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Standard Test Conditions (STC) for Specifying Solar Panels
The I-V curve is also used to compare the performance of Solar Panel. The curve is,
therefore, generated based on the performance under Standard Test Conditions (STC)
of sunlight and device temperature of 25°C. It assumes there is no shading on the
device. Standard sunlight conditions on a clear day are assumed to be 1,000 Watts of
solar energy per square meter (1000 W/m
2
or 1 kW/m
2
). This is sometimes called one
sun, or a peak sun. Less than one sun will reduce the current output of the PV device
by a proportional amount. For example, if only one-half sun: (500 W/m
2
) is available,
the amount of output current is roughly cut in half.
Factors Affecting Voltage and Current Output of Solar Cell
The amount of electric current generated by photon excitation in a Solar Cell at a
given temperature is affected by the incident light in two ways:
•
By the intensity of the incident light.
•
By the wavelength of the incident rays.
The materials used in 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 solar cell will be a combination of direct solar radiation, as well as diffused light
bounced off of surrounding surfaces. Solar Cells are usually coated with anti-reflective
material so that they absorb the maximum amount of radiation possible.
The output current of the Solar Panel 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 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 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. As a Rule of Thumb, the voltage rating of the Charge Controller
should be sized as 1.25 times the Open Circuit Voltage rating Voc of the Solar
Panel to ensure that the Charge Controller is not damaged due to over voltage.
SECTION 2 |
General Description of Solar System
Summary of Contents for samlexpower SCC-30AB
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