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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-reflective 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 reflected 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 Coefficient – 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 Coefficient –
The output voltage increases with decrease in temperature. For example, a Silicon
Cell has a Temperature Coefficient 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.