Samlex America SC-10 - Manual (Page 7)

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PRINCIPlES OF OPERATION
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
Temperature Coefficient of -2.3 mV / °C / Cell resulting in increase in the voltage at
lower temperature and decrease in the voltage at higher temperature
• Variation in temperature has negligible effect on the current output
• 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
Battery charging operation using a solar panel (See Fig 1).
When a battery is directly connected to the solar panel, 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 V-I Curve
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 V-I curve that as the battery voltage
rises, the charging current will start reducing.
When a battery is fully charged, it will not require any further current for charging except
the very low self discharge current. If a charging current higher than the self discharge
current is continued to be fed to a fully charged battery, it will lead to damage to the
battery due to overcharging resulting in overheating and loss of water due to excessive
electrolysis (conversion of water to oxygen and hydrogen).
Charging a battery by a solar panel using a Charge Controller
For full scale charging of a battery from a solar panel, the output of the solar panel is
required to be fed to the battery through a Charge Controller. The Charge Controller
transforms the input power from the solar panel to regulated voltage and current necessary
to safely charge the battery as per the required charging algorithm e.g. 2/3/4 Stage Charging
Algorithm.