Batteries: thermoelectric and photoelectric – Photoelectric – Panel or array
Reexamination Certificate
2001-04-27
2002-09-10
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Panel or array
C136S291000, C136S293000, C363S070000, C363S095000, C363S097000, C323S906000, C320S101000
Reexamination Certificate
active
06448489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solar generation system. More specifically, the present invention relates to a solar generation system in which a DC power generated by an independent DC power source such as a solar cell is boosted by a booster unit and converted to an AC voltage by an inverter apparatus to supply power to general AC load for home and office use, or to feed power to existing utility power supply.
2. Description of the Background Art.
A solar cell as a DC power source outputs a DC power when there is high solar insolation. The DC power can be output solely by the solar cell without using other energy source such as a storage battery, and no poisonous substance is discharged. Therefore, the solar cell has been known as a simple and clean energy source.
FIG. 15
is a block diagram showing an example of a conventional solar generation system. For simplicity of the drawing, only two solar cell strings
1
a
and
1
b
are shown in the solar generation system. It is needless to say that normally, a larger number of solar cell strings are provided. Generally, one standard solar cell string includes eight or nine solar cell modules (not shown) connected in series with each other.
In the solar generation system, when the DC output power from solar cell strings
1
a
and
1
b
is converted to an AC power and interconnected to a utility power supply
4
, it is necessary to interpose a power conditioner
3
between the solar cell strings
1
a
,
1
b
and the utility power supply
4
. When a plurality of solar cell strings
1
are to be interconnected to the utility power supply
4
, the plurality of solar cell strings
1
are connected in parallel with the power conditioner
3
. Power conditioner
3
includes backflow preventing diodes
50
a
and
50
b
, so as to prevent backflow of the current generated by the plurality of solar cell strings
1
connected in parallel. The DC power that has passed through backflow preventing diodes
50
a
and
50
b
is converted to an AC power by a DC/AC inverter
60
, and supplied through a protection circuit
70
to the utility power supply
4
.
Conventionally, it is a common practice for the solar generation system in Japan that a plurality of solar cell strings included therein are placed on a main portion of a roof facing southward, and lines from the solar cell strings are connected to power conditioner
3
.
When the solar cell strings are to be placed on the roof of a house, sometimes it is difficult to configure solar cell strings by arranging solar cell modules only that surface of the roof which faces southward and receiving the most of the sunshine. Solar cell modules that are positioned not on the southward surface of the roof may be arranged on the eastward or westward surface of the roof to form the solar cell strings. Sometimes, the solar cell strings are configured by placing small size solar cell modules arranged in the remaining peripheral regions after the solar cell modules are placed on the main portion of the southward surface of the roof. More specifically, sometimes the number of series-connected solar cell modules included in some solar cell strings is different from other solar cell strings. In such a case, different output voltages result from different solar cell strings.
For example, when a standard solar cell string including the standard number of series-connected solar cell modules and a substandard solar cell string including series-connected modules of smaller than the standard number are connected in parallel to the power conditioner
3
, only the power from the standard solar cell having the standard output voltage is input to power conditioner
3
, and the power from the substandard solar cell string having the substandard output voltage lower than the standard output voltage cannot be fed to the power conditioner
3
. Even when the power from the substandard solar cell string is adapted to be fed to power conditioner
3
, it is impossible to obtain the maximum output power that is the sum of the maximum power from the standard solar cell string and the maximum power from the substandard solar cell string, as can be seen from
FIGS. 16A and 16B
.
Unless the power from such a substandard solar cell string can be fed efficiently to power conditioner
3
, the area occupied by the substandard solar cell string would be wasted.
In the graphs of
FIGS. 16A and 16B
, the abscissa represents output voltage V and the ordinate represents output power P. In the graph of
FIG. 16A
, the curve S represents an output power from the standard solar cell string, while the curve N represents the output power from the substandard solar cell string. More specifically, the standard solar cell string has the maximum output power Ps, while the substandard solar cell string has the maximum output power Pn. The output power that is the sum of these two output powers is as shown in FIG.
16
B. The maximum output power Psn of the output power curve (S+N) shown in
FIG. 16B
is considerably smaller than the sum (Ps+Pn) of the maximum output powers Ps and Pn shown in FIG.
16
A. The reason for this is that the voltage position for the maximum output power Ps of the standard solar cell string
1
a
is different from the voltage position of the maximum output power Pn from the substandard solar cell string
1
b.
In view of the foregoing, a possible solution is to adjust output voltages from the plurality of solar cell strings. For this purpose, an impedance may be interposed between standard solar cell string
1
a
and power conditioner
3
. This method, however, is not practical, as the power is lost by the impedance. Another possibility is to use MG (Motor Generator) method to change the DC voltage. This method, however, is not preferable as mechanical vibration or noise is generated and the motor generator itself is bulky.
In the solar cell generation system disclosed in Japanese Patent Laying-Open No. 8-46231, boosted type DC-DC converter
80
b
having maximum power point tracking function are incorporated in each solar cell module or in each substandard solar cell string, as shown in FIG.
17
. Such a solar generation system is disadvantageous in that the circuit structure becomes complicated and in that voltage adjustment for the solar generation system as a whole must be performed in the initial design stage of each solar cell string having different output voltages.
In Japanese Patent Laying-Open No. 8-46231, an isolation transformer is connected. This increases the weight of the system and lowers power conversion efficiency. In case of a malfunction of the boosting circuit caused by a surge, it will trouble a repair person to climb on the roof and to exchange the solar cell module.
SUMMARY OF THE INVENTION
Therefore, a main object of the present invention is to enable interconnection of a plurality of solar cell strings having different output voltages to a utility power supply in a simple manner, and to enable efficient use of the maximum output power of the solar cell strings.
Briefly stated, the present invention relates to a solar generation system in which a DC voltage output from a solar cell is boosted, and the boosted DC voltage is supplied to an inverter apparatus converting the DC voltage to an AC power, including a standard solar cell string having a standard number of solar cell modules connected in series, a substandard solar cell string having solar cell modules smaller in number than the standard number connected in series, a boosting circuit for boosting the DC voltage output from the substandard solar cell string to a DC voltage output from the standard solar cell string, and an input connecting circuit for supplying the DC voltage boosted by the boosting circuit and the DC voltage output from the standard solar cell string to the inverter apparatus.
Therefore, according to the present invention, as the DC voltage from the substandard solar cell string is increased to the DC voltage of the standard solar cell string, interconnection to the u
Kimura Fumiya
Kodama Hirokazu
Nakata Hirofumi
Nishida Kiyoshi
Takebayashi Tsukasa
Diamond Alan
Sharp Kabushiki Kaisha
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