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A commissioning record should contain, at minimum, the measured open-circuit voltage and short-circuit current for every string, the irradiance and module temperature at the moment of measurement, the inverter’s first logged production figures, and the serial numbers of the modules and inverter. The instruments that capture those figures are a panel tester such as [[the LODESTAR LD673PV]] or [[the ALLmeter 3-90V]] for string-level electrical measurements, an irradiance meter such as [[the Triplett SPLT400]] for the environmental conditions, and the inverter’s own monitoring for the first production log. The record is only useful if the conditions are written down alongside the numbers, because a current reading without irradiance cannot be compared to anything later.
The Four Numbers That Make a Record Defensible
A commissioning record exists to answer one question months or years later: was the array working as designed on the day it was handed over? Four measured quantities answer that question. Everything else in the record supports them.
The first is open-circuit voltage (Voc) per string. This confirms the string is wired as drawn, that no module is reversed, and that the number of modules in series matches the design. Voc is relatively insensitive to irradiance, which makes it a reliable wiring check even on a hazy day. The second is short-circuit current (Isc) per string. This is the figure that reveals a missing module, a bad connector, or a string that is partly shaded. Unlike Voc, Isc scales almost linearly with irradiance, so it is only meaningful when the irradiance at the moment of measurement is written down beside it.
The third number is irradiance in watts per square metre at the plane of the array. The fourth is module temperature. Without these two, the first two numbers are uncomparable. A string reading 8 A at 400 W/m² is healthy. The same string reading 8 A at 1000 W/m² is failing. The record must contain all four together or it contains none of them usefully.
An irradiance meter such as the [[the Triplett SPLT400]] captures the third and fourth figures directly, with a cosine-corrected sensor that reads in W/m² and a temperature probe. A panel tester such as [[the LODESTAR LD673PV]] captures the first two. Neither substitutes for the other, and a record that contains only the electrical figures is a record that cannot be checked.
Why Irradiance and Temperature Belong Beside Every Electrical Reading
Solar cells are current sources, not voltage sources. The current they produce is very nearly proportional to the light falling on them, and the voltage they produce falls as they heat up. This means a raw current reading is meaningless without the conditions under which it was taken. The commissioning record has to capture those conditions at the same moment as the electrical measurement, not estimated afterwards from a weather app.
The standard way to make the comparison is to translate the measured current to standard test conditions using the irradiance ratio. If a string measures 6.4 A at 800 W/m², the expected current at 1000 W/m² is 6.4 multiplied by 1000 divided by 800, which is 8.0 A. That translated figure can then be compared to the module’s datasheet Isc. The arithmetic is simple, but it only works if the 800 W/m² was actually measured and recorded. A record that says “measured on a sunny day” is not a record.
Temperature matters in the same way for voltage. A string of ten modules with a datasheet Voc of 40 V each reads 400 V at 25 C, but closer to 370 V on a hot roof. The commissioning record should note the module temperature so that a later reading can be corrected back to the same reference. The [[the Triplett SPLT400]] displays irradiance and temperature simultaneously, which is exactly the pairing the record needs.
The same discipline applies to any sensor log that accompanies the record. If the site has an environmental monitoring station, its sampling interval should be written into the record too, because a ten-minute average and a one-minute sample describe different things. The principles in how often environmental sensors should record data apply directly to the irradiance figures that sit beside a commissioning measurement.
What the Panel Tester Can and Cannot Put in the Record
A panel tester measures the electrical behaviour of a single module or a single string. The [[the LODESTAR LD673PV]] measures Pmax, Vmp, Voc and Isc up to 1000 W and 35 A, with a Voc range of 12 to 80 V. The listing is explicit that it is for single panel measurement and must not be used on series or parallel connected panels. That limitation is important for commissioning, because most residential arrays are series strings. The tester is useful for checking individual modules before they go on the roof, and for diagnosing a suspect module after the array is built, but it is not the instrument for measuring a completed string.
The [[the ALLmeter 3-90V]] covers a wider voltage range at 3 to 90 V and 40 A, and its MC4 connectors suit direct connection to a string or a single module. Its listing does not state a maximum power figure in the bullet text, so the record should not claim one. What the record can state is the measured Voc and Isc, the irradiance at the time, and the instrument used. The [[the Fabater FT Solar]] adds a curve display, which lets the commissioning technician see the shape of the power-voltage curve rather than a single point. A curve that is flattened or stepped is evidence of shading or mismatch that a single Voc reading would miss.
None of these testers measures irradiance. None measures temperature. None logs the reading with a timestamp. The commissioning record has to supply those things by hand or with a separate instrument. The tester gives the electrical figures; the record gives them meaning.
| Record item | Instrument that captures it | What the listing states |
|---|---|---|
| String Voc | Panel tester | LODESTAR LD673PV: 12 to 80 V; the ALLmeter 3-90V: 3 to 90 V |
| String Isc | Panel tester | LODESTAR LD673PV: up to 35 A; the ALLmeter 3-90V: up to 40 A |
| Pmax | Panel tester | LODESTAR LD673PV: up to 1000 W; the ALLmeter 3-90V: not stated in the listing bullets |
| Irradiance | Irradiance meter | Triplett SPLT400: W/m² readout, 300 ms sampling |
| Module temperature | Irradiance meter | Triplett SPLT400: temperature displayed simultaneously with irradiance |
| Tilt and direction | Irradiance meter | Triplett SPLT400: tilt angle and compass readings |
The table makes the gap obvious. The tester columns are well populated; the environmental columns depend on a second instrument. A record built from a tester alone is half a record.
The Paperwork That Turns Measurements Into a Baseline
The numbers are the hard part, but the paperwork is what makes them usable. A commissioning record should identify the site, the date of commissioning, the serial numbers of every module and the inverter, the string layout as installed, and the name and signature of the person who took the measurements. Without serial numbers, a later warranty claim cannot be tied to the modules actually on the roof. Without a string layout, a later reading cannot be compared to the right string.
The record should also contain the inverter’s first production log. Most inverters log daily yield, and the first full day of production is a useful baseline that requires no separate instrument. The record should note the time the inverter was energised and the first recorded yield figure. If the inverter has a monitoring portal, the record should name the portal and the site identifier so that the log can be retrieved later.
Finally, the record should state the instruments used, including their model and the date of their last calibration if known. A measurement taken with an uncalibrated tester is still a measurement, but its uncertainty is unknown. The listing for [[the Fabater FT Solar]] does not publish a calibration specification, so the record should say so rather than imply a precision the instrument has not demonstrated. Honesty in the record about what was and was not verified is what makes the rest of it trustworthy.
The broader question of which instruments belong in a commissioning kit is covered in PV testing kits for system commissioning, and the practical comparison of tester models is in best PV commissioning testers.
Where the Commissioning Record Stops Being the Right Tool
A commissioning record is a snapshot, not a monitoring system. It captures the array on one day under one set of conditions. It cannot detect a fault that develops the following week, and it cannot substitute for an alarm or a monitoring platform. If the owner wants to know when a string fails, the record is the wrong instrument; a monitoring system with string-level current sensing is the right one.
The record also cannot verify performance ratio over time. That requires continuous irradiance and production data, which is a monitoring task rather than a commissioning task. The commissioning record provides the baseline against which that monitoring is judged, but it does not replace it. A record that claims to prove annual yield is overreaching.
Nor does the record replace a safety inspection. A panel tester measures electrical performance; it does not verify that the array is correctly earthed, that the DC isolator is rated for the voltage, or that the mounting structure is mechanically sound. Those are separate checks with separate instruments, and they belong in the record as pass or fail entries rather than as measured numbers. The commissioning record is a measurement document, and it should be clear about which entries are measurements and which are inspections.
The Record Is Only as Good as the Conditions Written Beside It
A PV commissioning record that lists voltages and currents without irradiance and temperature is a list of numbers that cannot be checked. The instruments exist to capture all four figures together: a panel tester for the electrical side, an irradiance meter for the environmental side, and the inverter log for the first production baseline. Write down the conditions, the serial numbers and the instrument models, and the record becomes a baseline that survives the first fault, the first warranty claim and the first anniversary.
Frequently Asked Questions
Do I need an irradiance meter to commission a solar array?
Strictly, no, but without one the current readings in the record cannot be compared to the module datasheet or to any later measurement. An irradiance meter such as the Triplett SPLT400 captures the W/m² and temperature figures that make the electrical readings meaningful. A record without them is a record of unknown conditions.
Can I use a single panel tester on a whole string?
It depends on the tester. The LODESTAR LD673PV listing states it is for single panel measurement only and must not be used on series or parallel connected panels. The ALLmeter 3-90V lists a voltage range of 3 to 90 V and 40 A, which suits many residential strings, but the listing does not state a maximum string power, so the record should not claim one. Check the tester's stated range against the string's Voc and Isc before connecting.
What should the commissioning record say about the weather?
It should state the measured irradiance in W/m² and the module temperature at the time of each electrical measurement. A description such as sunny or cloudy is not a measurement. The irradiance figure is what allows the current reading to be translated to standard test conditions.
Does the record need the inverter's production log?
Yes, if the inverter logs production. The first full day of yield is a baseline that requires no separate instrument, and it ties the electrical measurements to actual energy production. The record should note the time the inverter was energised and the first recorded yield.
How long should I keep a PV commissioning record?
For the life of the array. Warranty claims and performance disputes can arise many years after commissioning, and the record is the only evidence of the array's condition on the day it was handed over. Keep it with the module and inverter serial numbers so that it can be matched to the equipment.
Is a commissioning record the same as a monitoring system?
No. A commissioning record is a one-day snapshot under recorded conditions. A monitoring system watches the array continuously and raises an alarm when a string fails. The record provides the baseline against which the monitoring is judged, but it cannot detect a fault that develops after the day of commissioning.