Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Utility Patent
1998-06-30
2001-01-02
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
Utility Patent
active
06169414
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a measuring apparatus and method of measuring a characteristic of a solar cell and, more particularly, to a measuring apparatus and method of measuring a photoelectric conversion characteristic of a solar cell having a broader photo-sensing area than an illuminated area by a light source.
Photovoltaic power generation has been collecting interests of many people as a clean power generation method which will meet an increasing demand for electric power and does not cause the destruction of the environment, since it does not cause environmental problems, such as radioactive contamination and anathermal of the earth, further, sunlight falls everywhere on the earth with some distribution inequality, and relatively large power generation efficiency is realized without a complicated and large facility. Accordingly, various studies and development are made on photovoltaic power generation to fit for practical use.
Upon studying and developing a solar cell, not only manufacturing technique of a solar cell, but also technique for evaluating the output characteristic of a manufactured solar cell are very important items. As a method of evaluating an output characteristic of a solar cell, a method of studying a voltage vs. current characteristic (voltage/current characteristic) of a solar cell is generally used.
FIG. 2
shows a configuration of an apparatus for evaluating the voltage/current characteristic. In
FIG. 2
, reference numeral
201
denotes a solar cell which is the object of evaluation;
202
, a direct current (DC) power source;
203
, wires;
204
, an ammeter;
205
, a voltmeter;
206
, wires used for measuring voltage;
207
, a computer;
208
, a light source; and
209
, a shutter.
The DC power source
202
, controlled by the computer
207
, is connected to the solar cell
201
via the wire
203
and the ammeter
204
. Generally, a bipolar DC power source is used as the DC power source
202
; however, an electronic load may be used instead. Further, the voltmeter
205
is connected across the solar cell
201
. The values of current and voltage measured by the ammeter
204
and the voltmeter
205
, respectively, are inputted to the computer
207
. The light source
208
emits standard light for characteristic measurement set to the quantity of light of 1 sun (=1000 W/m
2
) and spectrum of AM1.5, which conforms to Japan Industrial Standards (JIS). Illuminating and shielding of light on/from the solar cell
201
are performed by controlling open/close of the shutter
209
by the computer
207
.
A method of measuring the voltage/current characteristic of the solar cell
201
using the above apparatus is explained below.
First, the light source
208
is warmed up and adjustment for emitting a standard quantity of light is performed. In this stage, the light source
208
is on and the shutter
209
is closed. Next, the solar cell
201
, which is the object of the measurement, is set. Then, the shutter
209
is opened and the entire surface of the solar cell
201
is illuminated with the standard light. Under this condition, the computer
207
controls the DC current source
202
to output a voltage. The voltage to be applied across the solar cell
201
depends upon the type of the solar cell
201
, and the optimum voltage is predetermined for each type of a solar cell.
In an operational sequence for measuring the voltage/current characteristic, while gradually changing output voltage of the DC power source
202
, voltage values across the solar cell
201
measured by the voltmeter
205
and current values measured by the ammeter
204
are stored in memory of the computer
207
.
After changing the output voltage of the DC power source
202
across the voltage range necessary for the measurement, the shutter
209
is closed, and the solar cell
201
is removed. Then, the voltage value data and the current value data stored in the memory of the computer
207
is graphed using a proper software, and a voltage/current characteristic curve as shown in
FIG. 3
is obtained.
FIG. 3
is a graph showing an example of voltage/current characteristic of the solar cell
201
. In
FIG. 3
, V in the abscissa shows voltage, and I in the ordinate shows current. A curve C in
FIG. 3
is obtained by connecting points representing the measured voltage values and current values plotted on the graph. A point K on the curve C is the point where the product of the voltage and the current becomes maximum, i.e., the point where maximum electric power is taken out, and generally called the optimum working point. The electric power taken out at the optimum working point is the rated power.
Photovoltaic power generation has been rapidly spreading recently. In a residence, a solar panel is often installed on the roof, for instance, and in an isolated island, a solar panel is often installed on a rack. In order to reduce the number of steps for installing the solar panel, a photo-sensing surface of each solar cell tends to be broadened. For measuring characteristics of such a solar cell having a broad surface, a light source capable of illuminating an area corresponding to the entire surface of the solar cell is necessary; however, it is very hard to obtain a light source of that kind.
Generally, a Xenon lamp is most widely used as the light source, and a solar simulator using the Xenon lamp is used. However, the price of the solar simulator increases rapidly as the area that the Xenon lamp can illuminate increases. The increase in price is caused since it becomes harder to manufacture an air-mass filter and a condenser lens, both included in a solar simulator, as their sizes become larger, and the required output power from a power source for the lamp is extremely large. As a practical fixed-light type solar simulator, one having a light source capable of illuminating an area of about 50 cm by 50 cm is the largest on the current market. There is a simulator, capable of illuminating an area of about 1 m by 1 m, in which a lamp, the light source, pulses to decrease the required output power of a power source for the lamp. However, since the sizes of parts other than the power source for the lamp are the same as those of the fixed-light type solar simulator, such a solar simulator is also very expensive.
Thus, the solar simulator for measurement and test having a light source is expensive as described above; therefore, manufacturing cost of a solar cell increases. Accordingly, a method capable of measuring the characteristic of a solar cell having a broad surface at low cost is desired earnestly. Further, regarding a solar cell having a photo-sensing surface much greater than 1 m by 1 m, since a light source capable of illuminating such a broad area is not available, it is not possible, practically, to measure the characteristic of the solar cell.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide a measuring apparatus and method of measuring a characteristic of a solar cell having a large photo-sensing surface at low cost.
According to the present invention, the foregoing object is obtained by providing a measuring method of measuring a characteristic of a solar cell comprising the steps of: measuring a first characteristic of the solar cell while illuminating a predetermined area of a photo-sensing surface of the solar cell, wherein an area of the photo-sensing surface which is not illuminated is called a dark area; measuring a second characteristic of the solar cell in a dark state in which the photo-sensing surface is shielded from light; calculating a third characteristic by multiplying the second characteristic by an area ratio of an area of the dark area to an area of the photo-sensing surface; and calculating a characteristic of the predetermined illuminated area on the basis of the first and third characteristics.
Further, according to the present invention, the foregoing object is also attained by providing a measuring method of measuring a characteris
Ohtsuka Takashi
Yoshino Takehito
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Kobert Russell M.
Metjahic Safet
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