samlexsolar SCC-30AB - Page 9

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GENERAL DESCRIPTION OF PV / SOLAR SYSTEM
The materials used in PV / Solar Cells have different spectral responses to incident
light, and exhibit a varying sensitivity with respect to the absorption of photons at
given wavelengths.Each semiconductor material will have an incident radiation
threshold frequency, below which no electrons will be subjected to the photovoltaic
effect. Above the threshold frequency, the kinetic energy of the emitted
photoelectron varies according to the wavelength of the incident radiation, but
has no relation to the light intensity. Increasing light intensity will proportionally
increase the rate of photoelectron emission in the photovoltaic material. In actual
applications, the light absorbed by a PV cell will be a combination of direct solar
radiation, as well as diffused light bounced off of surrounding surfaces. PV / Solar
Cells are usually coated with anti-reective material so that they absorb the maximum
amount of radiation possible.
The output current of the PV / Solar Panel (Module) can increase due to what is
known as the “Edge of the Cloud Effect”. As the sun moves into a hole between the
clouds, your solar panels will see full direct sunlight combined with reected light
from the clouds! They will absorb more energy than they could on a cloudless day!
Thus, a factor of 1.25 times the Short Circuit Current Isc is recommended when sizing
the current capacity of the Charge Controller
The output current of the PV / Solar Cell has a positive Temperature Coefcient – The
output current increases with the rise of temperature. However, it is negligible – less
than 0.1 % / °C of the Short Circuit Current Isc
The output voltage of the PV / Solar Cell has a Negative Temperature Coefcient –
The output voltage increases with decrease in temperature. For example, a Silicon
Cell has a Temperature Coefcient of – 2.3 mV / °C / Cell. Hence, during cold winter
days, the voltage will rise. Hence, as a Thumb Rule, the voltage rating of the Charge
Controller should be sized as 1.25 times the Open Circuit Voltage rating Voc of the PV
/ Solar Panel (Module) to ensure that the Charge Controller is not damaged due to
over-voltage.