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4. INTRODUCTION
Photovoltaic systems are in two main parts:
A photovoltaic generator comprising one or more strings of photovoltaic panels that generate a direct current.
An inverter that converts the direct current generated by the panel into alternating current so it can be used in the grid.
The I-V TRACER 935 has two measurement inputs, one for measuring voltage (V
DC
) and one for measuring current (I-
DC). Measurements can be made on a single panel or on a string of panels (the latter measure is not provided for in the
standard).
There are also inputs for a pyranometer sensor and a temperature probe.
The temperature probe input accepts both the ambient temperature probe and the contact probe used to measure the
temperature of the photovoltaic panels.
The I-V TRACER 935 instrument also lets you enter a percentage of "degradation" and the age (years) of the PV module
or of the PV string, further improving the accuracy of the test results.
To make the instrument easier to use in difficult conditions, an UT925 REMOTE UNIT accessory is available to allow
wireless connection of the pyranometer sensor and the temperature probe; the sensor measurements are transmitted
to the instrument by BLUETOOTH, via a pair of adapters connected to the respective communication ports.
The main measurements made are:
measurement of solar radiation by pyranometer (up to 2000W/m²)
measurement of the ambient temperature or panel temperature by Pt100 sensor (up to 120°C)
possibility of measuring both single panels and strings of panels
measurement of the no-load voltage and the MPP voltage (up to 1000 V
DC
)
measurement of the short-circuit current and the MPP current (up to 10 A
DC
)
graphic representation of the I-V curve with marker at the MPP.
graphic representation of the power curve with marker at the MPP.
comparison of the measurements with the panel nameplate data and indication of the result:
OK/NO
calculation of the efficiency of the solar panels and display of the difference between the nominal value
and the measured value
measurement of the series resistance, Rs, in compliance with the requirements of standard EN60981
The I-V TRACER 935 is a measuring instrument designed and built to meet the needs of technicians doing
troubleshooting or maintenance work on the photovoltaic generator or module in conformity to the IEC/EN 60891
standard.
All the electrical data measured in OPC operating conditions are “transferred” to radiation STC standard conditions equal
to 1000W/m2 and module temperature of 25°C applying the calculation formulas in conformity to the IEC/EN
60891standard.
The user may request the comparison (DPmax) between the maximum power (Pmax) stated by the manufacturer and
the maximum power measured during the test (OPC), transferred to the STC standard conditions (as stipulated in the
IEC/EN 60891 standard).
If the comparison value is within the manufacturer’s stated tolerance, the test result is "OK"; otherwise, it is "NO".
N.B.: the IEC/EN 60891 standard indicates the procedures for transferring the values measured under real OPC
operating 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.
