samlexsolar SC-05, Owner'S Manual

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10 | SAMLEX AMERICA INC.
SECTION 4 | Principles of Operation
Electrical power ( P ) in Watts fed to the load = Voltage ( V ) X Current ( I ).
If the output of the panel is short circuited, the output current will be limited to the maximum
current that the panel can provide. This Short Circuit Current is designated as
Isc
.
The maximum power
Pmp
is fed to the load when the operating point is near the knee of the
curve as shown. At this operating point for maximum power output, the voltage is designated
as
Vmp
and the current is designated as
Imp
.
Please note that for the portion of the curve between Voc to Vmp , the current drops at a faster
rate. After that, the current is almost constant and equal to the Short Circuit Current
Isc
.
4.2 FACTORS AFFECTING VOLTAGE AND CURRENT OUTPUT OF A
SOLAR PANEL
The following factors affect the voltage and current of a solar panel:
• The output voltage is not affected very much by the light conditions - under shaded / cloudy
condition, the output voltage will not vary very much as compared to bright sunshine
• The output current is very sensitive to the intensity of light and will drop considerably
under shaded or cloudy conditions
• Variation in temperature has a sizable effect on the output voltage – a Negative Voltage
Temperature Coefficient results in increase in the voltage at lower temperature and
decrease in the voltage at higher temperature. For SC-05 and SC-10, the Voltage
Temperature Coefficient is -0.29% per oC.
• Variation in temperature has negligible effect on the current output. Current Temperature
Coefficient of SC-05 and SC-10 is +0.05% per oC.
• The output current can increase by 25 % due to what is known as the “Edge of the Cloud
Effect”. As the sun moves between a hole in the clouds, the solar panel will see the full
direct sunlight combined with the reflected sunlight from the clouds
4.3 BATTERY CHARGING USING A SOLAR PANEL DIRECTLY CONNECTED
TO THE BATTERY
Refer to the I-V Curves of the panels at Fig 4.1.
When a battery is directly connected to the solar panel (without external Charge Controller),
the voltage of the loaded panel will be equal to the initial battery voltage. At this point, the
charging current (
I
) will be equal to the corresponding value of the initial battery voltage on the
I-V Curve (Fig 4.1).
The current (
I
) fed from the panel will start charging the battery and the battery voltage will
start rising. As the battery is always connected to the panel, the panel voltage will be the same
as the battery voltage. It will be seen from the I-V curve (Fig 4.1) that as the battery voltage
rises, the charging current will start reducing.