How the photocurrent is related to the light intensity in solar cell?

TEST METHOD FOR PHOTOVOLTAIC MODULE RATINGS
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5.3 Measurements and Translation of Data

Purpose:
The purpose of this test is to determine the PV module’s rated power, Pmp, at STC and/or SOC, along with other performance parameters, Voc, Isc, Vmp and Imp, from the measurements conducted on at least five test modules - where

Voc = open circuit voltage
Isc = short circuit current
Vmp = voltage at peak power
Imp = current at peak power


Procedure:
The module's optical surface shall be cleaned prior to the electrical performance measurements. The I-V curve for each module shall be measured in accordance with ASTM E 1036 or IEC 904-1. Using the procedure defined in ASTM E 1036 or IEC 891, the performance data from I-V curves will be translated to Standard Test Conditions (STC): 25°C module temperature, 1000 W/ m2 total irradiance and AM1.5 global spectral irradiance per ASTM E 892 and IEC 904-3 and Standard Operating Conditions (SOC, same as STC except that the module temperature is 45°C). The translated values of the performance parameters at STC are determined from the equations given below:

Isc (STC) = Isc (1000/E) / [1+ a (Tm-25)]
Voc (STC) = Voc / [1+b(Tm-25)] [1+dxln(E)- dx ln (1000)]

For all other I-V points I(STC) = I x Isc (STC)/Isc and V(STC) = V x Voc (STC)/Voc

...where E, Tm, I and V are measured values of irradiance, module temperature, current and voltage, respectively. a and b are the temperature coefficients of current and voltage, and d is the voltage irradiance correction factor. The translated value of the performance parameters at SOC are determined from similar equations replacing 25 by 45 as the module temperature. From the translated data, Pmp, Voc, Isc, Vmp, and Imp at STC and SOC are determined and recorded.

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EVALUATING MPPT CONVERTER TOPOLOGIES USING A MATLAB PV MODEL
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Abstract

An accurate PV module electrical model is presented based on the Shockley diode equation. The simple model has a photo-current current source, a single diode junction and a series resistance, and includes temperature dependences. The method of parameter extraction and model evaluation in Matlab is demonstrated for a typical 60W solar panel. This model is used to investigate the variation of maximum power point with temperature and insolation levels. A comparison of buck versus boost maximum power point tracker (MPPT) topologies is made, and compared with a direct connection to a constant voltage (battery) load. The boost converter is shown to have a slight advantage over the buck, since it can always track the maximum power point.

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