Civil Engineering Reference
In-Depth Information
7 Photovoltaic Panels
Sergiu Caraman
7.1 General Aspects
A photovoltaic cell produces a power that is the product between the current
imposed by the load and the photocell voltage. Obviously, in the case of short
circuit, the power is zero, due to the fact that the voltage is zero and in open circuit
it is zero also, due to the fact that the value of the current is zero. A maximum point
of the power produced by a photovoltaic cell can be de
ned and called the maxi-
mum power point. It is given by the coordinates: V = V
max
and I = I
max
.
The technical characteristics of a photovoltaic cell are the following:
The tension of backlash, V
OC
;
The short circuit current, I
SC
;
The tension in the optimum point of operation, V
max
;
The current in the point of maximum power I
max
;
The maximum power estimated P
max
;
The
filling factor FF;
Coefficient of modifying power with cell temperature.
ned as the ratio between the maximum
electric power and the continuous power in the total incidental light (the power
received from the Sun by the photovoltaic cell
The ef
ciency of the conversion is de
—
P
in
), so:
V
max
I
max
P
in
¼ FF
V
OC
I
SC
g
¼
ð
14
Þ
H
A
where V
OC
—
the tension given by the solar cell in the open circuit, I
SC
—
the short
the irradiance [kW/m
2
], and A
circuit current, FF
—
the
filling factor, I
—
—
the sur-
face of the solar cell. The
filling factor, FF,isde
ned as the ration between the
maximum electric power and the product V
OC
I
SC
:
V
max
I
max
V
OC
I
SC
FF
¼
ð
15
Þ
The technical characteristics of photovoltaic cells are de
ned in keeping with
their operation in standard test conditions, which are:
Irradiance (Luminous intensity) of 1,000 W/m
2
in the panel area;
The temperature of the solar cell
—
constant 25
°
C;
The spectrum of light AM 1.5 global.
It can be noticed that, especially at noon, during summer, the temperature of the
solar cells (depending on position, wind conditions etc.) may reach 30 up to 60
°
C,
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