PV System Commissioning

Tests and Tools
Intermediate

Inside this Article

Fluke Meter
A Fluke Meter
Measuring PV output
Measuring the array’s output during operation (DC voltage and current, and calculating power). Low irradiance (at top of screen) causes the very low kW measurement.
A ground continuity test
A ground continuity test—One clamp is attached at the main ground wire (EGC) going to the ground rod at the pole-mounted array. The other clamp (not pictured) is attached to the module frame. Voltage-rated insulated gloves should always be worn when making electrical connections for specific commissioning procedures.
The Seaward PV150 Solar Installation Test Kit
The Seaward PV150 Solar Installation Test Kit (with 200R irradiance meter).
A performance validation test
A performance validation test measures irradiance, cell and ambient temperatures (not shown), DC input voltage and current, and AC output voltage and current. The Hukseflux Solar I-V automatically calculates DC and AC efficiencies based on these measurements.
Hukseflux Solar I-V and components.
The Hukseflux Solar I-V and its components.
A temperature sensor
A sensor placed on the module backing measures cell temperature.
Irradiance measurement
The Seaward Solar 200R measures the irradiance (w/m2) on the array. This measurement, along with the cell temperature, is used in performance verification calculations.
Average IV curve for a module
This shows a typical, average IV curve for a module. Here, the string measurements were averaged to calculate the average module IV curve for comparison to manufacturer’s data.
Typical power curve for an entire string
A typical power curve for an entire string—in this case, ten 240 WDC modules in series.
Performance analysis test results
The performance analysis test results showing DC performance measurements for a 2,400-watt array.
The Hukseflux irradiance meter
The Hukseflux irradiance meter includes calibrated multi- and monocrystalline PV cells for accurate irradiance measurements.
The Solar02 transmitter
The Solar02 transmitter combines the temperature and irradiance readings into one unit that can transmit data back to the meter through radio frequency (RF) or record data that is synchronized with the main Solar IV meter when that unit is out of RF range.
Infrared camera (detail)
Infrared camera
Infrared camera (In Use)
Infrared cameras give installers a quick way to identify the source of array performance problems. Additionally, the images can be helpful in supporting a warranty claim.
Fluke Meter
Measuring PV output
A ground continuity test
The Seaward PV150 Solar Installation Test Kit
A performance validation test
Hukseflux Solar I-V and components.
A temperature sensor
Irradiance measurement
Average IV curve for a module
Typical power curve for an entire string
Performance analysis test results
The Hukseflux irradiance meter
The Solar02 transmitter
Infrared camera (detail)
Infrared camera (In Use)

The modules are mounted, the inverter placed, and the wiring is done—but before you (or your installer) put away the tools, commissioning procedures are necessary to verify system safety and initial performance.

Although recommended in the North American Board of Certified Energy Practitioners (NABCEP) resource guide, a universal procedure for PV system commissioning has not been implemented in the United States. In Europe, many agencies are following the commissioning recommendations of the International Electrotechnical Commission (IEC). Extensive commissioning testing is commonplace for commercial-scale PV systems, and having a solid procedure for residential systems helps ensure the system is properly installed and performing optimally. This article focuses on the tests performed and tools used to commission the PV system at the Cloudview Ecofarm (see the “Commissioning Cloudview” sidebar in this article and ”Increasing Production with Single-Axis Tracking” in HP153).

The Tests

The following electrical tests are recommended by IEC 62446 (and by NABCEP) for commissioning:

  • Polarity of each module string to verify that wires are marked and connected properly—check before connecting to the inverter, since reverse polarity could harm it.
  • Open-circuit voltage (Voc) to confirm that series strings are properly wired. All parallel strings’ Voc should be within 5% of each other and within manufacturer’s tolerances for the given irradiance and cell temperatures of the test conditions.
  • Short-circuit current (Isc) to confirm that all strings’ short-circuit currents are within 5% of each other.
  • Grounding continuity to verify that adequate grounding has been established by measuring the array to earth ground resistance. A very high resistance means that there’s a bad connection (for example, an improperly torqued ground screw) in the grounding system.
  • Insulation resistance testing (sometimes referred to as “megger testing”) confirms that there is no short-circuit connection between the positive and negative conductors and ground (see “Insulation Resistance” table for the pass/fail criteria and test voltages as recommended by IEC62446).
  • Performance verifications ensure that the inverter is supplying the predicted output under operation based on the irradiance, ambient and cell temperatures, AC and DC voltage drop, and the inverter’s efficiency.

Comments (3)

Marc Fontana's picture

Great Article ! One question - the caption below the center photo of the Array Power Curve on page 63 reads "...240 VDC modules in Series" Is this a typographical mistake or is the voltage of the whole string? The screenshot shows a Voc of 342 volts (34.2 volts per module). Shouldn't this caption be 240W DC?

Scott Russell's picture

The online version of the article has been corrected. Thanks for keeping us on our toes, Marc. -Scott, HP

Joe Schwartz's picture

Great catch, Marc! That was a typo on our part and you are correct that the caption should have stated "240 W DC". Thanks again for your sharp eye. -Joe, editor

Show or Hide All Comments

Advertisement

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading