).dV is a
value resulting from the subtraction of a loss due to the
conversion from Vmax.dI. In this case, the weight of the low-output
type DC/DC converter 5 was about 8 kg, which is about 13% of the
weight of a high-output type DC/DC converter, and the efficiency
was equal to or higher than 94%.
[0029] In example 2, FIG. 3 shows a mode when the maximum output
from the photovoltaic generator 2 has been varied. A line L1
indicates an IV characteristic of the photovoltaic generator 2 at
28.degree. C. (an insolation amount: 1040 W/m.sup.2), and a line L2
indicates an output characteristic of the photovoltaic generator 2,
as in example 1. In this case, In this case, an optimal point P1 of
operation of the photovoltaic generator 2 is a point at which the
output is a maximum value. Such maximum output Emax is 1506 W. On
the other hand, a line L3 indicates an IV characteristic of a water
electrolyzer (number of water electrolytic cells: 6) 4.
[0030] When the photovoltaic generator 2 and the water electrolyzer
4 has been connected in series, a point of intersection between the
line L1 indicating the IV characteristic of the photovoltaic
generator 2 and the line L3 indicating the IV characteristic of the
water-electrolyzing device 4 is a point P2 of operation of the
water electrolyzer 4. This point P2 of operation is at a location
displaced from the optimal point P1 of operation of the
photovoltaic generator 2 toward a higher current and lower voltage
side and hence, the highly efficient operation of the water
electrolytic system 1 cannot be desired.
[0031] To deal with this, in example 2, a peak power tracking is
carried out, which comprises controlling a low-output type DC/DC
converter 5, so that the operating current Imax at the optimal
point P1 of operation of the photovoltaic generator 2 is increased,
and the operating voltage Vmax is decreased, measuring a current
Imax+dI and a voltage Vmax-dV lying on the line L3 indicating the
IV characteristic of the water electrolyzer 4, and determining
these current and voltage as an operating current and an operating
voltage for the water electrolyzer 4.
[0032] As in FIG. 4A, in example 2, the low-output type DC/DC
converter 5 is connected in parallel between the photovoltaic
generator 2 and the water electrolyzer 4. The low-output type DC/DC
converter 5 has a function to conduct the conversion of current and
voltage for a portion of the maximum output from the photovoltaic
generator 2, thereby converting the maximum output into a current
and a voltage corresponding to the IV characteristic of the water
electrolyzer 4 and inputting the current and the voltage to the
water electrolyzer 4, in order to carry out the peak power
tracking. FIG. 4B shows an equivalent circuit shown in FIG. 4A.
[0033] To operate the water electrolyzer 4 under a situation shown
in FIG. 3, the operating current Imax (92.4 A) and the operating
voltage Vmax (16.3 V) at the optimal point P1 of operation of the
photovoltaic generator 2 are first determined. When the
photovoltaic generator 2 and the water electrolyzer 4 have been
connected in series to each other, the point P2 of operation of the
water electrolyzer 4 is a point at which the operating current is
100 A and the operating voltage is 13.8 V.
[0034] When the low-output type DC/DC converter 5 is then operated
to increase the resistance value of a variable resistor R, as shown
in FIG. 2B, a current dI flows. Therefore, the current to the water
electrolyzer 4 is decreased into Imax+dI, while the voltage is
increased into Vmax-dV. This is continued to measure a current
Imax+dI (108.2 A) and a voltage Vmax-dV (13.9 V) lying on the line
L3 indicating the IV characteristic of the water electrolyzer 4. A
point P3 having these current and voltage is determined as a point
of operation of the water electrolyzer 4.
[0035] Namely, an output of (Vmax-dV).(Imax+dI) is supplied from
the photovoltaic generator 2 to the water electrolyzer 4. In this
case, a portion Imax.dV of the maximum output Imax.Vmax from the
photovoltaic generator 2 has been converted into (Vmax-dV).dI at
the supplied output (Vmax-dV).(Imax+dI), wherein (Vmax-dV).dI is a
value resulting from the subtraction of a loss due to the
conversion from Imax.dV.
[0036] FIGS. 5 to 7 show a second embodiment of the present
invention. In example 1 of the second embodiment shown in FIG. 5, a
DC power source 6 is connected in series between a photovoltaic
generator and a water electrolyzer 4. The DC power source 6 has a
function to add an external output to the maximum output from the
photovoltaic generator 2 in order to provide a current and a
voltage corresponding to the IV characteristic of the water
electrolyzer 4.
[0037] In FIG. 6, a curve L1 indicates an IV characteristic of the
photovoltaic generator 2 at 80.degree. C. (an insolation amount:
905 W/m.sup.2), and a line L2 indicates an output characteristic of
the photovoltaic generator 2. An optimal point of operation of the
photovoltaic generator 2 is a point at which a relative output
assumes a maximum value; an operating voltage is 13.3 V, and an
operating current is 92 A (1224 W). On the other hand, a line L3
indicates an IV characteristic of the water electrolyzer (number of
water electrolytic cells: 7) 4, and a line L4 indicates a power
characteristic of the water electrolyzer 4.
[0038] When the photovoltaic generator 2 and the water electrolyzer
4 have been connected in sires to each other, a point of
intersection between the line L1 indicating the IV characteristic
of the photovoltaic generator 2 and the line L3 indicating the IV
characteristic of the water electrolyzer 4, namely, a point of a
lower current and higher voltage than those at the optimal point of
operation, is a point P2 of operation of the water electrolyzer
4.
[0039] Therefore, when the optimal point P1 of operation is shifted
toward a higher voltage side in a state of a constant current (92
A), the optimal point P1 is in accord with the line L3 indicating
the IV characteristic of the water electrolyzer 4 at a voltage of
15.6 V. An operating voltage at the optimal point P1 of operation
is 13.3 V, and 15.6 V-13.3 V=2.3 V. Therefore, when an external
output of 2.3 V from the DC power source 6 is added to the IV
characteristic of the photovoltaic generator 2, a secondary IV
characteristic provided by cooperation of the photovoltaic
generator 2 and the DC power source 6 with each other is as
indicated by a line L5 shown by a dotted line, and a new optimal
point of operation in such IV characteristic is a point of
operation of the water electrolyzer 4.
[0040] When the maximum output from the photovoltaic generator 2
has been varied, as described above, a new optimal point P3 of
operation corresponding to such variation, i.e., a point having an
operating voltage of 15.6 V and an operating current of 92 A (1435
W) can be allowed to appear by adding an external output
corresponding to such variation to the varied maximum output. Such
optimal point P3 can be matched with the IV characteristic of the
water electrolyzer 4 and determined as a point of operation for the
water electrolyzer 4. The water electrolyzer 4 can be operated with
a good efficiency by such peak power tracking.
[0041] In this case, a power of 1435 W corresponding to the optimal
point P3 of operation in the water electrolyzer 4 is indicated by a
point P4 on the line L4. This power is a value provided by
increasing, by 47%, a power of 976 W shown by a point P5 on the
line L4 before addition of the external output in the water
electrolyzer 4. The details of the increase rate of 47% are as
follows: If the maximum output from the photovoltaic generator 2
shown by a point P6 on the line L2 is 1223 W, a component A of the
increase rate provided by a peak power tracking effect is 25.3%,
and a component B provided by the external output is 21.7%. In this
case, the efficiency is 94%.
[0042] In example 2 of the second embodiment shown in FIG. 7, a DC
power source 6 is connected in parallel between as a photovoltaic
generator 2 and a water electrolyzer 4. Even in example 2, a peak
power tracking can be carried out.
* * * * *