Page 25 - Issue 4 2023

TECHNICAL

Commissioning a PV system for

best performance

Fluke, locally represented by Comtest, provides high-precision handheld devices for measuring
photovoltaic (PV) systems.

Information from Comtest

o find the expected production at a site, use the Fluke IRR-1 Solar Irradiance Meter To test I sc, disconnect all parallel
to determine the actual solar irradiance (W/m ) and shading to develop a baseline. circuits and safely short the circuit.
2
TThe solar resource is measured in peak sun hours, which is the number of hours Measure the current between the
the installation achieves 1000 W/m per day. If the solar resource is good: 6000 W/m , or positive and negative terminals through
2
2
six peak sun hours. For example, consider a 10 kW PV array. Calculate expected annual a multimeter. Set the dial to a current
production by multiplying the 10 kW array x six peak sun hours x 365 days per year x 0,85 greater than expected. Record the values
(15% derating due to power losses in wiring and inverter). This array should produce 18 of I sc and V oc on the Fluke Connect app
615 kWh of energy per year, or 51 kWh per day. and save them for trending and reporting
The performance of a PV array is based on its current-voltage (IV) curve. The short Check the insulation resistance
circuit current (I sc) is the maximum current from a cell, but no power will be produced of your conductors, the connections
because there is no voltage difference: the positive and negative wires are touching. between modules and between modules
The open circuit voltage (V oc) is the maximum voltage from a cell, but no power will be and racking, and your resistance to
produced because the circuit is open. The point at which the module produces the most ground. Use the Fluke 1625-2 FC Earth
power is called the maximum power point (MPP). Ground Tester to measure earth ground
resistance to ensure a resistance of less
than 25 ohms.
Even when installed correctly, a PV
system may not meet the expected

Figure 1: Current-voltage (IV) curve of a PV module

To know if an array is working as designed, know the values of the V oc and I sc, listed on the
module datasheet. Measure the V oc and I sc before and after installation.
V oc is measured by using the Fluke 393 FC CAT III Solar Clamp to determine the voltage
between the positive and negative terminals. The 393 FC is CAT III 1500 V / CAT IV 600V
rated, making it safe and reliable for making measurements in CAT III environments like
solar installations. Use the Fluke 64 MAX IR Thermometer to determine the temperature
of the module to account for the effect of temperature on V oc (the lower the temperature,
the higher the voltage and vice versa). The 393 FC provides audio polarity warning while
testing V oc. If it’s reversed, the combiner box or other circuits may be unintentionally
connected in series, resulting in voltages over the maximum inverter input voltage. V2 12975 Fluke 393 FC

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