|SEMICONDUCTOR NON-TRADITIONAL ENERGY SOURCES|
The photo converters according to their design are accepted for dividing into three basic groups: • stand alone solar elements (solar cells); • solar modules (sub-assemblies solar cells); • flat panels (flat modules); The measurement I-V characteristics (IVС) of the photo converter is usually carried out by their exposition at not varied illumination and known temperature. As a light source the Sun or simulator of solar illumination can serve. The received results, as a rule, are normalized in standard conditions of measurement (STC - Standard Test Conditions). The corrected output power and voltage are resulted as nominal. As on the output solar converter characteristics the significant influence renders radiation spectrum, the output power at the same measured falling radiation power can differ on some percents. Therefore as standard radiation the radiation with the strictly certain spectrum is accepted. In practice for updating use an exemplary solar element (reference SC), which has the same spectral response, as the tested solar element, and for which calibration curve of a short circuit current (Isc) from power of radiation , measured at standard spectrum, is present. As test the radiation of the standard spectrum by intensity 1000 W/m2 (condition АМ 1,5), falling on a plane inclined under a corner 37 o to horizon and having reflective ability 0,2 is used. The following meteorological conditions are registered: humidity, ozone content, haziness. In figure on the right is shown typical I-V curve. The point A characterizes a current of short circuit Isc, the point - open circuit voltage of Uoc, point C - point of the maximal power, the point D - corresponds to the given loading. Factor of filling is calculated as follows:
FF = Pmax / (Isc·Uoc) = (IPmax·UPmax)/(Isc·Uoc).
The load power is calculated as follows:
PL = IL·UL.
In figure the basic circuit of I-V curve measurement is shown. The circuit include two-coordinate recording (at the left). One of inputs accepts the voltage from a solar element, another accepts- the voltage proportional to a current generated by a solar element (two entrance points at them have internal connection). In order to measure the all curve, the variable source is connected seriously. On I-V curve, measured in standard conditions, it is possible to determine factor of filling (FF), SС efficiency, open circuit voltage (Uoc), current of short circuit (Isc). The shunting resistance is measured in darkness at return voltage (Rp = U/I). For measurement of series resistance (Rs) special procedure, as a rule, is used.
In order to determine the value RS, I-V curve (IVC) measure under two different illuminations. It is not necessary, that for illuminations were known. At each measurement some points on IVC with currents I1 and I2 of smaller than currents of short circuit ISC1 and ISC2 are fixed. Then for currents it is possible to write down the following expressions
From which having excluded I we shall receive:
A little having transformed the equation, we have received expression for Rs. This method allows to determine value Rs precisely enough. To determine Rs is direct under the IVC inconveniently because of low values of it, as rule..
In order to compare the experimental characteristics with calculated ones, it is necessary to determine Is, Io, m. In order to exclude influence on results of measurements of cseries resistance Rs, the dependence Isc from Uoc is measured at various illuminations (at measurement Uoc a current does not proceed, and it does not influence on result of measurement Rs). Thus, having constructed on the measured points dependence Isc from Uoc, we shall receive dфкс IVC, in which there is no Rs influence . Then IМС is reconstructed in logarithmic scale and, after an appropriate extrapolation, we shall receive values Is, Io and m.