18
Measurement graphs with comparison results
Measurements:
Press the "Measurements" button on the command bar below the graph to access the menu for the following
functions:
Rs:
use this command to activate the
Series Resistance
measurement function.
The RS series resistance is one of the main features of PV modules and significantly influences their I-V characteristics.
The series resistance is measured
only on individual modules
and, as stipulated in standard IEC/EN 60891, it is
measured in two stages, under different solar radiation conditions.
The first measurement must be made with a solar radiation value greater than 500W/m
2
. The second measurement
must be made with a solar radiation value that is at least 50 W/m
2
lower. The conditions necessary to ensure that the
measurements are correct are checked automatically by the instrument. The measurements made will later be saved
along with the measurements of the I-V curve in the panel tab, following the procedure described in the
Save
(bold)
section.
To make this measurement, proceed as follows:
When the
Rs
function is selected, two commands are proposed:
Calculation:
pressing this button starts phase 1 of the measurements; a window opens on the monitor, highlighting the
measured radiation value Irr (W/m²) and the "
Phase 1 Measurement
" button. Press this button to make the
measurements. If the solar radiation value is not correct, a warning message appears on the screen.
When the phase 1 measurements have been made, a window with a "
Phase 2 Measurement
" button appears.
If the solar radiation condition is correct, pressing this button starts the second measurement session; otherwise, a
warning message appears on the screen. In this case you must wait until the solar radiation conditions are within the
proper range as described previously. When these conditions are correct, the second measurement phase can begin.
NOTE:
To make the
Phase 2
measurement without waiting for the natural atmospheric variation of the solar radiation,
a screen, for example a sheet of polycarbonate like those used in shop windows, can be placed over the panel being
tested and the pyranometer measuring the radiation to filter the sun's rays and so create the right conditions for the
measurement.
NOTE:
the IEC/EN 60891 standard indicates the procedures for transferring the values measured under real OPC
conditions to the reference standard STC conditions for a single module. Consequently, a negative result for a
measurement test on one string of modules could mean that every single module has to be measured in order to identify
the defective module or modules in the string.
